Electron Transport Chain and ATP Synthesis Notes

The Electron Transport Chain (ETC)

  • Location: Inner mitochondrial membrane.
  • Function: Convert energy from food into ATP via a series of redox reactions using NADH and FADH₂.

Key Steps in ATP Synthesis

  • Electron Donation:

    • NADH and FADH₂ donate energy-rich electrons to the ETC.
    • Electrons are passed through a series of protein complexes (NADH dehydrogenase, bc₁ complex, cytochrome oxidase).

  • Electron Flow and Energy Transfer:

    • As electrons move through ETC, energy is released, activating proton pumps that transport H⁺ ions across the membrane.
    • This creates a proton concentration gradient across the inner mitochondrial membrane.

Role of Oxygen (O₂)

  • Final Electron Acceptor:

    • Oxygen is crucial as it removes electrons from the cytochrome oxidase complex, preventing backlog in the ETC.
    • Combines with electrons and H⁺ to form water (H₂O).

  • Oxidative Phosphorylation:

    • ATP production that requires oxygen, generating water as a byproduct.

Chemiosmosis and ATP Synthase

  • Proton Gradient:

    • The concentration gradient of H⁺ ions across the mitochondrial membrane is harnessed to synthesize ATP.
    • Approximately 400 ATP molecules can be synthesized per second by ATP synthase.

  • Structure of ATP Synthase:

    • Composed of F0 and F1 parts.
    • F0: Channel for H⁺ ion diffusion.
    • F1: Catalytic subunit that synthesizes ATP from ADP and inorganic phosphate (Pi).

Total ATP Production

  • Yields from One Glucose Molecule:
    • Glycolysis: ~7-8 ATP.
    • Pyruvate oxidation: ~5-6 ATP.
    • Krebs Cycle: ~20-24 ATP.
    • Total: ~32-38 ATP depending on cell type.
    • Efficiency of energy transfer: ~38% when 36 ATP are produced.

Effects of Inhibitors

  • Cyanide (CN):

    • Lethal poison that inhibits cytochrome c oxidase, halting electron flow and ATP production.

  • Dinitrophenol (DNP):

    • Reduces ATP synthesis by decreasing H⁺ ion availability affecting the concentration gradient.
    • Uncouples ATP synthesis from electron flow, leading to decreased ATP production per calorie consumed.

Summary of Cellular Respiration Processes in Mitochondria

  1. Glycolysis
  2. Pyruvate Oxidation
  3. Krebs Cycle
  • All require O₂ for maximal ATP generation.

Important Questions to Consider

  • How do ATP synthase enzymes work and why are they abundant?
  • What role does oxygen play in cellular respiration?
  • What are the consequences of inhibitors like cyanide and DNP on cellular respiration?