Electrochemical Gradients and Chemiosmotic Coupling

Flashcards covering electrochemical gradients, chemiosmotic coupling, ATP synthase mechanics and directionality, membrane transport, and experimental evidence.

What two gradients constitute the electrochemical H+ gradient across a membrane?

A chemical gradient (difference in H+ concentration) and an electrical gradient (membrane potential).

In the electrochemical H+ gradient, which side is negatively charged and why?

The side with low H+ is negatively charged, while the side with high H+ is positively charged due to charge separation.

What is chemiosmotic coupling?

The linking of proton pumping and gradient formation with ATP synthesis by ATP synthase.

What enzyme uses the energy of the proton gradient to synthesize ATP?

ATP synthase (F1F0 ATP synthase).

Where is the stationary part of ATP synthase anchored?

The stationary (stator) part is anchored to the membrane.

Can ATP synthase operate in reverse, hydrolyzing ATP to pump protons?

Yes; it can run in reverse under certain conditions to pump protons against the gradient.

What happens if the H+ electrochemical gradient is disrupted while ATP levels are high?

ATP synthase may hydrolyze ATP to try to restore the gradient, leading to ATP consumption.

Why is it important to maintain the H+ gradient in mitochondria?

To drive ATP synthesis and to power transport of molecules across the inner mitochondrial membrane.

What are the two types of coupled transport across membranes mentioned?

Symport (same direction) and antiport (opposite directions).

Why is Pi transport mentioned in the context of ATP synthesis?

Pi is needed to form ATP; its transport is important for ATP production.

What evidence supports chemiosmotic coupling?

A proton gradient is required for ATP synthesis; uncouplers that dissipate the gradient abolish ATP production.

What effect does an uncoupler have on ATP production in a system with a proton gradient?

The uncoupler dissipates the proton gradient, preventing ATP synthesis.

In the light-driven system with bacteriorhodopsin and ATP synthase, what happens when an uncoupler is present?

No ATP is generated because the proton gradient is dissipated.

In the ATP synthase rotor thought experiment, would ATP synthesis occur if protons cannot access the rotor?

No; protons must access the rotor to drive rotation and catalyze ATP synthesis.

What are the three key concepts summarized about membrane-based energy transduction?

1) Oxidative phosphorylation and photosynthesis depend on membrane-based mechanisms. 2) Electron transfers pump protons across the membrane to create an electrochemical gradient. 3) Chemiosmotic coupling links gradient formation with ATP synthesis.