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