Genetic Code and Codon Arrangement — NEET Biology

Correct answer: C — S1, S3 and S5 are correct

This question focuses on the mechanism of termination of translation, including the roles of stop codons and release factors. S1. Termination of translation occurs when a stop codon is encountered in the A-site of the ribosome. This is correct. The stop codon signals the end of translation when it enters the A-site. S2. Stop codons (UAA, UAG, UGA) are recognized by specific tRNAs that carry no amino acid. This is incorrect. NCERT states, 'There are no tRNAs for stop codons.' Stop codons are recognized by proteinaceous release factors, not tRNAs. S3. Release factors bind to the stop codon, promoting the hydrolysis of the bond between the polypeptide and the tRNA in the P-site. This is correct. NCERT states, 'At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.' This release involves hydrolysis of the ester bond linking the polypeptide to the tRNA in the P-site. S4. In the absence of functional release factors, the ribosome would dissociate prematurely from the mRNA. This is incorrect. Without functional release factors, the ribosome would stall at the stop codon, unable to release the polypeptide, and would not dissociate prematurely. It would remain associated with the mRNA and the peptidyl-tRNA. S5. The initiator tRNA is recycled and used again for subsequent rounds of initiation after termination. This is correct. tRNAs are adapter molecules that are reused multiple times in translation after their amino acid is detached and they are released from the ribosome. Therefore, statements S1, S3, and S5 are correct. Option C correctly identifies S1, S3, and S5 as correct. Option B is incorrect because S2 and S4 are false. Option C a A is incorrect because S4 is false. Option D is incorrect because S2 is false. The question tests the detailed understanding of translation termination.