Question 1

A poison that prevents the transfer of electrons from the last [Fe-S] cluster of Complex I to coenzyme Q is added to a suspension of actively respiring mitochondria.Which of the following will be observed?

Accepted Answer

DC) ATP production would be reduced due to a decrease in the number of protons pumped out of the mitochondrial matrix. This is because the blockage of electron transfer from Complex I to coenzyme Q would reduce the proton gradient necessary for ATP synthesis via oxidative phosphorylation.D) ATP production would be halted completely due to the block in electron transport through the electron transport chain. This statement is partially correct in the context that the blockage at Complex I would severely impair the electron transport chain's function, but it might not halt ATP production completely as electrons can still enter the electron transport chain via Complex II, albeit at a reduced efficiency.

Question 2

Consider the following half-reactions: $\varepsilon$^o' = -0.315 V NAD⁺ + H⁺ + 2 e^- $\leftrightarrow$ NADH $\varepsilon$^o' = 0.815 V 1/2 O₂ + 2 H⁺+ 2 e^-$\leftrightarrow$ H₂O What is the $\varepsilon$^o'for the following redox equation? O₂ + 2 NADH + 2 H⁺ $\to$ 2 H₂O + 2 NAD⁺

Accepted Answer

The standard electrode potential for a redox reaction can be calculated by subtracting the standard reduction potential of the reductant (which gets oxidized) from the standard reduction potential of the oxidant (which gets reduced). Here, the NADH is being oxidized (standard reduction potential = -0.315 V) and the 1/2 O2 is being reduced (standard reduction potential = 0.815 V). Therefore, the overall standard electrode potential is 0.815 V - (-0.315 V) = 1.130 V.

Question 3

Which of the following statements is(are)TRUE about oxidative phosphorylation?
(I)Electron transport provides energy to pump protons into the intermembrane space.
(II)An electrochemical gradient is formed across the inner mitochondrial membrane.
(III)Potassium and sodium ions form an ionic gradient across the inner mitochondrial membrane.
(IV)Complexes I,II,III,IV actively transport protons into the intermembrane space during electron transport.

Accepted Answer

Statement I is true as electron transport chain provides energy to pump protons into the intermembrane space.
Statement II is true as an electrochemical gradient of protons is formed across the inner mitochondrial membrane due to the pumping of protons.
Statement III is false as potassium and sodium ions do not contribute to the gradient formed during oxidative phosphorylation.
Statement IV is true for complexes I, III, and IV, but not for complex II. Complex II does not transport protons, it only passes electrons to coenzyme Q. Therefore, the correct answer is option B.

Question 4

The rate of oxidative phosphorylation (I)is regulated by the availability of ADP and P_i. (II)is reduced when the ratio of [NADH]/[NAD⁺] is high. (III)increases with a higher concentration of reduced cytochrome c (IV)is regulated by activity of the ADP-ATP translocator.

Accepted Answer

I is true, as the rate of oxidative phosphorylation is regulated by the availability of ADP and Pi.
II is also true, as the rate of oxidative phosphorylation reduces when the ratio of [NADH]/[NAD+] and [NADPH]/[NADP+] is high.
III is true, as the rate of oxidative phosphorylation increases with a higher concentration of reduced cytochrome c.
IV is true, as the rate of oxidative phosphorylation is regulated by activity of the ADP-ATP translocator.

Question 5

Which of the following is TRUE regarding heme proteins?
(I)Heme groups are capable of transferring electrons across large distances provided that some molecular network exists as a "path."
(II)Heme groups are often buried in protein structure because the protein protects the heme and prevents it from indiscriminately transferring electrons.
(III)The rate of electron transfer from a reduced heme is physiologically significant.
(IV)Heme groups are often differentiated by their absorption spectrum.

Accepted Answer

Heme proteins have several key characteristics: (I) Heme groups can indeed transfer electrons across distances if there is a molecular pathway, facilitating processes like respiration and photosynthesis. (II) Heme groups are typically buried within protein structures to protect them and prevent uncontrolled electron transfer, which could generate harmful radicals. (III) The electron transfer rate from reduced heme is significant for physiological functions, impacting processes like oxygen transport and enzymatic reactions. (IV) Heme groups can be distinguished by their unique absorption spectra, which is crucial for their identification and study in various biological contexts.

Question 6

Which of the following best describes the function of cytochrome c oxidase?

Accepted Answer

Cytochrome c oxidase oxidizes four cytochrome c molecules via one-electron transfers and reduces one O2 molecule to two H2O molecules.

Question 7

Which of the following are TRUE statements regarding the structure of ATP synthase?

Accepted Answer

The answer of Which of the following are TRUE statements...

Question 8

What is the net result of the successive reactions catalyzed by superoxide dismutase and catalase?

