Nucleotides, including ATP and ADP, consist of 3 main constituents: a pentose, that is, a five-carbon sugar, a nitrogen-containing organic base and a phosphate group. In ATP, that is, adenosine triphosphate molecules the pentose is a ribose, while the base is an adenine.Adenine is attached to the 1' carbon atom of ribose, while three phosphate groups are attached to its 5' carbon atom. The bond between the second and third phosphate groups is a high-energy bond, 31 kJ/mol of energy is released when the bond breaks and ADP, adenosine diphosphate is formed.
ATP is indispensable in the metabolism of living cells. During energy-absorbing processes, the high-energy bond breaks and the energy released is used in the processes that take place. In the case of energy-releasing biochemical processes, ADP and phosphoric acid attach and form ATP. The bond is formed using the energy released in the biochemical reaction.