A chemical compound consisting of two or more amino acids joined to each other through a bond between the nitrogen atom of one amino acid to an oxygen atom of its neighbor. A more precise term describes the number of amino acid units involved. A dipeptide or tripeptide consists of two or three amino acid units respectively. A few oligopeptides (about ten amino acid units) are of physiological importance. The antibiotics bacitracin, gramicidin S, and tyrocidin A are examples of oligopeptides. The largest polypeptides contain dozens or hundreds of amino acid units and are better known as proteins. The bond between peptide units is especially sensitive to attack by various types of corrosive poisons such as strong acids and bases.