Question 1

Which of the following statements best describes the role of the chemiosmotic theory in oxidative phosphorylation?

Accepted Answer

It states that transmembrane differences in proton concentration serve as the energy reservoir for ATP synthesis.

Question 2

Which toxin specifically inhibits the conversion of citrate to isocitrate in the TCA cycle, and what is the consequence for cellular respiration?

Accepted Answer

Fluoroacetate; it prevents the TCA cycle from proceeding, halting ATP production downstream.

Question 3

Which of the following electron carriers is lipid-soluble and freely diffusible within the inner mitochondrial membrane, shuttling electrons between less mobile carriers?

Accepted Answer

Ubiquinone (Coenzyme Q)

Question 4

Complex II of the electron transport chain is unique because:

Accepted Answer

It transfers electrons from succinate to ubiquinone but does not pump protons.

Question 5

Which equation correctly represents the free energy change for proton transport across the mitochondrial membrane?

Accepted Answer

$\Delta G = RT \ln \left( \frac{C_2}{C_1} \right) + ZF\Delta \Psi$

Question 6

A patient is exposed to cyanide poisoning. Which component of the electron transport chain is directly inhibited, and what is the immediate effect?

Accepted Answer

Complex IV (cytochrome oxidase); electron transfer to oxygen is blocked, halting ATP synthesis.

Question 7

Which of the following statements about NADH and FADH$_2$ is correct?

Accepted Answer

NADH is water soluble, associates reversibly with dehydrogenases, and cannot cross the inner mitochondrial membrane.

Question 8

Which of the following best explains why the actual free energy change for electron transfer from NADH to O$_2$ in mitochondria is more negative than the standard value?

Accepted Answer

The NAD$^+$/NADH ratio in mitochondria is much higher than in standard conditions.

Question 9

Which of the following is NOT a function of the mitochondrial matrix?

Accepted Answer

Contains enzymes for glycolysis.

Question 10

What is the net result of the Q cycle in Complex III of the electron transport chain?

Accepted Answer

Oxidation of ubiquinol (QH$_2$) and reduction of cytochrome c, with the translocation of 4 protons to the intermembrane space.

Question 11

Which of the following correctly describes the flow of electrons through the mitochondrial electron transport chain?

Accepted Answer

NADH → Complex I → CoQ → Complex III → cytochrome c → Complex IV → O$_2$

Question 12

Which of the following is a competitive inhibitor of succinate dehydrogenase?

Accepted Answer

Malonate

Question 13

Which statement about cytochromes is TRUE?

Accepted Answer

Cytochrome c is a soluble protein that associates with the outer surface of the inner mitochondrial membrane.

Question 14

Which of the following best describes the function of iron-sulfur proteins in the electron transport chain?

Accepted Answer

They contain iron associated with inorganic sulfur atoms and participate in one-electron transfers.

Question 15

Which of the following statements about ATP synthesis in mitochondria is correct?

Accepted Answer

ATP is synthesized when protons flow passively into the matrix through a pore in the F$_1$-F$_0$ ATP synthase.

Question 16

Which of the following is TRUE regarding the proton-motive force in mitochondria?

Accepted Answer

It is created by pumping protons from the matrix to the intermembrane space by Complexes I, III, and IV.

Question 17

Which of the following correctly matches the electron carrier with its property?

Accepted Answer

Ubiquinone: accepts one or two electrons and is freely diffusible within the inner mitochondrial membrane

Question 18

Which reaction is catalyzed by Complex IV (cytochrome oxidase) in the electron transport chain?

Accepted Answer

$2	ext{cyt c (red)} + 4	ext{H}^+ + \frac{1}{2}	ext{O}_2 ightarrow 2	ext{cyt c (ox)} + 2	ext{H}^+ + 	ext{H}_2	ext{O}$

Oxidative Phosphorylation and Electron Transport Chain: Structure, Function, and Mechanism

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