Peptide Bond
formation & growth of the polypeptide chain
The
amino
acids in the ribosome are
attached
to
their respective tRNAs by
an
ester bond (R - O - R) between the carboxyl terminus and the
amino acceptor stem
(left). During
formation of a peptide bond,
the ester bond of the amino acid in the (P)eptidyl site is
cleaved,
and
Peptidyl Transferase
catalyzes a reaction
(see Note)
between
its carboxyl
terminus
and the amino
terminus of the amino acid in the (A)mino
site. This transfes the P-site
amino
acid to the A-site
amino
acid, and the original
amino
terminus remains
unmodified. The
polypeptide thus "grows" from the amino terminus to the
carboxy
terminus (N
C).
Note: In vitro formation of the peptide bond is described as a dehydration reaction that involves the loss of a molecule of H20. In vivo, the equivalent reaction balances, without production of an H20 molecule, and is sometimes described as a condensation reaction.
C).Note: In vitro formation of the peptide bond is described as a dehydration reaction that involves the loss of a molecule of H20. In vivo, the equivalent reaction balances, without production of an H20 molecule, and is sometimes described as a condensation reaction.