QUESTION 20 "Nitrous acid causes all possible transitions (A<-- -->G, C<-- -->T). If a protein has an alanine at position 65, what amino acid(s) would be likely to replace alanine as a result of nitrous acid mutagenesis

Explanation:

Nitrous acid mutation occurs when a Nitrogenous base is replaced by a keto group.

Alanine is replaced by hypoxanthine,

Cytocine is replaced b Uracil

Guanine is replaced by Xanthine.

Nitrous mutation often affects Adenine, Cytocine and guanine. The Nitrogenous base is changed into another substance(keto group)

Alanine at position 65 would be replace by hypoxanthine a keto group which is a form of nitrous mutation.

Other forms of amino acid mutation

Mutation of amino acid nitrogenous base can either be transition or transversion.

Transition is the substitution of a purine base by another purine base. Since purine are Adenine and Guanine

Pyrimidine is cytocine and thymine or Uracil. Adenine can be substituted for by guanine or guanine by adenine

E.G A - G now G - A where Guanine substitute Adenine

Whole transversional substitution can also occur which involve a purine been substitued for by a pyrimidine or pyrimidine by a Purine.

A - G

Now C-G where cytosine substitute Adenine.