biology A wild-type strain of bacteria produces a protein with the amino acid pr

Question

biology A wild-type strain of bacteria produces a protein with the amino acid proline (Pro) at one site. Treatment of the strain with nitrous acid, which deaminates C to make it U, produces two different mutants. At the site, one mutant has a substitution of serine (Ser), and the other has a substitution of leucine (Leu). Treatment of the two mutants with nitrous acid now produces new mutant strains, each with phenylalanine (Phe) at the site. Treatment of these new Phe-carrying mutants with nitrous acid then produces no change. The results are summarized in the following figure: Using the appropriate codons, show how it is possible for nitrous acid to produce these changes, and why further treatment has no influence. Assume that only single-nucleotide changes occur at each step.

Explanation / Answer

Nitric acid causes mutation in the DNA sequence by converting C to U. Proline with CCU codon when deaminates, gives UCU codon (serine) and CUU (leucine). When seine with UCU and leucine with CCU when deaminates, both converted into UUU which codes for Phenylalanine. There is no C, to convert into other by Nitric acid. So Phenylalanine will not get mutated by Nitric acid.

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