CAIE A Level Biology 9700 · Nucleic acids and protein synthesis
In a eukaryotic gene, the coding strand (non-template strand) contains the following sequence:
5' – ATG GGA TAC CCT – 3'
The triplet GGA codes for the amino acid glycine. A substitution mutation changes this triplet to TGA, which corresponds to a stop codon in the mRNA.
(a) Outline the roles of tRNA molecules and their anticodons in the process of translation.
(b) Outline how this mutation could affect the polypeptide produced.
7 marks, so the mark scheme is looking for about 7 separate creditworthy points. Making the same point twice in different words earns it once.
Outline means: Give the main points briefly. Less detail than describe, but every key step has to be there. One short line per step, in order. The marks are for coverage, not depth.
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