Biomolecules

Living organisms are made from chemicals, and many of the most important chemicals in living systems are organic molecules containing carbon.

Four major classes of biomolecules are especially important:

• Carbohydrates
• Lipids
• Proteins
• Nucleic acids

These molecules perform different jobs, but together they make cells, store and transfer energy, control chemical reactions, carry genetic information, and build the structures needed for life.

A useful overview is:

The letters represent:

C = carbon
H = hydrogen
O = oxygen
N = nitrogen
P = phosphorus
S = sulfur

Carbon: The Foundation of Biological Molecules

Carbon is especially important in living systems because each carbon atom can form four covalent bonds.

Carbon atoms can bond with:

• other carbon atoms
• hydrogen
• oxygen
• nitrogen
• phosphorus
• sulfur

Carbon atoms can form:

• straight chains
• branched chains
• rings
• double bonds
• large complex molecules

This enormous variety allows organisms to contain millions of different organic compounds.

This is why organic chemistry forms much of the chemical foundation of biology.

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From Small Molecules to Large Biomolecules

Many biological molecules are constructed from smaller units.

A small building unit used to make a larger molecule is often called a:

monomer

A large molecule containing repeating or linked smaller units is called a:

polymer

For example:

amino acids → proteins

nucleotides → nucleic acids

many glucose molecules → some polysaccharides

However, not every major biomolecule fits a simple monomer-polymer model. Lipids, for example, are not generally considered true polymers.

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Condensation and Hydrolysis

Biological molecules are often assembled and broken apart through two important types of reaction.

Condensation

Smaller molecules join together and water is produced.

Simplified:

small molecule + small molecule → larger molecule + water

Hydrolysis

Water is used to split a larger molecule.

Simplified:

larger molecule + water → smaller molecules

These reaction patterns appear repeatedly in biological chemistry.

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Carbohydrates

Carbohydrates are organic compounds made mainly from:

• carbon
• hydrogen
• oxygen

Many carbohydrates contain hydrogen and oxygen in approximately a 2:1 ratio.

They include:

• sugars
• starches
• glycogen
• cellulose

Carbohydrates are particularly important for:

energy and energy storage

Some also have major structural roles.

Monosaccharides

The simplest carbohydrates are called:

monosaccharides

"Mono" means one.

"Saccharide" refers to sugar.

An important example is:

glucose

Molecular formula:

C₆H₁₂O₆

Glucose is extremely important because cells can use it during cellular respiration to release energy for biological processes.

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Glucose and Cellular Respiration

A simplified equation for aerobic cellular respiration is:

glucose + oxygen → carbon dioxide + water + energy

Symbolically:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

The released energy is used to produce ATP, which cells use to power many processes.

Therefore, carbohydrates provide an important connection between:

food → glucose → cellular respiration → usable cellular energy

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Disaccharides

Two monosaccharides can join together to form a:

disaccharide

Examples include:

• sucrose
• lactose
• maltose

For example, sucrose is formed from:

glucose + fructose

When two sugar molecules join, a condensation reaction can occur and water is released.

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Polysaccharides

Many monosaccharides can join to form:

polysaccharides

"Poly" means many.

Important polysaccharides include:

starch

glycogen

cellulose

Although all can be built largely from glucose units, differences in how those units are connected give them very different biological functions.

This is an excellent example of:

structure → function

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Starch

Starch is an important energy-storage carbohydrate in plants.

Plants produce glucose through photosynthesis.

Some glucose can then be converted into starch for storage.

Starch is commonly found in foods such as:

• potatoes
• rice
• wheat
• corn
• bread
• pasta

When starch is digested, it can eventually be broken down into glucose.

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Glycogen

Glycogen is an important carbohydrate used for glucose storage in animals and fungi.

In humans, substantial glycogen stores are found in:

• liver
• skeletal muscles

Glycogen is highly branched.

Its branching allows glucose units to be added or removed efficiently when required.

Again:

molecular structure supports biological function.

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Cellulose

Cellulose is a structural carbohydrate found in plant cell walls.

It provides:

• strength
• support
• resistance to stretching

Humans cannot digest cellulose because we lack enzymes capable of breaking its particular linkages efficiently.

However, cellulose is still important in the human diet as part of:

dietary fibre

Carbohydrate Structure and Function

Consider three molecules built largely from glucose:

starch → plant energy storage

glycogen → animal and fungal glucose storage

cellulose → plant structure

They contain related building units but differ in their bonding and arrangement.

Therefore:

same general building material ≠ same function

The arrangement of atoms matters.

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Lipids

Lipids are a diverse group of biological molecules that include:

• fats
• oils
• phospholipids
• steroids
• waxes

They contain large amounts of:

carbon and hydrogen

and often contain oxygen.

Unlike carbohydrates, proteins, and nucleic acids, lipids are not generally true polymers composed of repeating monomers.

Triglycerides

Many fats and oils are primarily composed of molecules called:

triglycerides

A triglyceride is formed from:

one glycerol + three fatty acids

These components are connected through:

ester linkages

This connects biological chemistry directly to the organic chemistry of esters.

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Fatty Acids

A fatty acid contains:

• a long hydrocarbon chain
• a carboxyl group, –COOH

A simplified representation is:

long carbon chain–COOH

The long hydrocarbon region is largely non-polar.

This helps explain why many lipids do not mix readily with water.

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Saturated and Unsaturated Fatty Acids

Fatty acids can be:

saturated

or:

unsaturated

A saturated fatty acid contains no carbon-carbon double bonds in its hydrocarbon chain.

An unsaturated fatty acid contains one or more:

C=C

double bonds.

Therefore, this topic also connects with our study of:

alkenes and unsaturation

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Fats and Oils

Fats and oils contain many of the same types of molecules but differ in their physical properties.

In general:

fats tend to be solid or semi-solid at room temperature.

oils tend to be liquid at room temperature.

The degree of unsaturation of their fatty acids can influence this difference.

C=C double bonds, particularly common cis double bonds in natural fatty acids, can introduce bends in the chains that make close packing more difficult.

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Functions of Lipids

Lipids have several important biological roles.

They can provide:

Long-Term Energy Storage

Lipids store large amounts of chemical energy.

Thermal Insulation

Fat beneath the skin can reduce heat loss.

Protection

Fat deposits can help cushion organs.

Cell Membranes

Phospholipids are major components of cell membranes.

Chemical Signalling

Some hormones are lipid-derived molecules.

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Phospholipids

A phospholipid has two very different regions:

• a water-attracting, or hydrophilic, head
• water-avoiding, or hydrophobic, tails

When placed in water, phospholipids naturally organize into structures such as a:

phospholipid bilayer

This forms the basic structure of cell membranes.

Structure Determines Membrane Function

The unusual structure of phospholipids makes cell membranes possible.

The hydrophilic heads interact with water.

The hydrophobic tails tend to avoid water and point inward.

This creates a stable bilayer.

The result is a flexible boundary separating:

the inside of a cell from its environment

The chemical structure of a phospholipid therefore directly determines its biological function.

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Proteins

Proteins are large biological molecules built from:

amino acids

Proteins commonly contain:

• carbon
• hydrogen
• oxygen
• nitrogen

Some amino acids also contain:

sulfur

Proteins perform an enormous variety of jobs in living organisms.

Amino Acids

A typical amino acid contains:

• an amino group, –NH₂
• a carboxyl group, –COOH
• a hydrogen
• an R group

A simplified general structure is:

H₂N–CH(R)–COOH

Different R groups produce different amino acids.

Proteins commonly use 20 standard amino acids encoded by the genetic code.

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Forming Proteins

Amino acids can join together by forming:

peptide bonds

A simplified reaction is:

amino acid + amino acid → dipeptide + water

Many amino acids can form:

polypeptide chains

These chains then fold into specific three-dimensional structures.

Therefore:

amino acids → polypeptide → folded protein

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Protein Structure Determines Function

The order of amino acids in a protein affects how the protein folds.

The folded shape affects what the protein can do.

This gives another important relationship:

amino-acid sequence → protein shape → protein function

Changing even a small part of a protein's structure can sometimes significantly alter its function.

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Functions of Proteins

Proteins perform many different roles.

Enzymes

Enzymes catalyse chemical reactions.

Structural Support

Examples include:

collagen and keratin

Transport

Hemoglobin transports oxygen.

Movement

Actin and myosin are involved in muscle contraction.

Defence

Antibodies help the immune system recognize and respond to foreign substances.

Signalling

Some hormones and receptors are proteins.

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Enzymes: Structure and Function

An enzyme has a specific three-dimensional structure.

Part of the enzyme forms an:

active site

A substrate interacts with the active site.

The shape and chemical properties of the active site help determine which substrates can bind.

Therefore:

enzyme structure → active-site properties → enzyme function

Changes in temperature or pH can disrupt protein structure and reduce enzyme activity.

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Nucleic Acids

The fourth major class is:

nucleic acids

The two most important examples are:

DNA — deoxyribonucleic acid

RNA — ribonucleic acid

Nucleic acids store, transmit, and help express genetic information.

They contain:

• carbon
• hydrogen
• oxygen
• nitrogen
• phosphorus

This is often summarized as:

CHONP

Nucleotides

Nucleic acids are built from smaller units called:

nucleotides

A nucleotide contains three main components:

• a phosphate group
• a five-carbon sugar
• a nitrogen-containing base

Therefore:

phosphate + sugar + base = nucleotide

Many nucleotides can join to form a nucleic acid.

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DNA

DNA stores hereditary information.

DNA molecules contain two nucleotide strands arranged in a:

double helix

DNA contains four bases:

• adenine (A)
• thymine (T)
• cytosine (C)
• guanine (G)

Base pairing follows:

A pairs with T

C pairs with G

The sequence of bases stores biological information.

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DNA Structure and Function

DNA is an excellent example of the relationship between structure and function.

Its structure allows it to:

• store information
• be copied
• pass information between cells and generations
• provide instructions used in protein production

The sequence of DNA bases acts as biological information.

Different base sequences can ultimately result in different amino-acid sequences in proteins.

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RNA

RNA is another nucleic acid.

It differs from DNA in several ways.

RNA usually:

• contains ribose sugar
• uses uracil (U) instead of thymine
• exists primarily as a single strand, although it can fold into complex structures

RNA has several roles in cells, particularly in:

protein synthesis and gene regulation

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From DNA to Protein

One of the most important relationships in biology is:

DNA → RNA → protein

DNA contains genetic information.

RNA helps transfer and use that information.

Amino acids are assembled into proteins according to genetic instructions.

This creates a direct connection between:

nucleic acids and proteins

Comparing the Four Major Biomolecules

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Biomolecules and Energy

Different biomolecules play different roles in energy use.

Carbohydrates

Often provide readily accessible energy.

Glucose can enter cellular respiration.

Lipids

Are important for long-term energy storage and contain a large amount of stored chemical energy per unit mass.

Proteins

Can be used as an energy source, but their primary roles are usually structural and functional rather than energy storage.

Nucleic Acids

Their primary function is information storage and transfer rather than energy storage.

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Biomolecules in Food

The foods we eat contain mixtures of biomolecules.

For example:

Bread

Rich in:

carbohydrates

Cooking Oil

Rich in:

lipids

Eggs

Contain significant:

proteins and lipids

Beans

Contain:

proteins and carbohydrates

Fruits

Contain:

carbohydrates, including sugars and fibre

Foods are rarely made of only one class of biomolecule.

Biomolecules in a Cell

A single cell contains all four major classes.

Carbohydrates

Can provide energy and participate in cell recognition and structure.

Lipids

Form much of the cell membrane and store energy.

Proteins

Act as enzymes, receptors, transporters, structural components, and signalling molecules.

Nucleic Acids

Store and use genetic information.

Life depends not on one biomolecule, but on the interaction of all four classes.

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Organic Chemistry Connects the Biomolecules

The organic chemistry studied earlier appears throughout biological molecules.

Hydroxyl Groups

–OH

occur in sugars and many other biological molecules.

Carboxyl Groups

–COOH

occur in amino acids and fatty acids.

Amino Groups

–NH₂

occur in amino acids.

Ester Linkages

–COO–

occur in many lipids.

Carbon-Carbon Double Bonds

C=C

occur in unsaturated fatty acids.

Functional groups therefore help explain the chemical behaviour of biomolecules.

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Functional Groups in Glucose

Glucose contains several:

–OH

groups.

These hydroxyl groups make glucose highly polar and allow it to interact strongly with water.

This helps explain why glucose is:

water-soluble

That property is biologically important because glucose must move through aqueous environments such as:

• blood
• cytoplasm
• tissue fluids

Again:

structure → property → biological function

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Functional Groups in Fatty Acids

Fatty acids contain:

–COOH

at one end.

They also contain a long hydrocarbon chain.

The carboxyl end is relatively polar.

The hydrocarbon chain is largely non-polar.

This combination helps determine the behaviour of fatty acids and the larger lipid molecules constructed from them.

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Functional Groups in Amino Acids

Amino acids contain:

–NH₂

and:

–COOH

This allows amino acids to participate in acid-base chemistry and join together through peptide bonds.

Different amino acids also contain different:

R groups

These side chains give proteins enormous chemical diversity.

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Structure and Function: Carbohydrates

The structure of a carbohydrate influences its function.

For example:

glucose

is small and soluble, making it suitable for transport and cellular respiration.

glycogen

is highly branched, allowing rapid release of glucose units.

cellulose

forms strong fibres suitable for supporting plant cell walls.

Same broad biomolecule class:

different structures → different functions

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Structure and Function: Lipids

Lipids contain large non-polar regions.

This makes many lipids:

hydrophobic

That property is important for:

• energy storage
• waterproofing
• biological membranes

Phospholipids contain both hydrophilic and hydrophobic regions.

