Adenosine triphosphate (ATP) is converted to adenosine diphosphate (ADP) in the cells of plants and animals when energy is required to power processes in the cell. ATPase, an enzyme, cleaves one of the phosphate bonds on ATP (three phosphates), converting it to ADP (two phosphates) and releasing energy.
The ATP/ADP cycle is present in every living organism on Earth. ATP is present in the mitochondria in animal cells and in the chloroplast and mitochondria of plant cells. When ATP is converted to ADP by cleaving a phosphate bond, it produces 7.3 kilocalories per mole. This energy fuels both anabolic (synthesis of chemical bonds) and catabolic (breaking of chemical bonds) cellular processes.