Lecture Notes: Electron Transport Chain and Oxidative Phosphorylation

Overview

• Continuation of cellular respiration discussion
• Previous topics: Glycolysis and Citric Acid Cycle
• Focus on electron carriers: NADH and FADH2

Recap

• Glycolysis: Oxidation of glucose to pyruvate, reduction of NAD+ to NADH
• Conversion of Pyruvate to Acetyl-CoA: Further reduction of NAD+
• Citric Acid Cycle (Krebs Cycle): NAD+ and FADH2 reduced to NADH and FADH2
• Result: Production of electron carriers NADH and FADH2, which are oxidized in the Electron Transport Chain (ETC)

Electron Transport Chain (ETC)

• Location: Inner mitochondrial membrane
• Function: Oxidation of NADH and FADH2 to NAD+ and FADH, energy from electrons used to pump protons

ETC for NADH Electrons

• Complexes Involved:
  • Complex I: NADH-Ubiquinone Oxidoreductase
  • Complex III: Cytochrome c Reductase
  • Complex IV: Cytochrome c Oxidase
  • Cytochrome c: Mobile electron carrier
• Process:
  • Complex I: NADH oxidized, electrons transferred to ubiquinone
    • 4 protons pumped into intermembrane space
  • Complex III: Ubiquinol transfers electrons, 4 additional protons pumped
  • Cytochrome c: Transfers one electron at a time from Complex III to IV
  • Complex IV: Electrons transferred to oxygen, forming water; 2 protons pumped
• Total Protons Pumped: 10 protons per NADH

ETC for FADH2 Electrons

• Complexes Involved:
  • Complex II: Succinate-CoQ Reductase (not Complex I)
  • Follows the same path as NADH electrons after Complex II
• Process:
  • Complex II: Succinate oxidized to fumarate; electrons transferred to FAD, then COQ
    • 4 protons pumped
  • Complexes III and IV: Same as NADH
• Total Protons Pumped: 6 protons per FADH2

Proton Gradient and Oxidative Phosphorylation

• Electrochemical Proton Gradient: Created by ETC
• ATP Synthesis:
  • Involves ATP Synthase (Complex V)
  • Protons flow back to matrix via ATP Synthase
  • Chemiosmosis: Movement of ions across membrane
  • ATP Production: Rotation of F1 subunit driven by proton movement
• ATP Yield:
  • NADH: 10 protons yield 2.5 ATP
  • FADH2: 6 protons yield 1.5 ATP

Conclusion

• ETC and Oxidative Phosphorylation are integral parts of cellular respiration
• Difference in ATP yield between NADH and FADH2

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