Question

You

have isolated

a bacterial strain

with a mutation in a methionine tRNA (tRNA

met

) gene.

This mutation

chang

ed the

anticodon

sequence

of

tRNA

met

to 3

′

–

GAC

–

5

′

(tRNA

met

normal

anticodon is

3

′

–

UAC

–

5

′

)

.

A)

How would this mutation affect the synthesis of polypeptides

within the bacterium?

B)

What does this mutation tell you about the recognition between

met

-

tRNA synthetase and

tRNA

met

? Does

the enzyme primarily recognize the anticodon or not?

Answer 1

Ans a) In this the anticodon sequence is changed from 3’-UAC-5’ to 3’-GAC-5’ and this would impact the polypeptide sequence. The mutant tRNA was supposed to put leucine amino acid but due to the mutation, it would lead to recognizing the leucine codons in the mRNA but would put methionine amino acid in place of leucine.

Ans b) Due to this mutation, the tRNA synthase is an enzyme which helps in attaching the amino acid to the tRNA. Due to the mutation, it will lead to the binding of the wrong amino acid to the tRNA. It will lead to binding between the aminoacyl tRNA and amino acid but the binding will be wrong and hence it will lead to incorrect sequence formation of the polypeptide.