Anaerobic respiration

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Anaerobic respiration is used for different processes in medical and biological terminology. Both deal with oxydative processes that occur in the absence of oxygen and therefore require another electron acceptor to replace oxygen.

Table of contents

1 Glucose degradation
2 Fermentation
3 Microbiology

Glucose degradation

In medical parlance, anaerobic respiration is used for carbohydrate metabolism in the absence of oxygen. Energy stored in glucose, glycogen or other organic substrates is normally dependent on oxygen. If oxygen is absent, pyruvate from glycolysis does not enter the Krebs' cycle but is converted to lactate by lactate dehydrogenase. This process generates ATP while being independent of oxygen; muscle tissue is dependent on this process during strenuous exercise. The lactate is converted back to glucose in the liver in the energy-inefficient process of gluconeogenesis.

Fermentation

Fermentation is generally anaerobic, converting glucose into - for example - ethanol.

Microbiology

In the biological sense, anaerobic respiration is defined as a membrane bound biological process coupling the oxidation of electron donating substrates (e.g. sugars and other organic compounds, but also inorganic molecules like hydrogen, sulfide/sulfur, ammonia, metals or metal ions) to the reduction of suitable alternative electron acceptors other than molecular oxygen. During these redox processes, protons are translocated over the membrane from "inside" to "outside", establishing a concentration gradient over the membrane which temporarily stores the energy released in the chemical reactions. This energy is then converted into ATP by the same enzyme also used during aerobic respiration, ATP synthase. Possible electron acceptors for anaerobic respiration are nitrate, nitrite, nitrous oxide, oxidised amines and nitro-compounds, fumarate, oxidised metal ions, sulfate, sulfoxo-compounds or carbon dioxide (in acetogenesis and methanogenesis). All these types of anaerobic respiration are restricted to prokaryotic organisms.