Notes on ATP Synthesis

Electron Transport Chain and Oxidative Phosphorylation

  • Key Inputs and Outputs of Electron Transport Chain:

    • The third step of the catabolic pathway.
    • Electrons from NADH and FADH2 enter a series of complexes in the mitochondrial membrane.

  • Oxidative Phosphorylation and Chemiosmosis:

    • NADH and FADH2 donate electrons to the electron transport chain.
    • Electrons move from complex to complex, ultimately accepted by oxygen to form water.
    • Protons (H+) are pumped from the mitochondrial matrix to the intermembrane space, creating a proton gradient.
    • ATP synthesis occurs via the ATP synthase complex, driven by the proton gradient (chemiosmosis).
    • Large number of ATP generated by oxidative phosphorylation.

ATP Synthase Complex and ATP Production

  • Structure:
    • Rotor, internal rod, catalytic knob, and stator.
  • Mechanism:
    • Protons flow down their gradient from the intermembrane space into the catalytic knob of ATP synthase.
    • Proton binding causes the rotor to spin, activating catalytic sites.
    • ADP and inorganic phosphate combine to produce ATP.
    • The proton motive force drives ATP synthesis.

ATP Yield

  • Glycolysis: 2 ATP (substrate-level phosphorylation).
  • Citric Acid Cycle: 2 ATP (substrate-level phosphorylation).
  • Oxidative Phosphorylation: 26-28 ATP (depending on electron shuttle).
  • Total: 30-32 ATP per glucose molecule.

Conceptual Problem

  • Rising ADP levels increase electron flow through the electron transport chain.
  • Question: Which of the following best describes an effect of rising ADP levels in the mitochondria?
    • Fewer protons will be pumped across the inner mitochondrial membrane.
    • NADH and FADH2 will be oxidized to NAD+ and FAD less rapidly.
    • The flow of protons through ATP synthase will decrease.
    • Oxygen consumption will increase.