Question

Guest and Yanofsky observed the following amino acid substitutions at one particular site, originally gly, on protein A of E. coli tryptophan synthetase: from gly to cys, from gly to asp and from asp to ala.

A. Using a codon chart, what codons would fit this set of events if each of these mutations arose by a single base pair change? Indicate your answer for each amino acid change.

B. Which of these mutations are transitions and which are transversions? Explain.

C. Name a specific chemical mutagen capable of producing each mutational change from part B.

Answer 1

A. Glycine to Cystiene:

GGC to UGC

   Glycine to Aspartic acid:

GGC to GAC

Aspartic acid to Alanine

GAC to GCC

B. The mutation from Glycine to Cystiene is an example of Transversion because Purine (G) is replaced by Pyrimidine (U).

The mutation from Glycine to Aspartic acid is an example of Transition because Purine (G) is replaced by Purine (A)

The mutation from aspartic acid to alanine is an example of Transversion because Purine (A) is replaced by Pyrimidine (C).

Transitions are the point mutations in which purines are replaced by purines or pyrimidines are replaced by pyrimidines.

Transversions are the point mutations in which Purines are replaced by pyrimidines or pyrimidines are replaced by purines.

For Part C, I am not sure.