ATP (adenosine triphosphate) is the energy-carrying molecule used in cells because it can release energy very quickly.
Energy is released from ATP when the end phosphate is removed. Once ATP has released energy, it becomes ADP (adenosine diphosphate), which is a low energy molecule.
ADP can be recharged back into ATP by adding a phosphate. This requires energy.
These molecules can be recycled so that a constant stream of energy rich ATP is available for all metabolic pathways in the cell.
Almost all cellular processes need ATP to give a reaction its required energy.
ATP can transfer energy and phosphorylate (add a phosphate) to other molecules in cellular processes such as DNA replication, active transport, synthetic pathways and muscle contraction.