Scientists have used genetic engineering to produce insulin in bacteria. Explain how a human insulin gene is inserted into a bacterium to produce large quantities of insulin.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
People with Type 1 diabetes need regular doses of insulin. Before genetic engineering, insulin was extracted from the pancreases of pigs and cows. Today, genetically engineered bacteria are used to manufacture human insulin on a large scale.
Model answer (5 marks)
1. The human insulin gene is identified and isolated from a human chromosome.
2. Restriction enzymes cut the insulin gene from the human DNA.
3. A plasmid from a bacterium is cut open with the same restriction enzymes.
4. The cut insulin gene is inserted into the plasmid and the DNA strands are sealed by ligase.
5. The recombinant plasmid is introduced into a bacterium, which then replicates the plasmid and produces large quantities of insulin.
2. Restriction enzymes cut the insulin gene from the human DNA.
3. A plasmid from a bacterium is cut open with the same restriction enzymes.
4. The cut insulin gene is inserted into the plasmid and the DNA strands are sealed by ligase.
5. The recombinant plasmid is introduced into a bacterium, which then replicates the plasmid and produces large quantities of insulin.
Examiner tips
- Use the exact sequence of steps: identify, cut, insert, seal, transform. Mention restriction enzymes and ligase. Show that the plasmid is a vector for replication.
Common mistakes
- Confusing the role of the plasmid as a vector. Omitting the use of restriction enzymes or ligase. Failing to state that the plasmid is inserted into a bacterium.
Mark scheme (5 marks)
- The human insulin gene is identified/located on a human chromosome
- The gene is cut out using enzymes
- A plasmid (from a bacterium) is cut open using enzymes
- The insulin gene is inserted into the plasmid and sealed/joined using enzymes
- The plasmid is inserted into a bacterium, which then replicates/reproduces to produce large quantities of insulin
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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