Editing Adenosine diphosphate (section)

==Cellular respiration==

===Catabolism===
The ten-step [[catabolic]] pathway of [[glycolysis]] is the initial phase of free-energy release in the breakdown of  [[glucose]] and can be split into two phases, the preparatory phase and payoff phase. ADP and [[phosphate]] are needed as precursors to synthesize ATP in the payoff reactions of the [[TCA cycle]] and [[oxidative phosphorylation]] mechanism.<ref>{{cite journal |vauthors =Jensen TE, Richter EA |title=Regulation of glucose and glycogen metabolism during and after exercise |journal=J. Physiol. |volume=590 |issue=Pt 5 |pages=1069–76 |date=March 2012|pmid=22199166 |pmc=3381815 |doi=10.1113/jphysiol.2011.224972 }}</ref>  During the payoff phase of glycolysis, the enzymes phosphoglycerate kinase and pyruvate kinase facilitate the addition of a phosphate group to ADP by way of [[substrate-level phosphorylation]].<ref>{{cite journal |vauthors =Liapounova NA, Hampl V, Gordon PM, Sensen CW, Gedamu L, Dacks JB |title=Reconstructing the mosaic glycolytic pathway of the anaerobic eukaryote Monocercomonoides |journal=Eukaryotic Cell |volume=5 |issue=12 |pages=2138–46 |date=December 2006|pmid=17071828 |pmc=1694820 |doi=10.1128/EC.00258-06 }}</ref>
[[File:Glycolysis overview.svg|thumb|Glycolysis overview]]

===Glycolysis===
{{main|glycolysis}}
Glycolysis is performed by all living organisms and consists of 10 steps.  The net reaction for the overall process of [[glycolysis]] is:<ref>{{cite web|last=Medh|first=J.D|title=Glycolysis|url=http://www.csun.edu/~jm77307/Glycolysis.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.csun.edu/~jm77307/Glycolysis.pdf |archive-date=2022-10-09 |url-status=live|publisher=CSUN.Edu|access-date=3 April 2013}}</ref>
:Glucose + 2 NAD+ + 2 P<sub>i</sub> + 2 ADP → 2 pyruvate + 2 ATP + 2 NADH + 2 H<sub>2</sub>O
Steps 1 and 3 require the input of energy derived from the hydrolysis of ATP to ADP and P<sub>i</sub> (inorganic phosphate), whereas steps 7 and 10 require the input of ADP, each yielding ATP.<ref>{{cite web|last=Bailey|first=Regina|title=10 Steps of Glycolysis|url=http://biology.about.com/od/cellularprocesses/a/aa082704a.htm|access-date=2013-05-10|archive-date=2013-05-15|archive-url=https://web.archive.org/web/20130515102637/http://biology.about.com/od/cellularprocesses/a/aa082704a.htm|url-status=dead}}</ref>  The [[enzyme]]s necessary to break down glucose are found in the [[cytoplasm]], the viscous fluid that fills living cells, where the glycolytic reactions take place.<ref name=Lehninger/>

===Citric acid cycle===
{{main|citric acid cycle}}
The [[citric acid cycle]], also known as the Krebs cycle or the TCA (tricarboxylic acid) cycle is an 8-step process that takes the pyruvate generated by glycolysis and generates 4 NADH, FADH2, and GTP, which is further converted to ATP.<ref>{{cite web|title=Citric Acid Cycle |url=http://web.ku.edu/~crystal/taksnotes/Biol_638/notes/chp_16.pdf |publisher=Takusagawa’s Note |access-date=4 April 2013 |url-status=dead |archive-url=https://web.archive.org/web/20120324072437/http://web.ku.edu/~crystal/taksnotes/Biol_638/notes/chp_16.pdf |archive-date=24 March 2012 }}</ref> It is only in step 5, where GTP is generated, by succinyl-CoA synthetase, and then converted to ATP, that ADP is used (GTP + ADP → GDP + ATP).<ref>{{cite web|title=Biochemistry |url=http://www.uccs.edu/~sbraunsa/Images/482Notes/17-TCAcycle.pdf |publisher=UCCS.edu |url-status=dead |archive-url=https://web.archive.org/web/20130228175004/http://www.uccs.edu/~sbraunsa/Images/482Notes/17-TCAcycle.pdf |archive-date=2013-02-28 }}</ref>
<!-- Deleted image removed: [[File:Conversion of GTP to ATP.jpg|thumbnail|chemical conversion of GTP to ATP]] -->

===Oxidative phosphorylation===
{{main|oxidative phosphorylation}}
[[Oxidative phosphorylation]] produces 26 of the 30 equivalents of ATP generated in cellular respiration by transferring electrons from NADH or FADH2 to [[Oxygen|O<sub>2</sub>]] through electron carriers.<ref>{{cite web|title=Oxidative phosphorylation|url=https://www.ncbi.nlm.nih.gov/books/NBK21208/|publisher=W H Freeman, 2002|access-date=4 April 2013}}</ref> The energy released when electrons are passed from higher-energy NADH or FADH2 to the lower-energy O<sub>2</sub> is required to phosphorylate ADP and once again generate ATP.<ref>{{cite web|last=Medh|first=J. D.|title=Electron Transport Chain (Overview)|url=http://www.csun.edu/~jm77307/Oxidative%20Phosphorylation.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.csun.edu/~jm77307/Oxidative%20Phosphorylation.pdf |archive-date=2022-10-09 |url-status=live|publisher=CSUN.edu|access-date=4 April 2013}}</ref> It is this energy coupling and phosphorylation of ADP to ATP that gives the electron transport chain the name oxidative phosphorylation.<ref name=Lehninger/>
[[File:ATP-Synthase.svg|thumb|ATP-Synthase]]

====Mitochondrial ATP synthase complex====
{{main|ATP synthase}}
During the initial phases of [[glycolysis]] and the [[TCA cycle]], [[cofactor (biochemistry)|cofactors]] such as [[NAD+]] donate and accept electrons<ref>{{cite journal |vauthors =Belenky P, Bogan KL, Brenner C |title=NAD+ metabolism in health and disease |journal=Trends Biochem. Sci. |volume=32 |issue=1 |pages=12–9 |date=January 2007|pmid=17161604 |doi=10.1016/j.tibs.2006.11.006 }}</ref> that aid in the [[electron transport chain]]'s ability to produce a proton gradient across the inner mitochondrial membrane.<ref>{{cite book |author =Murray, Robert F. |title=Harper's illustrated biochemistry |publisher=McGraw-Hill |location=New York |year=2003 |isbn=0-07-121766-5 }}</ref> The ATP synthase complex exists within the mitochondrial membrane (F<sub>O</sub> portion) and protrudes into the matrix (F<sub>1</sub> portion).  The energy derived as a result of the chemical gradient is then used to synthesize ATP by coupling the reaction of inorganic phosphate to ADP in the active site of the [[ATP synthase]] enzyme; the equation for this can be written as ADP + P<sub>i</sub> → ATP.{{cn|date=April 2023}}