Adenosine triphosphate, or ATP, is one of the most important energy-providing compounds used by cells to maintain their metabolism. Often described as the "energy currency" of a cell, ATP is a nucleotide comprised of three phosphate groups, the sugar ribose and adenine. ATP is found within cell fluid in concentrations that range between 0.5 to 2.5 milligrams per milliliter.
As the primary energy source for most of a cell's functions, ATP transfers energy across separate metabolic processes, synthesizes macromolecules and proteins, plays a required role in muscle contraction and helps to transport molecules across cell membranes in endocytosis and exocytosis. ATP also enables extracellular signaling and it is an important part of the human peripheral and central nervous systems.
When combined with water in the process called hydrolysis, ATP breaks down into adenosine diphosphate, or ADP, and inorganic phosphate. Because the energy contained within the products of this reaction is less than what was present in the original reactants, energy is released. During hydrolysis, the bonds holding the naturally-repelling phosphate electrons together in ATP are broken, producing free energy/
The chemical formula for ATP is C10H16N5O13P3. It was first discovered in 1929. In 1941, it was proposed that ATP was a factor in the energy-releasing and energy-requiring reactions taking place within cells. ATP was first synthesized in a laboratory in 1948 by Alexander Todd.