Question

Complex III is

1. an integral membrane protein
2. a peripheral membrane protein
3. involved in active transport of H+
4. involved in redox reaction
5. a, c, and d are correct

Answer 1

Ans is option E

Complex III, also called cytochrome bc1 complex or ubiquinone : cytochrome c oxidoreductase, couples the transfer of electrons from ubiquinol (QH2) to cytochrome c with the vectorial transport of protons from the matrix to the intermembrane space.
The functional unit of Complex III is a dimer, with the two monomeric units of cytochrome b surrounding a “cavern” in the middle of the membrane (option a) in which ubiquinone is free to move from the matrix side of the membrane (site QN on one monomer) to the intermembrane space (site QP of the other monomer) as it shuttles electrons and protons across the inner mitochondrial membrane (option c).

Based on the structure of Complex III and detailed biochemical studies of the redox reactions (option d), a reasonable model, the Q cycle, has been proposed for the passage of electrons and protons through the complex.
QH2 + 2 cyt c1 (oxidized) + 2H+N--->
Q + 2cyt c1 (reduced) + 4H+p (option d)