Introduction

Every living organism—from the smallest bacterium to the largest blue whale—is built from millions of tiny molecules working together. These molecules provide energy, build cells, store genetic information, and carry out the countless chemical reactions needed to keep organisms alive. Collectively, these essential molecules are known as biomolecules.

Although there are many different biomolecules, most belong to four major groups: carbohydrates, lipids, proteins, and nucleic acids. Understanding these molecules helps us explain how living organisms grow, reproduce, obtain energy, and respond to their environment.

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What Are Biomolecules?

Biomolecules are molecules that are produced by living organisms or are essential for life.

They make up the structures of cells and perform the chemical processes that keep organisms alive.

Examples include:

• sugars
• fats
• enzymes
• DNA
• cell membranes
• hormones

Definition:
Biomolecules are chemical compounds found in living organisms that are essential for life.

Without biomolecules:

• cells could not grow,
• organisms could not obtain energy,
• genetic information could not be stored,
• life would not exist.

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Why Are Biomolecules Important?

Every cell contains thousands of different biomolecules working together.

Biomolecules help cells to:

• produce energy,
• build cell structures,
• repair damaged tissues,
• transport substances,
• communicate with other cells,
• store and use genetic information,
• control chemical reactions.

Different biomolecules have different specialised roles, but together they allow organisms to survive and reproduce.

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Carbon – The Foundation of Life

Almost all biomolecules contain the element carbon.

Carbon is often called the foundation of life because it can form stable bonds with many other atoms, including:

• carbon,
• hydrogen,
• oxygen,
• nitrogen,
• phosphorus,
• sulfur.

Carbon has four valence electrons, allowing it to form four covalent bonds.

This makes it possible to build:

• long chains,
• branched chains,
• rings,
• complex three-dimensional structures.

These structures give rise to the enormous variety of biomolecules found in living organisms.

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The Four Major Groups of Biomolecules

Scientists classify biomolecules into four major groups.

Each group has unique properties that make it suitable for its specific role.

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Carbohydrates

Carbohydrates are the body's main source of quick energy.

They are made of carbon, hydrogen, and oxygen.

Examples include:

• glucose,
• starch,
• glycogen,
• cellulose.

Functions:

• provide energy,
• store energy,
• strengthen plant cell walls.

Foods rich in carbohydrates include:

• bread,
• rice,
• pasta,
• potatoes,
• fruit.

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Lipids

Lipids include:

• fats,
• oils,
• waxes,
• phospholipids.

Unlike carbohydrates, lipids provide long-term energy storage.

Functions include:

• storing energy,
• insulating the body,
• protecting organs,
• forming cell membranes,
• producing certain hormones.

Foods rich in lipids include:

• butter,
• nuts,
• seeds,
• cooking oils,
• avocados.

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Proteins

Proteins are among the most versatile biomolecules.

They are made from smaller units called amino acids.

Functions include:

• building muscles,
• repairing tissues,
• transporting substances,
• defending against disease,
• acting as enzymes,
• acting as hormones.

Examples include:

• haemoglobin,
• collagen,
• insulin,
• digestive enzymes,
• antibodies.

Protein-rich foods include:

• meat,
• fish,
• eggs,
• beans,
• dairy products.

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Nucleic Acids

Nucleic acids store and transmit genetic information.

The two main nucleic acids are:

• DNA (Deoxyribonucleic Acid)
• RNA (Ribonucleic Acid)

Functions:

• store genetic instructions,
• direct protein synthesis,
• pass inherited characteristics from parents to offspring.

Every living cell contains DNA.

Without nucleic acids, organisms could not reproduce or pass on genetic information.

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Biomolecules and Cell Function

Each cell depends on all four biomolecule groups.

Together, these molecules allow cells to:

• grow,
• divide,
• respond to their environment,
• repair themselves,
• reproduce.

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Comparing the Four Biomolecule Groups

Although they all contain carbon, each group performs very different roles.

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Worked Example 1

Which biomolecule stores genetic information?

A. Carbohydrates

B. Lipids

C. Proteins

D. Nucleic acids

Answer

D. Nucleic acids

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Worked Example 2

A student says:

"Lipids are mainly used for quick energy."

Question

Is this correct?

Solution

No.

Carbohydrates provide quick energy, while lipids are mainly used for long-term energy storage, insulation, and forming cell membranes.

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Worked Example 3

Complete the table.

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Worked Example 4

Why is carbon considered the foundation of life?

Solution

Carbon has four valence electrons, allowing it to form four strong covalent bonds. This enables carbon atoms to form long chains, rings, and complex molecules that make up the biomolecules found in all living organisms.

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Real-World Connection

Understanding biomolecules helps scientists develop medicines, improve nutrition, diagnose diseases, and create new biotechnology products. Doctors study proteins to understand diseases, nutritionists examine carbohydrates and lipids when planning healthy diets, and geneticists investigate DNA to identify inherited conditions and develop gene therapies.

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Did You Know?

The DNA inside a single human cell is about 2 metres long if stretched out. Yet it fits inside a nucleus that is only about 0.000006 metres (6 micrometres) wide! This remarkable feat is possible because DNA is tightly coiled and packaged around proteins called histones.

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Key Terms

• Biomolecule — a chemical compound found in living organisms that is essential for life.
• Carbon — the element that forms the backbone of most biological molecules.
• Carbohydrate — a biomolecule that provides quick energy and structural support.
• Lipid — a biomolecule used for long-term energy storage, insulation, and cell membranes.
• Protein — a biomolecule made of amino acids that performs structural and functional roles in cells.
• Nucleic Acid — a biomolecule, such as DNA or RNA, that stores and transmits genetic information.
• Cell membrane — the thin boundary surrounding a cell, largely composed of lipids and proteins.

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Key Takeaways

• Biomolecules are essential chemical compounds that build living organisms and enable life processes.
• The four major groups of biomolecules are carbohydrates, lipids, proteins, and nucleic acids.
• Carbon is the foundation of most biological molecules because it can form four covalent bonds, allowing complex molecular structures to develop.
• Each biomolecule group has specialised functions: carbohydrates provide quick energy, lipids store energy and form membranes, proteins perform most cellular tasks, and nucleic acids store genetic information.
• All four groups work together to support the structure, growth, reproduction, and functioning of living cells.