What catalyzes the formation of peptide bonds?

The large ribosomal subunit catalyzes the formation of peptide bonds through using small aminoacyl- and peptidyl-RNA fragments of tRNA molecules. More specifically, the ribosome does this through the nucleophilic attack of an aminoacyl-tRNA in the A-site on ester bond carbon of the peptidyl-tRNA in the P-site. The enzyme peptidyl transferase catalyzes the addition of amino acid residues to increase the length of the polypeptide chain during formation of peptide bonds. This enzyme exists in the large subunit of the ribosome; it is composed almost entirely of the 29000 nucleotide rRNA of the large subunit.