What is Adenosine triphosphate?
[[File:Adenosintriphosphat.svg|thumb|180px|The molecular structure of ATP.]] '''Adenosine triphosphate''' ('''ATP''') is a [[Chemical substance|chemical]]. All living things make ATP to store energy and to move it to the [[cell]]s that need it. Cells get all their energy from ATP. They break ATP molecules apart to use the stored energy. The harder a cell works, the more ATP it needs. == Use == The ATP molecule is very versatile: it is used for many chemical reactions in the body. Energy is stored in its chemical bonds. The energy that is stored can be used later. When ATP breaks a bond with a phosphate group and becomes [[ADP]], energy is released. This is an [[exothermic]] reaction. The ATP phosphate exchange is a nearly never-ending cycle, stopping only when the cell dies. === Functions in cells === ATP is the main energy source for most cellular functions. This includes the synthesis of macromolecules. It is used in [[DNA replication|DNA]] and [[Transcription (genetics)|RNA]]. ATP also helps macromolecules get across cell membranes. === DNA and RNA synthesis === In all known organisms, [[DNA]] is made by the action of [[ribonucleotide reductase]] (RNR) enzymes.<ref name=Stubbe>{{cite journal | author = Stubbe J | title = Ribonucleotide reductases: amazing and confusing | url = http://www.jbc.org/cgi/reprint/265/10/5329 | journal = J Biol Chem | volume = 265 | issue = 10 | pages = 5329–32 | date = 5 April 1990 | pmid = 2180924 | access-date = 3 December 2010 | archive-date = 11 April 2008 | archive-url = https://web.archive.org/web/20080411054459/http://www.jbc.org/cgi/reprint/265/10/5329 | url-status = dead }}</ref> These enzymes reduce the sugar residue from [[ribose]] to [[deoxyribose]] by removing oxygen.<ref name=Stubbe/> ATP is one of the four [[nucleotide]]s put into RNA molecules by [[RNA polymerase]]s. The energy driving this polymerization comes from cutting off two [[phosphate]] groups.<ref>{{cite journal |author=Joyce C.M. & Steitz T.A. |title=Polymerase structures and function: variations