The peptidyl transferase reaction. In the second step of elongation, the α-amino group of the A-site aminoacyl-tRNA (shown here as the uncharged –NH₂ group) attacks the carbonyl carbon of the P-site fMet-tRNA, shifting the fMet to the A-site tRNA to form a dipeptidyl-tRNA. This reaction is catalyzed by the 23S rRNA.