Final answer:
The central reaction of protein synthesis (or transpeptidation), the actual peptide-bond forming step, occurs during translation. No energy input is needed for this step as the ester linking the peptidyl moiety to tRNA is intrinsically reactive. The option (A) is correct.
Step-by-step explanation:
The central reaction of protein synthesis (or transpeptidation), the actual peptide-bond forming step, is part of the process called translation. During translation, the ribosome catalyzes the formation of peptide bonds between amino acids.
This occurs between the -NH2 group of the amino acid on the second tRNA and the carboxylate group of the first by nucleophilic acyl substitution mechanism. No energy input is needed for this step as the ester linking the peptidyl moiety to tRNA is intrinsically reactive. Therefore, option (A) is correct.