Cori Cycle

Cori cycle 1

Cori cycleThe Cori cycle (also known as Lacticacid cycle), named after itsdiscoverers, Carl Cori and Gerty Cori,refers to the metabolic pathway inwhich lactate produced by anaerobicglycolysis in the muscles moves to theliver and is converted to glucose,which then returns to the muscles andis converted back to lactate.[1]

Cycle

Gerty Cori and Carl Cori jointly won the 1947Nobel Prize in Physiology or Medicine for their

discovery of the Cori cycle .

Muscular activity requires energy, which is provided by the breakdownof glycogen in the skeletal muscles. The breakdown of glycogen, aprocess known as glycogenolysis, releases glucose in the form ofglucose-6-phosphate (G-6-P). G-6-P is readily fed into glycolysis, aprocess that provides ATP to the muscle cells as an energy source.During muscular activity, the store of ATP needs to be constantlyreplenished. When the supply of oxygen is sufficient, this energycomes from feeding pyruvate, one product of glycolysis, into the Krebscycle.

When oxygen supply is insufficient, typically during intense muscularactivity, energy must be released through anaerobic metabolism. Lacticacid fermentation converts pyruvate to lactate by lactatedehydrogenase. Most important, fermentation regenerates NAD+,maintaining the NAD+ concentration so that additional glycolysisreactions can occur. The fermentation step oxidizes the NADHproduced by glycolysis back to NAD+, transferring two electrons fromNADH to reduce pyruvate into lactate. Refer to the main articles onglycolysis and fermentation for the details.

Instead of accumulating inside the muscle cells, lactate produced by anaerobic fermentation is taken up by the liver.This initiates the other half of the Cori cycle. In the liver, gluconeogenesis occurs. From an intuitive perspective,gluconeogenesis reverses both glycolysis and fermentation by converting lactate first into pyruvate, and finally backto glucose. The glucose is then supplied to the muscles through the bloodstream; it is ready to be fed into furtherglycolysis reactions. If muscle activity has stopped, the glucose is used to replenish the supplies of glycogen throughglycogenesis.[2]

Overall, the glycolysis part of the cycle produces 2 ATP molecules at a cost of 6 ATP molecules consumed in thegluconeogenesis part. Each iteration of the cycle must be maintained by a net consumption of 4 ATP molecules. As aresult, the cycle cannot be sustained indefinitely. The intensive consumption of ATP molecules indicates that theCori cycle shifts the metabolic burden from the muscles to the liver.

Cori cycle 2

SignificanceThe cycle's importance is based on the prevention of lactic acidosis in the muscle under anaerobic conditions.However, normally before this happens the lactic acid is moved out of the muscles and into the liver.[2]

The cycle is also important in producing ATP, an energy source, during muscle activity. The Cori cycle functionsmore efficiently when muscle activity has ceased. This allows the oxygen debt to be repaid such that the Krebs cycleand electron transport chain can produce energy at peak efficiency.[2]

References[1] Nelson, David L., & Cox, Michael M.(2005) Lehninger Principles of Biochemistry Fourth Edition. New York: W.H. Freeman and Company,

p. 543.[2] " Cori Cycle (http:/ / www. elmhurst. edu/ ~chm/ vchembook/ 615coricycle. html)". Retrieved May 3, 2008, from Elmhurst, pp. 1–3.

Sources• Smith, A.D., Datta, S.P., Smith, G. Howard, Campbell, P.N., Bentley, R., (Eds.) et al.(1997) Oxford Dictionary of

Biochemistry and Molecular Biology. New York: Oxford University Press.

Article Sources and Contributors 3

Article Sources and ContributorsCori cycle  Source: http://en.wikipedia.org/w/index.php?oldid=500383683  Contributors: Arcadian, Axl, Cbailey3765, Cetona08, Chibibrain, Christian75, Dillard421, Drphilharmonic, Epbr123,Eyal Bairey, Five-toed-sloth, Fuzbaby, Fyyer, Hosolof, Hurtdog2020, Iridescent, Isnow, Jag123, Jyril, Kaarel, Kazkaskazkasako, LOL, Lbiochem, Longhair, Louperivois, MacDaid, Mirabellen,Nephron, Neuroticopia, Nishantkumarnishu, Orchid Righteous, PDH, Parutakupiu, Perfecto, Pjlmac, Proofreader77, Rainbowwrasse, Rjwilmsi, Robbyjo, Sandstein, Shadibasyuni, Shrimp wong,ThinkerThoughts, Tillman, Twirligig, Una Smith, Verticalstall, Vovec, WATerian, Zanimum, 64 anonymous edits

Image Sources, Licenses and ContributorsFile:Cori Cycle.SVG  Source: http://en.wikipedia.org/w/index.php?title=File:Cori_Cycle.SVG  License: GNU Free Documentation License  Contributors: User:Petaholmes, user:PDH, user:EyalBaireyFile:Gerty Theresa Radnitz Cori (1896-1957) and Carl Ferdinand Cori.jpg  Source:http://en.wikipedia.org/w/index.php?title=File:Gerty_Theresa_Radnitz_Cori_(1896-1957)_and_Carl_Ferdinand_Cori.jpg  License: unknown  Contributors: Smithsonian Institution from UnitedStates

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