oxidative phosphorylation

Where exactly does oxidative phosphorylation take place, and how is this structure adapted for it?

• Location: Inner mitochondrial membrane (cristae).

• Adaptation: Highly folded to increase surface area for more electron transport chains and ATP synthase complexes.

What happens to NADH and FADH2 when they arrive at the inner mitochondrial membrane?

• They are oxidised (lose hydrogen).

• They release protons H+ and high-energy electrons e-

• Their coenzymes NAD+ and FAD are regenerated to return to glycolysis/Krebs cycle.

• How do electrons move through the electron transport chain (ETC), and what is the immediate result?

• Electrons move along a series of carrier proteins via continuous redox reactions (carriers are successively reduced then oxidised).

• As electrons pass to carriers of lower energy levels, they release energy.

How is the proton H+ gradient established across the inner membrane?

• Energy released from the ETC is used by electron carriers to actively pump protons (H+ ions)

• Protons move from the mitochondrial matrix into the intermembrane space.

• This creates a steep proton/electrochemical/pH gradient across the membrane.

• Define chemiosmosis in the context of respiration.

• The movement of protons (H+ ions) down their electrochemical gradient across a membrane.

• This movement occurs through a channel protein coupled to ATP synthase, releasing energy used to synthesise ATP.

• Why can protons only pass through ATP synthase to re-enter the matrix?

• The phospholipid bilayer of the inner mitochondrial membrane is impermeable to ions.

• H+ ions are charged and cannot diffuse directly through the hydrophobic core.

How exactly does ATP synthase produce ATP during chemiosmosis?

• Protons flow down their electrochemical gradient through the ATP synthase channel.

• This flow induces a conformational (shape) change in the enzyme (rotational energy).

• This drives the phosphorylation of ADP and inorganic phosphate to form ATP

Why is oxygen vital to oxidative phosphorylation, and what is the exact chemical equation for its role?

• Oxygen acts as the final/terminal electron acceptor.

• It removes electrons from the end of the ETC and protons from the matrix to form water.

• Equation: 4H^+ + 4e^- + O2 —> 2H2O

Why is the theoretical yield of ATP per glucose molecule (approx. 30–32 ATP) rarely achieved in reality? (Name 3 reasons).

1. Proton leakage: Some protons leak back across the inner membrane without passing through ATP synthase.

2. Active transport cost: Some ATP/energy is used to actively transport pyruvate and NADH (from glycolysis) into the matrix.

3. Alternative use of gradient: The proton gradient is sometimes used to drive the active transport of other phosphate ions into the matrix.

How would a chemical that makes the inner mitochondrial membrane permeable to protons affect ATP production and heat generation?

• ATP Production: Decreases significantly. The proton gradient collapses as protons diffuse freely across the bilayer, bypassing ATP synthase.

• Heat Generation: Increases. The energy from the ETC is dissipated as heat instead of being trapped as chemical energy in ATP (this is known as uncoupling).

Explain exactly what happens to aerobic respiration if oxygen is absent

• ETC Stops: Oxygen cannot act as the final electron acceptor. Electrons accumulate and stall ETC

• Coenzymes Stalled: NADH and FADH2 cannot be oxidised (cannot unload their electrons/protons at the inner membrane).

• No Gradient: Protons are no longer pumped into the intermembrane space; the proton/electrochemical gradient collapses.

• No Chemiosmosis: ATP synthase stops rotating; oxidative phosphorylation ceases.

• Krebs & Link Cycle Halt: The Link reaction and Krebs cycle stop completely because they run out of regenerated, empty NAD+ and FADcoenzymes.