Break down NAD⁺ (Nicotinamide Adenine Dinucleotide) and its role in the electron transport chain (ETC).
🔋 What is NAD⁺?
NAD⁺ is a coenzyme found in all living cells. It acts as an electron carrier — essential for cellular respiration.
NAD⁺ = oxidized form (can accept electrons)
NADH = reduced form (has accepted electrons)
🔁 NAD⁺ in Metabolism
In metabolic pathways like:
Glycolysis
Citric Acid Cycle (Krebs)
Beta-oxidation (fat metabolism)
NAD⁺ accepts 2 electrons and 1 proton → becomes NADH.
This NADH then carries electrons to the electron transport chain.
⚡ Role of NADH in the Electron Transport Chain (ETC)
1. Where: ETC is located in the inner mitochondrial membrane.
2. Goal: Generate ATP via oxidative phosphorylation.
🧬 ETC Step-by-Step (Simplified)
1. NADH donates electrons to Complex I (NADH dehydrogenase).
2. As electrons move through Complex I, III, and IV, protons (H⁺) are pumped from the mitochondrial matrix to the intermembrane space.
3. This creates a proton gradient (like a battery).
4. Oxygen is the final electron acceptor at Complex IV → combines with electrons and protons to make H₂O.
5. Protons flow back into the matrix through ATP synthase (Complex V) → powering the synthesis of ATP from ADP.
📊 ATP Yield
1 NADH = approx. 2.5–3 ATP
1 FADH₂ = approx. 1.5–2 ATP (enters at Complex II)
🧠 Summary
Molecule Role Destination in ETC
NAD⁺ Electron acceptor Becomes NADH in metabolism
NADH Electron donor Complex I
O₂ Final electron acceptor Complex IV → H₂O
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