The adenosine triphosphate (ATP) is the molecule responsible for its links stored in the energy produced in chemical reactions, but last only a short time. A person expends about 45 kg of ATP a day, although he has less than 1 gram at any one time.
As we saw when we talked about nucleotides, these energy-rich phosphate bonds are symbolized by the sign ~, little virgulilla. The inorganic phosphate is represented by Pi.
Through dephosphorylation, ATP transfers a phosphate group to another compound, leaving ADP (adenosine diphosphate) as the resulting molecule, and if another phosphate is lost, AMP (adenosine monophosphate). These reactions are reversible:
ATP ↔ ADP + Pi + energy
ADP ↔ AMP + Pi + energy
In the cell, ATP can be obtained by:
- Substrate level phosphorylation. A substrate molecule that contains a phosphate group gives it to ADP to form ATP.
- Oxidative phosphorylation. In mitochondria, through the ATP synthase complex, most of the ATP of the cell is obtained.
- Photophosphorylation or photosynthetic phosphorylation. In the chloroplasts of eukaryotic plant cells, through the ATP synthase complex.