Question

Given below are two statements: Assertion (A): The completion of polypeptide synthesis is signaled by the translocation of one of the stop codons into the A site. Reason (R): There are no t-RNA that recognize these codons under normal circumstances, termination of the chain does not involve the binding of a t-RNA.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Stop codons do not code for amino acids and are not recognized by tRNA. They are recognized by release factors during translation termination.

Answer 1

The Correct Option is A

Concept:
Translation is the process of protein synthesis. It stops when a stop codon enters the A-site of the ribosome.

Step 1: Check Assertion (A).
Polypeptide synthesis is completed when a stop codon such as UAA, UAG, or UGA reaches the A-site of the ribosome. \[ A \text{ is correct} \]

Step 2: Check Reason (R).
There is no normal tRNA molecule that recognizes stop codons. Instead, release factors bind to the stop codon and terminate translation. \[ R \text{ is correct} \]

Step 3: Check explanation.
Because no tRNA recognizes stop codons, the arrival of stop codon at A-site signals termination of protein synthesis. Thus, Reason correctly explains Assertion. \[ \therefore \text{Correct Answer is (A)} \]