electron donor

Examples of electron donor in the following topics:

• Electron Donors and Acceptors in Anaerobic Respiration

  • Sulfate reduction requires the use of electron donors, such as the carbon compounds lactate and pyruvate (organotrophic reducers), or hydrogen gas (lithotrophic reducers).
  • Some unusual autotrophic sulfate-reducing bacteria, such as Desulfotignum phosphitoxidans, can use phosphite (HPO3-) as an electron donor.
  • Others, such as certain Desulfovibrio species, are capable of sulfur disproportionation (splitting one compound into an electron donor and an electron acceptor) using elemental sulfur (S0), sulfite (SO3−2), and thiosulfate (S2O32-) to produce both hydrogen sulfide (H2S) and sulfate (SO2−).
  • Acetogenesis is a type of microbial metabolism that uses hydrogen (H2) as an electron donor and carbon dioxide (CO2) as an electron acceptor to produce acetate, the same electron donors and acceptors used in methanogenesis.
  • Describe various types of electron acceptors and donors including: nitrate, sulfate, hydrgoen, carbon dioxide and ferric iron

• Electron Donors and Acceptors

  • In prokaryotes (bacteria and archaea there are several different electron donors and several different electron acceptors.
  • In the present day biosphere, the most common electron donors are organic molecules.
  • Inorganic electron donors include hydrogen, carbon monoxide, ammonia, nitrite, sulfur, sulfide, and ferrous iron.
  • The use of inorganic electron donors as an energy source is of particular interest in the study of evolution.
  • NADH is the electron donor and O2 is the electron acceptor.

• The Energetics of Chemolithotrophy

  • Chemolithotrophs use electron donors oxidized in the cell, and channel electrons into respiratory chains, producing ATP.
  • Chemotrophs are organisms that obtain energy through the oxidation of electron donors in their environments.
  • In chemolithotrophs, the compounds - the electron donors - are oxidized in the cell, and the electrons are channeled into respiratory chains, ultimately producing ATP.
  • The electron acceptor can be oxygen (in aerobic bacteria), but a variety of other electron acceptors, organic and inorganic, are also used by various species.

• Oxygenic Photosynthesis

  • Carbon fixation is a redox reaction, so photosynthesis needs to supply both a source of energy to drive this process, and the electrons needed to convert carbon dioxide into a carbohydrate, which is a reduction reaction.
  • However, the two processes take place through a different sequence of chemical reactions and in different cellular compartments.The general equation for photosynthesis is therefore:2n CO2 + 2n DH2 + photons → 2(CH2O)n + 2n DOCarbon dioxide + electron donor + light energy → carbohydrate + oxidized electron donor.In oxygenic photosynthesis water is the electron donor and, since its hydrolysis releases oxygen, the equation for this process is:2n CO2 + 4n H2O + photons → 2(CH2O)n + 2n O2 + 2n H2Ocarbon dioxide + water + light energy → carbohydrate + oxygen + waterOften 2n water molecules are cancelled on both sides, yielding:2n CO2 + 2n H2O + photons → 2(CH2O)n + 2n O2carbon dioxide + water + light energy → carbohydrate + oxygen

