Peptides composed of amino acids that are linked together by peptide bonds, which are formed between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of another amino acid.
They have a wide range of functions in the body, including acting as signalling molecules and hormones, and as enzymes that catalyse biochemical reactions. Some peptides also play an important role in the immune system and in the regulation of gene expression.