Consider the following DNA sequence, which is the non-template (coding) strand o

Question

Consider the following DNA sequence, which is the non-template (coding) strand of the protein-coding region of a gene (in other words, this sequence will be represented in the open reading frame of an mRNA) 5'-ATGGGACTAGATACC-3' Check out each of the following altered sequences. For each sequence, state what kind of mutation has occurred (transition, transversion, insertion deletion and the genetic code table) state what the consequences of the mutation will be (silent, missense, frameshift nonsense. etc; assume translation would start at AUG) A. 5' ATGGGTCTAGATACC-3' B. 5'-ATGGGACTAAGATACC-3' C. 5'-ATGGGACTAAGATACC-3' D. 5'-ATGTGACTAGATACC-3' E. 5'-ATGGGACCAGATACC-3'

Explanation / Answer

1. NORMAL STRAND ATG GGA CTA GAT ACC

MUTATED STRAND ATG GGT CTA GAT ACC

This is a transversion (exchange of purine by pyramidine or vice versa) mutation which changes A ----- T. The product of the mutated codon is gly similar to normal codon. Hence there is no change in the end amino acid. Therefore it is a silence mutation.

2. NORMAL STRAND ATG GGA CTA GAT ACC

MUTATED STRAND ATG GTC TAG ATA CC

The amino acid of the normal codon is glycine but the mutaed codon produce val and a sudden stop codon UAG is formed resulting in immature polypeptide. This is a deletion mutation (deletion of A) and results in non sense mutation.

3. NORMAL STRAND ATG GGA CTA GAT ACC

MUTATED STRAND ATG GGA CTA AGA TACC

This is an insertion or addition of base A that results in the aleration of amino acid. Instead of asp , arg is produced. This type of mutation is called frameshift mutation as the insertion causes a shift in the frame of the DNA and alters the structure and number of nucleotides.

4. NORMAL STRAND ATG GGA CTA GAT ACC

MUTATED STRAND ATG TGA CTA GAT ACC

This is due to transversion where a purine is exchanged by pyramidine. This results in the production of a stop codon UGA and hence is a non sense mutation.

5. NORMAL STRAND ATG GGA CTA GAT ACC

MUTATED STRAND ATG GGA CCA GAT ACC

This is due to point mutation called transition where a pyramidine base is exchanged for another pyramidine. This results in the change of amino acid synthesized. The product of the mutated codon is pro whereas the normal codon codes for leu. Thus pro is substituted for leu hence is a missense mutation.

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