Consider a protein segment with the following amino acid sequence: Ala-Thr-Lys-G

Question

Consider a protein segment with the following amino acid sequence: Ala-Thr-Lys-Glu-Gly-Val-Ile First, write out the nucleotide sequence of the mRNA segment that codes for this protein, using the Table of Codons (Hartwell et al, p. 256). Note that some nucleotide positions will be uncertain. In these positions use "X" to denote any base, "R" to denote a purine (A or G) and "Y" to denote a pyrimidine (U or C). Now consider all possible single-base-change mutations in this region, and answer the following: a) What fraction of all such mutations cause premature termination of translation? b) What fraction cause a loss of a negative charge?

Explanation / Answer

Ala-Thr-Lys-glu-Val-Ile GCX-ACX-GAR-GUX-AUX A single change in thrid nitrogen base at AUX leads to .... GCX-ACX-GAR-GUX-AUG...............AUG is the codon for methionine or a start codon A change in first base ......GAR..........leads to UAA or UAG , a termination codon. These termination codons leads to nonsense mutations.

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