The peptide bond

A peptide bond is the link that joins one amino acid to the next.

How it forms

Every amino acid has two ends: an amino group (–NH₂) and a carboxyl group (–COOH). When the carboxyl end of one amino acid meets the amino end of another, they join and release one molecule of water. Chemists call this a condensation reaction.

The new link, –CO–NH–, is the peptide bond. A chain of n amino acids has n – 1 peptide bonds, so a tripeptide has two and oxytocin's nine amino acids have eight.

Its structure

The peptide bond is unusually rigid. It shares some character with a double bond, so the atoms around it lie flat in one plane and can't spin freely. That stiffness is part of why proteins fold into such reliable shapes.

Who discovered it

Between 1899 and 1908, Emil Fischer worked out the type of bond that links amino acids into chains, the peptide bond. He used it to make dipeptides, then tripeptides and longer chains. His group had made around 65 peptides by 1906, and the longest had 18 amino acids.