Question

The codon in the DNA coding strand has the following sequence: 5' - TAC -3' Which of the following codons (result of a mutation) represents a non-sense mutation?

Select one:

a. TAA

b. TAT

c. TTC

d. TCC

Answer 1

The correct option is a (TAA).

The DNA segment has sequence 5'-TAC-3'.

The type of point mutation which produces stop codon is called non sense mutation. Non sense mutation led stop codon causes pre mature termination of polypeptide synthesis. If non sense codon formation happens in start then it might cause no protein synthesis at all. We know that Uracil (U) is found in place of thymine (T) in case of RNA.. There are three known stop codons in RNA - UAA, UAG and UGA. In case of DNA the U should be replaced with T then the corresponding DNA sequence will be TAA, TAG and TGA,. Therefore, the point mutation on third position of DNA segment and replacement of Cytosine with Adenine will produce stop codon and hence, non stop mutation

Option B is incorrect as this codon (TAT) will transcribe as UAU which codes for amino acid Tyrosine. Therefore, it will not cause non sence mutation. hence, this option is incorrect.

Option C is incorrect as this codon (TTC) will transcribe as UUC which codes for amino acid Phenyl alanine, Therefore, it will not cause non sence mutation. hence, this option is incorrect.

Option D is incorrect as this codon (TCC) will transcribe as UCC which codes for amino acid Serine. Therefore, it will not cause non sence mutation. hence, this option is incorrect.