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5.3Use of Biological Resources

Genetic Modification (Genetic Engineering) — Edexcel Linear - OL Revision Notes & Topical Questions

10 min read 12 parts Lesson 7 of 8 Unit quiz

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Genetic Modification: Process, Insulin and GM Crops — EDEXCEL LINEAR - OL notes: Describe how a gene is transferred using restriction enzymes, ligase and vectors, explain how bacteria make human insulin, and evaluate GM crops.Genetic modification (genetic engineering) is the tran…

  • sticky ends
  • DNA ligase
  • Worked example 1
  • Worked example 2
  • Worked example 3
  • Worked example 4

Part 1 of 5Steps of genetic modification

Genetic modification (genetic engineering) is the transfer of a gene or section of DNA from one organism into the DNA of another. The sequence is:

1
Locate the gene to be transferred in the original organism.
2Restriction enzymes
Cut the gene out using restriction enzymes.
  • Different restriction enzymes cut at different DNA sequences, so the right enzyme isolates the required piece.
  • The cut leaves sticky ends, short single-stranded sections that will pair with complementary bases.
3
Cut a bacterial plasmid with the same restriction enzyme, so its sticky ends are complementary to those of the gene.
4DNA ligase
Join the gene and plasmid with DNA ligase, which links complementary sticky ends into one unbroken molecule (recombinant DNA).
5
Insert the recombinant plasmid into a bacterial cell.
6
The bacteria reproduce, copying the plasmid, so all make the protein; they are grown in a fermenter.

Think of restriction enzymes as DNA scissors and ligase as DNA glue. Plasmids and viruses act as vectors: plasmids carry DNA into bacteria or yeast, and viruses transfer DNA into human cells or bacteria.

Remember the order

  • locate the gene, cut it out, cut the plasmid, join them, insert into bacteria, grow in a fermenter.
  • Marks are often given for each step in this sequence, so write them in order and name the enzyme at each stage.

Part 2 of 5Human insulin from bacteria

The gene for human insulin is located on a human chromosome and cut out with a restriction enzyme.

Human insulin from bacteria
A bacterial plasmid is cut with the same enzyme, and ligase joins the gene into it.
The recombinant plasmid enters bacteria, which multiply in a fermenter under controlled conditions and make large quantities of human insulin.
The insulin is collected and purified for medical use to treat diabetes.

Bacteria are very useful because they have the same genetic code as other organisms, so they read the gene and make the same protein; they raise no ethical concerns about suffering, unlike animals; and plasmids separate from the main chromosome are easy to remove, alter and return.

Part 3 of 5GM plants and food production

GM plants have had foreign genes inserted into their genome to give new traits such as pest resistance, herbicide resistance, improved nutrition or drought tolerance. Examples: wheat and maize with a bacterial gene that makes an insect-killing poison (resistant to caterpillars), crops resistant to a herbicide so that only weeds are killed, "golden rice" with genes from another plant and a bacterium that make vitamin A to help prevent deficiency, and drought-resistant crops.

Part 4 of 5Advantages and disadvantages of GM crops

AdvantagesDisadvantages
Less use of herbicides and pesticides, better for the environmentGM seed costs more, so small farmers may not compete with larger ones
Cheaper and less time-consuming for farmersDependence on certain chemicals often sold by the seed company
Higher yields since crops do not compete with weeds or suffer pest damageGenes could pass to wild plants by pollination (for example resistant weeds)
Reduced biodiversity when herbicides remove weeds, harming insects and insect-eating birds; some GM plants grow less well; effects on health not fully explored

Consider the ethics too

  • some people worry about the long-term effects on health and the environment, others about companies owning seeds.
  • Supporters point to higher food supply, vitamin-enriched crops and less pesticide spraying.
  • In longer answers, give a balanced view and a judgement supported by one example from each side.

Part 5 of 5Worked examples

  1. Describe the roles of restriction enzymes and ligase in genetic engineering. [4]4 marks

  2. Explain why the same restriction enzyme is used for the gene and the plasmid. [2]2 marks

  3. State two reasons bacteria are used to make human insulin. [2]2 marks

  4. Give two benefits and two risks of GM crops. [4]4 marks

Key terms

TermMeaning
Restriction enzymeEnzyme that cuts DNA at specific sequences.
Sticky endsShort single-stranded ends on cut DNA that join complementary bases.
DNA ligaseEnzyme that joins DNA pieces.
PlasmidSmall circle of DNA in bacteria used as a vector.
VectorCarrier used to transfer DNA into cells.
Recombinant DNADNA made by joining DNA from different sources.

Avoid these mistakes

1
Mixing up the enzymes — restriction cuts, ligase joins.
2
Forgetting to cut the plasmid with the same enzyme.
3
Saying bacteria make insulin naturally — they do so only after the human gene is inserted.
4
Saying GM is the same as selective breeding.

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