OxPhos

Question 1

What is the basic gist of the OxPhos pathway?

Answer 1

NADH and FADH produced in catabolic pathway transfer electrons to intermediates of OxPhos pathway, which use the energy to pump H+ out of the cytosol and into the inner membrane space. This creates an electrochemical gradient which is later harnessed to convert ADP to ATP.

Question 2

Where are the proteins that are involved in OxPhos located?

Answer 2

The inner mitochondrial membrane

Question 3

The inner mitochondrial membrane does not have transporters for NADH. So how does NADH get inside the mitochondria to the cytosol where it donates its e- to OxPhos intermediates?

Answer 3

NADH is shuttled into the cytosol by either the malate-aspartate shuttle or the glycerol shuttle.

Question 4

Why does entrance of NADH via the malate-aspartate shuttle yield more ATP than entrance through the glycerol shuttle?

Answer 4

Entrance at the malate - aspartate shuttle results in donation of e- to complex 1, which in turn pumps 4 H+ across inner membrane. Entrance at the glycerol shuttle results in donation of e- to coenzyme Q or complex 2, which does not result in any proton pumping. Thus, the electrochemical gradient potential is reduced when NADH enters through the glycerol shuttle.

Question 5

Explain how ATP synthase works.

Answer 5

Protons move through the F0 subunit –> movement causes F0 subunit to rotate –> results in conformational change of beta subunits in F1 subunit that results in formation of ATP

Question 6

Explain this diagram.

Answer 6

Each subunit pair (alpha and beta) of F1 subunit has different affinity for different compounds. At beginning of rotation, high affinity binding for ADP + Pi is open so these molecules flood in and bind. Subunit rotates, now high affinity ATP site is exposed, nothing happens. Rotates, now low affinity ATP is exposed –> releases newly made ATP to cytosol of mitochondria.

Question 7

There area phosphate transporters and pyruvate transporters in the inner mitochondrial membrane that utilize H+ to transport. What effect does this have of OxPhos?

Answer 7

Reduces ATP produced b/c it is dissipating proton gradient.

Question 8

How are oxygen radicals tied to OxPhos? How do they decrease ATP production?

Answer 8

Occassionally an e- can escape OxPhos and result in free radical. This impacts OxPos b/c electrons that are lost to O2 cannot pump protons across membrane –> decreased electrochemical gradient. NADH is converted to NADPH to generate glutathione which will scavange these free radicals.

Question 9

Uncouplers

• Effect on electron flow?
• Effect on ATP synthesis?
• Effect on H+ gradient?
• Effect on heat generation?

Answer 9

• Unchanged from normal
• Inhibited
• Dissipated
• Increased