That special structure causes them to organize into membranes.

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Structure and Function: Proteins

Proteins provide perhaps the clearest example of structure determining function.

Their amino-acid sequence affects:

folding

Folding produces:

three-dimensional shape

Shape determines:

interactions with other molecules

Those interactions determine:

function

Therefore:

sequence → shape → function

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Structure and Function: DNA

DNA's structure allows it to store information in the sequence of its bases.

Complementary base pairing allows DNA to be copied with high fidelity.

The double-stranded structure also helps protect and organize genetic information.

Therefore:

DNA structure → reliable information storage and transmission

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The Chemistry of Life Is Interconnected

Consider what happens when a person eats food containing carbohydrates, lipids, and proteins.

Digestion breaks large molecules into smaller components.

Carbohydrates can yield:

monosaccharides

Proteins can yield:

amino acids

Lipids can yield:

fatty acids and other components

Cells then use these molecules to:

• release energy
• build new molecules
• repair tissues
• make membranes
• produce enzymes
• produce hormones and signalling molecules

DNA contains information that helps determine which proteins cells make.

All four biomolecule classes therefore interact.

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Worked Example: Identify the Biomolecule

A molecule is built from amino acids.

What class does it belong to?

Protein

Why?

Proteins consist of amino-acid residues joined by peptide bonds.

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Worked Example: Identify the Biomolecule

A molecule contains a phosphate group, a sugar, and a nitrogenous base.

What is the smaller unit?

Nucleotide

Which major biomolecule is constructed from these units?

Nucleic acid

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Worked Example: Energy Storage

A plant stores excess glucose as a large polysaccharide.

Which molecule?

Starch

An animal stores glucose in a highly branched polysaccharide.

Which molecule?

Glycogen

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Worked Example: Cell Membrane

Which biomolecule class forms the basic bilayer of a cell membrane?

Lipids

More specifically:

phospholipids

Why?

Their hydrophilic heads interact with water while their hydrophobic tails avoid it.

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Worked Example: Enzyme

An enzyme catalyses a reaction inside a cell.

Which biomolecule class does it most commonly belong to?

Protein

Why can enzymes perform specific reactions?

Their three-dimensional structures create active sites with specific chemical properties.

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Worked Example: Genetic Information

A molecule stores genetic instructions using a sequence of A, T, C, and G.

Which molecule?

DNA

Which biomolecule class?

Nucleic acid

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Common Mistakes

Thinking All Biomolecules Are Polymers

Lipids are major biomolecules, but they are not generally considered true polymers.

Thinking Carbohydrates Only Provide Energy

Some carbohydrates have structural functions.

Cellulose is an important example.

Thinking Lipids Only Store Energy

Lipids also form membranes, provide insulation, protect organs, and participate in signalling.

Thinking Proteins Are Only for Muscles

Proteins function as enzymes, antibodies, receptors, transporters, hormones, structural materials, and much more.

Thinking DNA Is a Protein

DNA is a:

nucleic acid

Confusing Amino Acids with Nucleotides

amino acids → proteins

nucleotides → nucleic acids

Confusing Fatty Acids with Amino Acids

Fatty acids are important components of many lipids.

Amino acids are the building blocks of proteins.

Thinking All Carbohydrates Are Sugars

Carbohydrates include sugars as well as large polysaccharides such as starch, glycogen, and cellulose.

Thinking All Lipids Are Fats

Lipids include fats, oils, phospholipids, steroids, and other molecules.

Thinking Structure Does Not Matter

Small structural differences can produce major differences in biological function.

Forgetting Nitrogen in Proteins

Proteins contain nitrogen because amino acids contain amino groups.

Forgetting Phosphorus in Nucleic Acids

DNA and RNA contain phosphorus in their phosphate groups.

Thinking Organic Means "Natural"

In chemistry, organic generally refers to carbon-based chemistry. It does not simply mean natural, healthy, or produced without synthetic chemicals.

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Key Terms

Biomolecule — A molecule associated with living organisms and biological processes.

Organic compound — A carbon-based compound belonging to the field of organic chemistry.

Carbon skeleton — The framework of carbon atoms forming part of an organic molecule.

Carbohydrate — A class of biomolecules including sugars, starch, glycogen, and cellulose.

Monosaccharide — A simple sugar molecule that can serve as a carbohydrate building unit.

Glucose — A monosaccharide with formula C₆H₁₂O₆ used extensively in cellular energy metabolism.

Disaccharide — A carbohydrate formed from two monosaccharides.

Polysaccharide — A carbohydrate consisting of many linked monosaccharide units.

Starch — A major glucose-storage polysaccharide in plants.

Glycogen — A highly branched glucose-storage polysaccharide in animals and fungi.

Cellulose — A structural polysaccharide found in plant cell walls.

Lipid — A diverse group of largely hydrophobic biological molecules including fats, oils, phospholipids, and steroids.

Triglyceride — A lipid formed from glycerol and three fatty acids.

Glycerol — A three-carbon alcohol component of triglycerides and many phospholipids.

Fatty acid — A molecule containing a hydrocarbon chain and carboxyl group that forms part of many lipids.

Saturated fatty acid — A fatty acid without C=C bonds in its hydrocarbon chain.

Unsaturated fatty acid — A fatty acid containing one or more C=C bonds.

Phospholipid — A lipid containing hydrophilic and hydrophobic regions and forming a major component of cell membranes.

Hydrophilic — Having an affinity for or interacting favourably with water.

Hydrophobic — Having little affinity for water.

Protein — A biological macromolecule composed of one or more polypeptide chains.

Amino acid — A building block of proteins containing amino and carboxyl functional groups.

Peptide bond — The –CO–NH– linkage joining amino-acid residues.

Polypeptide — A chain of amino-acid residues joined by peptide bonds.

Enzyme — A biological catalyst, usually a protein.

Nucleic acid — A biomolecule constructed from nucleotides and involved in genetic information.

DNA — Deoxyribonucleic acid, the primary hereditary information-storage molecule in cells.

RNA — Ribonucleic acid, a family of nucleic acids with important roles in gene expression and other cellular processes.

Nucleotide — A building unit of nucleic acids containing a sugar, phosphate group, and nitrogenous base.

Nitrogenous base — A nitrogen-containing component of a nucleotide.

Polymer — A large molecule formed from many linked smaller units.

Monomer — A smaller molecular unit that can be linked into a larger structure.

Condensation reaction — A reaction in which molecules join and a small molecule such as water is produced.

Hydrolysis — A reaction using water to break a larger molecule into smaller components.

Cellular respiration — A set of reactions through which cells transfer energy from molecules such as glucose into usable forms such as ATP.

ATP — Adenosine triphosphate, a molecule used in cellular energy transfer.

Functional group — A specific group of atoms that influences the characteristic reactions and properties of an organic molecule.

Structure-function relationship — The principle that molecular structure influences biological properties and function.

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Key Takeaways

• The four major classes of biomolecules are carbohydrates, lipids, proteins, and nucleic acids.
• Carbon forms the chemical backbone of an enormous variety of biological molecules.
• Carbon can form four covalent bonds.
• Biomolecules commonly contain C, H, O, N, P, and S in different combinations.
• Carbohydrates contain mainly carbon, hydrogen, and oxygen.
• Carbohydrates have important roles in energy supply, energy storage, and structure.
• Glucose is an important monosaccharide.
• Starch stores glucose in plants.
• Glycogen stores glucose in animals and fungi.
• Cellulose provides structural support in plant cell walls.
• Lipids contain large amounts of carbon and hydrogen.
• Lipids include fats, oils, phospholipids, and steroids.
• Triglycerides contain glycerol and three fatty acids.
• Lipids provide long-term energy storage, insulation, protection, and membrane structure.
• Phospholipids form the basic bilayer of cell membranes.
• Proteins are constructed from amino acids.
• Proteins contain carbon, hydrogen, oxygen, and nitrogen, and some contain sulfur.
• Amino acids join through peptide bonds.
• Protein shape is closely related to protein function.
• Proteins can act as enzymes, transporters, antibodies, receptors, structural materials, and signalling molecules.
• Nucleic acids are built from nucleotides.
• DNA and RNA are nucleic acids.
• Nucleic acids contain carbon, hydrogen, oxygen, nitrogen, and phosphorus.
• DNA stores hereditary information.
• RNA has important roles in using and regulating genetic information.
• DNA information can ultimately determine amino-acid sequences in proteins.
• Functional groups studied in organic chemistry occur throughout biomolecules.
• Fatty acids contain carboxyl groups.
• Amino acids contain amino and carboxyl groups.
• Many lipids contain ester linkages.
• Unsaturated fatty acids contain C=C bonds.
• Sugars contain several polar functional groups, including hydroxyl groups.
• Structure strongly influences biological function.
• Organic chemistry provides much of the chemical foundation needed to understand living systems.

A useful summary is:

Carbohydrates → energy, storage and structure

Lipids → long-term energy, membranes and insulation

Proteins → enzymes, structure, transport and countless cellular functions

Nucleic acids → genetic information

And the central theme is:

MOLECULAR STRUCTURE → CHEMICAL PROPERTIES → BIOLOGICAL FUNCTION

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Check Your Understanding

1. Name the four major classes of biomolecules.

2. Which element forms the backbone of organic molecules?

3. Why can carbon form such a large variety of molecules?

4. Which three elements are most commonly associated with carbohydrates?

5. What is a monosaccharide?

6. Give an important example of a monosaccharide.

7. State one major biological function of glucose.

8. What is a polysaccharide?

9. What is the main role of starch?

10. What is the main role of glycogen?

11. What is the main role of cellulose?

12. Name four types of lipid.

13. What components form a triglyceride?

14. What functional group occurs in fatty acids?

15. Explain the difference between saturated and unsaturated fatty acids.

16. Give three biological functions of lipids.

17. What type of lipid forms much of the cell membrane?

18. Explain why phospholipids naturally form bilayers in water.

19. What are the building blocks of proteins?

20. What bond joins amino acids?

21. Explain why protein shape is important.

22. Give four different functions of proteins.

23. What are the two major nucleic acids?

24. What are the building units of nucleic acids?

25. Name the three components of a nucleotide.

26. What is the main biological role of DNA?

27. Explain the relationship:

DNA → RNA → protein

28. Which major biomolecule contains phosphorus as a characteristic element?

29. Explain why lipids are not usually described as true polymers.

30. Challenge: A cell contains glucose, phospholipids, enzymes, and DNA.

a. Classify glucose by biomolecule type.
b. State one important function of glucose.
c. Identify the biomolecule class of phospholipids.
d. Explain why phospholipids are suitable for forming cell membranes.
e. Identify the biomolecule class to which most enzymes belong.
f. Identify the building blocks of proteins.
g. Name the bonds connecting amino-acid residues.
h. Explain why the shape of an enzyme affects its function.
i. Identify the biomolecule class of DNA.
j. Identify the building blocks of DNA.
k. Name the three components of a nucleotide.
l. State the main role of DNA.
m. Explain how information in DNA can influence the structure of a protein.
n. Identify a functional group found in amino acids.
o. Identify a functional group found in fatty acids.
p. Explain how ester chemistry is connected to many lipids.
q. Explain how C=C bonds are connected to unsaturated fatty acids.
r. Compare the major energy-related roles of carbohydrates and lipids.
s. Explain why proteins are generally better described as functional and structural molecules than as energy-storage molecules.
t. Use one example from each of the four biomolecule classes to explain the principle:

structure → properties → biological function.

Medicines and Pharmaceuticals

Pharmaceuticals are substances used to prevent, diagnose, treat, or manage disease and other health conditions. Many pharmaceuticals are organic compounds, meaning their molecular structures are based largely on carbon.

Organic chemistry is especially important in medicine because carbon can form an enormous variety of molecular structures. By changing a molecule's:

• functional groups
• size
• shape
• polarity
• charge
• arrangement of atoms

chemists can change how that molecule interacts with the human body.

Common medicines containing organic compounds include:

• paracetamol (acetaminophen)
• aspirin
• ibuprofen
• penicillin and related antibiotics
• antihistamines
• local anaesthetics
• many antiviral medicines

The central idea is:

molecular structure → molecular interactions → biological effect

What Is a Pharmaceutical?

A pharmaceutical is a substance developed or used for a medical purpose.

A pharmaceutical product may be designed to:

• relieve pain
• reduce inflammation
• lower fever
• fight infection
• reduce allergy symptoms
• alter blood pressure
• control blood glucose
• prevent blood clots
• affect the nervous system
• replace substances the body cannot produce adequately

The molecule responsible for the intended biological effect is called the:

active pharmaceutical ingredient (API)

A tablet or capsule usually contains other substances in addition to the API.

These additional substances are called:

excipients

They may help give the medicine its shape, stability, taste, release properties, or ease of manufacture.

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Medicines Are Chemicals

The word chemical does not mean harmful or artificial.

Everything around us is made from chemicals, including:

• water
• oxygen
• glucose
• DNA
• proteins
• vitamins
• medicines

Some medicines are obtained from natural sources.

Others are manufactured synthetically.

Some begin with molecules discovered in nature and are then chemically modified.

What matters medically is not whether something is "natural" or "synthetic," but properties such as:

• effectiveness
• dose
• purity
• safety
• interactions
• biological activity

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Why Organic Chemistry Is Important

Most drugs must interact with biological molecules.

These biological molecules include:

• proteins
• enzymes
• receptors
• ion channels
• DNA
• RNA
• cell membranes

Many of these targets are themselves organic molecules.

Organic chemistry allows scientists to understand how a drug's structure influences these interactions.

Molecular Shape Matters

Drug molecules have specific three-dimensional shapes.