• Oxidoreductase Protein Complexes

  • In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule to another.
  • In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another the oxidant, also called the electron acceptor.
  • In this example, A is the reductant (electron donor) and B is the oxidant (electron acceptor).
  • In this reaction, NAD+ is the oxidant (electron acceptor) and glyceraldehyde-3-phosphate is the reductant (electron donor).
  • Oxidoreductases can be further classified into 22 subclasses: EC 1.1 includes oxidoreductases that act on the CH-OH group of donors (alcohol oxidoreductases); EC 1.2 includes oxidoreductases that act on the aldehyde or oxo group of donors; EC 1.3 includes oxidoreductases that act on the CH-CH group of donors (CH-CH oxidoreductases); EC 1.4 includes oxidoreductases that act on the CH-NH2 group of donors (Amino acid oxidoreductases, Monoamine oxidase); EC 1.5 includes oxidoreductases that act on CH-NH group of donors; EC 1.6 includes oxidoreductases that act on NADH or NADPH; EC 1.7 includes oxidoreductases that act on other nitrogenous compounds as donors; EC 1.8 includes oxidoreductases that act on a sulfur group of donors; EC 1.9 includes oxidoreductases that act on a heme group of donors; EC 1.10 includes oxidoreductases that act on diphenols and related substances as donors; EC 1.11 includes oxidoreductases that act on peroxide as an acceptor (peroxidases); EC 1.12 includes oxidoreductases that act on hydrogen as donors; EC 1.13 includes oxidoreductases that act on single donors with incorporation of molecular oxygen (oxygenases); EC 1.14 includes oxidoreductases that act on paired donors with incorporation of molecular oxygen; EC 1.15 includes oxidoreductases that act on superoxide radicals as acceptors; EC 1.16 includes oxidoreductases that oxidize metal ions; EC 1.17 includes oxidoreductases that act on CH or CH2 groups; EC 1.18 includes oxidoreductases that act on iron-sulfur proteins as donors; EC 1.19 includes oxidoreductases that act on reduced flavodoxin as a donor; EC 1.20 includes oxidoreductases that act on phosphorus or arsenic in donors; EC 1.21 includes oxidoreductases that act on X-H and Y-H to form an X-Y bond; and EC 1.97 includes other oxidoreductases.

• Sulfate and Sulfur Reduction

  • Sulfate reduction is a type of anaerobic respiration that utilizes sulfate as a terminal electron acceptor in the electron transport chain.
  • Sulfate reduction is a type of anaerobic respiration that utilizes sulfate as a terminal electron acceptor in the electron transport chain.
  • Many sulfate reducers are organotrophic, using carbon compounds, such as lactate and pyruvate (among many others) as electron donors, while others are lithotrophic, and use hydrogen gas (H2) as an electron donor.
  • Some unusual autotrophic sulfate-reducing bacteria (e.g., Desulfotignum phosphitoxidans) can use phosphite (HPO3-) as an electron donor, whereas others (e.g., Desulfovibrio sulfodismutans, Desulfocapsa thiozymogenes, and Desulfocapsa sulfoexigens) are capable of sulfur disproportionation (splitting one compound into two different compounds, in this case an electron donor and an electron acceptor) using elemental sulfur (S0), sulfite (SO32−), and thiosulfate (S2O32−) to produce both hydrogen sulfide (H2S) and sulfate (SO42−).
  • In organisms that use carbon compounds as electron donors, the ATP consumed is accounted for by fermentation of the carbon substrate.

• The Acetyl-CoA Pathway

  • The acetyl-CoA pathway utilizes carbon dioxide as a carbon source and often times, hydrogen as an electron donor to produce acetyl-CoA.
  • This specific pathway is characterized by the use of hydrogen as an electron donor and carbon dioxide as an electron acceptor to produce acetyl-CoA as the final product.
  • In addition, the carbon dioxide is used as an electron acceptor in the production of methane.

• Shared Features of Archaea and Eukaryotes

  • In these reactions, one compound passes electrons to another (in a redox reaction), releasing energy to fuel the cell's activities.
  • One compound acts as an electron donor and another as an electron acceptor.

• Anoxygenic Photosynthesis

  • Water is therefore not used as an electron donor.
  • This restricts them to cyclic electron flow and are therefore unable to produce O2 from the oxidization of H2O.
  • The cyclic nature of the electron flow is typified in purple non-sulfur bacteria.
  • Excited P870 will then donate an electron to Bacteriopheophytin, which then passes it on to a series of electron carriers down the electron chain.
  • Therefore electrons are not left over to oxidize H2O into O2.

• Anoxygenic Photosynthetic Bacteria

  • Anoxygenic photosynthesis is the phototrophic process where light energy is captured and converted to ATP, without the production of oxygen; water is, therefore, not used as an electron donor.
  • When light is absorbed by the reaction center, P840 enters an excited state with a large negative reduction potential, and so readily donates the electron to bacteriochlorophyll 663 which passes it on down the electron chain.
  • The electron is transferred through a series of electron carriers and complexes until it either returns to P840 or is used to reduce NAD+.
  • If the electron leaves the chain to reduce NAD+, P840 must be reduced for the ETC to function again.
  • Excited P870 will then donate an electron to Bacteriopheophytin, which then passes it on to a series of electron carriers down the electron chain.