Adenosine triphosphate (ATP) is an energy-carrying molecule found in all living cells. It provides the energy that cells need to drive chemical reactions, transport substances across cell membranes, and perform mechanical work like muscle movement.
ATP is not actually a storage molecule for energy. That role belongs to molecules like carbohydrates and fats. When a cell needs energy, it converts the stored energy from those molecules into ATP. ATP then delivers the energy to wherever it is needed in the cell. So ATP acts like an energy shuttle within the cell.
The ATP molecule has three main parts – the base adenine, the sugar ribose, and a chain of three phosphate groups. The phosphate groups contain the energy. When one of the phosphates detaches, energy is released for the cell to use. This leaves ATP converted to adenosine diphosphate (ADP), which has only two phosphates.
ATP provides energy by transferring a phosphate to another molecule, a process called phosphorylation. Special enzymes couple the energy release from ATP to the cell processes that need energy input.
Although cells constantly break down ATP for energy, they also continuously resynthesize it from ADP and phosphate. Most ATP is made by the enzyme ATP synthase, found in cell structures called mitochondria and chloroplasts. ATP’s central role in cell energy metabolism was uncovered in 1941.
