Cellular Respiration: How Oxygen Powers Your Cells

Cellular respiration converts glucose + O₂ → ATP + CO₂ + H₂O via three main stages:

1. Glycolysis (Cytosol)

Glucose (6C) → 2 Pyruvate (3C) + 2 ATP (net) + 2 NADH. Anaerobic.

2. Pyruvate Oxidation & Citric Acid Cycle (Mitochondrial Matrix)

Pyruvate → Acetyl-CoA + CO₂ + NADH. Acetyl-CoA enters TCA cycle → 3 NADH, 1 FADH₂, 1 GTP per turn (×2 per glucose).

3. Oxidative Phosphorylation (Inner Mitochondrial Membrane)

Electron Transport Chain (Complexes I–IV): NADH/FADH₂ donate e⁻ → O₂ (final acceptor) → H₂O. Energy released pumps H⁺ → electrochemical gradient → ATP synthase (Complex V) makes ~26–28 ATP.

Overall Yield

~30–32 ATP per glucose (theoretical max 38; proton leak, transport costs reduce yield).

Alternative Fuels

Fatty acids → β-oxidation → Acetyl-CoA. Amino acids → deamination → TCA intermediates. All converge on ETC.

Key Takeaway

Oxygen is the final electron acceptor enabling high-yield ATP production. Without it, only 2 ATP/glucose (glycolysis + fermentation).