Oxidative Phosphorylation
ஆக்சிஜனேற்ற பாஸ்பாரிலேற்றம்
Stop confusing Oxidative Phosphorylation with Photophosphorylation. One uses light, the other uses the energy from redox reactions in the Electron Transport System. If you miss this distinction, you lose 4 marks instantly.
The idea
Oxidative phosphorylation is the synthesis of ATP from ADP and inorganic phosphate. This process is driven by the energy released during the oxidation-reduction reactions of the Electron Transport System (ETS). It occurs in the inner mitochondrial membrane. Oxygen acts as the final electron acceptor, making this an aerobic process.
Why it matters
It exists to efficiently capture the energy released from electron transfer to produce ATP, the universal energy currency of the cell.
NEET lens
NEET focuses on the location, the final electron acceptor, and the enzyme complexes involved. Memorize the sequence of complexes I through IV and the role of ATP synthase. Expect questions on the specific site of the process and the necessity of oxygen. Do not skip the stoichiometry of ATP yield per NADH and FADH2.
Clinical significance
Cyanide poisoning is a direct failure of this process. It binds to Cytochrome c oxidase, blocking the final step of the electron transport chain. Without ATP production, cellular respiration halts, leading to rapid tissue death and systemic collapse.
Introduction
Oxidative phosphorylation is the synthesis of ATP driven by the proton gradient generated by the electron transport chain, occurring at the inner mitochondrial membrane via ATP synthase (F₀F₁ complex).
Core concept
Steps: (1) NADH and FADH₂ (from glycolysis, pyruvate oxidation, Krebs) donate electrons to ETC. (2) Electrons flow through Complexes I→III→IV (or II→III→IV for FADH₂) → O₂ reduced to H₂O. (3) H⁺ pumped across inner mitochondrial membrane into intermembrane space (by Complexes I, III, IV). (4) H⁺ gradient (proton motive force) → H⁺ flows back through ATP synthase (F₁F₀) → ATP synthesized. ~34 ATP per glucose from oxidative phosphorylation.
Go deeper
P/O ratio: ATP synthesized per oxygen atom consumed. NADH: ~2.5 ATP per O atom. FADH₂: ~1.5 ATP per O atom. (NCERT values: NADH = 3 ATP, FADH₂ = 2 ATP — use these in NEET). H⁺:ATP ratio for ATP synthase: ~4 H⁺ needed per ATP synthesized by rotation.
From Class 10
The bulk of ATP in aerobic respiration is made by using the proton gradient from the electron transport chain to drive ATP synthase. This is oxidative phosphorylation.