Question

Hydroxylamine is a mutagen that acts only on cytosine and causes C-->T and G-->A base pair changes (i.e. it causes transition mutations at GC sites). A normal sequence of a protein contains a PROLINE residue (pro) at a particular place. What new amino acid(s) would appear in place of the proline residue as a result of hydroxylamine mutagenesis?

Answer 1

Options for the question are not given. They are as follows:

a. arg or lys

b. ala

c. thr

d. leu or ser

e. Only termination codons

Answer:

d. leu or ser

Explanation:

Four codons code for proline amino acid. These are CCT, CCC, CCA, and CCG. Hydroxylamine causes C to change into T or G to change into A.

If first position is changed in each codon:

CCT = TCT (UCU)

CCC = TCC (UCC)

CCA = TCA (UCA)

CCG = TCG (UCG)

These codons produce Serine amino acid.

If second position is changed in each codon:

CCT = CTT (CUU)

CCC = CTC (CUC)

CCA = CTA (CUA)

CCG = CTG (CUG)

These codons produce Leucine amino acid.

Hence, out of the given options, option d. leu or ser is correct.