Practice question

Peptidyl transferase center that catalyzes peptide bond formation resides in large subunit rRNA, not proteins. In prokaryotes, domain V of 23S rRNA folds into catalytic crevice containing conserved A-loop and P-loop positioning CCA ends of A-site and P-site tRNAs for nucleophilic attack of alpha-amino on peptidyl ester. Crystallographic studies reveal no protein within 18 angstroms of active site. Mutation of key 23S adenines abolishes activity while protein removal retains catalysis. Equivalent in eukaryotes is 28S rRNA, confirming ribosome is ribozyme.