Biological molecules also have specific shapes.

For a drug to work, it often needs to interact with a particular biological target.

Imagine a receptor containing a binding site.

A drug molecule may fit into this site because its:

• shape
• charge
• functional groups
• polarity

complement the chemical environment of the binding site.

This is sometimes compared to a:

lock and key

However, real molecular interactions are more complicated because molecules can change shape slightly and interact through several different forces.

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Drug–Target Interactions

A drug molecule may interact with its target through:

• hydrogen bonding
• ionic attractions
• dipole interactions
• dispersion forces
• hydrophobic interactions
• sometimes covalent bonding

The positions of functional groups on the drug molecule determine which interactions are possible.

Therefore, moving or replacing even one functional group can significantly change how well a drug works.

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Functional Groups in Medicines

Many functional groups studied in organic chemistry occur in pharmaceuticals.

Examples include:

hydroxyl groups: –OH

carboxyl groups: –COOH

amino groups

esters: –COO–

amides: –CONH–

aromatic rings

halogen-containing groups

These groups can influence:

• water solubility
• acidity
• basicity
• binding to proteins
• membrane crossing
• stability
• metabolism

This is why learning functional groups is directly relevant to pharmaceutical chemistry.

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Paracetamol

Paracetamol, also called acetaminophen, is widely used to relieve pain and reduce fever.

Its molecular formula is:

C₈H₉NO₂

Its structure contains several important features, including:

• an aromatic ring
• a hydroxyl group
• an amide group

These groups affect its:

• polarity
• intermolecular interactions
• metabolism
• biological activity

Paracetamol provides a good example of how several functional groups can occur within a single pharmaceutical molecule.

Benefits and Risks of Paracetamol

When used appropriately, paracetamol can be useful for:

• relieving mild to moderate pain
• reducing fever

However, excessive doses can cause severe poisoning, particularly damage to the liver.

This illustrates a fundamental principle of pharmacology:

A useful medicine can become harmful when used incorrectly.

Safety depends on factors such as:

• dose
• frequency
• duration
• interactions
• individual health circumstances

---

Aspirin

Aspirin, chemically known as acetylsalicylic acid, is another important organic pharmaceutical.

Its molecular formula is:

C₉H₈O₄

Its structure contains:

• an aromatic ring
• a carboxyl group
• an ester group

Aspirin can be used for purposes including pain relief and reduction of inflammation. In specific medical contexts and doses, it is also used for its effects on platelet function.

Its biological effects are related to interactions with enzymes involved in producing signalling molecules called prostaglandins and related compounds.

Ibuprofen

Ibuprofen is another organic medicine used to reduce:

• pain
• inflammation
• fever

Its molecular formula is:

C₁₃H₁₈O₂

Ibuprofen contains:

• a carboxyl group
• an aromatic ring
• a hydrocarbon-rich region

Different parts of the molecule contribute to different interactions with biological molecules.

Ibuprofen belongs to a group of medicines known as:

non-steroidal anti-inflammatory drugs (NSAIDs)

---

Comparing Three Familiar Medicines

These molecules have different structures.

Their different structures lead to different:

• properties
• biological targets
• metabolism
• effects
• risks

Antibiotics

Antibiotics are medicines used to treat bacterial infections.

Many antibiotics are organic molecules with complex structures.

One historically important example is:

penicillin

Penicillin and related antibiotics interfere with bacterial cell-wall formation.

This can prevent susceptible bacteria from successfully growing and dividing.

Antibiotics do not treat viral infections such as the common cold or influenza.

---

Penicillin and Organic Chemistry

Penicillin molecules contain several functional groups and ring structures.

One particularly important feature is the:

β-lactam ring

This structure is crucial to the antibacterial activity of penicillins.

Small structural changes can produce different members of the penicillin family with different pharmaceutical properties.

This provides another example of:

structure → function

Antibiotic Resistance

Bacterial populations can evolve resistance to antibiotics.

If an antibiotic kills susceptible bacteria while resistant bacteria survive, those resistant bacteria can reproduce.

Over time, resistant forms can become more common.

Antibiotic resistance can be encouraged by inappropriate or unnecessary antibiotic use.

This creates an important connection between:

• chemistry
• biology
• evolution
• medicine
• public health

---

Antihistamines

An antihistamine is a medicine that reduces certain effects of histamine.

Histamine contributes to symptoms associated with allergic responses, such as:

• itching
• sneezing
• runny nose
• watery eyes

Antihistamine molecules can interact with histamine receptors and reduce histamine's ability to produce these effects.

Again, their molecular structure determines how effectively they interact with the receptor.

---

Receptors

A receptor is usually a protein that can respond to particular molecules.

A drug may:

activate a receptor

or:

block a receptor

A molecule that activates a receptor is often called an:

agonist

A molecule that blocks or reduces receptor activation is often called an:

antagonist

Many pharmaceuticals work through one of these mechanisms.

---

Enzyme Inhibitors

Some medicines work by reducing the activity of enzymes.

These are called:

enzyme inhibitors

An inhibitor may bind:

• directly to an enzyme's active site
• elsewhere on the enzyme

This can change the enzyme's activity.

Because enzymes have specific three-dimensional structures, the structure of the inhibitor is extremely important.

---

Drug Structure and Solubility

A medicine cannot work simply because it can bind to a target.

It must also be able to reach that target.

One important property is:

solubility

Functional groups influence whether a drug interacts well with water.

Polar or charged groups can often increase interaction with aqueous environments.

Non-polar regions may help molecules interact with lipid membranes.

Drug designers often need to balance these properties.

---

Crossing Cell Membranes

Cell membranes contain a phospholipid bilayer.

The interior of this membrane is largely hydrophobic.

A highly polar molecule may have difficulty crossing the membrane directly.

A more lipid-soluble molecule may cross more easily.

However, many biological transport systems also help molecules cross membranes.

Therefore, drug absorption depends on several factors, including:

• molecular size
• charge
• polarity
• lipid solubility
• transport proteins
• route of administration

---

Acids, Bases, and Medicines

Many drug molecules contain acidic or basic functional groups.

For example:

–COOH

can contribute acidic behaviour.

Amines can contribute:

basic behaviour

Whether these groups are charged can depend on the surrounding pH.

This matters because charge can influence:

• water solubility
• membrane crossing
• protein binding
• absorption

Acid-base chemistry is therefore extremely important in pharmaceutical science.

---

Chirality

Some organic molecules can exist in forms that are mirror images of one another.

These are called:

enantiomers

This property is related to:

chirality

Two enantiomers contain the same types of atoms and bonds but differ in their three-dimensional arrangement.

Why Chirality Matters in Medicines

Biological molecules are three-dimensional.

Therefore, two mirror-image forms of a drug can interact differently with:

• enzymes
• receptors
• transport proteins

One enantiomer may interact more strongly with a particular target than another.

This means pharmaceutical chemists must consider not only:

which atoms are present

but also:

how those atoms are arranged in three dimensions.

---

Dose Matters

A dose is the quantity of medicine administered.

The appropriate dose should produce a useful therapeutic effect while minimizing harmful effects.

Too little medicine may:

fail to produce the desired effect

Too much may:

increase the risk of toxicity

Therefore:

more medicine does not mean better treatment.

---

Therapeutic Effects and Side Effects

A drug may produce several biological effects.

The intended beneficial effect is the:

therapeutic effect

An unintended effect is commonly called a:

side effect

Side effects occur because biological systems are complex.

A drug may:

• interact with more than one target
• affect the same target in different tissues
• be converted into other molecules during metabolism

A medicine can therefore provide substantial benefits while also carrying risks.

---

Drug Metabolism

The body can chemically modify drug molecules.

This process is called:

drug metabolism

The liver plays a major role in the metabolism of many medicines.

Chemical reactions may make a drug:

• less active
• more active
• easier to eliminate
• occasionally more toxic

Enzymes perform many of these reactions.

Organic chemistry helps scientists understand these molecular transformations.

---

Drug Elimination

After a drug has performed its role, it or its metabolites may be removed from the body.

Important organs involved include:

• liver
• kidneys

The kidneys can remove many substances from blood and eliminate them through urine.

The chemical properties of a molecule influence how easily it can be eliminated.

---

From Discovery to Medicine

Developing a pharmaceutical is usually a long process.

Scientists may begin by identifying a biological process involved in a disease.

They then identify a:

target

such as:

• enzyme
• receptor
• protein
• ion channel

Researchers search for molecules capable of interacting with that target.

Promising molecules are called:

lead compounds

---

Modifying a Lead Compound

Once a promising compound is identified, chemists can modify its molecular structure.

For example, they might:

• add a functional group
• remove a functional group
• replace one group with another
• change a carbon chain
• change a ring structure
• alter stereochemistry

They then investigate whether the new compound has improved properties.

This process is sometimes called:

lead optimization

---

What Are Drug Designers Trying to Improve?

A potential drug may need improvements in:

• effectiveness
• selectivity
• solubility
• stability
• absorption
• duration of action
• toxicity
• metabolism

For example, a molecule might bind strongly to its intended target but be poorly absorbed.

Chemists might modify its structure to improve absorption while trying to preserve biological activity.

---

Structure–Activity Relationships

Scientists often compare related molecules to determine how structural changes affect biological activity.

This is called studying:

structure–activity relationships (SAR)

Suppose molecule A works well.

Chemists modify one part of its structure to produce molecule B.

If B works better, the change may have improved its interaction with the target.

If B stops working, the changed part may have been essential.

Repeated comparisons help scientists understand which molecular features are important.

---

Computer-Aided Drug Design

Modern pharmaceutical research can use computer models to study possible drug molecules.

Computational tools can help scientists:

• visualize molecular structures
• model drug-target interactions
• compare candidate molecules
• predict some molecular properties
• prioritize compounds for laboratory testing

However, computer predictions do not replace experimental evidence.

Promising compounds still require laboratory and clinical testing.

Testing New Medicines

Before a new medicine can be widely used, scientists need evidence about:

effectiveness

and:

safety

Research progresses through stages that can include:

• laboratory studies
• preclinical studies
• clinical trials
• regulatory review
• continued monitoring after approval

Not every candidate drug succeeds.

Many potential medicines are abandoned because they are ineffective, unsafe, or unsuitable for practical use.

---

Clinical Trials

Clinical trials study medicines in human participants under controlled research conditions.

Depending on the stage and purpose, researchers may investigate:

• safety
• appropriate dose
• effectiveness
• side effects
• comparison with existing treatments

Well-designed trials attempt to reduce bias and produce reliable evidence.

---

Placebos and Controls

Some clinical trials use a:

control group

When scientifically and ethically appropriate, a control may receive a:

placebo

A placebo resembles the treatment but does not contain the tested active ingredient.

Researchers can compare outcomes between groups.

However, placebo use must be ethically appropriate; withholding an effective treatment can sometimes be unacceptable.

---

Benefits of Pharmaceuticals

Medicines have transformed human health.

Benefits can include:

• treating infections
• controlling pain
• managing chronic diseases
• reducing inflammation
• preventing complications
• improving quality of life
• extending life expectancy
• preventing some diseases

Modern medicine depends heavily on pharmaceutical chemistry.

---

Risks of Pharmaceuticals

Medicines can also involve risks.

Possible risks include:

• side effects
• allergic reactions
• toxicity
• interactions with other medicines
• incorrect dosing
• misuse
• antibiotic resistance
• environmental contamination from pharmaceutical residues

The existence of risk does not automatically mean a medicine should not be used.

Instead, the important question is:

Do the expected benefits outweigh the risks for the intended use?

---

Benefit–Risk Analysis

Imagine a medicine produces a major improvement in a serious disease but causes a mild temporary side effect in some patients.

The benefits may greatly outweigh the risks.

Now imagine another drug provides very little benefit but causes serious harmful effects.

Its benefit-risk balance may be poor.

Therefore, pharmaceutical decisions require evaluation of:

benefit + probability + severity + alternatives + risk

---

Medicines and Individual Differences

A medicine may not affect every person identically.

Differences can arise from:

• age
• body size
• genetics
• kidney or liver function
• other medicines
• diet
• other biological factors

This is one reason pharmaceutical treatment and dosing can require careful medical guidance.

---

Natural Products and Drug Discovery

Many important medicines or lead compounds have originated from natural organisms.

Scientists have studied chemicals produced by:

• plants
• fungi
• bacteria
• marine organisms

These molecules may provide starting points for pharmaceutical development.

Penicillin, for example, originated from observations involving Penicillium fungi.

Chemists can then study, produce, and modify biologically active compounds.

---

Synthetic Medicines

Other pharmaceuticals are produced through chemical synthesis.

Organic chemists may construct complex molecules through sequences of reactions.

Advantages of chemical synthesis can include:

• controlled purity
• large-scale production
• structural modification
• reliable supply
• development of molecules not readily available from nature

Natural-product chemistry and synthetic chemistry therefore both contribute to medicine.

---

Organic Chemistry Connects to Biology

Drug development combines many scientific fields.

Organic chemistry explains molecular structure and reactions.

Biochemistry explains interactions with biological molecules.

Cell biology explains effects on cells.

Physiology explains effects on organs and systems.

Pharmacology studies how drugs interact with biological systems.

Toxicology investigates harmful effects.

Together, these sciences help scientists develop useful medicines.

---

Worked Example: Functional Groups

A drug molecule contains:

–COOH

What functional group is present?

Carboxyl group

What behaviour might this contribute?

Acidic behaviour

What other property might it influence?

Possible answers include:

• water solubility
• charge
• protein binding
• membrane crossing

---

Worked Example: Amines

A pharmaceutical contains an amine group.

What chemical behaviour might you predict?

The nitrogen can often accept H⁺.

