You recycle roughly your own body weight in ATP every day
An average adult makes and breaks down about 50 kilograms of ATP daily, yet holds only a tiny amount at any moment. The molecule works like a rechargeable battery, spending one phosphate to power muscles, nerves and chemistry, then being recharged almost immediately. Every known living thing runs on it.
Structurally, ATP is modest: the base adenine, the sugar ribose and a chain of three phosphate groups. Cells tap its energy by snipping off the end phosphate to form ADP, or two phosphates to form AMP, while the adenine and sugar stay untouched. Under standard laboratory conditions, removing one phosphate releases about 30.5 kilojoules per mole. Inside a real cell the figure is nearly double, around 57 kilojoules, because cells keep the balance of ATP to ADP ten orders of magnitude away from chemical equilibrium, with ATP about five times as plentiful.
Magnesium is its constant companion. ATP binds the metal so strongly that it exists in cells mostly as a magnesium complex, which shapes how it interacts with proteins. Researchers interested in life's origins note that ATP carrying magnesium can help catalyse the linking of RNA, a hint of how early chemistry might have worked. ATP is also a building block for DNA and RNA themselves.
Most ATP is made in mitochondria, which fill almost a quarter of a typical cell's volume. Glycolysis in the cytoplasm splits glucose and nets a little ATP; the citric acid cycle and oxidative phosphorylation then do the heavy lifting. Electrons passed along a chain of proteins pump protons across the inner mitochondrial membrane, and as the protons flow back through the enzyme ATP synthase, they drive production. Fully oxidising one glucose molecule yields about 30 ATP, and breaking down fats through beta-oxidation can yield dozens more.
The system regulates itself neatly. A key glycolysis enzyme, phosphofructokinase, is slowed by abundant ATP and sped up by plenty of AMP, so the cell speeds energy production when it is running low. Pyruvate kinase is inhibited by ATP itself. Even exporting ATP from the mitochondrion costs energy: each molecule shipped out spends one proton, on top of about three used to make it.
Source: Adenosine triphosphate
