Name the three stop codons and what happens at termination.

• A. UAA, UAG, UGA; release factors recognize stop codons, promote hydrolysis of the polypeptide from the tRNA, and dissociate the ribosome.
• B. UAG, UGA, UAA; tRNA recognizes stop codons and terminates.
• C. UAA, UGA, UGU; ribosome stalls and pauses.
• D. UAA, UAG, UGA; methylation of tRNA terminates translation.

Answer: (A)

Stop codons UAA, UAG, and UGA signal the end of translation. When one of these is in the ribosome, release factors bind rather than a tRNA, triggering hydrolysis that releases the polypeptide from the tRNA in the P site. The ribosome then dissociates into subunits and the mRNA and tRNA are released, ready to be recycled. There are no tRNAs that recognize stop codons, and the codon UGU and the idea of ribosome stalling or tRNA methylation are incorrect mechanisms for termination.