Wednesday, February 3, 2010

Adenosine Triphosphate

Adenosine triphosphate (ATP) is a molecule used in cells as a coenzyme. Adenosine triphosphate is the immediate source of energy for the mechanical work performed by muscle. ATP is a nucleotide which causes the contraction of the muscle protein actomyosin with the formation of adenosine diphosphate and inorganic phosphate. ATP is also involved in the activation of amino acids, a necessary step in the synthesis of protein. It is often called the "molecular unit of currency" of intracellular energy transfer.

Adenosine triphosphate is the only compound which the body can use directly as fuel for energy-consuming activities, including movement. Without it, we would die. ATP is a high-energy compound made using the energy derived from the breakdown of food during respiration. Physical activity uses enormous quantities of ATP. An active muscle cell requires about two million ATP molecules per second to drive its biochemical machinery.

Adenosine triphosphate transports chemical energy within cells for metabolism. It is produced by photophosphorylation and cellular respiration and used by enzymes and structural proteins in many cellular processes, including biosynthetic reactions, motility, and cell division. One molecule of ATP contains three phosphate groups, and it is produced by ATP synthase from inorganic phosphate and adenosine diphosphate (ADP) or adenosine monophosphate (AMP). Metabolic processes that use ATP as an energy source convert it back into its precursors. ATP is therefore continuously recycled in organisms, with the human body turning over its own weight in ATP each day.

ATP is used as a substrate in signal transduction pathways by kinases that phosphorylate proteins and lipids, as well as by adenylate cyclase, which uses ATP to produce the second messenger molecule cyclic AMP. The ratio between ATP and AMP is used as a way for a cell to sense how much energy is available and control the metabolic pathways that produce and consume ATP. Apart from its roles in energy metabolism and signaling, ATP is also incorporated into nucleic acids by polymerases in the processes of DNA replication and transcription.