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- Ucd bis2a intro to biology v1.
- Ucd bis2a intro to biology v1.
- Bis2a 06.2 oxidative phosphorylation
The total difference in the reduction potential of the electron donor and the final electron acceptor can be thought of as the total energy available for the system. How that energy is released, in one big chunk or in small aliquots is dependent upon the number of red/ox complexes the electrons will travel through. Each complex (in general) can be thought of as a release valve, where the energy being generated by the various red/ox reactions can be captured by the translocation of a proton. NOTE, not all complexes can generate enough energy to translocate a proton. The number of protons being translocated is important because in general it takes 3 protons to enter the F
1 F
0 ATPase to generate 1 ATP molecule. The more protons translocated per 2 electrons that enter the chain, the more ATP that can be made.
How do etc complexes transfer electrons?
As previously mentioned the ETC is composed of a series of complexes that undergo a series of red/ox reactions. These complexes are in fact multiprotein enzyme complexes referred to as
oxidoreductases or simply
reductases . The one exception to this is the terminal complex in aerobic respiration that uses molecular oxygen as the terminal electron acceptor. That enzyme complex is referred to as an
oxidase . During the red/ox reaction the electrons are not carried directly on the proteins within the complex, but on a non-protein moiety called a
prosthetic group . This is true for all of the electron carriers with the exception of quinones, which are a class of lipids that can directly be reduced or oxidized by the oxidoreductases. In this case, both the Quinone
red and the Quinone
ox is soluble within the membrane and can move from complex to complex. The prosthetic groups are directly involved in the red/ox reactions being catalyzed by their associated oxidoreductases. In general these prosthetic groups can be divided into two general types: those that carry both electrons and protons and those that only carry electrons.
The electron and proton carriers
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Flavoproteins (
Fp ), these proteins contain an organic prosthetic group called a
flavin , which is the actual moiety that undergoes the oxidation/reduction reaction. FADH
2 is an example of a Fp.
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Quinones , are a family of lipids which means they are soluble within the membrane.
- It should also be noted that NADH and NADPH are considered electron (2e-) and proton (2 H
+ ) carriers.
Electon carriers
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Cytochromes are proteins that contain a heme prosthetic group. The Heme is capable of carrying a single electron.
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Iron-Sulfur proteins contain a non-heme iron-sulfur clusters that can carry an electron. The prosthetic group is often abbreviated as
Fe-S
Aerobic versus anaerobic respiration
In the world we live in, most of the organisms we interact with breath air, which is approximately 20% oxygen. Oxygen is our terminal electron acceptor. We call this process respiration, we breath in oxygen, our cells take it up and transport it into the mitochondria where it is used as the final acceptor of electrons from our electron transport chains. That is
aerobic respiration : the process of using oxygen as a terminal electron acceptor in an electron transport chain.
Source:
OpenStax, Ucd bis2a intro to biology v1.2. OpenStax CNX. Sep 22, 2015 Download for free at https://legacy.cnx.org/content/col11890/1.1
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