Genetic engineering can be used to produce human insulin in bacteria. Explain how bacteria are modified to produce human insulin.

Pearson Edexcel A-Level Biology A (9BI0) — Topic 8 Use of Biological Resources · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Before genetic engineering was developed, insulin for treating diabetes was extracted from the pancreases of pigs and cattle. Scientists can now use genetically engineered bacteria to produce large quantities of human insulin.

Model answer (5 marks)

1. The human insulin gene is identified in human DNA.
2. Restriction enzymes cut the insulin gene out of the human DNA.
3. A bacterial plasmid is cut open with the same or compatible restriction enzymes.
4. The cut insulin gene is ligated into the plasmid, and the plasmid is sealed by DNA ligase.
5. The recombinant plasmid is introduced into bacteria, which then express the human insulin gene and produce insulin.

Examiner tips

Use the exact sequence of steps: gene identification, restriction, plasmid cutting, ligation, transformation and expression.
Show the role of restriction enzymes and ligase clearly.
Mention that the plasmid is a vector that carries the gene into the bacterium.
Keep the answer concise and in the correct order to match the marking points.

Common mistakes

Confusing the roles of restriction enzymes and ligase; forgetting to mention ligase.
Mixing up the order of cutting the plasmid and inserting the gene.
Failing to state that the plasmid is inserted into a bacterium and that expression occurs.

Mark scheme (5 marks)

The gene for human insulin production is identified / located in human DNA
The gene is cut out using enzymes (restriction enzymes)
A bacterial plasmid is cut open using (restriction) enzymes
The human insulin gene is inserted into the plasmid / the plasmid is sealed using ligase enzyme
The plasmid (now containing the human insulin gene) is inserted into a bacterium / the bacterium expresses the gene and produces insulin

Key terms in this question

genetic engineering