Therefore, the molecule may show:

basic behaviour

Its charge may change depending on pH.

This can influence its solubility and movement through biological systems.

---

Worked Example: Molecular Shape

Two molecules contain the same atoms but have different three-dimensional arrangements.

Could they behave differently as medicines?

Yes.

Biological targets are three-dimensional.

Different arrangements may interact differently with receptors or enzymes.

---

Worked Example: Changing a Functional Group

A drug candidate binds strongly to its target but dissolves poorly in water.

A chemist modifies part of the molecule to increase its polarity.

Why?

Increasing suitable polar interactions may improve:

water solubility

However, the chemist must also determine whether the modification changes:

• target binding
• absorption
• metabolism
• toxicity

Drug design involves balancing several properties simultaneously.

---

Worked Example: Benefits and Risks

Suppose Medicine A greatly reduces symptoms but causes mild nausea in some patients.

Medicine B produces little improvement and causes serious liver toxicity.

Which has the more favourable benefit-risk profile?

Based only on the information provided:

Medicine A

because its potential benefit is greater while the described adverse effect is less severe.

Real pharmaceutical decisions require much more evidence, but the same principle applies.

---

Common Mistakes

Thinking "Organic" Means Natural

In chemistry, organic refers mainly to carbon-based chemistry.

Synthetic medicines can be organic compounds.

Thinking Natural Means Safe

Natural substances can be:

• beneficial
• harmless
• toxic
• deadly

Origin alone does not determine safety.

Thinking Synthetic Means Dangerous

Synthetic compounds can be safe and useful.

Safety depends on properties, dose, and use.

Thinking All Medicines Work the Same Way

Different medicines act through different molecular mechanisms.

Ignoring Molecular Shape

Three-dimensional structure can be critical to drug function.

Ignoring Functional Groups

Functional groups influence solubility, acidity, basicity, reactivity, and biological interactions.

Thinking More Medicine Works Better

Increasing the dose can increase toxicity rather than benefit.

Confusing Side Effect with No Effect

A side effect is an unintended effect, not the absence of a therapeutic effect.

Thinking Antibiotics Treat Viruses

Antibiotics target bacteria and do not treat ordinary viral infections.

Thinking a Drug Must Have Zero Risk

Few medical interventions are completely risk-free.

The goal is an acceptable:

benefit-risk balance

Thinking Computer Models Prove a Drug Works

Computer modelling can guide research, but experimental and clinical evidence is still required.

Assuming Similar Structures Mean Identical Effects

Small structural changes can sometimes cause major differences in biological activity.

---

Key Terms

Medicine — A substance or preparation used to prevent, diagnose, treat, or manage a medical condition.

Pharmaceutical — A substance developed or used for a medical purpose.

Active pharmaceutical ingredient (API) — The component responsible for a medicine's intended biological effect.

Excipient — An additional component of a pharmaceutical formulation other than the active ingredient.

Drug target — A biological molecule or structure with which a drug interacts to produce an effect.

Receptor — Usually a protein that responds to specific signalling molecules or drugs.

Agonist — A substance that activates a receptor.

Antagonist — A substance that blocks or reduces receptor activation.

Enzyme inhibitor — A substance that reduces the activity of an enzyme.

Binding site — A region of a biological molecule where another molecule can interact.

Functional group — A group of atoms responsible for characteristic chemical properties and reactions.

Polarity — Uneven distribution of electrical charge within a molecule.

Solubility — The extent to which a substance dissolves in a solvent.

Lipophilicity — The tendency of a substance to interact with or dissolve in lipid-like environments.

Chirality — A structural property in which a molecule may exist in non-superimposable mirror-image forms.

Enantiomer — One of two non-superimposable mirror-image forms of a chiral molecule.

Dose — The quantity of a medicine administered.

Therapeutic effect — The intended beneficial effect of a treatment.

Side effect — An unintended effect associated with a medicine.

Toxicity — The ability of a substance to cause harmful biological effects.

Drug interaction — A situation in which another substance changes the effects of a medicine.

Metabolism — Chemical modification of substances by the body.

Drug metabolism — Chemical transformation of pharmaceutical molecules within the body.

Lead compound — A promising molecule selected for further investigation during drug development.

Lead optimization — Modification of a lead compound to improve desirable pharmaceutical properties.

Structure–activity relationship (SAR) — The relationship between molecular structure and biological activity.

Medicinal chemistry — The field applying chemistry to the discovery and development of medicines.

Pharmacology — The study of drugs and their interactions with biological systems.

Toxicology — The study of harmful effects of substances on living organisms.

Clinical trial — A controlled research study involving human participants to investigate a medical intervention.

Placebo — An inactive treatment used as a comparison in some research studies.

Antibiotic — A medicine used to treat susceptible bacterial infections.

Antibiotic resistance — The ability of bacteria to survive or reproduce despite exposure to an antibiotic that would normally inhibit them.

Benefit-risk balance — Comparison of the expected benefits of a treatment with its potential harms.

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Key Takeaways

• Many medicines are organic compounds.
• Carbon's bonding versatility allows pharmaceutical molecules to have enormous structural diversity.
• Organic chemistry is fundamental to pharmaceutical development.
• Functional groups strongly influence drug properties.
• Drug molecules can contain hydroxyl, carboxyl, amino, ester, amide, and many other groups.
• Molecular shape can strongly influence biological activity.
• Drugs often work by interacting with specific biological targets.
• Important drug targets include receptors, enzymes, proteins, and ion channels.
• Drug-target interactions depend on molecular structure.
• Hydrogen bonding, ionic attraction, hydrophobic interactions, and other forces can contribute to drug binding.
• Paracetamol is an organic pharmaceutical used for pain relief and fever reduction.
• Aspirin is an organic pharmaceutical containing carboxyl and ester functional groups.
• Ibuprofen is an organic pharmaceutical containing a carboxyl group.
• Penicillins contain an important β-lactam ring.
• Antibiotics treat bacterial infections, not viral infections.
• Antibiotic resistance can evolve in bacterial populations.
• Some medicines activate receptors.
• Other medicines block receptors.
• Some pharmaceuticals inhibit enzymes.
• Solubility affects how medicines behave in the body.
• Polarity and charge can affect membrane crossing.
• Acid-base chemistry is important in pharmaceutical science.
• Three-dimensional molecular arrangement can matter as much as molecular formula.
• Enantiomers can interact differently with biological targets.
• Drug dose strongly influences both benefits and risks.
• More medicine is not necessarily better.
• Drugs can produce therapeutic effects and side effects.
• The body chemically modifies many drugs through metabolism.
• Scientists can modify molecular structures to improve potential medicines.
• Structure–activity relationships help scientists understand which parts of a molecule are important.
• Computer modelling can assist drug discovery but does not replace experimental testing.
• New medicines require extensive testing.
• Clinical trials provide evidence about safety and effectiveness.
• Medicines can provide enormous benefits while still carrying risks.
• Pharmaceutical decisions require consideration of benefit versus risk.
• "Natural" does not automatically mean safe.
• "Synthetic" does not automatically mean dangerous.
• Organic chemistry, biochemistry, biology, pharmacology, and medicine work together in pharmaceutical development.

The central relationship is:

MOLECULAR STRUCTURE → CHEMICAL PROPERTIES → BIOLOGICAL INTERACTIONS → DRUG EFFECT

And pharmaceutical development attempts to optimize:

effectiveness + selectivity + absorption + stability + safety

while minimizing:

toxicity + harmful interactions + unwanted effects

Check Your Understanding

1. What is a pharmaceutical?

2. What is an active pharmaceutical ingredient?

3. Why is organic chemistry important in medicine?

4. Give three examples of familiar medicines containing organic compounds.

5. Explain why molecular shape can influence drug activity.

6. What is a drug target?

7. Give three examples of biological drug targets.

8. Name three types of intermolecular interaction that can contribute to drug binding.

9. How can functional groups affect a drug's properties?

10. Identify two functional groups found in aspirin.

11. What class of medicine is ibuprofen?

12. What is an antibiotic?

13. Why should antibiotics not be used to treat ordinary viral infections?

14. What is antibiotic resistance?

15. What is a receptor?

16. Distinguish between an agonist and an antagonist.

17. What is an enzyme inhibitor?

18. Explain why water solubility can be important for a medicine.

19. Explain why lipid solubility can influence membrane crossing.

20. Why are acidic and basic functional groups important in pharmaceuticals?

21. What is chirality?

22. What is an enantiomer?

23. Why can two enantiomers behave differently in the body?

24. Explain why dose is important.

25. Distinguish between a therapeutic effect and a side effect.

26. What is drug metabolism?

27. What is a lead compound?

28. What is meant by a structure–activity relationship?

29. Why are clinical trials necessary?

30. Challenge: A pharmaceutical company discovers an organic molecule that blocks an enzyme involved in a disease.

a. What would the enzyme be called in relation to the drug?
b. Explain why the three-dimensional shape of the drug is important.
c. Explain how hydrogen bonding could contribute to drug binding.
d. Explain how an amine group might influence the drug's acid-base behaviour.
e. Explain how a carboxyl group might influence its behaviour.
f. Explain why polarity could affect water solubility.
g. Explain why polarity could also affect membrane crossing.
h. The molecule exists as two enantiomers. Explain why both should be investigated separately.
i. Scientists modify one functional group and the new molecule binds more strongly. What does this suggest about structure–activity relationships?
j. Explain why stronger binding does not automatically make the new molecule a better medicine.
k. Name three other properties scientists should investigate.
l. Explain why laboratory success does not prove that the compound will work safely in humans.
m. Explain the purpose of clinical trials.
n. Explain why researchers investigate both therapeutic effects and side effects.
o. Explain why increasing the dose may increase risk.
p. Explain why a medicine can be beneficial even if it has some side effects.
q. Explain why a natural origin would not prove that the drug is safe.
r. Explain why a synthetic origin would not prove that the drug is dangerous.
s. Describe how organic chemistry contributes to improving the molecule.
t. Use the example to explain:

structure → properties → biological interactions → pharmaceutical effect.

Food Chemistry

Food chemistry is the study of the substances that make up food and the chemical changes that occur when food is grown, stored, processed, cooked, digested, and used by the body.

Foods contain thousands of different chemical compounds. Many are organic compounds based on carbon.

Important groups include:

• carbohydrates — sugars, starches and fibre
• lipids — fats and oils
• proteins
• vitamins
• organic acids
• pigments
• flavour and aroma compounds

Food also contains important inorganic substances, especially:

• water
• minerals
• salts

Understanding food chemistry helps explain why bread browns, eggs become firm when heated, oil does not mix with water, fruit changes colour after cutting, and foods provide different nutrients.

Food Is Made of Chemicals

Everything we eat is made from chemicals.

An apple, for example, contains:

• water
• sugars
• fibre
• organic acids
• vitamins
• minerals
• pigments
• flavour compounds
• proteins
• small amounts of lipids

The word chemical does not mean artificial or dangerous.

Glucose is a chemical.

Water is a chemical.

Vitamin C is a chemical.

Proteins are chemicals.

Food chemistry examines these substances scientifically.

---

Organic Chemistry and Food

Organic chemistry is particularly important because many nutrients are carbon compounds.

Functional groups studied in organic chemistry appear throughout food molecules.

For example:

–OH groups occur extensively in sugars.

–COOH occurs in fatty acids, amino acids and many food acids.

–NH₂ occurs in amino acids.

–COO– ester linkages occur in fats and oils.

C=C bonds occur in unsaturated fatty acids.

Therefore, the organic chemistry studied earlier helps explain the chemistry of food.

---

The Major Nutrients

Four particularly important groups of organic compounds in nutrition are:

These nutrients have very different molecular structures.

Their structures help determine how they behave during:

• cooking
• digestion
• storage
• metabolism

---

Carbohydrates in Food

Carbohydrates contain mainly:

carbon, hydrogen and oxygen

Important dietary carbohydrates include:

• glucose
• fructose
• sucrose
• lactose
• starch
• dietary fibre

Carbohydrates are abundant in foods such as:

• bread
• rice
• pasta
• potatoes
• cereals
• fruit
• vegetables
• sugar

Sugars

Simple sugars include:

glucose

fructose

Glucose and fructose have the same molecular formula:

C₆H₁₂O₆

but different structures.

This demonstrates an important principle:

same molecular formula does not necessarily mean same molecular structure

Different structures can produce different chemical and physical properties.

---

Sucrose

Common table sugar is:

sucrose

Sucrose is a disaccharide formed from two monosaccharides:

glucose + fructose

During digestion, sucrose can be hydrolysed into its smaller sugar components.

Sucrose occurs naturally in plants and is particularly abundant in:

• sugar cane
• sugar beet

It is also added to many manufactured foods.

---

Starch

Starch is a polysaccharide made from many glucose units.

Plants use starch for:

energy storage

Foods rich in starch include:

• potatoes
• rice
• wheat
• corn
• bread
• pasta

During digestion:

starch → smaller carbohydrates → glucose

Enzymes help catalyse these reactions.

---

Dietary Fibre

Dietary fibre includes carbohydrate materials that human digestive enzymes cannot completely break down.

An important example is:

cellulose

Cellulose occurs in plant cell walls.

Although humans cannot digest cellulose into glucose efficiently, fibre contributes to healthy digestive function.

This demonstrates that:

not every carbohydrate has the same nutritional role.

---

Carbohydrates and Energy

Glucose can be used during cellular respiration.

A simplified equation is:

glucose + oxygen → carbon dioxide + water + energy

Symbolically:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

Some of this released energy is transferred into ATP.

