Final answer:
The first step of elongation in protein synthesis requires the energy from GTP hydrolysis for the binding of the aminoacyl-tRNA to the A site of the ribosome, facilitated by elongation factor Tu and catalyzed by peptidyl transferase for peptide bond formation.
Step-by-step explanation:
The first step of elongation in protein synthesis involves the binding of the second aminoacyl-tRNA to the A site of the ribosome. This critical process requires energy that is supplied by GTP hydrolysis. Specifically, elongation factor Tu (EF-Tu), bound to GTP, escorts the aminoacyl-tRNA to the A site. When the correct match between the tRNA anticodon and the mRNA codon is found, GTP is hydrolyzed to GDP and the elongation factor is released. This provides the energy necessary for the precise positioning of the aminoacyl-tRNA into the A site, readying it for the formation of a peptide bond with the amino acid at the P site, which is catalyzed by the enzyme peptidyl transferase.