Assertion : UAA, ,UAG and UGA terminate protein synthesis. Reason…

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MCQ

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

Reason : They are not recognised by $tRNA$.

✓
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.

✓

Answer

Correct option: A.

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

a
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.