Therefore:

food → glucose → cellular respiration → usable cellular energy

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Lipids in Food

Lipids include:

• fats
• oils
• phospholipids
• sterol-related molecules

Dietary lipids occur in foods such as:

• oils
• butter
• nuts
• seeds
• avocados
• dairy products
• eggs
• meat
• oily fish

Lipids are particularly important as a concentrated source of stored chemical energy.

Triglycerides

Many dietary fats and oils consist mainly of:

triglycerides

A triglyceride is constructed from:

one glycerol + three fatty acids

The molecules are connected through:

ester linkages

This directly connects food chemistry with our previous study of esters.

---

Fatty Acids

Fatty acids contain:

• a long hydrocarbon chain
• a carboxyl group, –COOH

They can be:

saturated

or:

unsaturated

A saturated fatty acid contains no carbon-carbon double bonds in its carbon chain.

An unsaturated fatty acid contains one or more:

C=C

bonds.

---

Saturated and Unsaturated Fats

Saturated fatty acid chains can often pack together relatively closely.

Many fats rich in saturated fatty acids are therefore solid or semi-solid at room temperature.

Many naturally occurring unsaturated fatty acids contain cis C=C bonds, which introduce bends or "kinks" into their chains.

These bends make close packing more difficult.

Many oils rich in unsaturated fatty acids are therefore liquid at room temperature.

The pattern is not absolute, but it demonstrates:

molecular structure → intermolecular interactions → physical properties

---

Why Oil and Water Separate

Water is:

polar

The long hydrocarbon regions of many lipid molecules are:

non-polar

Polar water molecules interact strongly with one another, while non-polar lipid molecules do not interact favourably with water.

Therefore:

oil and water separate

This can be summarized by the useful idea:

"like dissolves like."

Polar substances tend to interact well with other polar substances.

Non-polar substances tend to interact well with other non-polar substances.

Emulsions

Although oil and water normally separate, they can sometimes be mixed into an:

emulsion

An emulsion is a mixture in which droplets of one liquid are dispersed through another liquid.

Examples include:

• mayonnaise
• salad dressings
• cream
• some sauces

An emulsifier helps stabilize the mixture.

---

Lecithin and Mayonnaise

Egg yolk contains molecules including lecithin, a mixture rich in phospholipids that can act as emulsifiers.

These molecules contain regions that interact differently with water and lipids.

They help stabilize tiny oil droplets throughout the water-containing mixture.

This is why egg yolk is useful when making mayonnaise.

Food chemistry explains what appears to be a simple cooking technique.

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Proteins in Food

Proteins are constructed from:

amino acids

Dietary protein is found in foods such as:

• meat
• fish
• eggs
• milk
• cheese
• beans
• lentils
• soy
• nuts
• seeds

Proteins contain mainly:

C, H, O and N

and some also contain:

S

Amino Acids and Proteins

A typical amino acid contains:

–NH₂

and:

–COOH

Amino acids join through:

peptide bonds

to form polypeptide chains.

These chains fold into specific three-dimensional shapes.

Therefore:

amino acids → polypeptides → proteins

The shape of a protein strongly influences its properties.

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What Happens When an Egg Is Cooked?

Raw egg white contains proteins dissolved and dispersed in water.

When heated, protein molecules gain energy.

Some interactions maintaining their folded structures are disrupted.

The proteins unfold.

This is called:

denaturation

The unfolded protein molecules can then interact with one another and form a network.

The transparent egg white becomes:

opaque and firm

This is a chemical and structural transformation of the proteins.

---

Protein Denaturation

Proteins can be denatured by conditions such as:

• heat
• extreme pH
• some chemicals
• mechanical treatment in certain systems

Denaturation changes the protein's three-dimensional structure.

Importantly:

denaturation does not normally mean that all peptide bonds have been broken.

The amino-acid sequence usually remains largely intact while the protein's folding changes.

---

Cooking Meat

Heating meat causes several chemical and physical changes.

Proteins:

• denature
• change shape
• interact differently
• may lose water

Connective tissue can also change during prolonged cooking.

At the surface, sufficiently high temperatures can produce browning reactions that create new flavours and aromas.

Cooking is therefore a combination of:

heat transfer + physical changes + chemical reactions

---

The Maillard Reaction

One of the most important reactions in cooking is the:

Maillard reaction

It involves reactions between certain:

amino compounds and reducing sugars

during heating.

It contributes to the colour and flavour of foods such as:

• toasted bread
• roasted coffee
• grilled meat
• baked cookies
• roasted potatoes

Why Browning Creates New Flavours

The Maillard reaction is not one single simple reaction.

It involves a complex series of reactions producing many new molecules.

Some contribute:

• brown colour
• roasted aromas
• nutty flavours
• savoury flavours

This is why:

bread and toast

do not taste identical.

Heating has produced new compounds.

---

Caramelization

Caramelization is another type of food browning.

It involves chemical changes in:

sugars

when they are strongly heated.

Caramelization can produce:

• brown colours
• characteristic aromas
• new flavours

It occurs in foods such as:

• caramel
• heated sugar
• some baked goods

---

Maillard Reaction vs. Caramelization

These processes are related to browning but are not the same.

Maillard Reaction

Typically involves:

reducing sugars + amino compounds

Caramelization

Primarily involves:

sugars

Therefore, not all food browning should simply be called caramelization.

---

Starch Gelatinization

When starch is heated in water, starch granules can absorb water and swell.

This process is called:

gelatinization

The mixture becomes thicker.

This occurs when preparing foods such as:

• sauces
• gravy
• custard-like starch mixtures
• some soups

This is another example of molecular changes producing visible changes in food texture.

---

Why Pasta and Rice Change When Cooked

Rice and pasta contain large amounts of starch.

During cooking:

• water enters the food
• starch granules absorb water
• heating changes starch organization
• the texture softens

Protein changes can also contribute, especially in wheat-based foods.

Cooking therefore changes both:

molecular structure and macroscopic texture.

---

Baking Bread

Bread-making involves several areas of chemistry.

Yeast can ferment sugars.

A simplified reaction is:

glucose → ethanol + carbon dioxide

The carbon dioxide forms bubbles that help dough rise.

During baking:

• gases expand
• proteins change structure
• starch gelatinizes
• water evaporates
• crust browning occurs
• new flavour compounds form

A loaf of bread is essentially a complex chemistry experiment.

Fermentation

Microorganisms can perform chemical reactions that transform food.

Yeast can convert sugars into:

ethanol + carbon dioxide

Other microorganisms can produce organic acids.

Fermentation is important in foods including:

• bread
• yogurt
• cheese
• fermented vegetables

Different microorganisms and conditions produce different chemical products.

---

Acids in Food

Foods contain many organic acids.

Examples include:

citric acid — common in citrus fruits

acetic acid — characteristic acid in vinegar

lactic acid — associated with fermented dairy and other fermented foods

malic acid — found in many fruits

tartaric acid — found naturally in grapes and some other fruits

These acids contribute to:

• taste
• pH
• preservation
• chemical reactions during processing

---

Vitamin C

Vitamin C, or ascorbic acid, is an organic compound important in human nutrition.

It is found in foods including:

• citrus fruits
• peppers
• berries
• broccoli
• kiwi fruit

Vitamin C is water-soluble.

The body requires it for processes including collagen synthesis and normal physiological function.

Vitamins

Vitamins are organic compounds required in relatively small quantities for normal biological functions.

They do not all have the same chemical structure or function.

Some are:

water-soluble

while others are:

fat-soluble

---

Water-Soluble Vitamins

The major water-soluble vitamin groups are:

• vitamin C
• B vitamins

Their molecular structures allow substantial interaction with water.

Because of their water solubility, some can be lost into cooking water.

Their stability also varies, and heat, oxygen, light, and storage conditions can affect some vitamins.

---

Fat-Soluble Vitamins

The main fat-soluble vitamins are:

A, D, E and K

Their structures contain substantial non-polar regions.

They are absorbed and transported in association with dietary lipids.

This provides another example of:

molecular structure → solubility → biological behaviour

---

Minerals Are Not Vitamins

A common mistake is to call minerals vitamins.

Minerals such as:

• calcium
• iron
• magnesium
• potassium
• zinc

are:

inorganic nutrients

Vitamins are:

organic compounds

Both are important, but they are chemically different.

---

Food Processing

Food processing includes physical and chemical treatments used to prepare, preserve, modify, or package food.

Examples include:

• heating
• freezing
• drying
• fermentation
• pasteurization
• milling
• mixing
• emulsification

Processing can improve:

• safety
• storage life
• texture
• flavour
• convenience

It can also change nutrient composition.

---

Food Preservation

Food can spoil because of:

• microbial growth
• enzyme activity
• oxidation
• chemical reactions

Preservation methods attempt to slow or prevent these processes.

Examples include:

refrigeration — slows many reactions and microbial growth

freezing — greatly slows many biological and chemical processes

drying — reduces available water

acidification — lowers pH

heating — can destroy many microorganisms and deactivate enzymes

packaging — can reduce exposure to oxygen, moisture or microorganisms

---

Oxidation in Food

Food molecules can react with oxygen.

This can produce unwanted changes.

For example, oxidation can contribute to:

• rancidity in fats
• pigment changes
• flavour changes
• nutrient loss

Antioxidants can slow some oxidation processes.

---

Why Cut Fruit Turns Brown

When some fruits are cut, cells are damaged.

Enzymes and other compounds that were previously separated can come into contact with oxygen.

This can lead to:

enzymatic browning

Apples, bananas, pears, and avocados can show this effect.

Acidic conditions, lower temperatures, or reduced oxygen exposure can slow browning in some foods.

Rancidity

Fats and oils can undergo chemical changes during storage.

Oxidation of lipids can produce compounds with undesirable:

• smells
• flavours

This deterioration is associated with:

rancidity

Factors that can accelerate lipid oxidation include:

• oxygen
• light
• heat
• some metal ions

This is why storage conditions matter.

---

Antioxidants

An antioxidant is a substance that can help slow certain oxidation processes.

Antioxidants are used naturally or as food additives to help protect:

• flavours
• colours
• nutrients
• fats and oils

Some vitamins can also participate in antioxidant chemistry.

However, the term "antioxidant" does not automatically mean that consuming very large amounts of a substance provides additional health benefits.

---

Food Additives

A food additive is a substance added for a technological purpose.

Examples include:

• preservatives
• antioxidants
• colours
• flavourings
• emulsifiers
• stabilizers
• thickeners
• acidity regulators
• sweeteners

Additives have different chemical structures and functions.

Their presence does not automatically mean a food is unsafe.

Food safety depends on the identity, amount, exposure, and evidence concerning the substance.

---

Reading an Ingredient List

Ingredient lists can provide useful chemical information.

Suppose a product lists:

wheat flour, sugar, vegetable oil, milk powder, citric acid, lecithin, flavouring

Organic chemistry can help interpret these ingredients.

Sugar → carbohydrate

Vegetable oil → mainly lipids

Milk powder → contains proteins, carbohydrates and lipids

Citric acid → organic acid

Lecithin → phospholipid-rich emulsifier

Flavouring → may contain various organic compounds

An ingredient list therefore contains considerable chemical information.

---

Ingredient Order

In many food-labelling systems, ingredients are listed according to their amount by mass, generally from greatest to least at the time of manufacture, although exact labelling rules vary by jurisdiction.

Therefore, ingredients near the beginning usually make up a larger proportion of the product than ingredients near the end.

This can help consumers interpret what a food contains.

---

Nutrition Information

Nutrition labels commonly provide information about:

• energy
• protein
• carbohydrates
• sugars
• fat
• saturated fat
• sodium

Depending on the jurisdiction, they may also list:

• fibre
• vitamins
• minerals
• other nutrients

When comparing foods, it is important to check whether values refer to:

per serving

or:

per 100 g / 100 mL

---

"Sugar" Is Not One Chemical

The term sugar can refer to several carbohydrates.

Examples include:

• glucose
• fructose
• sucrose
• lactose
• maltose

These molecules have different structures.

Therefore, a food label containing terms such as glucose syrup, fructose, sucrose, or lactose is describing different carbohydrate ingredients.

---

"Fat" Is Also Chemically Diverse

Dietary fat is not one single molecule.

Food lipids can contain many different fatty acids.

The proportions of:

• saturated fatty acids
• monounsaturated fatty acids
• polyunsaturated fatty acids

vary among foods.

Therefore, two foods with the same total amount of fat can have different lipid compositions.

---

Food Chemistry and Nutrition

Chemistry helps us understand nutrition, but nutrition cannot usually be reduced to a single molecule.

Health effects depend on factors such as:

• overall dietary pattern
• quantities consumed
• nutrient balance
• energy intake
• individual biological needs
• preparation methods

For example, glucose is essential to metabolism, but this does not mean unlimited intake of added sugars is desirable.

Similarly, lipids perform essential biological functions, but different types and amounts matter.

---

Energy Density

Different nutrients provide different amounts of energy.

Approximately:

carbohydrate: 4 kcal/g

protein: 4 kcal/g

fat: 9 kcal/g

This explains why fat is a particularly concentrated energy source.

It also explains why organisms can store substantial energy in relatively small masses of lipid.

---

Protein and Nutrition

Dietary proteins provide amino acids.

The body can use these amino acids to produce:

• enzymes
• structural proteins
• transport proteins
• antibodies
• receptors
• many other molecules

Some amino acids must be obtained in sufficient quantities from the diet.

These are called:

essential amino acids

---

Food Chemistry and Digestion

Digestion involves chemical reactions that break large molecules into smaller molecules.

Carbohydrates

polysaccharides → smaller sugars → monosaccharides

Proteins

proteins → peptides → amino acids

Lipids

Many dietary lipids are broken into smaller components that can be absorbed and processed.

