Peptide Bond Formation

The amino acids that make up a protein are joined together covalently by peptide bonds. A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of a second amino acid, releasing a molecule of water and leaving the two residues joined by an amide linkage -- it is this specific amide linkage between two amino acids that is given the special name peptide bond. The compound produced by joining exactly two amino acids this way is called a dipeptide. Adding a third amino acid to a dipeptide, forming a second peptide bond, gives a tripeptide; continuing to add residues one at a time gives, in turn, a tetrapeptide, a pentapeptide, and so on. When a comparatively small number of amino acids are linked this way the chain is called a polypeptide; when a very large number of amino acids are linked, and the resulting chain has taken on a biological function, it is called a protein. …