Genetic modification (genetic engineering)
BiologyΒ· 5.12β5.16 (4BI1 2017 Issue 3)Β· 12 min read
1. Enzymes Used in Genetic Engineeringβ β ββββ± 2 min
Restriction enzyme
Enzyme that cuts DNA at specific, recognisable target sites, allowing isolation of desired genes or cutting of vector DNA
Ligase enzyme
Enzyme that seals the sugar-phosphate backbone of two cut pieces of DNA, joining them together permanently
Name the enzyme used to cut a human insulin gene out of human DNA, and state its core function.
- 1
- Identify the correct enzyme: restriction enzyme
- 2
- State its function: It cuts DNA at specific target sites to cleanly remove the insulin gene from the human genome.
Exam tip:
Mark schemes strictly distinguish these enzymes: never state that restriction enzymes join DNA, or ligase cuts DNA β this is a common 1β2 mark discriminator.
2. Vectors for Recombinant DNA Transferβ β ββββ± 2 min
Vector
Structure that carries recombinant DNA into a host cell, so the foreign gene can be expressed by the host
Name two structures that act as vectors in genetic engineering, and describe one feature of each that makes it suitable for this role.
- 1
- Plasmid: Small circular DNA found in bacteria, which is easily cut open to insert foreign DNA and taken up by bacterial host cells.
- 2
- Virus: Naturally inserts its own genetic material into host cells, so can be modified to carry recombinant DNA instead.
3. Manufacturing Human Insulin Using GM Bacteriaβ β β βββ± 3 min
Restriction enzyme cuts the desired human insulin gene out of human DNA, and cuts open a bacterial plasmid, leaving matching sticky ends
Ligase enzyme joins the insulin gene into the plasmid, forming recombinant DNA
The plasmid (vector) inserts the recombinant DNA into a host bacterial cell
GM bacteria are grown in large industrial fermenters under optimal conditions, reproducing rapidly and expressing the insulin gene to make insulin protein
Insulin is extracted and purified for medical use by people with diabetes
A 4-mark exam question asks you to outline the process of making human insulin using GM bacteria. List the key steps to gain full marks.
- 1
- Use restriction enzyme to cut out the human insulin gene and cut open a bacterial plasmid (1 mark)
- 2
- Use ligase to join the insulin gene into the plasmid to make recombinant DNA (1 mark)
- 3
- Insert the recombinant plasmid into a bacterial host cell using the plasmid as a vector (1 mark)
- 4
- Grow GM bacteria in a fermenter to produce large quantities of insulin, which is then purified (1 mark)
Exam tip:
Always list steps in order, and name both enzymes explicitly β you will lose marks if you miss the ligase or vector step.
4. GM Plants for Improved Food Productionβ β β βββ± 3 min
Common GM crop traits: pest resistance, herbicide resistance, higher yield, added nutrients (e.g. beta-carotene in golden rice), longer shelf life
Key benefits: reduces pesticide use, lowers food costs, reduces malnutrition, improves food security in low-income regions
Key concerns: unknown long-term health effects of consuming GM crops, risk of modified genes spreading to wild plant populations, ethical concerns about corporate control of seed supplies
Evaluate the use of GM crops to improve global food production, including one benefit and one concern.
- 1
- Benefit example: GM pest-resistant crops reduce pesticide use, increase yield, and lower food costs for consumers, improving food security for growing populations (2 marks)
- 2
- Concern example: There is uncertainty about long-term health effects of eating GM crops, and modified genes could spread to wild plants, reducing biodiversity (2 marks)
- 3
- Balanced conclusion: GM crops offer significant benefits for food security, but regulation is required to manage potential risks (1 mark for balanced evaluation)
5. Transgenic Organism Definitionβ βββββ± 1 min
Transgenic
Describes an organism that contains genetic material that has been artificially transferred from a different species
Explain why GM bacteria producing human insulin are classified as transgenic.
- 1
- State the definition of transgenic: An organism is transgenic if it carries genetic material transferred from a different species.
- 2
- Apply to the example: GM bacteria have a human insulin gene (from a different species, humans) inserted into their DNA, so they are transgenic.
6. Common Pitfalls
Wrong move:
Mixing up restriction and ligase enzyme roles, stating ligase cuts DNA or restriction joins it
Why:
Mark schemes strictly award marks for correct role assignment, so this error will lose all available marks for enzyme questions
Correct move:
Memorise: Restriction = Cut, Ligase = Join (mnemonic: Restriction Cuts, Ligase Locks)
Wrong move:
Only naming plasmids as vectors, forgetting viruses are also valid vectors
Why:
Exam questions often ask for two examples of vectors, so missing viruses will lose half the available marks
Correct move:
Memorise both plasmids and viruses as vector types, with one key feature of each
Wrong move:
Using 'recombinant DNA' and 'transgenic' interchangeably
Why:
Recombinant DNA refers to the modified DNA molecule, while transgenic describes the organism carrying cross-species DNA, so the terms are not synonymous
Correct move:
Distinguish explicitly: Recombinant = DNA molecule, Transgenic = organism with DNA from another species
Wrong move:
Classifying selective breeding as a type of genetic engineering
Why:
Selective breeding is a traditional, separate technique that does not involve cutting and joining DNA with enzymes, so it is not genetic modification
Correct move:
Only label processes using restriction enzymes, ligase and vectors as genetic engineering
Wrong move:
Omitting the fermenter step when describing insulin production
Why:
Fermenters are required to grow large quantities of GM bacteria to produce commercial volumes of insulin, so missing this step loses marks for full process questions
Correct move:
Always include the fermenter culture and insulin purification steps at the end of the insulin production process
7. Quick Reference Cheatsheet
Term/Process | Key Exam Details |
|---|---|
Restriction enzyme | Cuts DNA at specific sites |
Ligase enzyme | Joins/seals pieces of DNA together |
Vectors | Plasmids, viruses: carry recombinant DNA into host cells |
Insulin production steps (order) | Cut gene + plasmid β ligase joins β vector inserts into bacteria β fermenter culture β purify insulin |
GM crop benefits | Pest resistance, higher yield, added nutrients, longer shelf life |
GM crop concerns | Long-term health risk, gene flow to wild plants, ethical concerns |
Transgenic definition | Organism with DNA transferred from a different species |
8. Frequently Asked
What is the difference between restriction and ligase enzymes?
Restriction enzymes cut DNA at specific sites, while ligase enzymes join/seal cut pieces of DNA together. This is a common 2-mark exam question, so never mix up their roles.
Are both plasmids and viruses classified as vectors?
Yes: plasmids are small circular DNA molecules found in bacteria that can be easily modified to carry foreign DNA, while viruses naturally insert genetic material into host cells so can be adapted as vectors.
Going deeper
What's Next
Now that you have mastered genetic modification content for Edexcel IGCSE Biology, you can move on to related topics to complete the Use of Biological Resources unit. Next, learn about selective breeding, a traditional alternative to genetic engineering used to produce desired traits in plants and animals. You should also review fermenter operation to ensure you can answer full 6-mark questions on insulin production, and study cloning content for extended answer questions comparing different methods of manipulating biological resources. Practice past paper questions on this topic to familiarise yourself with mark scheme requirements for process and evaluation questions.