Many digestive reactions involve:

hydrolysis

Water participates in breaking chemical bonds.

---

Enzymes in Digestion

Digestive enzymes act as biological catalysts.

Examples include:

amylases — act on starch

proteases — act on proteins

lipases — act on lipids

Enzymes speed up chemical reactions without being permanently consumed.

Their specific three-dimensional structures allow them to interact with particular substrates.

---

Cooking and Digestibility

Cooking can change the digestibility of some foods.

For example:

• starch gelatinization can make starch more accessible to digestive enzymes
• protein denaturation can make some protein structures more accessible
• plant cell structures can soften

However, excessive processing or heating can also reduce levels of some heat-sensitive nutrients.

Cooking therefore produces both useful and sometimes undesirable chemical changes.

---

Structure → Properties → Food Function

Food chemistry repeatedly demonstrates the relationship:

STRUCTURE → PROPERTIES → FUNCTION

Glucose

Many –OH groups
→ polar
→ water-soluble
→ easily transported in aqueous biological fluids

Triglycerides

Large hydrocarbon-rich structures
→ largely hydrophobic
→ concentrated energy storage

Proteins

Specific amino-acid sequences
→ specific three-dimensional shapes
→ specific biological functions

Phospholipids

Hydrophilic region + hydrophobic region
→ self-assembly in water
→ cell membranes and useful emulsifying behaviour

---

Worked Example: Breakfast Chemistry

Consider a breakfast containing:

• toast
• egg
• butter
• orange

Toast

Contains substantial:

carbohydrate

Browning can involve:

Maillard reactions

Egg

Contains significant:

protein and lipid

Heating causes:

protein denaturation

Butter

Contains substantial:

lipid

particularly triglycerides.

Orange

Contains:

• water
• sugars
• organic acids
• fibre
• vitamin C

A simple breakfast therefore contains a wide variety of organic chemistry.

---

Worked Example: Mayonnaise

Why can mayonnaise contain both oil and water without immediately separating?

It is an:

emulsion

Egg yolk provides emulsifying substances such as phospholipids.

Their molecular structures contain regions that can interact with:

• water
• lipids

This helps stabilize dispersed oil droplets.

---

Worked Example: Apple Browning

An apple is cut and left exposed to air.

Observation:

the cut surface becomes brown

Why?

Cutting damages cells and allows enzymes and substrates to interact in the presence of oxygen.

This produces:

enzymatic browning

Cooling, acidic conditions, or reducing oxygen exposure can slow the process.

---

Worked Example: Egg White

Raw egg white is heated.

Observation:

clear liquid → opaque solid

Why?

Heat causes proteins to:

denature and form new interactions

The proteins form a network that changes the texture and appearance.

---

Worked Example: Nutrition Label

A food provides per serving:

Carbohydrate: 25 g

Protein: 6 g

Fat: 10 g

Approximate energy contribution:

Carbohydrate:

25 × 4 = 100 kcal

Protein:

6 × 4 = 24 kcal

Fat:

10 × 9 = 90 kcal

Approximate total:

100 + 24 + 90 = 214 kcal

This is an approximation because real food labels and energy calculations can involve additional factors.

---

Common Mistakes

Thinking "Chemical" Means Dangerous

All food consists of chemicals.

Thinking Organic Means Healthy

In chemistry, organic describes carbon-based chemistry. It does not automatically mean nutritious or healthy.

Thinking All Carbohydrates Are the Same

Glucose, sucrose, starch, glycogen and cellulose have different structures and functions.

Thinking All Fats Are Identical

Food lipids contain different fatty acids and molecular compositions.

Thinking Oil Contains No Fat

Oil is largely lipid and is nutritionally classified as fat.

Thinking Proteins Are Only Important for Muscles

Proteins also form enzymes, antibodies, receptors, transport proteins and many cellular structures.

Thinking Vitamins Provide Large Amounts of Energy

Vitamins support biological processes but are not major energy-providing nutrients like carbohydrates and fats.

Confusing Vitamins and Minerals

Vitamins are organic compounds.

Minerals are inorganic nutrients.

Thinking Browning Is Always Burning

Browning can involve reactions such as the Maillard reaction, caramelization, or enzymatic browning.

Confusing Maillard Browning with Caramelization

Maillard reactions involve amino compounds and reducing sugars.

Caramelization primarily involves sugars.

Thinking Cooking Only Produces Physical Changes

Cooking can produce both physical and chemical changes.

Thinking Denaturation Breaks Proteins Completely into Amino Acids

Denaturation mainly changes protein folding.

Thinking Oil and Water Separate Because Oil Is Heavier

Their separation is primarily related to differences in polarity and intermolecular interactions; density determines which layer sits above the other.

Assuming Every Food Additive Is Harmful

Food additives have different purposes and safety profiles. Their effects depend on the particular substance and exposure.

Judging a Food from One Nutrient

Overall nutrition depends on the complete diet and quantities consumed.

---

Key Terms

Food chemistry — The study of the chemical composition, properties and transformations of foods.

Nutrient — A substance required or used by the body for energy, growth, repair or regulation.

Carbohydrate — A class of organic compounds including sugars, starches and fibre.

Monosaccharide — A simple sugar such as glucose or fructose.

Disaccharide — A carbohydrate composed of two monosaccharide units.

Polysaccharide — A carbohydrate composed of many linked monosaccharide units.

Glucose — An important monosaccharide used in cellular respiration.

Fructose — A monosaccharide found naturally in many foods.

Sucrose — A disaccharide composed of glucose and fructose.

Starch — A glucose-storage polysaccharide in plants.

Cellulose — A structural polysaccharide in plant cell walls and an important component of dietary fibre.

Dietary fibre — Food components, largely from plants, that resist digestion by human digestive enzymes.

Lipid — A diverse group of largely hydrophobic organic compounds including fats and oils.

Triglyceride — A lipid formed from glycerol and three fatty acids.

Fatty acid — An organic molecule containing a hydrocarbon chain and carboxyl group.

Saturated fatty acid — A fatty acid containing no C=C bonds in its hydrocarbon chain.

Unsaturated fatty acid — A fatty acid containing one or more C=C bonds.

Protein — A biological macromolecule composed of amino-acid residues.

Amino acid — A building block of proteins containing amino and carboxyl functional groups.

Peptide bond — The linkage connecting amino-acid residues in proteins.

Vitamin — An organic compound required in relatively small quantities for normal physiological function.

Mineral — An inorganic nutrient required by the body.

Denaturation — A change in a protein's three-dimensional structure.

Maillard reaction — A complex set of browning reactions involving reducing sugars and amino compounds during heating.

Caramelization — Chemical transformations of sugars caused by strong heating.

Gelatinization — Changes occurring when starch granules absorb water and swell during heating.

Fermentation — Chemical transformation of substances by microorganisms or their enzymes.

Emulsion — A mixture in which droplets of one liquid are dispersed through another immiscible liquid.

Emulsifier — A substance that helps stabilize an emulsion.

Lecithin — A mixture rich in phospholipids commonly used for emulsifying properties.

Oxidation — A chemical process involving loss of electrons or an increase in oxidation state, often involving oxygen in food deterioration.

Rancidity — Deterioration of fats or oils producing undesirable flavours or odours.

Antioxidant — A substance capable of slowing certain oxidation processes.

Food additive — A substance added to food for a technological purpose.

Preservative — A substance or process used to help slow food deterioration.

Enzymatic browning — Enzyme-catalysed browning that can occur when cut plant tissues are exposed to oxygen.

Hydrolysis — A chemical reaction in which water participates in breaking a bond.

Enzyme — A biological catalyst.

Energy density — The amount of energy provided per unit mass of food.

---

Key Takeaways

• Food chemistry studies the substances in foods and how they change.
• Foods contain both organic and inorganic substances.
• Major organic nutrients include carbohydrates, lipids, proteins and vitamins.
• Water and minerals are important inorganic components of food.
• Carbohydrates contain mainly carbon, hydrogen and oxygen.
• Sugars, starch and fibre are carbohydrates.
• Glucose is an important source of energy for cellular respiration.
• Starch is a plant energy-storage polysaccharide.
• Cellulose contributes to dietary fibre.
• Lipids include fats and oils.
• Triglycerides contain glycerol and three fatty acids.
• Triglycerides contain ester linkages.
• Saturated fatty acids contain no C=C bonds in their carbon chains.
• Unsaturated fatty acids contain one or more C=C bonds.
• Molecular structure influences whether fats are solid or liquid.
• Lipids are largely hydrophobic.
• Oil and water separate because of differences in polarity and intermolecular interactions.
• Emulsifiers can help stabilize mixtures of oil and water.
• Proteins are made from amino acids.
• Heating can cause protein denaturation.
• Cooking an egg is a familiar example of protein denaturation.
• The Maillard reaction contributes to browning and flavour development.
• Maillard chemistry involves amino compounds and reducing sugars.
• Caramelization involves chemical changes in sugars.
• Starch gelatinization contributes to thickening and texture changes.
• Fermentation uses microorganisms to transform food chemicals.
• Vitamins are organic compounds needed in relatively small quantities.
• Vitamins B and C are water-soluble.
• Vitamins A, D, E and K are fat-soluble.
• Minerals are not vitamins.
• Food processing can improve safety, storage, flavour and texture.
• Oxidation can contribute to food deterioration.
• Lipid oxidation can contribute to rancidity.
• Enzymatic browning occurs in many cut fruits.
• Antioxidants can slow some oxidation processes.
• Ingredient lists contain useful chemical information.
• Food additives perform specific technological functions.
• Digestion involves chemical reactions including hydrolysis.
• Carbohydrates provide about 4 kcal/g.
• Proteins provide about 4 kcal/g.
• Fats provide about 9 kcal/g.
• Food chemistry helps connect organic chemistry with nutrition, biology and everyday life.

The major relationship throughout this topic is:

MOLECULAR STRUCTURE → CHEMICAL PROPERTIES → FOOD BEHAVIOUR → NUTRITIONAL/BIOLOGICAL FUNCTION

And everyday cooking provides many examples:

egg + heat → protein denaturation

bread + heat → Maillard browning

starch + water + heat → gelatinization

sugar + strong heat → caramelization

oil + water + emulsifier → stable emulsion

Check Your Understanding

1. What is food chemistry?

2. Name four major groups of organic compounds found in foods.

3. Why is carbon important in food chemistry?

4. Give three examples of carbohydrates found in food.

5. What is the molecular formula of glucose?

6. Distinguish between a monosaccharide and a polysaccharide.

7. What is the biological role of starch in plants?

8. Why is cellulose considered dietary fibre for humans?

9. What type of molecules make up most fats and oils?

10. What components form a triglyceride?

11. What type of linkage occurs in triglycerides?

12. Distinguish between saturated and unsaturated fatty acids.

13. Why are many unsaturated oils liquid at room temperature?

14. Why do oil and water normally separate?

15. What is an emulsion?

16. What is the role of an emulsifier?

17. Why can egg yolk help stabilize mayonnaise?

18. What are proteins made from?

19. What happens to many proteins when heated?

20. Explain why egg white becomes firm when cooked.

21. What is the Maillard reaction?

22. How does caramelization differ from the Maillard reaction?

23. What is starch gelatinization?

24. Explain the role of yeast in bread making.

25. Distinguish between water-soluble and fat-soluble vitamins.

26. Why are minerals not classified as vitamins?

27. What is enzymatic browning?

28. What is rancidity?

29. What does an antioxidant do?

30. Challenge: A student prepares a meal containing pasta, grilled chicken, mayonnaise, and sliced apple.

a. Identify the major carbohydrate source.
b. Explain what happens to starch while the pasta cooks.
c. Identify an important biomolecule in the chicken.
d. Explain what happens to chicken proteins during heating.
e. Explain why browning can develop on the surface of the chicken.
f. Name the reaction that contributes to this browning.
g. Identify the two broad types of reactant involved in that reaction.
h. Explain why mayonnaise contains both oil and water without immediately separating.
i. Define an emulsion.
j. Explain the role of an emulsifier.
k. Identify a substance in egg yolk that can help emulsification.
l. Explain why lipid molecules do not normally mix readily with water.
m. Identify the major type of lipid present in many food oils.
n. Describe the basic structure of a triglyceride.
o. Explain the difference between saturated and unsaturated fatty acids.
p. Explain why the cut apple may become brown.
q. Name this type of browning.
r. Suggest one condition that could slow the apple's browning.
s. Explain how organic chemistry helps us understand all four foods.
t. Use one example from the meal to demonstrate:

structure → chemical properties → food behaviour → biological or nutritional function.

Green Chemistry and Sustainability

Modern chemistry gives society medicines, plastics, fuels, fertilizers, electronics, cleaning products, building materials, clothing, and thousands of other useful products. However, producing and using chemicals can also consume large amounts of energy and resources and can create waste or pollution.

Green chemistry is an approach to chemistry that aims to design chemical products and processes that reduce or eliminate the use and generation of hazardous substances.

Instead of asking only:

"Can we make this chemical?"

green chemistry also asks:

"Can we make it using fewer resources, less energy, safer substances, and less waste?"

The goal is not simply to clean up pollution after it has occurred. Whenever possible, green chemistry tries to prevent environmental problems during the design of a chemical process or product.

Why Do We Need Green Chemistry?

Traditional chemical processes can sometimes involve:

• toxic reactants
• hazardous solvents
• large amounts of waste
• high temperatures
• high pressures
• fossil-fuel energy
• non-renewable raw materials
• products that persist in the environment

These problems can affect:

• human health
• wildlife
• air quality
• water quality
• soil
• climate
• natural resources

Green chemistry attempts to reduce these impacts without giving up the useful products chemistry provides.

