Peptide
A short chain of amino acids linked by peptide bonds, typically containing between 2 and 50 residues. Peptides are smaller than proteins and play diverse roles in the body as hormones, neurotransmitters, and signalling molecules. Many therapeutic drugs are based on natural or synthetic peptides.
Technical Context
Peptides are classified by length: dipeptides (2 amino acids), tripeptides (3), oligopeptides (fewer than 20), and polypeptides (20-50, though the boundary with proteins is not precise). Many naturally occurring hormones are peptides, including insulin (51 aa), oxytocin (9 aa), and growth hormone-releasing hormone (44 aa). Therapeutic peptides may be bio-identical to natural peptides (e.g. synthetic oxytocin), modified analogues designed for improved pharmacological properties (e.g. semaglutide), or entirely synthetic sequences designed to interact with specific biological targets. The peptide therapeutics market has grown substantially, driven by advances in synthesis technology and delivery systems.