Important points
- ATP or adenosine triphosphate is the energy currency of the cell.
- ATP is a type of nucleoside triphosphate (NTP), which consists of a ribose sugar, 3 phosphate groups, and adenine as a nitrogenous base.
Structure
- The adenine is attached to the ribose sugar by an N-glycosidic bond.
- The triphosphate is attached to the ribose sugar by a phosphoester bond.
Adenine + ribose = adenosine (a nucleoside). Adding phosphates gives the nucleotides: AMP (1 phosphate), ADP (2) and ATP (3). The two bonds between the phosphate groups are high-energy phosphoanhydride bonds.
ATP cycle
- The energy released from ATP comes from the hydrolysis of the high-energy bond present between the 2nd and 3rd phosphate groups. ATP undergoes hydrolysis to release a phosphate group and ADP, i.e. adenosine diphosphate, and around 30.5 kJ of energy per mol of ATP is released. A phosphate group is added to ADP by a phosphorylation reaction to convert it back into ATP.
- ATP is mainly synthesised in the mitochondria of eukaryotes during aerobic respiration. This energy is used for almost all the processes of the body, including muscle contraction, active transport and even DNA replication.
ATP is made in three ways: substrate-level phosphorylation (glycolysis in the cytoplasm and the Krebs cycle), oxidative phosphorylation (by ATP synthase in the inner mitochondrial membrane) and photophosphorylation (in chloroplasts during photosynthesis).