Q: Given the following standard reduction potentials: $E'^_{NAD^+/NADH} = -0.32\ V$ and $E'^_{O_2/H_2O} = +0.82\ V$, what is the standard free energy change ($\Delta G'^$) for the transfer of electrons from NADH to O$_2$? (Use $\Delta G'^ = -nF\Delta E'^$, $n=2$, $F=96,485\ \mathrm{C/mol}$)

$\Delta G'^ = -220\ \mathrm{kJ/mol}$

Question 1

Which of the following best describes the primary function of the electron transport chain (ETC) in mitochondria?

Accepted Answer

To transfer electrons from NADH and FADH$_2$ to oxygen, generating a proton gradient used to produce ATP

Question 2

Which of the following correctly matches the electron carrier with its role in the electron transport chain?

Accepted Answer

Ubiquinone (CoQ): Accepts electrons from Complex I and II and donates them to Complex III

Question 3

Given the following standard reduction potentials: $E'^ _{NAD^+/NADH} = -0.32\ V$ and $E'^ _{O_2/H_2O} = +0.82\ V$, what is the standard free energy change ($\Delta G'^ $) for the transfer of electrons from NADH to O$_2$? (Use $\Delta G'^  = -nF\Delta E'^ $, $n=2$, $F=96,485\ \mathrm{C/mol}$)

Accepted Answer

$\Delta G'^  = -220\ \mathrm{kJ/mol}$

Question 4

Which of the following statements about Complex II (succinate dehydrogenase) is CORRECT?

Accepted Answer

It transfers electrons from FADH$_2$ to ubiquinone (CoQ)

Question 5

A mutation impairs the function of cytochrome c. Which of the following would most likely be the immediate consequence?

Accepted Answer

Electron transfer from Complex III to Complex IV would be blocked

Question 6

Which of the following best explains why the inner mitochondrial membrane is impermeable to protons, and why this is essential for ATP synthesis?

Accepted Answer

It allows the establishment of a proton gradient, which is used by ATP synthase to generate ATP from ADP and $P_i$

Question 7

Which of the following is a unique feature of Complex I (NADH:ubiquinone oxidoreductase) compared to Complex II?

Accepted Answer

It pumps protons from the matrix to the intermembrane space

Question 8

Which of the following correctly describes the Q-cycle in Complex III?

Accepted Answer

It involves the transfer of electrons from reduced CoQH$_2$ to cytochrome c, with the recycling of CoQ

Question 9

Which of the following best explains why FADH$_2$ yields less ATP than NADH when oxidized in the electron transport chain?

Accepted Answer

FADH$_2$ donates electrons to Complex II, which does not pump protons, resulting in fewer protons being translocated across the membrane

Question 10

A patient is diagnosed with a genetic defect that impairs the function of copper centers in Complex IV. Which of the following would most likely be observed?

Accepted Answer

Decreased reduction of oxygen to water and impaired proton pumping at Complex IV

Question 11

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

Accepted Answer

Complex I → CoQ → Complex III → cytochrome c → Complex IV

Question 12

Which of the following statements about iron-sulfur proteins in the electron transport chain is TRUE?

Accepted Answer

They participate in one-electron transfers involving Fe$^{2+}$ and Fe$^{3+}$ oxidation states

Question 13

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

Accepted Answer

ATP synthesis by ATP synthase will decrease or stop

Question 14

Which of the following best describes the role of cytochrome c in the electron transport chain?

Accepted Answer

It is a mobile electron carrier that transfers electrons from Complex III to Complex IV

Question 15

Which of the following is a direct result of electron transfer from cytochrome c to Complex IV?

Accepted Answer

Reduction of O$_2$ to H$_2$O

Question 16

A researcher isolates mitochondria and adds NADH, ADP, and inorganic phosphate, but omits oxygen. What will be the result?

Accepted Answer

Electron transport will halt and ATP synthesis will be minimal

Question 17

Which of the following best explains why the electron transport chain is organized into complexes embedded in the inner mitochondrial membrane?

Accepted Answer

To facilitate sequential electron transfer and efficient coupling of electron flow to proton pumping

Question 18

Which of the following statements about the Q-cycle in Complex III is FALSE?

Accepted Answer

It directly reduces oxygen to water

Question 19

Which of the following is the main reason why the electron transport chain is essential for aerobic organisms?

Accepted Answer

It allows for the complete oxidation of glucose to CO$_2$ and H$_2$O, maximizing ATP yield

The Electron Transport Chain: Structure, Function, and Components

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