Anaerobic respiration

Anaerobic respiration

Anaerobic respiration (anaerobiosis) refers to the oxidation of molecules in the absence of oxygen to produce energy, in opposition to aerobic respiration which does use oxygen. Anaerobic respiration processes require another electron acceptor to replace oxygen. Anaerobic respiration is often used interchangeably with fermentation, especially when the glycolytic pathway is used for energy production in the cell. They are not synonymous terms, however, since certain anaerobic prokaryotes can generate all of their ATP using an electron transport system and ATP synthase. Definition of anaerobic respiration: the breakdown of food substances in the absence of oxygen with a small amount of energy. General word and symbol equations for the anaerobic respiration of glucose can be shown as

"glucose o lactic acid (+ energy) (ATP);"

"C6H12O6 o 2C3H6O3 + 2 ATP."

The energy released is about 120 kJ per mole of glucose, but under higher temperatures can be increased to 540 kJ per mole of glucose.

Obligate (strict) Anaerobes

In some organisms called "obligate (strict) anaerobes" (ex: "Clostridium tetani" (causes tetanus), "Clostridium perfringens" (causes gangrene)), the presence of oxygen is lethal. This is because the presence of oxygen is processed by the organisms into the extremely toxic molecules of singlet oxygen (1O2), superoxide ion (O2-), hydrogen peroxide (H2O2), hydroxyl ion (OH-), and other toxic molecules.

Facultative anaerobes and obligate aerobes

Facultative anaerobic organisms can survive in either oxygenated or deoxygenated environments and can switch between cellular respiration or fermentation, respectively) and "obligate (strict) aerobes" (organisms that can survive only with oxygen) have special enzymes (superoxide dismutase and catalase) that can safely handle these products and transform them into harmless water and diatomic oxygen in the following reactions:

"2O2- + 2H+ –superoxide dismutase–> H2O2 (hydrogen peroxide) + O2."

The hydrogen peroxide produced is then transferred to a second reaction:

"2H2O2 –catalase–> 2H2O + O2."

The oxidative powers of the superoxide ion have now been neutralized. Only facultative anaerobes and obligate aerobes possess the two enzymes necessary to reduce the superoxide.

In organisms which use glycolysis, the absence of oxygen prevents pyruvate from being metabolised to CO2 and water via the citric acid cycle and the electron transport chain (which relies on O2) does not function. Fermentation does not yield more energy than that already obtained from glycolysis (2 ATPs) but serves to regenerate NAD+ so glycolysis can continue. Various end products can also be created, such as lactate or ethanol.

Fermentation in animals is essential to human life.

In lactic acid fermentation, the following reaction occurs:

1. "Glycolysis":
"C6H12O6 (glucose) + 2 NAD+ o 2 C3H4O3 (pyruvic acid) + 2 NADH"

2. "Lactic acid creation":
" 2 C3H4O3 (pyruvic acid) + 2 NADH o 2 C3H6O3 (lactic acid) + 2 NAD+"

"Net reaction"::
"C6H12O6 (glucose) o 2 C3H6O3 (lactic acid)"

Fermentation in other organisms

In some plant cells and yeasts, fermentation produces CO2 and ethanol. The conversion of pyruvate to acetaldehyde generates CO2 and the conversion of acetaldehyde to ethanol regenerates NAD+.

Anaerobic respiration in prokaryotes

In the field of prokaryotic metabolism, anaerobic respiration has a more specific meaning. In this case, 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 "external" electron acceptors other than molecular oxygen. In contrast, in fermentation the oxidation of molecules is coupled to the reduction of an "internally"-generated electron acceptor, usually pyruvate. Hence, scientists who study prokaryotic physiology view anaerobic respiration and fermentation as distinct processes and therefore do not use the terms interchangeably.

In anaerobic respiration, as the electrons from the electron donor are transported down the electron transport chain to the terminal electron acceptor, protons are translocated over the cell membrane from "inside" to "outside", establishing a concentration gradient across the membrane which temporarily stores the energy released in the chemical reactions. This potential energy is then converted into ATP by the same enzyme 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, sulfur, sulfoxo-compounds, halogenated organic compounds, selenate, arsenate, bicarbonate or carbon dioxide (in acetogenesis and methanogenesis). All these types of anaerobic respiration are restricted to prokaryotic organisms.

Examples of anaerobic respiration

"glucose + 3NO3- + 3H2O o 6HCO3- + 3NH4+, ΔG0' = -1796 kJ"

"glucose + 3SO42- + 3H+ o 6HCO3- + 3SH-, ΔG0' = -453 kJ"

"glucose + 12S - 12H2O o 6HCO3- + 12HS- + 18H+, ΔG0' = -333 kJ"

All of these terminal electron acceptors are further upstream in the electron transport chain, compared to O2. Consequently, anaerobic respiration is less effective than aerobic respiration. The ΔG0' of aerobic respiration is -2844 kJ.

Commercial applications of anaerobic respiration

*Anaerobic digestion
*Mechanical biological treatment

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • anaerobic respiration — UK US noun [uncountable] biology respiration that takes place where there is little or no oxygen. This produces less energy than aerobic respiration , and a lot of it is lost as heat. Thesaurus: biological processeshyponym See also …   Useful english dictionary

  • anaerobic respiration — anaerobinis kvėpavimas statusas T sritis ekologija ir aplinkotyra apibrėžtis Cheminis procesas, kai energija iš maisto išgaunama nenaudojant deguonies. atitikmenys: angl. anaerobic respiration vok. anaerobe Atmung, f rus. анаэробное дыхание, n …   Ekologijos terminų aiškinamasis žodynas

  • anaerobic respiration — Respiration in which foodstuffs are partially oxidized, with the release of chemical energy, in a process not involving atmospheric oxygen. A notable example is in alcoholic fermentation, where sugar is metabolized into ethanol …   Glossary of Biotechnology

  • anaerobic respiration — UK / US noun [uncountable] biology respiration that takes place where there is little or no oxygen. This produces less energy than aerobic respiration, and a lot of it is lost as heat. See: aerobic respiration …   English dictionary

  • anaerobic respiration — a form of respiration in which energy is released from chemical reactions in which free oxygen takes no part …   Medical dictionary

  • anaerobic respiration — (an a er o bik) An energy yielding process in which the electron transport chain acceptor is an inorganic molecule other than oxygen …   Dictionary of microbiology

  • anaerobic respiration — Metabolic processes in which organic compounds are broken down to release energy in the absence of oxygen. Requires inorganic oxidizing agents or accumulation of reduced coenzymes …   Dictionary of molecular biology

  • Anaerobic digestion — and regenerative thermal oxidiser component of Lübeck mechanical biological treatment plant in Germany, 2007 …   Wikipedia

  • Anaerobic lagoon — or Manure Lagoon is a man made outdoor earthen basin filled with excrement. Lagoons are part of a system designed to manage and treat waste created by Concentrated Animal Feeding Operations (CAFO). Anaerobic lagoons are created from a manure… …   Wikipedia

  • Anaerobic — is a technical word which literally means without air (where air is generally used to mean oxygen), as opposed to aerobic. In wastewater treatment the absence of oxygen is indicated as anoxic ; and anaerobic is used to indicate the absence of a… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.