Foundations of Biotechnology
4. Cells, DNA, and Biotechnology
Learning outcomes
- I can describe the relationship between cells, DNA, and genes.
- I can explain how genetic information controls traits.
- I can identify cellular components involved in biotechnology.
- I can explain why DNA is important in biotechnology applications.
- I can describe how scientists manipulate genetic material.
Cells, DNA, and Biotechnology
Modern biotechnology depends on understanding how cells store and use genetic information. Inside cells, DNA contains instructions that influence how organisms grow, develop, function, and reproduce.
Scientists can study and sometimes modify this genetic information to produce useful organisms, substances, medicines, and technologies.
A useful relationship to remember is:
Cells contain DNA → DNA contains genes → Genes contain instructions → Instructions influence traits
Cells: The Basic Units of Life
A cell is the basic structural and functional unit of a living organism.
Some organisms, such as bacteria and yeast, consist of only one cell, while plants and animals contain enormous numbers of specialised cells.
Cells carry out essential processes including:
- obtaining and using energy
- producing proteins
- removing waste
- responding to their environment
- growing
- reproducing
Biotechnology often involves using or modifying these natural cellular processes.
Where Is DNA Found?
In eukaryotic cells, such as plant and animal cells, most DNA is located inside the nucleus.
The DNA is organised into structures called chromosomes.
Therefore:
Cell → Nucleus → Chromosomes → DNA → Genes
Bacteria are different because they do not have a nucleus. Their main chromosome is found in the cytoplasm, in a region called the nucleoid.
Many bacteria also contain small circular pieces of DNA called plasmids.
Plasmids are especially important in biotechnology.
What Is DNA?
DNA stands for deoxyribonucleic acid.
DNA is the molecule that stores hereditary genetic information in living organisms.
A DNA molecule consists of two strands twisted into a structure called a double helix.
DNA contains four different bases:
- adenine (A)
- thymine (T)
- cytosine (C)
- guanine (G)
The order, or sequence, of these bases stores genetic information.
What Is a Gene?
A gene is a section of DNA containing information used to produce a functional product, often a particular protein.
A single DNA molecule contains many genes.
For example, genes can influence characteristics associated with:
- blood groups
- pigmentation
- growth
- metabolism
- production of particular enzymes
- many other biological characteristics
Genes do not usually produce traits directly. Instead, many genes contain instructions that cells use to make proteins, and those proteins help produce observable characteristics.
A simplified relationship is:
Gene → Protein → Cell function → Trait
How Can Genetic Information Control Traits?
Proteins perform many important functions inside organisms.
They can act as:
- enzymes
- hormones
- receptors
- antibodies
- structural components
- transport proteins
Because genes provide information for making proteins, differences in DNA can sometimes result in different versions or amounts of proteins.
This can contribute to differences in traits.
For example, a gene may contain instructions for an enzyme involved in producing a pigment.
DNA sequence
↓
Gene information
↓
Protein produced
↓
Chemical reaction occurs
↓
Pigment produced
↓
Observable characteristic
However, most traits are more complicated than a single gene producing a single characteristic. Many traits are influenced by multiple genes and environmental factors.
DNA, RNA, and Protein Production
Cells generally do not use DNA directly as the template at the site of protein synthesis.
Instead, information from DNA can be copied into a molecule called RNA.
A simplified pathway is:
DNA → RNA → Protein
This is sometimes called the central dogma of molecular biology.
The process of making RNA from DNA is called transcription.
The information in RNA can then be used by ribosomes to build proteins. This process is called translation.
These processes are extremely important in biotechnology because scientists can introduce genetic instructions into cells and use the cells to manufacture particular proteins.
Important Cellular Components in Biotechnology
Several cell structures are particularly important.
| Component | Function | Biotechnology Importance |
|---|---|---|
| DNA | Stores genetic information | Can be analysed or modified |
| Genes | Contain specific genetic instructions | Can be transferred or edited |
| Nucleus | Contains most DNA in eukaryotic cells | Important when modifying plant or animal cells |
| Ribosomes | Build proteins | Produce proteins encoded by genes |
| Enzymes | Control chemical reactions | Used extensively in biotechnology |
| Plasmids | Small DNA molecules in many bacteria | Can carry genes into bacterial cells |
| Cell membrane. | Controls movement into and out of cells. | Important when introducing material into cells |
Why Are Plasmids Important?
Plasmids are small, usually circular DNA molecules found naturally in many bacteria.
They are separate from the bacterium's main chromosome.
Scientists can modify plasmids so that they carry useful genes.
This makes plasmids useful as vectors.
A vector is something used to carry genetic material into a cell.
Why Is DNA Important in Biotechnology?
DNA is important because it contains the instructions used by cells.
If scientists can identify, copy, transfer, or modify those instructions, they can influence what a cell does.
DNA technology can therefore be used to:
- identify organisms
- diagnose some diseases
- study inherited conditions
- identify particular genes
- produce useful proteins
- genetically modify crops
- investigate biological relationships
- study evolution
- edit particular DNA sequences
DNA is therefore one of the central materials of modern biotechnology.
Manipulating Genetic Material
Scientists have developed several methods for working with DNA.
Depending on the application, scientists may:
Extract → Cut → Copy → Analyse → Transfer → Edit
different pieces of genetic material.
Let's examine some of these processes.
Extracting DNA
The first step in many biotechnology procedures is to extract DNA from cells.
Cells must be broken open so their DNA can be released.
