Aerobic Respiration: Equation, Reactants, Products & Energy Yield

Overall Balanced Equation

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + Energy (ATP + Heat)

Reactants

• Glucose (C₆H₁₂O₆): Primary fuel; from diet or glycogenolysis.
• Oxygen (O₂): Final electron acceptor in mitochondrial electron transport chain (ETC).

Products

• Carbon Dioxide (CO₂): Waste gas; exhaled via lungs.
• Water (H₂O): Metabolic water; formed at Complex IV (cytochrome c oxidase).
• Energy: Captured as ~30–32 ATP per glucose (substrate-level: 4 ATP; oxidative phosphorylation: ~26–28 ATP).

Four Stages

1. Glycolysis (Cytosol): Glucose → 2 Pyruvate + 2 ATP + 2 NADH.
2. Pyruvate Oxidation (Mitochondrial Matrix): 2 Pyruvate → 2 Acetyl-CoA + 2 NADH + 2 CO₂.
3. Citric Acid / Krebs Cycle (Matrix): 2 Acetyl-CoA → 6 NADH + 2 FADH₂ + 2 ATP (GTP) + 4 CO₂.
4. Oxidative Phosphorylation (Inner Mitochondrial Membrane): NADH/FADH₂ → ETC → proton gradient → ATP synthase → ~26–28 ATP. O₂ + 4H⁺ + 4e⁻ → 2 H₂O.

Key Points

• Requires mitochondria, O₂, intact ETC.
• Yield varies slightly by shuttle system (malate-aspartate vs. glycerol-3-phosphate) and proton leak.
• Complete oxidation maximizes energy capture; anaerobic glycolysis yields only 2 ATP.