ATP definition
(2) An organic compound composed of adenosine (an adenine ring and a ribose sugar) and three phosphate groups, hence, the name. Supplement. ATP is a nucleotide that contains a large amount of chemical energy stored in its high-energy phosphate bonds.It releases energy when it is broken down (hydrolyzed) into ADP (or Adenosine Diphosphate). The energy is used for many metabolic processes.upplement. ATP is a nucleotide that contains a large amount of chemical energy stored in its high-energy phosphate bonds. It releases energy when it is broken down (hydrolyzed) into ADP (or Adenosine Diphosphate).