Question

A mutation causing an addition or a deletion of one base pair resulted in the production of a nonfunctional mutant protein. The sequences of the normal and mutant proteins are given below.

Normal: Met - Leu - Ala - Thr - Gln

Mutant: Met - Leu - Ala - His - Pro - Ile - Glu - Ser - Thr -

Was this mutation cause by an insertion or a deletion?

Answer Below, fill in the codons in the coding sequence of the mRNA that is translated into the mutant protein. If more than one codon is possible, just enter a single codon.

NH2 Met Leu Ala His Pro Ile codons

5' AUG UUG

Answer 1

Answer-

Normal protein sequence- Met - Leu - Ala - Thr - Gln

Normal mRNA sequence- 5'- AUG UUG GCU ACC CAA UAG-3'

The mutation in DNA causes mutant mRNA production that produces mutant protein. Here the mutation is addition mutation causes frame shift mutation which changes open reading frame of mRNA causes change in amino acid sequence from the site of mutation. Insertion mutation causes shift in open reading frame one nucleotide back causes change in sequence of amino acids from where mutation occurs.

Mutant protein sequence- Met - Leu - Ala - His - Pro - Ile - Glu - Ser - Thr

Mutant mRNA sequence- 5'- AUG UUG GCU CAC CCA AUA GAA UCU ACC - 3'

This addition mutation causes production of nonfunctional protein with abnormal sequence. The 5'- UAG -3' is present in normal mRNA after glutamine codon but after addition mutation stop codon is disturbed and now it is unable to terminate translation so that longer polypeptide chain is synthesized.