Question

This question relates to complex III of the electron transport chain Identify the electron carrier that directly donates electrons to complex III and the electron carrier that ultimately receives electrons from complex III 1^st (donating) carrier: _________ 2^nd (receiving) carrier: _______ How much energy is released by transferring one pair of electrons from the donating electron carrier to the receiving electron carrier? How many protons are transferred out of the intermembrane space as a transferring one pair of electrons from the donating carrier to the receiving carrier? Suppose a drug acted to inhibit the transfer of electrons through briefly describe the effect this drug would have on the electron citric acid Electron transport chain

Answer 1

Answer:
a) The first donating carrier to complex III is ubiquinol or plastoquinol (QH₂) after accepting the electrons from
complex I and Complex II donate it to the Complex III, and starts a cascade of events where the electrons are finally accepted by Cytochrome C.
1st Donating Carrier = Ubiquinol (QH₂) 2nd Recieving Carrier= Cytochrome C.

b) The two electrons of a bound QH₂ are transferred, one electron to cytochrome c and the other to a bound Q to form the semiquinone Q•-. This newly formed Q dissociates and is replaced by a second QH2, which also gives up its electrons, one to a second molecule of cytochrome c and the other to reduce Q•- to form QH2. This second electron transfer results in the uptake of two protons from the matrix.
Therefore the energy produced is 1ATP (4 H⁺ -------> 1ATP)

c) The number of protons being transferred out of the inner membrane space are 4 H⁺ per pair of electron transported.

d) Antimycin A distrupts the complex III and prevents the oxidation of Ubiqinol leading to
   loss of mitochondrial membrane potential
Increased production of Reactive Oxygen Species
   Decreased proton gradient across the membrane hence disruption in the ATP production in ETC.
Since going through the proton pump is the only way for the H^{+ to enter the matrix, since the membrane permiability and ATP synthesis are affected, the citric acid cycle too is rendered ineffecient by the inhibitors.}