electron acceptor

Examples of electron acceptor in the following topics:

• Electron Donors and Acceptors in Anaerobic Respiration

  • In anaerobic respiration, a molecule other than oxygen is used as the terminal electron acceptor in the electron transport chain.
  • This method still incorporates the respiratory electron transport chain, but without using oxygen as the terminal electron acceptor .
  • Many different types of electron acceptors may be used for anaerobic respiration.
  • 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.
  • Organic compounds may also be used as electron acceptors in anaerobic respiration.

• Electron Donors and Acceptors

  • In prokaryotes (bacteria and archaea there are several different electron donors and several different electron acceptors.
  • These levels correspond to successively more positive redox potentials, or to successively decreased potential differences relative to the terminal electron acceptor.
  • Bacteria can use a number of different electron donors, a number of different dehydrogenases, a number of different oxidases and reductases, and a number of different electron acceptors.
  • Just as there are a number of different electron donors (organic matter in organotrophs, inorganic matter in lithotrophs), there are a number of different electron acceptors, both organic and inorganic.
  • NADH is the electron donor and O2 is the electron acceptor.

• Methanogenesis

  • Methanogenesis is a form of anaerobic respiration that uses carbon as a electron acceptor and results in the production of methane.
  • The two best described pathways of methanogenesis use carbon dioxide or acetic acid as the terminal electron acceptor:
  • During advanced stages of organic decay, all electron acceptors become depleted except carbon dioxide, which is a product of most catabolic processes.
  • It is not depleted like other potential electron acceptors.
  • Only methanogenesis and fermentation can occur in the absence of electron acceptors other than carbon.

• Iron Oxidation

  • Ferric iron is an anaerobic terminal electron acceptor, with the final enzyme a ferric iron reductase.
  • Ferric iron (Fe3+) is a widespread anaerobic terminal electron acceptor both for autotrophic and heterotrophic organisms.
  • Electron flow in these organisms is similar to those in electron transport, ending in oxygen or nitrate, except that in ferric iron-reducing organisms the final enzyme in this system is a ferric iron reductase.
  • Although ferric iron is the most prevalent inorganic electron acceptor, a number of organisms (including the iron-reducing bacteria mentioned above) can use other inorganic ions in anaerobic respiration.
  • While these processes may often be less significant ecologically, they are of considerable interest for bioremediation, especially when heavy metals or radionuclides are used as electron acceptors.

• 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.

• 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.

• Lewis Acid and Base Molecules

  • Lewis bases are electron-pair donors, whereas Lewis acids are electron-pair acceptors.
  • A Lewis acid is defined as an electron-pair acceptor, whereas a Lewis base is an electron-pair donor.
  • Under this definition, we need not define an acid as a compound that is capable of donating a proton, because under the Lewis definition, H+ itself is the Lewis acid; this is because, with no electrons, H+ can accept an electron pair.
  • A Lewis base, therefore, is any species that donates a pair of electrons to a Lewis acid.
  • The "neutralization" reaction is one in which a covalent bond forms between an electron-rich species (the Lewis base) and an electron-poor species (the Lewis acid).

• Electron Affinity

  • The electron affinity (Eea) of a neutral atom or molecule is defined as the amount of energy released when an electron is added to it to form a negative ion, as demonstrated by the following equation:
  • Mulliken used a list of electron affinities to develop an electronegativity scale for atoms by finding the average of the electron affinity and ionization potential.
  • A molecule or atom that has a more positive electron affinity value is often called an electron acceptor; one with a less positive electron affinity is called an electron donor.
  • To use electron affinities properly, it is essential to keep track of the sign.
  • Electron affinity follows the trend of electronegativity: fluorine (F) has a higher electron affinity than oxygen (O), and so on.

• Semiconductors

  • For example, in III-V semiconductors such as gallium arsenide, silicon can be a donor when it substitutes for gallium or an acceptor when it replaces arsenic.
  • This type of doping agent is also known as an acceptor material, and the vacancy left behind by the electron is known as a hole.
  • This is why these dopants are called acceptors.
  • When a sufficiently large number of acceptor atoms are added, the holes greatly outnumber thermally excited electrons.
  • This allows for easier electron flow.

• Hydrogen Bonding

  • The electronegative atom attracts the electron cloud from around the hydrogen nucleus and, by decentralizing the cloud, leaves the hydrogen atom with a positive partial charge.
  • A hydrogen bond results when this strong partial positive charge attracts a lone pair of electrons on another atom, which becomes the hydrogen bond acceptor.
  • Greater electronegativity of the hydrogen bond acceptor will create a stronger hydrogen bond.
  • The diethyl ether molecule contains an oxygen atom that is not bonded to a hydrogen atom, making it a hydrogen bond acceptor.
  • Diethyl ether contains an oxygen atom that is a hydrogen bond acceptor because it is not bonded to a hydrogen atom and so is slightly negative.