Adenosine triphosphate (ATP) is a nucleotide that serves as the main energy carrier in living cells. It consists of the nitrogenous base adenine, the sugar ribose and a chain of three phosphate groups.
Explanation
ATP captures chemical energy released during the breakdown of nutrients and transfers it to cellular processes that require energy. Its three phosphate groups are linked by high‑energy bonds; when the terminal phosphate is cleaved by hydrolysis, energy is released and ATP is converted to adenosine diphosphate (ADP). Cells use this energy for many tasks, such as driving biosynthetic reactions, transporting substances across membranes and powering movement in muscle and flagella. ATP is continually regenerated from ADP and inorganic phosphate through cellular respiration. Enzymes like ATP synthase, located in the inner membranes of mitochondria and in the chloroplasts of plant cells, couple the flow of electrons or protons to the synthesis of ATP. In this way, cells maintain a pool of ATP that can be tapped when energy is needed quickly. The structure of ATP was clarified in the early twentieth century, and its central role in metabolism was recognized in the 1940s by researchers like Fritz Albert Lipmann. Though it is often called the energy currency of the cell, ATP is not a long‑term storage molecule; instead it functions as a transient carrier that shuttles energy between reactions.
Roles in Cellular Processes
Examples of ATP use include muscle contraction, where myosin heads rely on ATP hydrolysis to change conformation; active transport, in which membrane pumps such as the sodium–potassium pump consume ATP to move ions against their gradients; and biosynthetic pathways, where energy from ATP drives the formation of macromolecules. ATP also participates in signal transduction, acting as a substrate for kinases that transfer phosphate groups to proteins.
ATP is indispensable for life because it provides a common link between energy‑producing and energy‑requiring processes. Its quick turnover and ability to be recycled make it an efficient vehicle for delivering energy on demand.
Related Terms: ADP, ATP synthase, mitochondria, phosphorylation, energy metabolism