Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Citric acid cycle
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
{{Short description|Interconnected biochemical reactions releasing energy}} {{cs1 config|name-list-style=vanc|display-authors=6}} [[File:Citric acid cycle with aconitate 2.svg|thumb|upright=2|Overview of the citric acid cycle]] The '''citric acid cycle'''—also known as the '''Krebs cycle''', '''Szent–Györgyi–Krebs cycle''', or '''TCA cycle''' ('''tricarboxylic acid cycle''')<ref name="isbn0-12-181870-5">{{cite book|vauthors=Lowenstein JM|title=Methods in Enzymology, Volume 13: Citric Acid Cycle|publisher=Academic Press|location=Boston|year=1969|isbn=978-0-12-181870-8}}</ref><ref name="isbn0-904498-22-0">{{cite book|vauthors=Kay J, Weitzman PD|title=Krebs' citric acid cycle: half a century and still turning|publisher=Biochemical Society|location=London|year=1987|pages=[https://archive.org/details/krebscitricacidc0000unse/page/25 25]|isbn=978-0-904498-22-6|url=https://archive.org/details/krebscitricacidc0000unse/page/25}}</ref>—is a series of [[chemical reaction|biochemical reactions]] that release the energy stored in [[nutrient]]s through [[acetyl-CoA]] [[Redox|oxidation]]. The energy released is available in the form of [[Adenosine triphosphate|ATP]]. The [[Hans Krebs (biochemist)|Krebs]] cycle is used by [[organism]]s that generate energy via [[Cellular respiration|respiration]], either [[anaerobic respiration|anaerobically]] or [[aerobic respiration|aerobically]] (organisms that [[Fermentation|ferment]] use different pathways). In addition, the cycle provides [[precursor (chemistry)|precursors]] of certain [[amino acid]]s, as well as the [[reducing agent]] [[nicotinamide adenine dinucleotide|NADH]], which are used in other reactions. Its central importance to many [[Metabolic pathway|biochemical pathways]] suggests that it was one of the earliest [[metabolism]] components.<ref>{{cite book|vauthors=Wagner A|title=Arrival of the Fittest|date=2014|publisher=PenguinYork|isbn=978-1-59184-646-8|page=100|edition=First}}</ref><ref name="isbn0-393-06596-0">{{cite book|vauthors=Lane N|title=Life Ascending: The Ten Great Inventions of Evolution|url=https://archive.org/details/lifeascendingten0000lane|url-access=registration|publisher=W. W. Norton & Co|location=New York|year=2009|isbn=978-0-393-06596-1}}</ref> Even though it is branded as a "cycle", it is not necessary for [[metabolite]]s to follow a specific route; at least three alternative pathways of the citric acid cycle are recognized.<ref>{{cite journal|vauthors=Chinopoulos C|title=Which way does the citric acid cycle turn during hypoxia? The critical role of α-ketoglutarate dehydrogenase complex|journal=Journal of Neuroscience Research|volume=91|issue=8|pages=1030–1043|date=August 2013|pmid=23378250|doi=10.1002/jnr.23196|url=http://real.mtak.hu/56447/1/Which_way_does_the_citric_acid_cycle_turn_during_hypoxia_u.pdf|doi-access=free}}</ref> Its name is derived from the [[citric acid]] (a [[tricarboxylic acid]], often called citrate, as the ionized form predominates at biological pH<ref name="Voet_2004" />) that is consumed and then regenerated by this sequence of reactions. The cycle consumes [[acetate]] (in the form of acetyl-CoA) and [[water]] and reduces NAD<sup>+</sup> to NADH, releasing carbon dioxide. The NADH generated by the citric acid cycle is fed into the [[oxidative phosphorylation]] (electron transport) pathway. The net result of these two closely linked pathways is the oxidation of [[nutrient]]s to produce usable chemical energy in the form of ATP. In [[eukaryotic]] cells, the citric acid cycle occurs in the [[mitochondrial matrix|matrix]] of the [[mitochondrion]]. In [[prokaryotic]] cells, such as bacteria, which lack mitochondria, the citric acid cycle reaction sequence is performed in the cytosol with the proton gradient for [[Chemiosmosis|ATP production]] being across the cell's surface ([[Cell membrane|plasma membrane]]) rather than the [[inner membrane of the mitochondrion]]. For each [[pyruvate]] molecule (from [[glycolysis]]), the overall yield of energy-containing compounds from the citric acid cycle is three NADH, one [[Flavin adenine dinucleotide|FADH<sub>2</sub>]], and one [[guanosine triphosphate|GTP]].<ref>{{Cite book|title=Marks' basic medical biochemistry : a clinical approach|vauthors=Lieberman M|date=2013|publisher=Wolters Kluwer Health/Lippincott Williams & Wilkins|others=Marks, Allan D., Peet, Alisa|isbn=978-1-60831-572-7|edition=Fourth|location=Philadelphia|oclc=769803483}}</ref>
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)