Heterolactic fermentation proceeds in two steps. First, the enzyme pyruvate dehydrogenase converts pyruvate to acetaldehyde. In the second step, the enzyme alcohol dehydrogenase transfers hydrogen from NADH to the acetaldehyde, converting it into ethanol and carbon dioxide. If you've ever felt your muscles burn during heavy physical activity, you are experiencing the effect of homolactic fermentation in your muscle cells.
Under these conditions, muscles metabolize pyruvate into lactic acid, which produces the familiar burning sensation. However, this is a stopgap reaction to low oxygen levels. Without oxygen, cells can quickly die. It can, but it does have limitations. There are two types of cellular respiration see Cellular Respiration concept : aerobic and anaerobic.
One occurs in the presence of oxygen aerobic , and one occurs in the absence of oxygen anaerobic. Both begin with glycolysis - the splitting of glucose.
Glycolysis see "Glycolysis" concept is an anaerobic process - it does not need oxygen to proceed. This process produces a minimal amount of ATP. The Krebs cycle and electron transport do need oxygen to proceed, and in the presence of oxygen, these process produce much more ATP than glycolysis alone.
Text adapted from: OpenStax , Concepts of Biology. OpenStax CNX. Skip to content In aerobic respiration, the final electron acceptor for the electron transport chain is an oxygen molecule, O 2. How is this done? Lactic Acid Fermentation The fermentation method used by animals and some bacteria like those in yogurt is lactic acid fermentation Figure 1.
Next: Metabolism of molecules other than glucose. Anaerobic bacteria : The green color seen in these coastal waters is from an eruption of hydrogen sulfide-producing bacteria.
These anaerobic, sulfate-reducing bacteria release hydrogen sulfide gas as they decompose algae in the water. Eukaryotes can also undergo anaerobic respiration. Some examples include alcohol fermentation in yeast and lactic acid fermentation in mammals. The fermentation method used by animals and certain bacteria like those in yogurt is called lactic acid fermentation.
This type of fermentation is used routinely in mammalian red blood cells and in skeletal muscle that has an insufficient oxygen supply to allow aerobic respiration to continue that is, in muscles used to the point of fatigue. The excess amount of lactate in those muscles is what causes the burning sensation in your legs while running. This pain is a signal to rest the overworked muscles so they can recover. In these muscles, lactic acid accumulation must be removed by the blood circulation and the lactate brought to the liver for further metabolism.
The chemical reactions of lactic acid fermentation are the following:. Lactic acid fermentation : Lactic acid fermentation is common in muscle cells that have run out of oxygen.
The enzyme used in this reaction is lactate dehydrogenase LDH. The reaction can proceed in either direction, but the reaction from left to right is inhibited by acidic conditions.
Such lactic acid accumulation was once believed to cause muscle stiffness, fatigue, and soreness, although more recent research disputes this hypothesis. Once the lactic acid has been removed from the muscle and circulated to the liver, it can be reconverted into pyruvic acid and further catabolized for energy.
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