Chapter 9, Problem 41P

Summary Introduction

To review:

In the given table, find which pair of wild type and mutant amino acid undergoes a single base substitution mutation and gives the possible wild type and mutant codon for each pair. Enlist if there is any other possibility or more than one option.

(Use either Figure $\text{9}\text{.13}$ or the genetic code inside the front cover to help solve this problem).

Wild-type	Mutant
Serine	Alanine
Cysteine	Serine
Proline	Glutamine
lysine	Stop codon
Methionine	Histidine
Methionine	Isoleucine

Introduction:

Mutation can damage or change the DNA of gene in such a way that it alters the genetic message carried by the gene. The mutation in the codon changes the nucleotide bases which sometimes adversly affects the amino acids formed by the codon. The frequent mutations occuring in codons are insertion/deletion mutation or the base substitution mutation.

In base substitution mutation, one nucleotide in the codon is replaced by the other nucleotide. The changes in a single letter in the codon results in changes in the amino acid. Base substitution mutation does not always cause the change in amino acid synthesis, for example, silent mutation. The silent mutation is a type of base substitution mutation in which the change in a nucleotide in the codon does not affect the amino acid synthesis because of the changed codon code for the same amino acid.

A nonsense mutation is the type of base substitution mutation. In nonsense mutation, the changed nucleotide transforms the codon into the stop codon. Such a mutation causes premature termination of the translation which imperfectly affects protein synthesis.