The challenge is to make chemistry:

effective + economical + safe + sustainable

---

Green Chemistry and Environmental Chemistry

These two fields are related but not identical.

Environmental chemistry studies chemicals and chemical processes occurring in the environment.

It might investigate:

• pollutants in rivers
• atmospheric chemistry
• soil contamination
• chemical breakdown in ecosystems

Green chemistry focuses more strongly on designing chemical products and processes to prevent environmental problems in the first place.

A useful distinction is:

Environmental chemistry → What happens to chemicals in the environment?

Green chemistry → How can we design chemistry to reduce environmental harm?

---

Sustainability

Sustainability means meeting present needs while protecting the ability of future generations to meet their needs.

Sustainable chemistry considers questions such as:

• Where do our raw materials come from?
• Are they renewable?
• How much energy is required?
• How much waste is produced?
• Is the product toxic?
• How long does the product remain in the environment?
• Can it be reused or recycled?
• What happens at the end of its useful life?

This requires thinking about the entire life cycle of a product.

The Life Cycle of a Chemical Product

A product's environmental impact does not begin when we throw it away.

Consider a plastic bottle.

Its life cycle may involve:

raw materials → chemical production → manufacturing → transportation → use → collection → reuse/recycling/disposal

Environmental impacts can occur during every stage.

For example:

Raw Materials

Petroleum may need to be extracted and transported.

Manufacturing

Energy and chemicals are required to produce the polymer.

Transportation

Fuel is needed to move raw materials and products.

Use

The product performs its intended function.

End of Life

The bottle may be:

• reused
• recycled
• incinerated
• placed in landfill
• lost to the environment

Green chemistry considers this complete picture.

---

The Principles of Green Chemistry

Green chemistry is commonly described using 12 principles, developed by chemists Paul Anastas and John Warner.

Students do not always need to memorize every principle, but understanding the major ideas is important.

They include:

• prevent waste
• maximize atom economy
• use safer chemical syntheses
• design safer chemicals
• use safer solvents
• improve energy efficiency
• use renewable feedstocks
• reduce unnecessary chemical modifications
• use catalysts
• design chemicals to degrade safely
• monitor processes to prevent pollution
• reduce the risk of chemical accidents

Together, these principles provide a framework for designing more sustainable chemistry.

---

Preventing Waste

One of the most important ideas is:

It is better to prevent waste than to clean it up later.

Suppose two processes produce the same useful chemical.

Process A

Produces:

1 kg product + 5 kg waste

Process B

Produces:

1 kg product + 0.5 kg waste

If the products are otherwise equivalent, Process B has a major environmental advantage.

It:

• uses resources more efficiently
• requires less waste treatment
• reduces disposal
• may reduce costs

Waste prevention is therefore both an environmental and economic goal.

---

Atom Economy

Chemists can examine how many atoms from the reactants actually become part of the desired product.

This concept is called:

atom economy

A simplified expression is:

Atom economy (%) = (Mr of desired product ÷ total Mr of reactants) × 100

A reaction with high atom economy incorporates a large proportion of reactant atoms into the desired product.

A reaction with low atom economy produces more unwanted by-products.

---

Worked Example: Atom Economy

Suppose:

Total relative formula mass of reactants = 200

Relative formula mass of desired product = 160

Then:

Atom economy = (160 ÷ 200) × 100

Atom economy = 80%

This means 80% of the reactant mass, based on the balanced reaction and formula masses, becomes part of the desired product.

The remaining 20% becomes other products.

---

Atom Economy Is Not Percentage Yield

These ideas are different.

Atom Economy

Describes how efficiently the reaction equation uses reactant atoms.

Percentage Yield

Describes how much product was actually obtained compared with the theoretical maximum.

A reaction could have:

high atom economy but low yield

or:

low atom economy but high yield

A good industrial process ideally performs well in both areas.

---

Addition Reactions and Atom Economy

Addition reactions can sometimes have excellent atom economy.

For example:

ethene + hydrogen → ethane

C₂H₄ + H₂ → C₂H₆

All atoms from the reactants appear in the desired product.

Therefore, the atom economy is:

100%

This is one reason addition reactions can be attractive from a green-chemistry perspective.

---

Safer Chemical Synthesis

Green chemistry aims to reduce the use or production of substances that are:

• toxic
• corrosive
• carcinogenic
• environmentally persistent
• highly flammable
• explosive

If two chemical pathways produce the same useful product, chemists may prefer the pathway using safer substances.

However, replacing a chemical requires careful evaluation.

A replacement should not simply move the hazard somewhere else.

---

Safer Solvents

Chemical reactions are often carried out in:

solvents

Traditional organic chemistry may use solvents that are:

• volatile
• flammable
• toxic
• environmentally damaging

Green chemistry encourages scientists to:

• avoid solvents when practical
• reduce the quantity used
• recycle solvents
• select safer alternatives

In some processes, possible alternatives include:

• water
• ethanol
• supercritical carbon dioxide
• other lower-impact solvent systems

The best solvent depends on the particular chemical process.

Energy Efficiency

Chemical manufacturing can require large amounts of energy.

Energy may be needed for:

• heating
• cooling
• distillation
• pumping
• compression
• maintaining high pressure

Green chemistry aims to reduce unnecessary energy consumption.

When practical, reactions carried out near:

room temperature and atmospheric pressure

may require less energy than reactions requiring extreme conditions.

However, the complete process must be considered rather than assuming that a lower reaction temperature automatically makes a process greener.

---

Why Energy Matters

If industrial energy comes from fossil fuels, greater energy consumption can contribute to:

greenhouse gas emissions

Reducing energy use can therefore reduce:

• fuel consumption
• operating costs
• associated emissions

Using low-carbon renewable energy can further reduce environmental impact.

---

Catalysts

A catalyst increases the rate of a chemical reaction without being consumed overall.

Catalysts are extremely important in green chemistry.

They can allow reactions to:

• occur faster
• operate at lower temperatures
• use less energy
• become more selective
• produce fewer unwanted products

Catalysts and Activation Energy

Chemical reactions require particles to overcome an:

activation energy

A catalyst provides an alternative reaction pathway with a lower activation energy.

Therefore:

lower activation energy → more successful reactions at a given temperature → potentially lower energy requirements

Catalysts can also improve selectivity, meaning more reactant may form the desired product rather than unwanted products.

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Enzymes as Green Catalysts

Enzymes can be used as:

biocatalysts

They are attractive for some industrial processes because they can be:

• highly selective
• effective under relatively mild conditions
• derived from biological systems

Enzymes are used in areas such as:

• food processing
• detergents
• pharmaceutical production
• biotechnology

Biocatalysis is an important connection between:

chemistry + biology + sustainability

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Renewable Feedstocks

A feedstock is a raw material used to produce chemicals.

Many traditional organic chemicals are produced from:

• petroleum
• natural gas
• coal

These are:

non-renewable resources

Green chemistry encourages the use of renewable feedstocks where this genuinely reduces overall environmental impact.

Examples can include materials derived from:

• plants
• algae
• agricultural waste
• forestry residues
• microorganisms

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Biomass

Biomass is biological material that can be used as a source of chemicals, materials, or energy.

Examples include:

• wood
• crop residues
• plant oils
• sugar
• starch
• cellulose
• food-processing waste

Organic chemistry can transform biomass into useful products.

These may include:

• fuels
• solvents
• polymers
• pharmaceutical intermediates
• industrial chemicals

Renewable Does Not Automatically Mean Sustainable

This is an important distinction.

A material may be renewable but still cause environmental problems.

For example, growing crops for industrial chemicals may require:

• farmland
• water
• fertilizers
• pesticides
• transportation
• energy

It could also compete with:

food production

Therefore, chemists must evaluate the entire system.

A better question is not simply:

"Is it renewable?"

but:

"What is its total environmental impact?"

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Bioplastics

Some plastics can be produced partly or entirely from renewable biological resources.

These are often called:

bioplastics

Possible feedstocks include:

• corn starch
• sugar cane
• cellulose
• plant oils

One example is:

polylactic acid (PLA)

PLA can be produced using lactic-acid-derived building blocks, with the carbon feedstock commonly originating from fermented plant sugars.

It is used in some:

• packaging
• disposable products
• fibres
• medical applications

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Bio-Based Does Not Mean Biodegradable

This distinction is extremely important.

Bio-based describes where the carbon feedstock comes from.

Biodegradable describes what can happen to the material under suitable biological conditions.

Therefore:

bio-based ≠ automatically biodegradable

and:

fossil-derived ≠ automatically non-biodegradable

These describe different properties.

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Biodegradable Materials

A biodegradable material can be broken down through biological processes involving organisms such as microorganisms, under appropriate conditions.

Possible products of degradation can include:

• water
• carbon dioxide
• biomass
• methane under some oxygen-poor conditions
• other smaller compounds

The actual products depend on the material and environmental conditions.

Biodegradable Does Not Mean "Disappears Anywhere"

A biodegradable plastic may require specific conditions such as:

• suitable temperature
• moisture
• microorganisms
• oxygen level
• sufficient time

Some compostable plastics break down effectively only in:

industrial composting facilities

They may break down very slowly in:

• oceans
• ordinary soil
• landfill
• cool environments

Therefore, calling a product biodegradable does not mean it can safely be discarded anywhere.

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Compostable Materials

A compostable material is designed to break down under specified composting conditions within defined standards.

Industrial composting facilities may carefully control:

• temperature
• moisture
• oxygen
• microbial activity

This creates conditions very different from ordinary litter in the natural environment.

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Traditional Plastics

Many conventional plastics have valuable properties.

They can be:

• lightweight
• strong
• durable
• inexpensive
• corrosion-resistant
• easily shaped

These properties explain why plastics became so widely used.

Unfortunately, the same property that makes plastic useful can also cause environmental problems:

durability

A material designed not to break down easily can persist after disposal.

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Plastic Waste

Poorly managed plastic waste can:

• accumulate in landfills
• enter rivers
• enter oceans
• harm wildlife
• fragment into smaller pieces
• persist for long periods

Large pieces can gradually break into:

microplastics

These are plastic particles smaller than 5 mm.

Even smaller particles may also form.

Designing Better Plastics

Green chemistry can approach plastic pollution in several ways.

Chemists can design polymers that:

• use renewable feedstocks
• require less energy to manufacture
• use safer additives
• are easier to recycle
• can be chemically recycled
• degrade appropriately after use
• remain durable only as long as needed

This creates an important design question:

How long should a material last?

A bridge component may need to last decades.

Food packaging may be needed for days or months.

Designing every material for maximum permanence may not always be appropriate.

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Recycling

Recycling attempts to return materials to useful applications.

Mechanical Recycling

Plastic is:

• collected
• sorted
• cleaned
• shredded
• melted
• reshaped

This can reduce demand for new raw materials.

However, polymer quality can sometimes decline after repeated processing.

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Chemical Recycling

Chemical recycling attempts to break polymers into:

• monomers
• smaller molecules
• chemical feedstocks

These can potentially be used to produce new materials.

Organic chemistry is central to developing these processes.

Chemical recycling can offer possibilities for materials that are difficult to recycle mechanically, although energy use, cost, emissions, and overall environmental performance must still be evaluated.

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The Circular Economy

Traditional manufacturing is often described as:

take → make → use → dispose

A circular economy aims instead for:

reduce → reuse → repair → recycle → recover

Products and materials are designed to remain useful for as long as practical.

Chemistry plays a major role because materials must be designed with their end of life in mind.

Designing for Degradation

Sometimes a product should remain stable during use but break down after disposal.

Chemists can design molecules containing chemical bonds that are more susceptible to processes such as:

• hydrolysis
• oxidation
• enzymatic degradation
• photochemical reactions

The challenge is controlling:

when and where degradation occurs

A material that degrades during use is not useful.

A material that never degrades may create long-term waste.

Green chemistry attempts to balance these requirements.

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Carbon Dioxide and Organic Chemistry

Carbon dioxide is a major greenhouse gas associated with climate change.

Organic chemistry contributes to efforts to reduce net greenhouse-gas emissions.

Possible approaches include:

• more energy-efficient synthesis
• renewable energy for chemical manufacturing
• renewable carbon feedstocks
• longer-lasting products where appropriate
• recycling carbon-containing materials
• capturing and using CO₂ as a chemical feedstock

Researchers are investigating ways to convert CO₂ into useful chemicals and materials.

However, converting CO₂ usually requires energy, so the source of that energy matters.

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Biofuels

Organic chemistry also contributes to the development of:

biofuels

Examples include:

• bioethanol
• biodiesel
• biogas

Bioethanol can be produced through fermentation of sugars.

A simplified equation is:

glucose → ethanol + carbon dioxide

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

Ethanol can then be used as a fuel or blended with gasoline in some applications.

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Biodiesel

Biodiesel can be produced from materials such as:

• vegetable oils
• used cooking oils
• animal fats

These contain triglycerides.

Through chemical processing, they can be converted into fuel molecules including:

fatty acid esters

This connects sustainable chemistry directly to our earlier study of:

• lipids
• esters
• functional groups
• organic reactions

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Are Biofuels Carbon Neutral?

It is tempting to say:

"Plants absorb CO₂, so biofuels are carbon neutral."

The real situation is more complicated.

Their environmental impact depends on:

• farming
• fertilizer production
• land-use changes
• processing
• transportation
• energy sources
• the original feedstock

Life-cycle analysis is therefore necessary.

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Life-Cycle Assessment

A life-cycle assessment (LCA) evaluates environmental impacts across the stages of a product's life.

It may examine:

• resource extraction
• raw materials
• manufacturing
• energy use
• transportation
• product use
• recycling
• disposal

Possible impacts include:

• greenhouse-gas emissions
• water consumption
• energy consumption
• land use
• toxicity
• resource depletion
• waste generation

LCA helps prevent decisions based on only one part of the environmental picture.

