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Lactic acid fermentation is a metabolic process by which glucose or other six-carbon sugars (also, disaccharides of six-carbon sugars, e.g. sucrose or lactose) are converted into cellular energy and the metabolite lactate, which is lactic acid in solution.
Despite the bactericidal effects of ethanol, acidifying effects of fermentation, and low oxygen conditions of industrial alcohol production, bacteria that undergo lactic acid fermentation can contaminate such facilities because lactic acid has a low pKa of 3.86 to avoid decoupling the pH membrane gradient that supports regulated transport. [7]
While fermentation produces adenosine triphosphate (ATP) only in low yield compared to the citric acid cycle and oxidative phosphorylation of aerobic respiration, it allows proliferating cells to convert nutrients such as glucose and glutamine more efficiently into biomass by avoiding unnecessary catabolic oxidation of such nutrients into ...
Lactic acid fermentation is relatively inefficient. The waste products lactic acid and ethanol have not been fully oxidized and still contain energy, but it requires the addition of oxygen to extract this energy. [8] Generally, lactic acid fermentation occurs only when aerobic cells are lacking oxygen.
In lactic acid fermentation, each pyruvate molecule is directly reduced by NADH. The only byproduct from this type of fermentation is lactate . Lactic acid fermentation is used by human muscle cells as a means of generating ATP during strenuous exercise where oxygen consumption is higher than the supplied oxygen.
These lactic acid bacteria can carry out either homolactic fermentation, where the end-product is mostly lactic acid, or heterolactic fermentation, where some lactate is further metabolized to ethanol and carbon dioxide [19] (via the phosphoketolase pathway), acetate, or other metabolic products, e.g.: C 6 H 12 O 6 → CH 3 CHOHCOOH + C 2 H 5 ...
The total ATP yield in ethanol or lactic acid fermentation is only 2 molecules coming from glycolysis, because pyruvate is not transferred to the mitochondrion and finally oxidized to the carbon dioxide (CO 2), but reduced to ethanol or lactic acid in the cytoplasm.
Within the human body, lactic acid is the by-product of ATP-producing fermentation, which produces energy so the body can continue to exercise in situations where oxygen intake cannot be processed fast enough. Although fermentation yields less ATP than aerobic respiration, it can occur at a much higher rate.