Electron Transport System
எலக்ட்ரான் கடத்தும் அமைப்பு
Stop confusing the Electron Transport System with Glycolysis. Glycolysis happens in the cytosol; ETS is strictly confined to the inner mitochondrial membrane. If you miss the location, you lose the mark. Precision is your only currency here.
The idea
The ETS consists of Complexes I through IV. NADH and FADH2 donate electrons to these complexes, creating a proton gradient across the inner membrane. This gradient drives ATP Synthase to produce ATP via oxidative phosphorylation. Oxygen acts as the final electron acceptor, reducing to water.
Why it matters
It exists to convert the chemical energy stored in reduced coenzymes (NADH/FADH2) into a proton gradient, which is then used to drive ATP synthesis.
NEET lens
NEET focuses on the specific electron donors for each complex: NADH for Complex I and FADH2 for Complex II. Memorize the sequence of carriers: Ubiquinone and Cytochrome c. Expect questions on the final electron acceptor and the role of ATP Synthase in the F0-F1 particle.
Clinical significance
Cyanide poisoning is a direct failure of this system. It binds to Cytochrome c oxidase (Complex IV), halting electron flow and ATP production. The cell dies rapidly due to energy starvation, leading to systemic organ failure.
Introduction
The electron transport system (ETS/chain) in mitochondria is a series of protein complexes (I, II, III, IV) in the inner mitochondrial membrane that transfer electrons from NADH/FADH₂ to O₂, pumping protons to drive ATP synthesis.
Core concept
Components: Complex I (NADH dehydrogenase) — oxidizes NADH, pumps 4H⁺. Complex II (succinate dehydrogenase) — oxidizes FADH₂, NO H⁺ pumping. Complex III (cytochrome bc1/ubiquinol-cytochrome c reductase) — pumps 4H⁺. Complex IV (cytochrome c oxidase) — transfers electrons to O₂ → H₂O, pumps 2H⁺. Electron carriers between complexes: ubiquinone/CoQ (between I/II and III), cytochrome c (between III and IV). Total H⁺ pumped per NADH: 10. Per FADH₂: 6. ATP synthase: 3-4 H⁺ per ATP.
Go deeper
O₂ is the final electron acceptor (terminal electron acceptor) — reduced to water at Complex IV. This is why aerobic organisms need O₂: without it, electrons cannot flow → ETC backs up → no proton pumping → no ATP → cell death.
From Class 10
In mitochondria, electrons from food molecules flow through a series of proteins, releasing energy to make ATP. This chain is the electron transport system.