4.3Unit 2 · Use of Biological Resources
Genetic Modification (Genetic Engineering) — Unit 2 — Edexcel IGCSE Biology Modular - UNIT 2 Revision Notes & Topical Questions
10 min read 4 parts Lesson 4 of 5 1 quiz
Lesson summary
Describe the use of restriction enzymes, ligase and vectors.The genetic code is universal, so bacteria can read a human gene and make the human protein.The same restriction enzyme must cut both the gene and the plasmid so the sticky ends match.Human insulin from GM bacteria is us…
- Genetic modification
- DNA ligase
- Manufacturing insulin
- Food production benefits
- GMO or transgenic?
- Plasmids and viruses as vectors
Section 1 of 4Genetic Modification (Genetic Engineering) — Unit 2
Genetic modification:
a gene for a desired characteristic is taken from one organism and inserted into another. The organism receiving the gene is transgenic. This works because all organisms use the same DNA code.Restriction enzymes
recognise specific base sequences and cut DNA there, often in a staggered way producing sticky ends. Using the same enzyme on the donor DNA and the plasmid gives complementary sticky ends that can pair up.DNA ligase
seals the gene into the cut plasmid, forming recombinant DNA. The plasmid acts as a vector; viruses can also be vectors.Manufacturing insulin:
the recombinant plasmid is taken up by bacteria.- These are grown in large fermenters with controlled temperature, pH, nutrients and oxygen.
- The bacteria divide rapidly and each produces human insulin, which is extracted and purified.
- This gives a reliable, large supply of insulin identical to human insulin.
GM plants:
genes can be inserted into crop plants to give resistance to insect pests (reducing insecticide use), resistance to herbicides (so fields can be sprayed to kill weeds), tolerance of drought or salt, or improved nutritional value (e.g. golden rice producing beta-carotene).Food production benefits:
higher yields, less crop loss, less use of chemical sprays, and more nutritious food, helping feed a growing population.Concerns:
possible transfer of genes to wild plants creating herbicide-resistant weeds, effects on insects and food chains, reduced biodiversity, unknown long-term health effects, and high cost of seed for farmers.GMO or transgenic?
Any organism with altered DNA is a GMO. It is only transgenic if the new DNA came from a different species, so every transgenic organism is a GMO but not every GMO is transgenic.Plasmids and viruses as vectors:
Plasmids are used to carry genes into bacteria or yeast; viruses can carry genes into bacteria or human cells. When GM bacteria divide, the recombinant plasmid is copied too, so all offspring make the protein.Why bacteria are used:
They share the same genetic code as us, so they can make human proteins;- they reproduce rapidly;
- their plasmids are separate from the main chromosome and easy to remove and modify;
- and there are no ethical concerns about pain or distress.
Further concerns about GM crops:
GM seed is expensive, so poorer farmers may be unable to compete.- Farmers may become dependent on the herbicide sold with herbicide-resistant crops.
- Heavy herbicide use reduces wild plant diversity, affecting insects and the birds that eat them.
Section 2 of 4Process & sequence
- Identify and cut out the human insulin gene using a restriction enzyme.
- Cut a bacterial plasmid with the same restriction enzyme, producing matching sticky ends.
- Mix gene and plasmid; DNA ligase joins them to form recombinant DNA.
- Insert the recombinant plasmid into a bacterium.
- Grow the transgenic bacteria in a fermenter where they multiply.
- Bacteria express the gene and make human insulin, which is extracted and purified.
Making human insulin — write these steps in this order; each step is a marking point.
- Cut insulin gene out
- Cut plasmid open
- Ligase joins gene into plasmid
- Plasmid enters bacterium
- Bacteria grow in fermenter
- Insulin extracted and purified
Section 3 of 4Compare
| Tool | Role |
|---|---|
| Restriction enzyme | Cuts the gene out and cuts the plasmid open at the same sequence |
| DNA ligase | Joins the gene into the plasmid |
| Plasmid / virus | Vector carrying the gene into the host cell |
| Host bacterium | Multiplies rapidly and expresses the gene |
| Fermenter | Grows large numbers of GM bacteria to make the product |
| Modification | Benefit | Concern |
|---|---|---|
| Pest resistance (Bt toxin gene) | Less insecticide, higher yield | Pests may evolve resistance; harm to non-target insects |
| Herbicide resistance | Weeds killed without harming crop | Genes may spread to wild relatives |
| Golden rice (vitamin A precursor) | Reduces vitamin A deficiency | Cost, reduced variety |
| Drought tolerance | Grows in dry areas | Unknown long-term effects |
Section 4 of 4Worked examples
Explain why the same restriction enzyme is used to cut both the human DNA and the plasmid.
- Each restriction enzyme cuts at a specific base sequence and leaves particular sticky ends.
- Using the same enzyme gives the gene and plasmid complementary sticky ends, so they can base pair and be joined by DNA ligase.
- Each restriction enzyme cuts at a specific base sequence and leaves particular sticky ends.
Give two advantages of producing insulin with GM bacteria rather than extracting it from animal pancreases.
- 1) The insulin is identical to human insulin, so fewer allergic reactions.
- 2) Bacteria reproduce rapidly, so large quantities can be made reliably and cheaply, without using animals.
- 1) The insulin is identical to human insulin, so fewer allergic reactions.
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