Adenosine triphosphate (ATP) is a nucleoside triphosphate, a small molecule used in cells as a coenzyme. It is often referred to as the “molecular unit of currency” of intracellular energy transfer.
ATP transports chemical energy within cells for metabolism. Most cellular functions need energy in order to be carried out: synthesis of proteins, synthesis of membranes, movement of the cell, cellular division, etc. need energy to be performed. The ATP is the molecule that carries energy to the place where the energy is needed. When ATP breaks into ADP (Adenosine diphosphate) and Pi (phosphate), the breakdown of the last covalent link of phosphate (a simple -P04) liberates energy that is used in reactions where it is needed.