Mitochondria: Structure and Role in Cellular Respiration

Mitochondrial Architecture

• Outer membrane: Porins allow small molecule passage.
• Intermembrane space: Proton gradient reservoir.
• Inner membrane: Impermeable; houses ETC complexes I–IV, ATP synthase. Folded into cristae → ↑surface area.
• Matrix: Krebs cycle enzymes, mtDNA, ribosomes, Ca²⁺ buffering.

Respiration Stages

1. Glycolysis: Cytosol → pyruvate (2 ATP, 2 NADH).
2. Pyruvate oxidation: Matrix → acetyl‑CoA + CO₂ + NADH.
3. Krebs cycle: Matrix → 2 ATP (GTP), 6 NADH, 2 FADH₂ per glucose.
4. Oxidative phosphorylation: Inner membrane. ETC pumps H⁺ → gradient → ATP synthase makes ~26–28 ATP.

Total Yield

~30–32 ATP per glucose. Mitochondria = “powerhouses.” Dysfunction underlies metabolic, neurodegenerative, and aging‑related diseases.