Cleavage of one phosphate group from ATP results in a free energy that biomolecular machinery uses as an energy source. The resulting Adenosine Diphosphate (ADP) contains only two phosphate groups, but can then be recharged to ATP by means of ATP synthase. The ratio of [ATP]/[ADP] within a cell is known as the "energy charge" and provides a measure of the free energy immediately available in the form of ATP.