Accepted Answer

Superoxide dismutase converts the free radical O₂F1F1F1S1^F1F1F10 to H₂O₂, which is then converted to water and O₂ by catalase.

Question 9

In theory how many protons could be pumped under standard state conditions by Complex III per mol of CoQ oxidized,considering the following information? (NOTE: mt = mitochondria) Coenzyme Q + 2H⁺ + 2 e^- → coenzyme QH₂ $\varepsilon$^o ' ≈ 0.040 V Cytochrome c (Fe³⁺)+ e^- → cytochrome c (Fe²⁺)$\varepsilon$^o' ≈ 0.270 V H⁺ (outside mt)→ H⁺ (inside mt)∆G ≈ -20kJ/mol Faraday constant (F)≈ 100 kJ/Vmol ∆Gº' = -nF∆E₀'

Accepted Answer

The number of protons pumped by Complex III per mole of CoQ oxidized can be estimated using the given standard reduction potentials and the Gibbs free energy change for proton translocation. The difference in standard reduction potentials between cytochrome c and CoQ is 0.270 V - 0.040 V = 0.230 V. Using the equation ∆Gº' = -nF∆Eº', where n is the number of electrons (2 in this case), F is the Faraday constant (100 kJ/Vmol), and ∆Eº' is the difference in standard reduction potentials, we can calculate the Gibbs free energy change for the electron transfer process. Substituting the values, we get ∆Gº' = -2 * 100 kJ/Vmol * 0.230 V = -46 kJ/mol. Given that the translocation of one proton across the mitochondrial membrane has a Gibbs free energy change of about -20 kJ/mol, approximately 46 kJ / 20 kJ/mol ≈ 2.3 protons could be translocated per electron, or about 4.6 protons per two electrons. Therefore, the correct answer is that greater than four protons but less than or equal to six protons could be pumped by Complex III per mole of CoQ oxidized.

Question 10

Which statement concerning Complex II of the electron transport chain is FALSE? (I)This complex oxidizes FADH₂ and reduces coenzyme Q. (II)This complex includes the covalently bound enzyme succinate dehydrogenase. (III)This complex pumps protons from the matrix to the intermembrane space. IV)This complex also oxidizes succinate to fumarate in the citric acid cycle.

Accepted Answer

Complex II does not pump protons from the matrix to the intermembrane space; this is a key difference from other complexes in the electron transport chain.

Question 11

Phosphate (P_i)is transported into the mitochondria from the cytosol by a phosphate carrier which is driven by the

Accepted Answer

The phosphate carrier is driven by the simultaneous transport of H+ into the mitochondrion, creating an electrochemical gradient that drives the transport of Pi into the matrix.

Question 12

Cyclonite is a poison that blocks electron transfer between cytochromes b_L and b_H.When this poison is added to a suspension of isolated mitochondria,and when spectroscopic analysis is performed,

Accepted Answer

Blocking electron transfer between cytochromes b_L and b_H would prevent the oxidation of coenzyme Q, leading it to accumulate in the reduced state. Cytochrome c, downstream in the electron transport chain, would not receive electrons and thus remain in the oxidized state.

Question 13

The effects of a poison on actively respiring mitochondria are being studied to determine its mode of action.When the poison is added,every component of the electron transport chain is found to be in its reduced form based on spectroscopic analysis,and ATP production ceases entirely.It is reasoned that the poison is either blocking the final transfer of electrons to oxygen or is blocking the ATP synthase.Which of the following experiments will help unravel this dilemma?

Accepted Answer

Adding an uncoupling agent along with the poison will help to distinguish between two possibilities as it will allow to bypass ATP synthase and electron transfer to oxygen. If the addition of the uncoupling agent can restore electron transport and reduce the component of the electron transport chain, it would mean that the poison is blocking ATP synthase and not the final transfer of electrons to oxygen. On the other hand, if no restoration is seen, it would mean the poison is blocking the final transfer of electrons to oxygen. Adding a second blocking agent or an artificial electron donor would not help to differentiate between these two possibilities.

Question 14

Cyanide (CN^-) (I)inhibition can be restored by addition of succinate. (II)inhibition can be restored by addition of cytochrome c. (III)inhibits electron transport which stops consumption of oxygen. (IV)blocks transfer of electrons from CoQ to Complex III.

Accepted Answer

Cyanide inhibits electron transport by binding to cytochrome c oxidase (Complex IV), preventing oxygen consumption.

Question 15

In the electron transport chain,FMN can adopt ____ oxidation state(s)and is capable of accepting or donating ____ electron(s).

Accepted Answer

FMN (Flavin mononucleotide) in the electron transport chain can adopt three oxidation states: oxidized, semiquinone (partially reduced), and fully reduced. It is capable of accepting or donating one or two electrons, making it versatile in electron transfer processes.

