Adenosine triphosphate (ATP) is a small molecule that is used as a coenzyme in cells. The nucleotide, which belongs to the group of nucleoside triphosphates, is often referred to as the molecular unit of intercellular energy exchange. Within the cell metabolism, ATP is responsible for the transport of chemical energy. Most cell functions – such as synthesis – can only be performed when energy is supplied. When ATP breaks down (hydrolyses) to adenosine diphosphate (ADP) and phosphate (Pi), energy is released during the degradation of the last covalent phosphorus compound and can be used, if necessary, for chemical reactions.