In elongation, which step involves peptide bond formation?

In elongation, which step involves peptide bond formation?

• A. Peptide bond formation (P->A)
• B. Binding of next charged tRNA (A site)
• C. Translocation of ribosomes (tRNA a->P)
• D. Release of free tRNA

Answer: (A)

The step being tested is the chemical bond-making event that links the growing polypeptide to the incoming amino acid. During elongation, the ribosome catalyzes the formation of a peptide bond between the polypeptide chain attached to the tRNA in the P site and the aminoacyl-tRNA that has just bound in the A site. This peptidyl transferase reaction transfers the growing chain to the A-site tRNA, creating the new bond and extending the chain. After this bond forms, translocation moves the ribosome to the next codon, shifting tRNAs from A to P to E sites, and the cycle repeats with another aminoacyl-tRNA entering the A site. The release of free tRNA is not the bond-forming step; it occurs later in the cycle as tRNAs exit after their roles are finished. This is why the option describing peptide bond formation between the P-site and A-site tRNAs best fits the question.

The step being tested is the chemical bond-making event that links the growing polypeptide to the incoming amino acid. During elongation, the ribosome catalyzes the formation of a peptide bond between the polypeptide chain attached to the tRNA in the P site and the aminoacyl-tRNA that has just bound in the A site. This peptidyl transferase reaction transfers the growing chain to the A-site tRNA, creating the new bond and extending the chain. After this bond forms, translocation moves the ribosome to the next codon, shifting tRNAs from A to P to E sites, and the cycle repeats with another aminoacyl-tRNA entering the A site. The release of free tRNA is not the bond-forming step; it occurs later in the cycle as tRNAs exit after their roles are finished. This is why the option describing peptide bond formation between the P-site and A-site tRNAs best fits the question.