Question

19. Identify the three types of mutations. Give an example of two of the three types using the lettering system (A, C, G, and U).

Answer 1

Ans. The three types of mutations are silent mutation, missence mutation and nonsense mutation.

Example of two types of mutations are -

In case of missense mutation, there is substitution of a single nucleotide and this causes change in single amino acid encoded by the triplet codon undergoing base substitution.

CCA CGG UUG GCA GGC will encode Pro Arg Leu Ala Gly.

Substitution mutation at third base of third codon from G to U is CCA CGG UUU GCA GGC. This would cause alteration in amino acid of the third codon is Pro Arg Phe Ala Gly.

In case of nonsense mutation, there is formation of nonsense codon due to single nucleotide substitution.

CCA CGG UUG GCA GGC will encode Pro Arg Leu Ala Gly. Substitution at second base of third codon will be CCA CGG UAG GCA GGC. UAG is nonsense codon and does not code for any amino acid (termination codon) and hence protein synthesis stops. Hence, after first two codons encoding Pro Arg, protein synthesis is terminated due to formation of UAG which is nonsense codon.