Definition of Fermentation (biochemistry)
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Fermentation (biochemistry) Definition from Encyclopedia Dictionaries & Glossaries
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Fermentation is a metabolic process that converts sugar to acids, gases and/or alcohol. It occurs in yeast and bacteria, but also in oxygen-starved muscle cells (see "Lactic acid fermentation" below). Fermentation takes place in the absence of oxygen, when the electron transport chain is unusable. It is used by the cell not to generate energy directly, but to recycle NADH into NAD+ so that glycolysis can continue, as long as glucose is present. The energy generated by the glycolysis-fermentation pathway, a form of substrate-level phosphorylation, is small compared with that of oxidative phosphorylation. Fermentation consumes NADH, which in aerobic conditions might have been used to generate energy in the electron transport chain. For that reason, cells generally benefit from avoiding fermentation when oxygen is available. Exceptions include obligate anaerobes, which cannot tolerate oxygen.
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