Q: What is the net reaction for the transfer of electrons from NADH to oxygen in the electron transport chain, including the change in free energy?

$$ \mathrm{NADH} + \mathrm{H}^+ + \frac{1}{2} \mathrm{O}_2 \rightarrow \mathrm{NAD}^+ + \mathrm{H}_2\mathrm{O} $$ $$ \Delta G^\circ = -52.4 \text{ kcal/mol} $$

Question 1

Which of the following statements best describes the role of Complex I in the electron transport chain?

Accepted Answer

Complex I transfers electrons from NADH to CoQ via FMN and Fe-S proteins, pumping 4 protons across the membrane.

Question 2

What is the net reaction for the transfer of electrons from NADH to oxygen in the electron transport chain, including the change in free energy?

Accepted Answer

$$ \mathrm{NADH} + \mathrm{H}^+ + \frac{1}{2} \mathrm{O}_2 ightarrow \mathrm{NAD}^+ + \mathrm{H}_2\mathrm{O} $$ 
 $$ \Delta G^\circ = -52.4 	ext{ kcal/mol} $$

Question 3

Which electron carrier in the electron transport chain is NOT a protein and is capable of accepting both electrons and protons?

Accepted Answer

Coenzyme Q (ubiquinone)

Question 4

During the Q cycle in Complex III, how does CoQH2 facilitate the transfer of electrons to single electron carriers?

Accepted Answer

CoQH2 passes one electron to cytochrome c1 and one electron via cytochrome b to another CoQ, forming semiquinone.

Question 5

Which of the following best explains why cyanide is toxic to aerobic cells?

Accepted Answer

Cyanide binds to the Fe-Cu center of cytochrome c oxidase (Complex IV), blocking electron transport to oxygen.

Question 6

How many protons are pumped across the inner mitochondrial membrane for each pair of electrons transported through Complexes I, III, and IV?

Accepted Answer

10 protons

Question 7

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

Accepted Answer

Iron-sulfur proteins transfer one electron at a time and no protons.

Question 8

Which respiratory complex is directly involved in the oxidation of succinate and does NOT pump protons across the membrane?

Accepted Answer

Complex II

Question 9

What is the primary function of the electrochemical proton gradient established by the electron transport chain?

Accepted Answer

To drive ATP synthesis via oxidative phosphorylation

Question 10

Which of the following best describes the relationship between electron transport and ATP synthesis?

Accepted Answer

ATP synthesis is dependent on electron transport, but electron transport can occur without ATP synthesis if uncouplers are present.

Question 11

Which of the following is a consequence of incomplete reduction of oxygen by Complexes I and III?

Accepted Answer

Generation of toxic superoxide anion ($$ \mathrm{O}_2^- ) or $$hydrogen peroxide ($$ \mathrm{H}_2\mathrm{O}_2 )$$

Question 12

Which of the following best describes the role of cytochrome c oxidase (Complex IV) in the electron transport chain?

Accepted Answer

It transfers electrons from cytochrome c to oxygen, reducing O2 to H2O.

Question 13

Which of the following is TRUE regarding the reduction of Coenzyme Q (CoQ) in the electron transport chain?

Accepted Answer

CoQ is reduced in two successive steps: first to semiquinone (CoQH), then to dihydroquinone (CoQH2).

Question 14

A patient is exposed to an uncoupler that abolishes the interdependence of electron transport and ATP synthesis. What would you expect to observe in their mitochondria?

Accepted Answer

Electron transport and O2 consumption continue, but ATP synthesis stops.

Question 15

Which of the following best describes the function of flavoproteins in the electron transport chain?

Accepted Answer

Flavoproteins use FAD or FMN as prosthetic groups and transfer both electrons and protons.

Question 16

Which of the following is a correct sequence of electron carriers in the electron transport chain?

Accepted Answer

NADH → FMN → Fe-S → CoQ → cytochrome b → cytochrome c1 → cytochrome c → cytochrome a → cytochrome a3 → O2

Question 17

Which of the following best explains the role of the Fe-Cu center in cytochrome c oxidase?

Accepted Answer

It keeps O2 bound to the complex until it has picked up four electrons and four protons, releasing two water molecules.

Question 18

Which of the following respiratory complexes is involved in the Q cycle and pumps 4 protons across the membrane per electron pair?

Accepted Answer

Complex III

Question 19

If a mutation prevents the formation of semiquinone (CoQH) in the Q cycle, which process would be most directly affected?

Accepted Answer

Transfer of electrons from CoQH2 to cytochrome c1 and cytochrome b

Ch 10b - Electron Transport Chain and Oxidative Phosphorylation

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