Question

Observe the following messenger RNA:

Due to a mutation, the guanine nucleotide in the sixth position is replaced by an adenine nucleotide. What will the correct effect on the sequence of amino acids due to this mutation?

• A. The sequence of amino acids in the mutated protein is exactly the same as the sequence of amino acids in the original protein.
• B. Only the second amino acid in the mutated protein will be different while the rest will be same as that of the original protein.
• C. All amino acids except the first one will be different in the mutated protein.
• D. Second and third amino acids in the mutated protein will be different while the rest will be same as that of the original protein.

Answer 1

Answer: (A)

Original mRNA is 5' AUG GGG AAA CCC UUU UAA 3'
The sequence of amino acids coded by this mRNA is Methionine - Glycine - Lysine - Proline- Phenylalanine.
Mutated mRNA 5' AUG GGA AAA CCC UUU UAA 3'
The sequence of amino acids coded by this mRNA is Methionine - Glycine - Lysine - Proline- Phenylalanine. Since GGG and GGA both code for the same amino acid glycine, there is no change in the sequence. This is called Silent mutation. It occurs due to degeneracy of codons.