Question

The normal sequence of mRNA transcribed from a particular DNA strand is

5'-AUG GUC GGA CUG GGC GUC UAA-3'.

As a result of mutation in DNA, the mRNA sequence is changed to

5'-AUG GUC UGA CUG GGC GUC UAA-3'.

Identify the type of mutation?
[1 mark]

• A. Silent
• B. Non sense
• C. Missense
• D. Frameshift

Answer 1

The correct option is B Non sense

Mutation refers to the change in the nucleotide sequence in DNA of an organism. It can be of many types.

1. A type of mutation in which the resulting codon is a stop codon is called nonsense mutation. In the given sequence the 3rd codon GGA is mutated and is changed to UGA which is a stop codon. It causes the termination of protein synthesis. Hence option b is correct.
2. In a missense mutation, the substitution of a nucleotide results in incorporation of an amino acid different from the original one. For example if GGA (glycine) changed to AGA (arginine).
3. In frameshift mutation, the reading frame of the template changes due to addition or deletion of nucleotides. For example, if C got added in front of GGA, then it will be CGG (arginine).
4. A silent mutation is a change in the nucleotide sequence without a subsequent change in the sequence of amino acids of the corresponding protein. For example if GGA (glycine) changes to GGC (glycine). Hence the function of the protein produced from a gene which has a silent mutation will not be affected.