Give the Details of Respiratory Complexes
The mitochondrial electron transport chain (ETC) is a sequence of protein complexes embedded in the inner mitochondrial membrane that plays a key role in cellular respiration. These complexes transfer electrons from electron carriers (NADH and FADH₂) to molecular oxygen while pumping protons across the membrane to generate a proton gradient. This proton motive force is then used to synthesize ATP through oxidative phosphorylation. The major respiratory complexes include:
Complex I: NADH: Ubiquinone Oxidoreductase
- Accepts electrons from NADH and transfers them to ubiquinone (coenzyme Q).
- Pumps four protons (H⁺) from the matrix into the intermembrane space.
- Contains FMN and iron-sulfur (Fe-S) clusters as cofactors.
Complex II: Succinate Dehydrogenase
- Receives electrons from FADH₂ (produced in the TCA cycle) and transfers them to ubiquinone.
- Unlike Complex I, it does not pump protons.
- Contains FAD and Fe-S clusters.
Complex III: Cytochrome bc₁ Complex
- Transfers electrons from reduced ubiquinone (QH₂) to cytochrome c.
- Pumps four protons per two electrons transferred.
- Contains cytochromes b and c₁ and a Rieske Fe-S protein.
Complex IV: Cytochrome c Oxidase
- Transfers electrons from cytochrome c to molecular oxygen, reducing it to water.
- Pumps two protons across the membrane per electron pair.
- Contains heme groups (cytochromes a and a₃) and copper centers (CuA and CuB).
ATP Synthase (Complex V)
- Utilizes the proton gradient created by complexes I, III, and IV to synthesize ATP from ADP and inorganic phosphate (Pi).
- Consists of two parts: F₀ (proton channel) and F₁ (catalytic site).
These complexes work in concert to efficiently convert biochemical energy from nutrients into usable cellular energy in the form of ATP.