Scientists then separate the DNA from other cellular materials such as:
- proteins
- membranes
- carbohydrates
The purified DNA can then be analysed or manipulated.
DNA extraction is used in research, medicine, agriculture, and forensic science.
Cutting DNA
Scientists can use specialised proteins called restriction enzymes to cut DNA.
Different restriction enzymes recognise particular DNA sequences.
They act like molecular scissors, cutting DNA at specific locations.
This allows scientists to isolate particular sections of genetic material.
Joining DNA
Pieces of DNA can also be joined together.
An enzyme called DNA ligase can connect pieces of DNA.
A simplified genetic-engineering process might therefore involve:
Cut DNA → Insert desired gene → Join DNA
When DNA from different sources is combined, the resulting DNA is called recombinant DNA.
Copying DNA
Scientists often need more DNA than is available in the original sample.
A technique called polymerase chain reaction (PCR) can make enormous numbers of copies of a selected DNA region.
Starting with a tiny amount of DNA:
Small DNA sample
↓
PCR
↓
Millions or billions of copies of the target DNA region
This makes the DNA much easier to analyse.
Transferring Genes Between Organisms
One important biotechnology technique involves transferring a gene into another organism.
For example, scientists can insert a useful gene into a bacterial plasmid.
A simplified process is:
- Identify the desired gene.
- Obtain or make the DNA sequence.
- Insert the DNA into a plasmid.
- Introduce the plasmid into bacterial cells.
- Grow the bacteria.
- The cells may express the inserted gene and produce the desired protein.
Example: Producing Human Insulin
The production of human insulin is a classic example of biotechnology connecting cells, DNA, and proteins.
Scientists can place DNA encoding human insulin into microorganisms such as bacteria or yeast.
The engineered cells can then use the genetic instructions to help manufacture insulin.
The cells are grown in large quantities, and the insulin is collected and purified for medical use.
The basic idea is:
DNA containing insulin instructions
↓
DNA introduced into microorganism
↓
Cell reads genetic information
↓
Protein produced
↓
Insulin collected and purified
This works because the fundamental genetic code and protein-production machinery are shared across living organisms.
Editing DNA
Scientists can also make targeted changes to genetic material.
Modern gene-editing techniques such as CRISPR-based systems can be programmed to target particular DNA sequences.
Depending on the method and purpose, scientists may attempt to:
- remove a DNA sequence
- replace a sequence
- alter individual DNA bases
- disable a gene
- change how a gene functions
Gene editing has applications in biological research, agriculture, medicine, and biotechnology.
It also raises important questions about safety and ethics, particularly when changes could be inherited by future generations.
Using Cells as Biological Factories
Once scientists understand how cells use genetic information, they can use cells to manufacture useful products.
A genetically modified microorganism can essentially become a microscopic biological factory.
For example:
New gene
↓
DNA
↓
RNA
↓
Protein
↓
Useful biotechnology product
Millions or billions of cells can then be grown in bioreactors, allowing large quantities of the product to be manufactured.
Putting the Relationship Together
The connections between these ideas are important:
Cells
Cells provide the biological machinery needed to carry out life processes.
↓
DNA
DNA stores genetic information.
↓
Genes
Genes are specific regions of DNA containing biological instructions.
↓
Proteins
Cells use genetic information to manufacture proteins.
↓
Traits and Functions
Proteins influence cellular functions and many characteristics of organisms.
↓
Biotechnology
Scientists can study or manipulate DNA to change what cells do or what substances they produce.
This gives us the central idea:
Biotechnology uses our understanding of cells and genetic information to produce useful biological outcomes.
Did You Know?
The DNA molecules inside cells are extremely long compared with the cells themselves.
A human cell contains roughly 2 metres of DNA when the DNA in all of its chromosomes is stretched out end to end. Yet this DNA is packaged into a nucleus only a few micrometres across.
Cells accomplish this by tightly organising and packaging DNA into chromatin and chromosomes.
Key Terms
Cell – The basic structural and functional unit of life.
DNA – The molecule that stores hereditary genetic information.
Gene – A region of DNA containing information for a functional product, often a protein.
Chromosome – A structure containing a long DNA molecule associated with proteins.
Protein – A biological molecule with structural, chemical, signalling, or other cellular functions.
Plasmid – A small DNA molecule found naturally in many bacteria and often used as a biotechnology vector.
Vector – A carrier used to introduce genetic material into a cell.
Restriction enzyme – An enzyme that cuts DNA at particular sequences.
DNA ligase – An enzyme that joins pieces of DNA.
Recombinant DNA – DNA formed by combining genetic material from different sources.
Genetic engineering – The deliberate modification of genetic material using biotechnology.
Key Takeaways
- Cells contain genetic information in the form of DNA.
- In eukaryotic cells, most DNA is organised into chromosomes inside the nucleus.
- Genes are regions of DNA containing genetic instructions.
- Genetic information influences traits largely by controlling the production and regulation of proteins.
- A useful simplified pathway is DNA → RNA → protein.
- Important biotechnology components include DNA, genes, plasmids, enzymes, and ribosomes.
- Bacterial plasmids can be used as vectors for carrying genes.
- Scientists can extract, copy, cut, join, transfer, analyse, and edit DNA.
- Manipulating DNA allows scientists to influence what cells produce or how organisms behave.
- Genetically modified microorganisms can be used as biological factories to manufacture useful substances.
- Understanding the relationship between cells, DNA, genes, and proteins provides the foundation for much of modern biotechnology.