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A-Level Biology May/June 2025 Q5(d): Recombinant human insulin analogues are insulin proteins that have slightly altered ami…
A-Level Biology · Paper 9700/42 · May/June 2025 · Question 5(d) · [4 marks]
Recombinant human insulin analogues are insulin proteins that have slightly altered amino acid sequences compared with recombinant human insulin. These analogues can be more effective than human insulin. Synthetic genes coding for insulin analogues have been developed. The bacterium Escherichia coli can be used as a host for a synthetic gene for the large-scale manufacture of an analogue. When scientists have determined the changes that are needed to produce an insulin analogue, they can obtain a synthetic gene coding for the analogue by making changes to a length of DNA using genetic engineering. Suggest how scientists genetically engineer a synthetic gene coding for the insulin analogue and explain how the changes they make allow the correct analogue to be produced.
A full-marks model answer with a mark-by-mark examiner breakdown is below.
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First, scientists would find the nucleotide sequence for the normal human insulin gene from a bioinformatics database. They would then use a gene editing technique to modify this DNA sequence.
This involves the replacement of specific nucleotides at a precise site within the gene. This change in the DNA base sequence alters a DNA triplet. During protein synthesis, this new triplet now codes for a different amino acid to be incorporated into the polypeptide chain, resulting in the production of the insulin analogue with the desired altered primary structure.
How the marks are awarded
- MP 1 — Awarded for stating that scientists find the nucleotide sequence of the human insulin gene, which is the starting point for any modification.
- MP 4 — Awarded for describing the specific genetic modification as the 'replacement of... nucleotides', which is a key mechanism in gene editing.
- MP 6 — Awarded for explaining the consequence of the nucleotide change at the level of the genetic code, stating that it 'alters a DNA triplet'.
- MP 7 — Awarded for linking the change in the genetic code to the final protein product, by explaining that the new triplet 'codes for a different amino acid'.
Common mistakes
- Describing the process of inserting the gene into a plasmid and transforming bacteria, which is about manufacturing the protein, not creating the synthetic gene itself.
- Using vague terms like 'the gene is changed' without specifying the mechanism, such as nucleotide replacement, insertion, or deletion.
- Confusing the central dogma terminology, for example by stating that the DNA 'codes for a different codon' (DNA has triplets, mRNA has codons) or that the amino acid itself is changed in the gene.
- Failing to explain the consequence of the DNA change, stopping after stating that the gene is edited without linking it to the altered amino acid sequence.
Examiner tip: For process-based questions, break your answer into a logical sequence of steps, ensuring you clearly link each cause to its specific biological effect.
AI-generated model answer, grounded in the official Cambridge mark scheme and reviewed by the MarkScheme team. Mark your own answer to this question →
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