Question

1. What is meant by a missense mutation?

2. What is a nonsense mutation?

3. What is a silent mutation?

4. What is a frameshift mutation? Give an example of each type of mutation and discuss the effect on a protein product.

Answer 1

A. Missense mutation is a kind of mutation that changes one amino acid to a different amino acid. It can be of 2 types- conservative and non-conservative. Conservative missense mutations change one amino acid to a similar amino acid. This is less damaging to the protein structure. Eg Mutation of CGU to CAU. The first one codes for arginine, the second one for histidine, both positively charged amino acid. Non-conservative missense mutation changes one amino acid to a completely dissimilar amino acid. This heavily disrupts the protein structure. Eg Mutation of CGU to GGU. First one codes for arginine(positively charged Amino acid), second one codes for glutamate (negatively charged amino acid).

B. Nonsense mutation is a mutation that changes a codon to a stop codon. The protein synthesis terminated prematurely and functional protein product is not obtained. Eg. Mutation of AAA to AGA. The first codes for lysine, the second is a stop codon.

C. Silent mutation is a kind of mutation that doesn't change the amino acid. This kind of mutation doesn't have any effect on the structure of the protein. Eg. Mutation of AAA to AAG. Both these codons code for lysine.

D. Frameshift mutation happens because of insertion or deletion of nucleotides greater or less than 3, but not equal to 3. Due to this, the reading frame shifts in the mRNA, codons are read in a completely different manner, and the functional protein is not obtained at all. Eg. Deletion of one base from the sequence, will lead to a frameshift mutation.