Question 16

Rotenone and amytal
(I)inhibition can be restored by addition of succinate
(II)inhibition can be restored by addition of cytochrome c.
(III)blocks consumption of oxygen.
(IV)blocks transfer of electrons from CoQ to Complex III.

Accepted Answer

Rotenone and amytal are inhibitors of Complex I in the electron transport chain. 
(I) The addition of succinate bypasses Complex I and donates electrons downstream to Complex II, restoring electron flow and ATP production. 
(II) Cytochrome c is not involved in Complex I, so its addition would not restore function.
(III) Rotenone and amytal block the transfer of electrons in Complex I, leading to a buildup of electron carriers downstream and a decrease in oxygen consumption. 
(IV) Rotenone and amytal specifically block the transfer of electrons from CoQ to Complex III, leading to a buildup of CoQ and a decrease in electron flow downstream.

Question 17

Based on the information in the chapter,which of the following is TRUE regarding Complex III? (I)A large portion of Complex III dissociates from the membrane bound portion of the complex. (II)Complex III contains three identical cytochrome redox centers. (III)The Q cycle allows stepwise reoxidation of the two electrons from CoQH₂. (IV)A change in conformation of iron sulfur protein (ISP)ensures that the Reiske center is reduced preferentially by CoQ^.-.

Accepted Answer

From the information provided in the chapter, only statement III is true regarding Complex III. The Q cycle in Complex III allows for the stepwise reoxidation of the two electrons from CoQH2 to cytochrome c, and this is an essential process in the electron transport chain. Statements I and IV are both false, and statement II is partially incorrect as Complex III contains three cytochrome redox centers, but they are not necessarily identical.

Question 18

Antimycin A
(I)inhibition can be restored by addition of succinate.
(II)inhibition can be restored by addition of cytochrome c.
(III)blocks consumption of oxygen.
(IV)blocks transfer of electrons from CoQ to Complex III.

Accepted Answer

Antimycin A blocks transfer of electrons from CoQ to Complex III, which means that electrons cannot be transferred to cytochrome c. Therefore, addition of cytochrome c cannot restore inhibition. However, inhibition can be restored by addition of succinate, which allows electrons to be directly added to Complex II and bypass Complex III. Antimycin A also blocks consumption of oxygen, which is a consequence of the blockage in electron transfer. Therefore, choices II, III, and IV are correct, while choice I is incorrect. Thus, the best choice is C.

Question 19

Which statement(s)concerning the mitochondrial F₀F₁ ATP synthase is FALSE? (I)The F₁ subunit includes rotating sets of $\alpha$$\beta$ dimers. (II)The F₀ subunit includes a ring of between 9 and 12 proton-carrying polypeptides. (III)The F₁ subunit undergoes a series of conformational changes throughout the course of reaction.

Accepted Answer

The statement about the F1 subunit including rotating sets of αβ dimers is false. The F1 subunit of ATP synthase is involved in ATP synthesis, but it does not include rotating sets of αβ dimers. Instead, it contains a stationary part made of α and β subunits where ATP synthesis occurs, and a rotating γ subunit. The rotation is driven by the flow of protons through the F0 subunit, which is the part that includes a ring of proton-carrying polypeptides.

Question 20

Which of the prosthetic groups listed can accept or donate either one or two electrons due to the stability of the semiquinone state?

Accepted Answer

CoQ (coenzyme Q) is the only prosthetic group listed that can accept or donate either one or two electrons due to the stability of the semiquinone state. This property makes it a versatile electron carrier in the electron transport chain. Cytochrome c and the iron-sulfur centers listed (2Fe-2S and Rieske center) can only accept or donate one electron at a time, while NADH can only donate two electrons at a time.

Quiz 18: Electron Transport and Oxidative Phosphorylation

A poison that prevents the transfer of electrons from the last [Fe-S] cluster of Complex I to coenzyme Q is added to a suspension of actively respiring mitochondria.Which of the following will be observed?

Consider the following half-reactions: $\varepsilon$ ^o' = -0.315 V NAD⁺ + H⁺ + 2 e^- $\leftrightarrow$ NADH $\varepsilon$ ^o' = 0.815 V 1/2 O₂ + 2 H⁺+ 2 e^- $\leftrightarrow$ H₂O What is the $\varepsilon$ ^o'for the following redox equation? O₂ + 2 NADH + 2 H⁺ $\to$ 2 H₂O + 2 NAD⁺

The rate of oxidative phosphorylation (I) is regulated by the availability of ADP and P_i. (II) is reduced when the ratio of [NADH]/[NAD⁺] is high. (III) increases with a higher concentration of reduced cytochrome c (IV) is regulated by activity of the ADP-ATP translocator.

