Q: If the standard reduction potential ($$E'^{\circ}) $$for NAD+/NADH is $$-0.315\,\mathrm{V}$$ and for O2/H2O is $$+0.816\,\mathrm{V}$$, what is the standard free energy change ($$\Delta G'^{\circ}) $$for the transfer of electrons from NADH to O2? Use $$\Delta G'^{\circ} = -nF\Delta E'^{\circ}$$, $$n=2$$, $$F=96.5\,\mathrm{kJ/V\cdot mol}.$$

$$\Delta G'^{\circ} = -2 \times 96.5 \times (0.816 - (-0.315)) = -218.8\,\mathrm{kJ/mol}$$

Question 1

Which of the following best describes the chemiosmotic coupling mechanism in mitochondria?

Accepted Answer

It is the coupling of electron transport and ATP synthesis via a proton gradient across the inner mitochondrial membrane.

Question 2

Given the following reaction for NADH oxidation: $$\mathrm{NADH} + \mathrm{H}^+ + 1/2\,\mathrm{O}_2 \rightarrow \mathrm{NAD}^+ + \mathrm{H}_2\mathrm{O}$$, and $$\Delta G^\circ' = -220\,\mathrm{kJ/mol}$$, what is the primary use of this free energy in the electron transport chain?

Accepted Answer

To pump protons from the mitochondrial matrix to the intermembrane space, creating a proton gradient.

Question 3

Which complex in the electron transport chain does NOT contribute to proton pumping across the inner mitochondrial membrane?

Accepted Answer

Complex II

Question 4

If the proton gradient across the inner mitochondrial membrane is dissipated (e.g., by an uncoupler), what is the most immediate effect on ATP synthesis?

Accepted Answer

ATP synthesis ceases because the proton-motive force is lost.

Question 5

The overall reaction for electron transport beginning with FADH2 is: $$\mathrm{FADH}_2 + 1/2\,\mathrm{O}_2 + \mathrm{ADP} + \mathrm{P}_i \rightarrow \mathrm{FAD} + \mathrm{ATP} + \mathrm{H}_2\mathrm{O}. $$Why does FADH2 yield less ATP than NADH?

Accepted Answer

FADH2 donates electrons to Complex II, which does not pump protons, resulting in fewer protons being translocated.

Question 6

Which of the following equations correctly represents the relationship between the proton-motive force ($$\Delta p$$), membrane potential ($$\Delta \Psi$$), and pH gradient ($$\Delta pH$$)?

Accepted Answer

$$\Delta p = \Delta \Psi + 2.3RT/F \cdot \Delta pH$$

Question 7

A mutation in the c-subunit of ATP synthase prevents rotation of the c-ring. What is the most likely consequence?

Accepted Answer

ATP synthesis will be inhibited because the conformational changes in the F1 subunits cannot occur.

Question 8

Which of the following best explains why the F1 portion of ATP synthase has three different conformational states?

Accepted Answer

The rotation of the gamma subunit induces conformational changes in the three beta subunits, cycling them through open, loose, and tight states.

Question 9

If the standard reduction potential ($$E'^{\circ}) $$for NAD+/NADH is $$-0.315\,\mathrm{V}$$ and for O2/H2O is $$+0.816\,\mathrm{V}$$, what is the standard free energy change ($$\Delta G'^{\circ}) $$for the transfer of electrons from NADH to O2? Use $$\Delta G'^{\circ} = -nF\Delta E'^{\circ}$$, $$n=2$$, $$F=96.5\,\mathrm{kJ/V\cdot mol}.$$

Accepted Answer

$$\Delta G'^{\circ} = -2 	imes 96.5 	imes (0.816 - (-0.315)) = -218.8\,\mathrm{kJ/mol}$$

Question 10

Which of the following statements about the structure of ATP synthase is CORRECT?

Accepted Answer

The F1 portion protrudes into the mitochondrial matrix and contains the catalytic sites for ATP synthesis.

Question 11

A patient is exposed to a chemical that specifically inhibits Complex IV of the electron transport chain. Which of the following would you expect to occur?

Accepted Answer

Oxygen consumption by mitochondria will decrease.

Question 12

Which of the following best describes the role of the gamma ($$\gamma) $$subunit in ATP synthase?

Accepted Answer

It rotates within the alpha3beta3 hexamer, inducing conformational changes necessary for ATP synthesis.

Question 13

Which of the following is the correct sequence of electron flow through the complexes of the electron transport chain starting from NADH?

Accepted Answer

Complex I → Complex III → Complex IV

Question 14

If 10 protons are pumped across the inner mitochondrial membrane per pair of electrons from NADH, and 4 protons are required to synthesize and export 1 ATP, how many ATP molecules are produced per NADH?

Accepted Answer

2.5

Question 15

Which of the following best explains why the ATP synthase can operate in reverse under certain conditions?

Accepted Answer

If the proton gradient collapses, ATP synthase can hydrolyze ATP to pump protons from the matrix to the intermembrane space.

Question 16

Which of the following is a direct consequence of inhibiting the rotation of the central stalk (gamma subunit) of ATP synthase?

Accepted Answer

Protons will continue to flow through F0, but ATP will not be synthesized.

Question 17

Which of the following best describes the function of the c-ring in the F0 portion of ATP synthase?

Accepted Answer

It rotates as protons move through, driving conformational changes in the F1 portion.

Question 18

Which of the following is TRUE regarding the energy conversion in oxidative phosphorylation?

Accepted Answer

The energy from electron transfer is used to create a proton gradient, which is then used to drive ATP synthesis.

Chemiosmotic Coupling and ATP Synthase: Mechanisms of Oxidative Phosphorylation

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