Describe how bacteria are genetically engineered to produce human insulin.

Cambridge International IGCSE Biology (0610) — 21.1 Biotechnology and genetic modification · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

1. The human insulin gene is excised from human DNA with restriction enzymes.
2. The same enzymes cut a bacterial plasmid, creating complementary sticky ends.
3. The insulin gene is inserted into the plasmid and joined by DNA ligase, forming a recombinant plasmid.
4. The recombinant plasmid is introduced into bacteria, which replicate and produce large amounts of human insulin.

Examiner tips

  • Use the exact sequence of steps, include enzymes and ligase
  • Mention ‘recombinant plasmid’ and ‘bacteria’
  • Show the flow from gene cutting to insulin production

Common mistakes

  • Omitting the role of restriction enzymes or DNA ligase
  • Failing to state that the plasmid is inserted into bacteria
  • Using vague terms like ‘engineered’ without describing the process

Mark scheme (4 marks)

  1. The gene coding for insulin is cut from human DNA using restriction enzymes
  2. The same restriction enzymes are used to cut open a bacterial plasmid, leaving complementary sticky ends
  3. The insulin gene is inserted into the plasmid and joined using DNA ligase to form a recombinant plasmid
  4. The recombinant plasmid is inserted into a bacterium, which reproduces to produce large quantities of human insulin

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