Anaerobic respiration 435420 217279784 2008-06-05T10:46:48Z ClueBot 4928500 Reverting possible vandalism by [[Special:Contributions/220.245.96.12|220.245.96.12]] to version by Captain panda. False positive? [[User:ClueBot/FalsePositives|Report it]]. Thanks, [[User:ClueBot]]. (407242) (Bot) {{Disputeabout|'''Lactic acid fermentation'''|date=March 2008}} {{seealso|Fermentation (biochemistry)}} '''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 (biochemistry)|fermentation]], especially when the [[glycolysis|glycolytic pathway]] is used for energy production in the cell. They are not synonymous terms, however, since certain anaerobic [[prokaryote]]s can generate all of their [[adenosine triphosphate|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 :<center>''[[glucose]] <math>\to</math> [[lactic acid]] (+ energy) ([[adenosine triphosphate|ATP]]);''</center> :<center>''C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> <math>\to</math> 2C<sub>3</sub>H<sub>6</sub>O<sub>3</sub> + 2 ATP.''</center> 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 anaerobe|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]] (<sup>1</sup>O<sub>2</sub>), [[superoxide]] [[ion]] (O<sub>2</sub><sup>-</sup>), [[hydrogen peroxide]] (H<sub>2</sub>O<sub>2</sub>), [[hydroxyl]] [[ion]] (OH<sup>-</sup>), and other toxic molecules. ===Facultative anaerobes and obligate aerobes=== [[Facultative anaerobic organism]]s can survive in either oxygenated or deoxygenated environments and can switch between cellular respiration or fermentation, respectively) and ''[[obligate aerobe|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: :<center>''2O<sub>2</sub><sup>-</sup> + 2H<sup>+</sup> –superoxide dismutase–> H<sub>2</sub>O<sub>2</sub> (hydrogen peroxide) + O<sub>2</sub>.''</center> The hydrogen peroxide produced is then transferred to a second reaction: :<center>''2H<sub>2</sub>O<sub>2</sub> –catalase–> 2H<sub>2</sub>O + O<sub>2</sub>.''</center> 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 [[metabolism|metabolised]] to [[carbon dioxide|CO<sub>2</sub>]] and [[water]] via the [[citric acid cycle]] and the [[electron transport chain]] (which relies on O<sub>2</sub>) does not function. Fermentation does not yield more energy than that already obtained from [[glycolysis]] (2 ATPs) but serves to regenerate [[NADH|NAD<sup>+</sup>]] so glycolysis can continue. Various end products can also be created, such as [[lactic acid|lactate]] or [[ethanol]]. Fermentation in animals is essential to human life. In [[lactic acid fermentation]], the following reaction occurs: 1. ''[[Glycolysis]]'' :<center>''C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> (glucose) + 2 NAD<sup>+</sup> <math>\to</math> 2 C<sub>3</sub>H<sub>4</sub>O<sub>3</sub> ([[pyruvic acid]]) + 2 NADH''</center> 2. ''[[Lactic acid]] creation'' :<center>'' 2 C<sub>3</sub>H<sub>4</sub>O<sub>3</sub> (pyruvic acid) + 2 NADH <math>\to</math> 2 C<sub>3</sub>H<sub>6</sub>O<sub>3</sub> (lactic acid) + 2 NAD<sup>+</sup>''</center> ''Net reaction'': :<center>''C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> (glucose) <math>\to</math> 2 C<sub>3</sub>H<sub>6</sub>O<sub>3</sub> (lactic acid)''</center> ===Fermentation in other organisms=== In some plant cells and yeasts, fermentation produces CO<sub>2</sub> and ethanol. The conversion of [[pyruvate]] to [[acetaldehyde]] generates [[carbon dioxide|CO<sub>2</sub>]] and the conversion of acetaldehyde to [[ethanol]] regenerates [[nicotinamide adenine dinucleotide|NAD<sup>+</sup>]]. ==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 (biochemistry)|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== :<center>''glucose + 3NO<sub>3</sub><sup>-</sup> + 3H<sub>2</sub>O <math>\to</math> 6HCO<sub>3</sub><sup>-</sup> + 3NH<sub>4</sub><sup>+</sup>, ΔG<sup>0</sup>' = -1796 kJ''</center> :<center>''glucose + 3SO<sub>4</sub><sup>2-</sup> + 3H<sup>+</sup> <math>\to</math> 6HCO<sub>3</sub><sup>-</sup> + 3SH<sup>-</sup>, ΔG<sup>0</sup>' = -453 kJ''</center> :<center>''glucose + 12S - 12H<sub>2</sub>O <math>\to</math> 6HCO<sub>3</sub><sup>-</sup> + 12HS<sup>-</sup> + 18H<sup>+</sup>, ΔG<sup>0</sup>' = -333 kJ''</center> All of these terminal electron acceptors are further upstream in the electron transport chain, compared to O<sub>2</sub>. Consequently, anaerobic respiration is less effective than aerobic respiration. The ΔG<sup>0</sup>' of aerobic respiration is -2844 kJ. ==Commercial applications of anaerobic respiration== *[[Anaerobic digestion]] *[[Mechanical biological treatment]] {{Cellular respiration}} {{metabolism}} {{MetabolismMap}} [[Category:Anaerobic digestion]] [[Category:Biodegradation]] [[Category:Biodegradable waste management]] [[Category:Cellular respiration]] [[da:Anaerob respiration]] [[es:Respiración anaeróbica]] [[fr:Respiration anaérobie]] [[he:נשימה אל-אווירנית]] [[ja:嫌気呼吸]] [[pl:Oddychanie beztlenowe]] [[ru:Анаэробное дыхание]] [[zh:缺氧呼吸]]