Electron transport chain (ETC) and its mechanism

• The Electron Transport Chain (ETC), located in the inner mitochondrial membrane, is the final phase of cellular respiration and a key step in ATP production through oxidative phosphorylation.
• ETC involves a series of protein complexes and electron carriers that transfer electrons from NADH and FADH2 to molecular oxygen, creating a proton gradient that drives ATP synthesis.

Steps of the Electron transport chain and Mechanism

1. Electron Donation of Electron transport chain

   • NADH and FADH2 (from glycolysis, the citric acid cycle, and beta-oxidation) donate electrons to the ETC.
   • NADH transfers electrons to Complex I, while FADH2 transfers to Complex II.

2. Complex I: NADH oxidoreductase

   • Accepts electrons from NADH, transferring them to ubiquinone (Q).
   • Pumps 4 protons (H+) into the intermembrane space, contributing to the proton gradient.

3. Complex II: Succinate oxidoreductase

   • Accepts electrons from FADH2 and transfers them to ubiquinone.
   • Does not pump protons.

4. Ubiquinone (Q) and Complex III: Cytochrome bc1

   • Ubiquinol (QH2) transfers electrons to Complex III, which passes them to cytochrome c.
   • Pumps additional protons into the intermembrane space.

5. Cytochrome c and Complex IV: Cytochrome c oxidase

   • Cytochrome c transfers electrons from Complex III to Complex IV, which transfers them to oxygen (O2), forming water (H2O).
   • Complex IV also pumps protons, increasing the proton gradient.

6. Proton Gradient and ATP Synthesis of Electron transport chain

   • The proton gradient (proton motive force) drives protons back into the mitochondrial matrix through ATP synthase, coupling their movement with the conversion of ADP to ATP.

• In summary, the ETC transfers electrons from NADH and FADH2 to oxygen, generating a proton gradient that powers ATP synthesis.

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