Peptide

Peptide, one of a group of organic chemicals found in most living tissues, with a wide range of biological functions. The chemicals are relatively low-weight polymers of amino acids, as contrasted with the high-weight proteins. The acids are linked together by so-called peptide bonds between their carboxyl (COOH) and alpha amino (NH₂) groups. Those peptides containing fewer than ten amino acids are called oligopeptides; those with more, polypeptides. Hormones such as ACTH and vasopressin (see Endocrine System) are important polypeptides.