CAIE A Level Biology 9700 · Nucleic acids and protein synthesis

Nucleic acids and protein synthesis: explain question

Explain5 marksStandard

Part of the coding strand (non-template strand) of a bacterial gene is shown below. The start codon is ATG and the sequence is read from left to right.

Normal: 5' – ATG GCA TCG TAA – 3'

Two mutant versions of this gene have been isolated.

Mutant 1 has a substitution of the fourth base from G to C.
Mutant 2 has a deletion of the sixth base (the A in the second codon).

Explain how each mutation is likely to affect the polypeptide produced from this gene. Use your knowledge of the genetic code and the processes of transcription and translation.

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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.

Nucleic acids and protein synthesis: explain question

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