adenosine triphosphate
Meaning of adenosine triphosphate: Cells hold only a tiny standing amount and recycle it endlessly, so adenosine triphosphate works as a currency rather than as a store of energy.
Definition of adenosine triphosphate
Adenosine triphosphate is the molecule cells use to carry energy from where it is released to where it is needed. It is built from adenine and a ribose sugar with a chain of three phosphate groups attached, and breaking the outermost phosphate off releases energy the cell can put to work. Every living cell makes it constantly and spends it just as fast.
How does it carry energy?
The energy sits in the bonds joining the phosphate groups, which push against one another because each carries a negative charge. Removing the outermost phosphate relieves that strain and frees energy the cell couples to useful work, leaving adenosine diphosphate behind. Putting a phosphate back rebuilds the molecule, and the cycle turns over without pause. The quantity present at any instant is small, nowhere near enough to power a cell for long, so the total recycled across a day vastly exceeds the amount in existence at any one moment. That is the sense in which it is a currency: earned and spent rather than stockpiled.
Where is it made?
| Route | Where it happens | Relative yield |
|---|---|---|
| Glycolysis | The fluid of the cell, without needing oxygen | Small |
| Citric acid cycle | Mitochondria | Small directly, but feeds the next step |
| Oxidative phosphorylation | The inner mitochondrial membrane, using oxygen | By far the largest |
| Creatine phosphate | Muscle | A brief reserve, regenerating it for seconds of hard effort |
Because most of the supply depends on oxygen reaching the mitochondria, tissue starved of blood runs short within minutes. A cell that cannot maintain its supply loses control of the pumps holding its internal chemistry steady, and that failure is a common final step in cell death from many different causes, which is why metabolic demand and blood supply are so often discussed together.
What else does it do?
Energy transfer is the main role but not the only one. It is one of the four building blocks from which RNA is assembled, placing it directly in the path of genetic information. Transferring a phosphate taken from it switches proteins on and off, which is how a great deal of signaling inside cells is controlled. Released outside the cell it acts as a messenger in its own right, binding receptors involved in pain sensation, inflammation and the behavior of platelets. It is also the raw material for cyclic AMP, the second messenger many hormones work through. A laboratory made form given by infusion has been studied in people with advanced cancer to see whether it slows weight and muscle loss, a question that remains under investigation rather than an established use.
Also known as
Used in a sentence
Researchers measured adenosine triphosphate levels within the cells to assess their metabolic activity.
Good to know
Adenosine triphosphate manufactured in a laboratory and studied as a possible treatment is a separate matter from the molecule's constant ordinary role supplying energy inside every living cell.