Adenosine Triphosphate (ATP), an energy-bearing molecule found in all living cells. Formation of nucleic acids, transmission of nerve impulses, muscle contraction, and many other energy-consuming reactions of metabolism are made possible by the energy in ATP molecules. The energy in ATP is obtained from the breakdown of foods.

An ATP molecule is composed of carbon, hydrogen, nitrogen, oxygen, and phosphorus atoms. There are three phosphorus atoms in the molecule. Each of these phosphorus atoms is at the center of an atomic group called a phosphate. The phosphate groups are linked to one another by chemical bonds called phosphate bonds. The energy of ATP is locked in these bonds.

The energy in ATP can be released as heat or can be used in the cell as a power source to drive various types of chemical and mechanical activities. For example, when the terminal phosphate group of the ATP molecule is removed by hydrolysis (a decomposition process that occurs when a substance reacts with water), energy in the form of heat is released and adenosine diphosphate (ADP) and inorganic phosphate (Pi) are formed.

The hydrolysis of ATP is accelerated by an enzyme called adenosine triphosphatase, or ATP-ase. The reaction can be written as:

ATP ® ADP + Pi + energy

The regeneration of ATP from ADP requires energy, which is obtained in the process of oxidation. The energy released in the oxidation of carbohydrates and fats initiates a complex series of chemical reactions that ultimately regenerate ATP molecules from ADP molecules. The complete oxidation of a typical molecule of fat results in the formation of about 150 molecules of ATP.

ATP was discovered in muscle tissue by scientists in Germany and the United States in 1929. Its role in the storage and supply of energy was first explained in 1941 by the German-American biochemist Fritz A. Lipmann. For this achievement, he shared the 1953 Nobel Prize in physiology or medicine.