What are the three stages of translation and the main events in each?

• A. Initiation: ribosome assembles at start codon with initiator tRNA; Elongation: aminoacyl-tRNA entry and peptide bond formation; Termination: stop codon recognized and polypeptide released.
• B. Initiation: RNA polymerase binds promoter; Elongation: RNA synthesis; Termination: ligase seals nicks.
• C. Initiation: tRNA charging; Elongation: splicing; Termination: transcription ends.
• D. Initiation: ribosome disassembles; Elongation: translation; Termination: mRNA is degraded.

Answer: (A)

Translation unfolds in three stages: initiation, elongation, and termination. In initiation, the ribosome assembles at the start codon with the initiator tRNA, setting the reading frame so the first amino acid (methionine in eukaryotes; formyl-Met in bacteria) is positioned for the growing chain. In elongation, the correct aminoacyl-tRNA pairs with the mRNA codon in the ribosome, a peptide bond forms to attach the new amino acid to the chain, and the ribosome shifts to the next codon to continue adding amino acids. In termination, a stop codon is encountered, release factors prompt release of the finished polypeptide, and the ribosomal subunits, tRNA, and mRNA dissociate.

The other options mix in steps from transcription or RNA processing (like RNA polymerase binding a promoter or splicing) or describe events not part of translation (such as ligation or mRNA degradation), which is why they don’t correctly represent the three stages of translation.