Adenosine triphosphate

Adenosine triphosphate is a universal energy store within the cell. It consists of:

• 1 molecule of adenine
• 1 molecule of ribose
• 3 phosphate groups joined by ester linkages

Energy is liberated on the hydrolysis of the terminal phosphate group to yield ADP, or two phosphate groups to yield AMP. Conversely, the degradation of organic molecules, usually by oxidation, yields energy which can be used directly to form ATP from inorganic phosphate and ADP or AMP. AMP, ADP and ATP are in equilibrium.

Alternatively, the energy liberated by catabolic reactions can form reduced compounds such as NADH and FADH2. Indirectly, these compounds can form ATP via the electron transfer chain and oxidative phosphorylation.