The reaction between amine (NH2) and carboxyl (COOH) group of two or more amino acids (same or different) results in the formation of amide linkage (−CO−NH−), upon elimination of water molecule. This amide linkage is called peptide linkage and the product is called a peptide. This process is termed as peptization. Depending on the number of amino acids linked together such as 2, 3 or more, they are refered as dipeptide, tripeptide or polypeptides, respectively.