Adenosine triphosphate (ATP) is a neucleotide. ATP consists of 3 units: ribose (a pentose sugar), adenine (a purine base) and a triphosphate group. ATP is a energy coin or energy carrier because hydrolis of ATP releases free energy. The ATP-p bond itself does not store energy but the system absent whole releases energy when the reaction takes place.
ATP – H2O ADP – Pi – H+
If one phosphate group is removed by hydrolysis ADPC (adenosine diphosphate and orthophosphate) (H3PO32-) are formed and in the same way removal of two phosphate a pyrophosphate forms an AMP (adenosine monophosphate). ATP is an all purpose carrier of free energy in the biological system.