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Worked Example: Two Plastic Cups

Suppose:

Cup A is made from petroleum-derived plastic but can be reused hundreds of times.

Cup B is made from renewable plant material but is used once.

Can we automatically conclude that Cup B is more sustainable?

No.

We would need to consider:

• manufacturing energy
• raw materials
• number of uses
• transportation
• washing
• recycling
• degradation
• disposal

Sustainability requires comparing the complete life cycles.

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Worked Example: Reaction Pathways

Two reactions produce the same organic product.

Reaction A

• 60% atom economy
• toxic solvent
• high temperature
• large quantity of waste

Reaction B

• 95% atom economy
• safer solvent
• catalyst
• lower temperature
• little waste

Which appears more consistent with green chemistry?

Reaction B

It:

• uses reactant atoms more efficiently
• reduces hazardous substances
• reduces waste
• uses a catalyst
• requires less severe conditions

However, a complete comparison would still consider factors such as feedstocks, yield, energy source, toxicity, separation, and life cycle.

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Worked Example: Catalyst

A reaction normally requires:

200°C

A catalyst allows the reaction to proceed efficiently at:

80°C

Why could this be beneficial?

Potentially:

less heating → lower energy demand

If the energy comes from fossil fuels, this could also reduce associated greenhouse-gas emissions.

However, the catalyst itself must also be considered.

Questions include:

• Is it toxic?
• Is it rare?
• Can it be recovered?
• How long does it last?

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Worked Example: Biodegradable Packaging

A company develops packaging that biodegrades rapidly in an industrial composting facility.

Does this mean throwing it into the ocean is environmentally acceptable?

No.

The ocean does not necessarily provide the conditions needed for rapid biodegradation.

The material could still persist and cause environmental harm.

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Worked Example: Renewable Feedstock

A chemical company replaces petroleum with plant material.

Has the process automatically become sustainable?

No.

We must consider:

• land use
• water
• fertilizers
• energy
• transportation
• biodiversity
• competition with food production

Renewability is one important factor, not the only factor.

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Trade-Offs in Green Chemistry

There is rarely a perfect chemical process.

Imagine three alternatives:

Process A

Low energy use but produces hazardous waste.

Process B

Little waste but requires a scarce metal catalyst.

Process C

Uses renewable materials but requires large amounts of water.

Which is best?

There may be no simple answer.

Scientists must compare:

benefits + risks + resource use + waste + energy + life cycle

Green chemistry therefore requires systems thinking rather than focusing on a single environmental measure.

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Organic Chemistry and Environmental Solutions

Organic chemistry is particularly important because many major environmental challenges involve carbon compounds.

Examples include:

• plastics
• fuels
• solvents
• pesticides
• pharmaceuticals
• detergents
• dyes
• industrial chemicals

Organic chemists can modify molecular structures to change:

• toxicity
• biodegradability
• stability
• solubility
• recyclability
• performance

This gives chemistry enormous potential to reduce environmental impacts.

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Green Chemistry in Pharmaceuticals

Pharmaceutical manufacturing can require many reaction steps.

Each step may involve:

• reactants
• solvents
• purification
• heating
• waste

Green pharmaceutical chemistry attempts to:

• reduce reaction steps
• improve atom economy
• use catalysts
• reduce solvent use
• select safer solvents
• improve yields
• reduce energy consumption

Even small improvements can have large effects when production occurs on an industrial scale.

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Green Chemistry in Food Production

Chemistry can also contribute to more sustainable food systems.

Examples include:

• biodegradable packaging
• improved food preservation
• reducing food waste
• safer processing chemicals
• extracting useful chemicals from food waste
• converting agricultural waste into materials

For example, cellulose-rich agricultural residues may become feedstocks for useful chemical products rather than simply becoming waste.

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Waste as a Resource

Green chemistry increasingly asks:

Can waste from one process become a raw material for another?

Examples might include:

• used cooking oil → biodiesel feedstock
• agricultural residues → chemicals or materials
• waste polymers → recycled feedstocks
• food-processing waste → useful organic compounds

This approach supports a more circular economy.

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Common Mistakes

Thinking Green Chemistry Means Cleaning Up Pollution

Green chemistry primarily emphasizes preventing pollution through better design.

Thinking "Natural" Automatically Means Green

Natural substances can still be toxic, scarce, environmentally damaging, or resource-intensive.

Thinking Synthetic Means Environmentally Harmful

Synthetic materials can sometimes be designed to be safer, recyclable, durable, or biodegradable.

Thinking Renewable Means Sustainable

Renewable feedstocks can still require large amounts of land, water, fertilizer, and energy.

Thinking Bio-Based Means Biodegradable

These terms describe different characteristics.

Thinking Biodegradable Means It Can Be Littered

Biodegradation often requires specific environmental conditions.

Thinking Compostable Means It Quickly Degrades Everywhere

Some compostable materials require industrial composting conditions.

Thinking Recycling Has No Environmental Cost

Collection, sorting, transportation, cleaning, and processing all require resources.

Thinking Atom Economy and Percentage Yield Are the Same

Atom economy concerns how reactant atoms are incorporated into products.

Percentage yield concerns how much product is actually obtained.

Thinking Catalysts Make Every Process Green

A catalyst may improve efficiency, but its toxicity, source, lifetime, and recovery must also be considered.

Thinking Lower Temperature Always Means Greener

The entire process must be evaluated.

Focusing Only on Carbon Emissions

Sustainability also includes:

• toxicity
• water use
• land use
• waste
• biodiversity
• resource depletion

Thinking One Material Is Always Better

Environmental impact depends strongly on how a material is produced, used, reused, and disposed of.

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Key Terms

Green chemistry — The design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances.

Sustainability — Meeting current needs while protecting the ability of future generations to meet their needs.

Sustainable chemistry — Chemical practices that consider environmental, resource, economic, and societal impacts over the long term.

Pollution prevention — Avoiding the creation of pollution rather than treating it after formation.

Waste prevention — Designing processes to minimize unwanted materials.

Atom economy — A measure of how effectively reactant atoms are incorporated into the desired product.

Percentage yield — The percentage of the theoretical maximum product actually obtained.

Catalyst — A substance that increases reaction rate without being consumed overall.

Activation energy — The minimum energy barrier associated with a reaction pathway.

Selectivity — The tendency of a reaction to form a particular desired product rather than alternatives.

Biocatalyst — A biological catalyst, often an enzyme, used to promote a chemical reaction.

Solvent — A substance in which other substances are dissolved or in which a reaction is conducted.

Feedstock — A raw material used in a chemical or manufacturing process.

Renewable feedstock — A raw material replenished naturally on a human timescale.

Non-renewable resource — A resource that is not replenished quickly enough to replace its consumption.

Biomass — Biological material that can be used as a source of energy, chemicals, or materials.

Bio-based material — A material made partly or entirely from biological feedstocks.

Bioplastic — A plastic that is bio-based, biodegradable, or both, depending on the specific material and terminology used.

Biodegradable — Capable of being broken down through biological processes under suitable conditions.

Compostable — Able to break down under specified composting conditions according to relevant requirements or standards.

Polymer — A large molecule composed of many repeating or linked molecular units.

Microplastic — A plastic particle smaller than 5 mm.

Mechanical recycling — Recycling involving physical processing such as sorting, shredding, melting, and reshaping.

Chemical recycling — Processes that chemically convert polymers into smaller molecules or feedstocks.

Circular economy — A system designed to keep products and materials in useful circulation and reduce waste.

Life cycle — The stages of a product from raw-material production through manufacturing, use, and end of life.

Life-cycle assessment (LCA) — A method for evaluating environmental impacts across a product's life cycle.

Carbon footprint — The greenhouse-gas emissions associated with a product, activity, organization, or process, usually expressed as CO₂-equivalent.

Biofuel — A fuel produced from biological material.

Bioethanol — Ethanol produced from biological feedstocks, commonly through fermentation.

Biodiesel — A fuel containing fatty acid esters produced from materials such as oils or fats.

Renewable energy — Energy obtained from sources naturally replenished on human timescales.

Hazard — The inherent potential of something to cause harm.

Risk — The likelihood and severity of harm under particular conditions of exposure.

Degradation — Chemical or biological breakdown of a material.

Resource efficiency — Producing useful outcomes while minimizing resource consumption.

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Key Takeaways

• Green chemistry aims to make chemical products and processes safer and more sustainable.
• Prevention is generally preferable to cleaning up pollution after it occurs.
• Green chemistry considers waste, toxicity, energy, resources, and product design.
• Sustainability requires thinking beyond the immediate chemical reaction.
• A product's entire life cycle can contribute to environmental impacts.
• Green chemistry is commonly organized around 12 principles.
• Waste prevention is one of its central principles.
• Atom economy measures how efficiently reactant atoms enter the desired product.
• High atom economy generally means fewer atoms are directed into unwanted by-products.
• Atom economy is different from percentage yield.
• Addition reactions can sometimes achieve 100% atom economy.
• Green chemistry aims to use safer reactants and produce safer products.
• Safer solvents and reduced solvent use can lower environmental impacts.
• Energy-efficient processes can reduce resource use and associated emissions.
• Catalysts can reduce activation energy and improve reaction efficiency.
• Catalysts can also improve selectivity and reduce waste.
• Enzymes can act as biocatalysts.
• Renewable feedstocks can reduce dependence on fossil resources.
• Biomass can provide renewable carbon for fuels, chemicals, and materials.
• Renewable does not automatically mean sustainable.
• Bioplastics can be produced from biological feedstocks.
• Bio-based and biodegradable do not mean the same thing.
• Biodegradable materials require appropriate conditions to break down.
• Compostable materials may require specialized composting conditions.
• Traditional plastics are useful partly because they are durable.
• That same durability can contribute to persistent waste.
• Organic chemists can design polymers for improved recyclability or controlled degradation.
• Mechanical recycling physically reprocesses materials.
• Chemical recycling uses chemical reactions to recover smaller molecules or feedstocks.
• Circular-economy approaches attempt to keep materials useful for longer.
• Bioethanol and biodiesel are examples of biofuels.
• Biofuel sustainability depends on the complete life cycle.
• Life-cycle assessment compares impacts from raw materials through disposal or recycling.
• Green chemistry involves trade-offs rather than simple labels such as "good" or "bad."
• Organic chemistry is central to addressing challenges involving plastics, fuels, solvents, pharmaceuticals, and other carbon-based products.
• Waste materials can sometimes become valuable chemical feedstocks.
• Molecular design can influence toxicity, biodegradability, stability, and recyclability.
• Sustainable chemistry requires considering environmental performance alongside useful chemical function.

The central goal is:

USE LESS → WASTE LESS → USE SAFER CHEMISTRY → USE LESS ENERGY → DESIGN FOR THE FUTURE

A useful way to think about green chemistry is:

raw materials → synthesis → product → use → end of life

At every stage, chemists can ask:

Can we make this safer, cleaner, more efficient, and more sustainable?

Check Your Understanding

1. Define green chemistry.

2. How does green chemistry differ from simply cleaning up pollution?

3. What is sustainability?

4. Why should chemists consider the complete life cycle of a product?

5. Give four goals of green chemistry.

6. Why is preventing waste preferable to treating waste afterward?

7. Define atom economy.

8. Write the equation used to calculate atom economy.

9. Distinguish between atom economy and percentage yield.

10. Why can addition reactions have high atom economy?

11. Why are solvents important when evaluating the environmental impact of a chemical process?

12. Explain how reducing reaction temperature can potentially improve sustainability.

13. What is a catalyst?

14. How can catalysts reduce environmental impact?

15. What is a biocatalyst?

16. Define renewable feedstock.

17. Give three examples of potential renewable feedstocks.

18. Why does renewable not automatically mean sustainable?

19. What is a bioplastic?

20. Distinguish between bio-based and biodegradable.

21. Why does biodegradable not mean that a material can safely be littered?

22. What is the difference between mechanical and chemical recycling?

23. What is a circular economy?

24. What is a life-cycle assessment?

25. Give four environmental factors that an LCA might investigate.

26. Explain one way organic chemistry can help reduce plastic pollution.

27. What is bioethanol?

28. How can biodiesel be connected to the chemistry of esters?

29. Why are biofuels not automatically carbon neutral?

30. Challenge: A company wants to replace a conventional petroleum-derived plastic package with a new plant-derived polymer.

a. What is meant by a renewable feedstock?
b. Why could using plant material reduce dependence on fossil resources?
c. Does being plant-derived prove that the polymer is biodegradable? Explain.
d. Does being biodegradable mean the package will quickly disappear if littered? Explain.
e. What environmental conditions might influence degradation?
f. Why should land use be considered?
g. Why should water consumption be considered?
h. Why should energy used during manufacturing be considered?
i. Why should transportation be considered?
j. What is meant by the product's life cycle?
k. What type of analysis could compare the two packages across their entire life cycles?
l. Explain why recycling should be considered during product design.
m. Distinguish between mechanical and chemical recycling.
n. Explain how a circular-economy approach could improve packaging sustainability.
o. Explain why a reusable petroleum-derived product might sometimes have a lower total impact than a single-use bio-based product.
p. Explain why "natural" does not automatically mean environmentally safe.
q. Explain why "synthetic" does not automatically mean environmentally harmful.
r. Identify two ways organic chemists could modify a polymer to improve its environmental performance.
s. Explain why sustainability decisions often involve trade-offs.
t. Use this example to explain the relationship:

MOLECULAR DESIGN → MATERIAL PROPERTIES → PRODUCT PERFORMANCE → ENVIRONMENTAL IMPACT.