<P> When two amino acids form a dipeptide through a peptide bond it is called condensation . In condensation, two amino acids approach each other, with the acid moiety of one coming near the amino moiety of the other . One loses a hydrogen and oxygen from its carboxyl group (COOH) and the other loses a hydrogen from its amino group (NH). This reaction produces a molecule of water (H O) and two amino acids joined by a peptide bond (- CO-NH -). The two joined amino acids are called a dipeptide . </P> <P> The amide bond is synthesized when the carboxyl group of one amino acid molecule reacts with the amino group of the other amino acid molecule, causing the release of a molecule of water (H O), hence the process is a dehydration synthesis reaction (also known as a condensation reaction). </P> <P> The formation of the peptide bond consumes energy, which, in living systems, is derived from ATP . Polypeptides and proteins are chains of amino acids held together by peptide bonds . Living organisms employ enzymes to produce polypeptides, and ribosomes to produce proteins . Peptides are synthesized by specific enzymes . For example, the tripeptide glutathione is synthesized in two steps from free amino acids, by two enzymes: gamma - glutamylcysteine synthetase and glutathione synthetase . </P> <P> A peptide bond can be broken by hydrolysis (the addition of water). In the presence of water they will break down and release 8--16 kilojoule / mol (2--4 kcal / mol) of free energy . This process is extremely slow, with the half life at 25C of between 350 and 600 years per bond . </P>

Where does the energy to form a peptide bond come from