Anaerobic respiration

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Anaerobic respiration the process of synthesizing ATP using the electron transport chain, with inorganic molecules other than oxygen used as a final electron acceptor.

Contents 1 Anaerobic respiration in prokaryotes 2 In Plants 3 Examples of anaerobic respiration 4 Commercial applications of anaerobic respiration

[edit] Anaerobic respiration in prokaryotes

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).

[edit] In Plants

Equation:

C₆H₁₂O₆→ 2CH₃CH₂OH + 2CO₂ + 118kJ of Energy

This equation simply describes the fermentation of glucose as written. As such this is not an example of anaerobic respiration since no electron transport chain is involved.

[edit] Examples of anaerobic respiration

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

glucose + 3SO₄^2- + 3H⁺ 6HCO₃^- + 3SH^-, ΔG⁰' = -453 kJ

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

All of these terminal electron acceptors have smaller reduction potentials than O₂, meaning that less energy is released per oxidised molecule of primary electron donor than in aerobic respiration (i.e. it is less energetically efficient). The ΔG⁰' of aerobic respiration is -2844 kJ.

Fermentation is the process by which yeast cells carry out anaerobic respiration, producing ethanol and CO2 as a by-product.

[edit] Commercial applications of anaerobic respiration

• Anaerobic digestion
• Mechanical biological treatment

v • d • e Cellular Respiration Aerobic Respiration Glycolysis → Pyruvate Decarboxylation → Citric Acid Cycle → Oxidative Phosphorylation (Electron Transport Chain + ATP synthase) Anaerobic Respiration Glycolysis → Lactic Acid Fermentation or Ethanol Fermentation

v • d • e Metabolism (Catabolism, Anabolism) General Metabolic pathway · Metabolic network · Cellular respiration (Anaerobic/Aerobic) Specific paths Protein metabolism Protein synthesis · Amino acid synthesis · Catabolism Nucleotide metabolism: Purine metabolism  · Nucleotide salvage · Pyrimidine metabolism Carbohydrate metabolism Anabolism Gluconeogenesis · Glycogenesis · Photosynthesis (Carbon fixation) Carbohydrate catabolism Glycolysis · Glycogenolysis · Fermentation (Ethanol, Lactic acid)  · Cellular respiration · Xylose metabolism Other Pentose phosphate pathway Lipid metabolism Fatty acid metabolism Fatty acid degradation (Lipolysis, Beta oxidation) · Fatty acid synthesis Other Eicosanoid metabolism · Sphingolipid metabolism · Steroid metabolism Other Metal metabolism (Iron metabolism) · Ethanol metabolism

v • d • e Metabolism map Glucuronate metabolism Pentose interconversion Inositol metabolism Cellulose and sucrose metabolism Starch and glycogen metabolism Other sugar metabolism Pentose phosphate pathway Glycolysis and Gluconeogenesis Amino sugars metabolism Small amino acid synthesis Branched amino acid synthesis Purine biosynthesis Histidine metabolism Aromatic amino acid synthesis Pyruvate decarboxylation Fermentation Fatty acid metabolism Urea cycle Aspartate amino acid group synthesis Porphyrins and corrinoids metabolism Citric acid cycle Glutamate amino acid group synthesis Pyrimidine biosynthesis  v • d • e  All pathway labels on this image are links, simply click to access the article. A high resolution labeled version of this image is available here.