Adenosine diphosphate

Adenosine diphosphate is a universal energy intermediate within the cell. It consists of:

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

Energy is liberated on the hydrolysis of the terminal phosphate group to yield AMP. Conversely, the degradation of organic molecules, usually by oxidation, yields energy which can be used directly to form:

• ADP from inorganic phosphate and AMP
• ATP from inorganic phosphate and ADP

ADP, ATP and AMP are in equilibrium.

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