Describe the role of restriction enzymes, plasmids, and ligase in the genetic modification of bacteria to produce insulin.

Pearson Edexcel International GCSE Biology (4BI1) — 5.3 Genetic modification (genetic engineering) · Describe · 4 marks · View as Markdown

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

Genetic modification is used to produce human insulin from bacteria grown in fermenters. The process involves transferring the human insulin gene into bacterial cells.

Model answer (4 marks)

Restriction enzymes cut the human DNA at specific sites, isolating the insulin gene.
The insulin gene is inserted into a plasmid, creating recombinant DNA.
Ligase seals the gene into the plasmid by joining the DNA ends.
The plasmid vector is taken up by bacteria, which then produce insulin.

Examiner tips

Use the exact terms: restriction enzymes, plasmid, ligase, recombinant DNA, vector, bacterial host.
Show the sequence: cut → insert → ligate → transform.
Mention that the plasmid is a loop of DNA in the cytoplasm.
Keep the answer concise and to the point.

Common mistakes

Confusing plasmid with chromosome or saying it’s in the nucleus.
Omitting the role of ligase or saying it just ‘adds’ the gene.
Using vague terms like ‘DNA cutter’ instead of ‘restriction enzyme’.

Mark scheme (4 marks)

Restriction enzymes cut DNA at specific regions to isolate the insulin gene from the human chromosome
The insulin gene is inserted into a plasmid (loop of DNA found in the cytoplasm of prokaryotic cells) to form recombinant DNA
Ligase joins / seals the insulin gene into the plasmid (joining the pieces of DNA together)
The plasmid (vector) transfers the recombinant DNA into the bacterial host cell, which then produces insulin

Key terms in this question

restriction enzymes · plasmids · ligase · insulin

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