Microbial Metabolism - Electron Transport and the Proton Motive Force

What are iron-sulfur proteins?
Iron-sulfur proteins contain clusters of iron and sulfur. They carry electrons.
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Where do protons originate from during electron transport?
  1. NADH
  2. The dissociation of H2O into H+ and OH- in the cytoplasm.
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What is the result of the extrusion of H+ to the environment during electron transport?
The accumulation of OH- on the inside of the cytoplasmic membrane.
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What is the result of the separation of H+ and OH- during electron transport?
The inner and outer surfaces of the membrane differ in charge, pH, and electrochemical potential.
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What is oxidative phosphorylation in prokaryotes?
Oxidation (1) pluspmf (2) plus phosphorylation (3):

  1. Stepwise cytoplasmic membrane-bound oxidation of an electron donor by an electron acceptor via a respiratory chain
  2. Associated generation of a proton motive force (pmf) via the translocation of protons across the membrane (DpH and DY)
  3. Phosphorylation of ADP with Pi to ATP via the ATP-synthase with the aid of influx of energized protons
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What is Complex I of the proton motive force?
Following the oxidation of NADH + H+ to form FMNH2, 4H+ are released to the outer surface of the membrane when FMNH2 donates 2e+ to nonheme iron (Fe/S) proteins. Two protons are taken from the cytoplasm by ubiquinone when it is reduced by the Fe/S protein.
It's also called NADH: quinone oxidoreductase, because NADH is oxidized and quinone reduced.
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What is Complex II of the proton motive force?
It bypasses Complex I and feeds electrons from FADH2 directly to quinones. Succinate and fatty acids donate electrons throug FADH2 when they are oxidized. Therefore Complex II is also called succinate dehydrogenase complex. The ATP yield is one per two electrons consumed.
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What are the functions of Complex III (cytochrome bc1 complex) of the proton motive force?
To transfer electron from quinones to cytochrome c.
To interact with quinones in such a way that two additional protons are pumped at the Q-bc1 site.
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What is the function of cytochrome c?
It functions as a periplasmic shuttle to transfer electrons to the high-redox-potential cytochromes a and a3 (Complex IV).
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What is Complex IV?
It functions as the terminal oxidase and reduces O2 ato H2O in the final step of the electron transport chain. It also pumps protons to the outer surface of the membrane, thereby increasing the strength of the proton motive force.
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