The peptide bond is one of the hallmarks of proteins. Here a simple reaction between two amino acids yields a dipeptide (glycyclalanine) containing one peptide bond.
A peptide is a sequence of amino acids held together by peptide bonds, in which the amino group (–NH2) of one acid links to the carboxyl group (–COOH) of another. Peptides can vary in length from dipeptides, with two amino acids (e.g., glycyclalanine, which is a combination of glycine and alanine), to polypeptides with several hundred. Polypeptides, in turn, link together to form proteins.