Which of the following best describes the function of cytochrome c oxidase?

Which of the following are TRUE statements regarding the structure of ATP synthase?

What is the net result of the successive reactions catalyzed by superoxide dismutase and catalase?

Phosphate (P_i) is transported into the mitochondria from the cytosol by a phosphate carrier which is driven by the

Cyclonite is a poison that blocks electron transfer between cytochromes b_L and b_H.When this poison is added to a suspension of isolated mitochondria,and when spectroscopic analysis is performed,

Cyanide (CN^-) (I) inhibition can be restored by addition of succinate. (II) inhibition can be restored by addition of cytochrome c. (III) inhibits electron transport which stops consumption of oxygen. (IV) blocks transfer of electrons from CoQ to Complex III.

In the electron transport chain,FMN can adopt oxidation state(s) and is capable of accepting or donating electron(s) .

Rotenone and amytal (I) inhibition can be restored by addition of succinate (II) inhibition can be restored by addition of cytochrome c. (III) blocks consumption of oxygen. (IV) blocks transfer of electrons from CoQ to Complex III.

Antimycin A (I) inhibition can be restored by addition of succinate. (II) inhibition can be restored by addition of cytochrome c. (III) blocks consumption of oxygen. (IV) blocks transfer of electrons from CoQ to Complex III.

Which of the prosthetic groups listed can accept or donate either one or two electrons due to the stability of the semiquinone state?

Quiz 18: Electron Transport and Oxidative Phosphorylation

A poison that prevents the transfer of electrons from the last [Fe-S] cluster of Complex I to coenzyme Q is added to a suspension of actively respiring mitochondria.Which of the following will be observed?

Consider the following half-reactions: ε\varepsilonε o' = -0.315 V NAD+ + H+ + 2 e- ↔\leftrightarrow↔ NADH ε\varepsilonε o' = 0.815 V 1/2 O2 + 2 H+ + 2 e- ↔\leftrightarrow↔ H2O What is the ε\varepsilonε o'for the following redox equation? O2 + 2 NADH + 2 H+ →\to→ 2 H2O + 2 NAD+

The rate of oxidative phosphorylation (I) is regulated by the availability of ADP and Pi. (II) is reduced when the ratio of [NADH]/[NAD+] is high. (III) increases with a higher concentration of reduced cytochrome c (IV) is regulated by activity of the ADP-ATP translocator.

Which of the following best describes the function of cytochrome c oxidase?

Which of the following are TRUE statements regarding the structure of ATP synthase?

What is the net result of the successive reactions catalyzed by superoxide dismutase and catalase?

Phosphate (Pi) is transported into the mitochondria from the cytosol by a phosphate carrier which is driven by the

Cyclonite is a poison that blocks electron transfer between cytochromes bL and bH.When this poison is added to a suspension of isolated mitochondria,and when spectroscopic analysis is performed,

Cyanide (CN-) (I) inhibition can be restored by addition of succinate. (II) inhibition can be restored by addition of cytochrome c. (III) inhibits electron transport which stops consumption of oxygen. (IV) blocks transfer of electrons from CoQ to Complex III.

In the electron transport chain,FMN can adopt ____ oxidation state(s) and is capable of accepting or donating ____ electron(s) .

Rotenone and amytal (I) inhibition can be restored by addition of succinate (II) inhibition can be restored by addition of cytochrome c. (III) blocks consumption of oxygen. (IV) blocks transfer of electrons from CoQ to Complex III.

Antimycin A (I) inhibition can be restored by addition of succinate. (II) inhibition can be restored by addition of cytochrome c. (III) blocks consumption of oxygen. (IV) blocks transfer of electrons from CoQ to Complex III.

Which of the prosthetic groups listed can accept or donate either one or two electrons due to the stability of the semiquinone state?

The rate of oxidative phosphorylation (I) is regulated by the availability of ADP and P_i. (II) is reduced when the ratio of [NADH]/[NAD⁺] is high. (III) increases with a higher concentration of reduced cytochrome c (IV) is regulated by activity of the ADP-ATP translocator.

Phosphate (P_i) is transported into the mitochondria from the cytosol by a phosphate carrier which is driven by the

Cyclonite is a poison that blocks electron transfer between cytochromes b_L and b_H.When this poison is added to a suspension of isolated mitochondria,and when spectroscopic analysis is performed,

Cyanide (CN^-) (I) inhibition can be restored by addition of succinate. (II) inhibition can be restored by addition of cytochrome c. (III) inhibits electron transport which stops consumption of oxygen. (IV) blocks transfer of electrons from CoQ to Complex III.

In the electron transport chain,FMN can adopt oxidation state(s) and is capable of accepting or donating electron(s) .