Fermentation: Encyclopedia II - Fermentation - Biochemistry

Fermentation - Biochemistry

Fermentation is a process that is important in anaerobic conditions when there is no oxidative phosphorylation to maintain the production of ATP by glycolysis. During fermentation pyruvate is metabolised to various different compounds. Textbook examples of fermentation products are ethanol (drinkable alcohol), lactic acid, and hydrogen. However, more exotic compounds can be produced by fermentation, such as butyric acid and acetone.

Although the final step of fermentation (conversion of pyruvate to fermentation end-products) does not produce energy, it is critical for an anaerobic cell since it regenerates nicotinamide adenine dinucleotide (NAD⁺), which is required for glycolysis. This is important for normal cellular function, as glycolysis is the only source of ATP in anaerobic conditions.

Fermentation products contain chemical energy (they are not fully oxidised) but are considered waste products since they cannot be metabolised further without the use of oxygen (or other more highly-oxidised electron acceptors). A consequence is that the production of ATP by fermentation is less efficient than oxidative phosphorylation, where pyruvate is fully oxidised to carbon dioxide. Fermentation produces two ATP molecules per molecule of glucose compared to approximately 36 by aerobic respiration. Even in vertebrates, however, it is used as an effective means of energy production during short, intense periods of exertion, where the transport of oxygen to the muscles is insufficient to maintain aerobic metabolism. While fermentation is helpful during short, intense periods of exertion, it is not sustained over extended periods in complex aerobic organisms. In humans, for example, lactic acid fermentation provides energy for a period ranging from 30 seconds to 2 minutes. The speed at which ATP is produced is about 100 times that of oxidative phosphorylation. The pH in the cytoplasm quickly drops when lactic acid accumulates in the muscle, eventually inhibiting enzymes involved in glycolysis.

Adapted from the Wikipedia article "Biochemistry", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki