Lactic acid fermentation

Lactic acid fermentation is a metabolic process by which glucose and 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. It is an anaerobic fermentation reaction that occurs in some bacteria and animal cells, such as muscle cells.

Process

If oxygen is present in the cell, many organisms will bypass fermentation and undergo cellular respiration; however, facultative anaerobic organisms will both ferment and undergo respiration in the presence of oxygen. Sometimes even when oxygen is present and aerobic metabolism is happening in the mitochondria, if pyruvate is building up faster than it can be metabolized, the cell will carry out fermentation anyway.

Types

There are two types of lactic acid fermentation:

• Homolactic fermentation: The end product is lactic acid. Occurs in many bacteria, yeast, and human muscle cells.
• Heterolactic fermentation: In addition to lactic acid, ethanol and carbon dioxide are also produced. Occurs in some bacteria, including Leuconostoc and some species of Lactobacillus.

Role in disease

Lactic acid fermentation is important in the development and progression of cancer. The Warburg effect is the observation that most cancer cells predominantly produce energy by a high rate of glycolysis followed by lactic acid fermentation in the cytosol, rather than by a comparatively low rate of glycolysis followed by oxidation of pyruvate in mitochondria as in most normal cells.

See also

• Fermentation (biochemistry)
• Ethanol fermentation
• Glycolysis
• Lactic acidosis
• Lactic acid bacteria

References

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