Lecture Notes on Oxidative Phosphorylation and ATP Yield
Overview of Electron Carriers
- Processes Producing Electron Carriers:
- Glycolysis: Produces 2 NADH.
- Preparatory Step: Produces 2 NADH.
- Krebs Cycle: Produces 6 NADH and 2 FADH₂.
ATP Yield Calculation
Glycolysis
- NADH in Electron Transport Chain:
- Complex I: 8 H⁺ ions pumped for 2 NADH.
- Complex II: 0 H⁺ ions.
- Complex III: 8 H⁺ ions for 2 NADH.
- Complex IV: 4 H⁺ ions for 2 NADH.
- Total: 20 H⁺ ions provide 5 ATP (4 H⁺ per ATP).
Preparatory Step
- Identical to Glycolysis:
- Complex I, III, IV pump a total of 20 H⁺ ions.
- Produces 5 ATP from 20 H⁺ ions.
Krebs Cycle
- NADH Contributions:
- Complex I: 24 H⁺ ions for 6 NADH.
- Complex III: 24 H⁺ ions for 6 NADH.
- Complex IV: 12 H⁺ ions for 6 NADH.
- Total: 60 H⁺ ions provide 15 ATP.
- FADH₂ Contributions:
- Complex II: Does not contribute to H⁺ pumping.
- Complex III: 8 H⁺ ions for 2 FADH₂.
- Complex IV: 4 H⁺ ions for 2 FADH₂.
- Total: 12 H⁺ ions provide 3 ATP (FADH₂ produces less ATP as it skips Complex I).
Mechanism of Electron Transport for FADH₂
- Starts at Complex II (Succinate Dehydrogenase):
- Electrons are transferred through iron centers to ubiquinone, forming ubiquinol.
- Complex III and IV: Electrons continue through, pumping H⁺ ions.
Glycolysis NADH Shuttle Systems
- Cytoplasmic NADH Transport:
- Shuttles: Mechanisms needed to transport NADH from cytoplasm to the matrix.
- Glycerol 3-Phosphate Shuttle:
- Bypasses Complex I, reducing H⁺ pumping (12-20 H⁺ ions variance).
- Effect: 3 to 5 ATP produced due to shuttle mechanism.
Total ATP Yield from Oxidative Phosphorylation
- Range: 26 to 28 ATP per glucose molecule.
- Dependent on Shuttle Used: Glycerol 3-Phosphate Shuttle impacts total yield.
Key Points
- Oxidative Phosphorylation: Complex process not fully understood.
- Variability in ATP production due to cytoplasmic shuttle systems.
Note: The information is based on current understanding and may evolve with further research.