Oxidative Phosphorylation

Question 0

How is ATP generated in oxidative phosphorylation?

Answer 0

Discharging the proton motive force drives ATP synthase as H+ floods back into matrix.

Question 1

What is the proton motive force? How is it generated?

Answer 1

H+ conc. gradient across inner mitochondrial membrane

Electron transport chain drives movement of H+ through proton translocating complexes into the intermembrane space.

Reducing agents donate electrons to transport chain.

Terminal electron acceptor is oxygen (produces water)

Question 2

How do high energy signals inhibit oxidative phosphorylation?

Answer 2

No substrate for ATP synthase, therefore H+ flows inwards, which halts the electron transport chain.

Question 3

In what ways can the electron transport chain be inhibited?

Answer 3

Irreversible inhibition of electron acceptors -> no ATP synthesised ——–> DEATH
e.g. cyanide, CO

Uncouplers = increases permeability of inner membrane to protons, therefore dissipates proton motive force
e.g. dinitrophenol, thermogenin

Question 4

What are the main differences between oxidative and substrate-level phosphorylation?

Answer 4

ENZYMES:
Oxidative phosphorylation = membrane-associated complexes on inner mitochondrial membrane
Substrate-level phosphorylation = soluble enzymes in cytoplasm and mitochondrial matrix

ENERGY COUPLING:
Oxidative phosphorylation = indirect (generation of pmf)
Substrate-level phosphorylation = direct (formation of high energy compounds)

CAN OCCUR IN ABSENCE OF O2?
Oxidative phosphorylation = cannot occur in absence of O2 (O2 is terminal electron acceptor)
Substrate-level phosphorylation = can occur to a limited extent in absence of O2

AMOUNT OF ATP SYNTHESISED?
Oxidative phosphorylation = lots of ATP (organs with many mitochondria)
Substrate-level phosphorylation = little ATP

Question 5

How does thermogenin cause non-shivering thermogenesis?

Answer 5

Natural uncoupling protein thermogenin uncouples electron transport chain, causing energy to be released as heat instead of pumping H+ across membrane.

Activated by noradrenaline release, which causes lipolysis, the release of NADH & FAD2H, and the activation of thermogenin.