Gujarati
Hindi
5.Molecular Basis of Inheritance
medium

Assertion : $UAA,\,UAG$ and $UGA$ terminate protein synthesis.

Reason : They are not recognised by $tRNA$.

A

If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

B

If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

C

If the Assertion is correct but Reason is incorrect.

D

If both the Assertion and Reason are incorrect.

(AIIMS-2011) (AIIMS-2014)

Solution

Synthesis of polypeptide terminates when a nonsense codon of $mRNA$ reaches the $A-$ site. There are three nonsense codons-$UAA, \,UAG$ and $UGA$. These codons are not recognised by any of the $tRNAs$. Therefore, no more aminoacyl $tRNA$ reaches the $A$ site. The $P-$ site $tRNA$ is hydrolysed and the completed polypeptide is released in the presence of a release factor.

Standard 12
Biology

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