CAIE A Level Biology 9700 · Nucleic acids and protein synthesis
A short section of the coding (non-template) strand of a gene has the base sequence:
ATG GGT TAC CTA
The mRNA transcribed from this gene is translated to produce a polypeptide.
Two different mutations occur in this section of the gene.
Mutation 1: The ninth base (T) is substituted with A.
Mutation 2: The ninth base (T) is deleted.
Explain how each mutation affects the polypeptide produced.
Refer to the roles of mRNA, codons, and tRNA in your answer.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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