Adenosine triphosphate, or ATP, is a molecule which acts as a universal energy currency for living cells. Its structure consists of the nucleoside adenosine and a tail of three phosphate groups.
During ATP synthesis via reactions or by ATP synthase energy is safely stored as chemical energy in the structure of ATP, specifically in the high energy phosphate bonds. The negative charges in the phosphate groups repel each other and need high amounts of energy to bond them together. When these high-energy bonds are broken, this energy is released through ATP hydrolysis.
Figure 1: Structure of ATP