Peptide Bond
A covalent chemical bond formed between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water. Peptide bonds are the fundamental linkages that hold amino acid chains together in all peptides and proteins.
Technical Context
Peptide bonds have partial double-bond character due to resonance, which gives the bond a planar, rigid structure. This rigidity constrains the three-dimensional folding of peptide chains. The bond length is approximately 1.33 Å, intermediate between a single C-N bond (1.49 Å) and a double C=N bond (1.27 Å). Peptide bonds are cleaved by proteolytic enzymes (proteases) in the body, which is why many therapeutic peptides have short half-lives and require injection. Modifications such as N-methylation, incorporation of D-amino acids, cyclisation, or use of reduced peptide bonds (CH2-NH) can protect peptide bonds from enzymatic degradation.