Question

Describe the flow of electrons through the Q cycle and describe the benefits and rationale for such an intricate mechanism.

Answer 1

The series of oxidation and reduction of the electron carrier coenzyme Q10 (CoQ10) forms ubiquinol and ubiquinone that result in the proton movement across the lipid barrier, i.e. the inner mitochondrial membrane. This cycle describes how the complex III is involved in the generation of the proton or pH gradient.

The first reaction in the Q cycle is,

CoQH₂ + cytochrome c₁ (Fe³⁺) --à CoQ^?• + cytochrome c₁ (Fe²⁺) + 2 H⁺ (mitochondrial intermembrane)

The second reaction is,

CoQH₂ + CoQ^?• + cytochrome c₁ (Fe³⁺) + 2 H⁺ (matrix) ? CoQ + CoQH₂ + cytochrome c₁ (Fe²⁺) + 2 H⁺ (mitochondrial intermembrane)

The net reaction is,

CoQH₂ + 2 cytochrome c₁ (Fe³⁺) + 2 H⁺ (matrix) ? CoQ + 2 cytochrome c₁ (Fe²⁺) + 4 H⁺ (intermembrane)