Lactic acid fermentation: Difference between revisions

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'''[[Lactic acid]] [[fermentation (biochemistry)|fermentation]]''' is a form of fermentation that occurs in [[animal cell]]s in the absence of [[oxygen]]. Under these conditions, [[Glycolysis]] occurs normally, producing 2 molecules of [[adenosine triphosphate|ATP]], 2 molecules of [[NADH]] and 2 molecules of [[pyruvate]]. However, the lack of O<sub>2</sub> prevents the NADH from being recycled to NAD<sup>+</sup> (which is required for glycolyis) through the [[electron transport chain]]. Instead, it transfers electrons to pyruvate:
#redirect [[Lactic fermentation]]
:pyruvate + NADH <math>\longrightarrow</math> lactate + NAD<sup>+</sup>
 
Lactate then diffuses out of the cell and into the [[blood]]. Certain cells, such as [[cardiac muscle]] cells, are highly permeable to [[lactate]]. Lactate is converted into pyruvate and metabolised normally (ie: via the citric acid cycle). Since these cells are highly oxygenated, it is unlikely that lactate would accumulate (as is the case in oxygen-starved muscle cells). This also allows circulating [[glucose]] to be available to muscle cells.
 
Any excess lactate is taken up by the [[liver]], converted to pyruvate and then to [[glucose]]. This, along with the production of lactate from glucose in muscle cells constitutes the [[Cori cycle]].
 
[[Phosphofructokinase]] ('''PFK'''), which catalyses an irreversible step in [[glycolysis]], is inhibited by a low [[pH]] and this prevents the formation of excess lactate and/or lactic [[acidosis]] (sudden drop in [[blood]] pH).
 
Lactic fermentation is much faster than the [[Krebs cycle]] or [[oxidative phosphorylation]], and is therefore the preferred pathway for energy generation in muscle cells under strenuous exercise.
 
Muscle cramps have been associated with levels of lactic acid in the blood, especially as a result of [[electrolyte]] imbalance caused by [[sweating]]. However, certain activities, which do not induce sweating or seem strenuous, still produce cramps (such as writing or playing an instrument) so it is unlikely that lactic acid is anything more than a minor factor.
 
[[Category:Cellular respiration]]
[[Category:Metabolism]]
[[Category:CZ Live]]

Latest revision as of 14:38, 10 April 2007

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