Chapter 18- Electron Transport Chain

The stoichiometric relationship of ATP synthesis to ______ is referred to as the P/O ratio. Entry field with correct answer shuttle matrix respiration copper heme

respiration

Electrons from cytosolic NADH are transferred to the matrix via electron ______ systems.

shuttle

The cytochromes within complex III all contain _____ groups.

heme

Assume that one mol of phosphoenol pyruvate is completely catabolized under aerobic conditions to CO2 and H2O. What is the net yield of ATP (or equivalents) that can be expected from this? (Assume that re-oxidation of NADH via the electron transport chain yields the equivalent of 3 ATP, and that re-oxidation of FADH2 yields 2 ATP.) Entry field with correct answer 16 mol ATP 13 mol ATP 15 mol ATP 12 mol ATP

16 mol ATP

Approximately how many ATP molecules are synthesized from the oxidation of 1 NADH? Entry field with correct answer 1 1.5 2 2.5 3

2.5

Based on the estimation presented in the chapter, how many ATP per glucose are synthesized by the aerobic metabolism in eukaryotes? Entry field with correct answer 2 4 32 38 60

32

In the electron transport chain, FMN can adopt ____ oxidation state(s) and is capable of accepting or donating ____ electron(s). Entry field with correct answer 2; 2 2; 1 or 2 3; 2 3; 1 or 2 3; 1

3; 1 or 2

Oligomycin is an inhibitor of proton transfer by ATP synthase. Which of the following would occur in response to administration of oligomycin? Entry field with correct answer A. An increase in CO2 production. B. A decrease in the rate of QH2 oxidation. C. Uncoupling electron transport from ATP synthesis. Both A and B are correct. Both B and C are correct.

A decrease in the rate of QH2 oxidation. During electron transport Q undergoes cyclic reduction to QH2 followed by oxidation to Q. When ATP synthesis is inhibited the rate of electron transport is inhibited, and so the rate of oxidation of QH2 will decrease.

Why does re-oxidation of FADH2 via the electron transport chain ultimately produce fewer molecules of ATP than the re-oxidation of NADH? Entry field with correct answer A smaller H+ gradient is generated when FADH2 is oxidized compared to that generated by the oxidation of NADH. Electrons from NADH do not pass through complex II. A larger H+ gradient is generated when FADH2 is oxidized compared to that generated by the oxidation of NADH. Electrons from FADH2 do not pass through complex II.

A smaller H+ gradient is generated when FADH2 is oxidized compared to that generated by the oxidation of NADH.

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? Entry field with correct answer ATP production would be impaired due to the uncoupling of oxidative phosphorylation from electron transport. ATP production would be reduced due to inhibition of the CoQ subunit of ATP synthase. ATP production would be reduced due to a decrease in the number of protons pumped out of the mitochondrial matrix. ATP production would be halted completely due to the block in electron transport through the electron transport chain. ATP production would be maintained at the normal rate due to functional overlap between Complex I and Complex II.

ATP production would be reduced due to a decrease in the number of protons pumped out of the mitochondrial matrix.

In a preparation of isolated mitochondria, the magnitude of the H+ ion concentration gradient across the inner mitochondrial membrane can be increased by adding acid to the medium. What would be the effect of this increase on the rate of ATP synthesis in coupled mitochondria? Entry field with correct answer ATP synthesis would decrease. ATP synthesis would be unaffected. ATP synthesis would increase.

ATP synthesis would be unaffected.

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? Entry field with correct answer Add a second blocking agent to interfere with either Complex I or Complex II along with the poison. Add an artificial electron donor along with the poison. Add an uncoupling agent along with the poison. Any of the above would allow differentiation between these two possibilities. None of the above will help distinguish between these two possibilities.

Add an uncoupling agent along with the poison.

Which of the following accurately describe(s) how the rate of re-oxidation of FADH2 varies in mitochondria? Entry field with correct answer A. Re-oxidation is fastest when ATP synthase is inactive. B. Re-oxidation is increased in active muscle, decreased in inactive muscle. C. Re-oxidation is fastest when the concentration of ADP in the mitochondria is low. Both A and C are true. A, B and C are true.

B. Re-oxidation is increased in active muscle, decreased in inactive muscle.

Why is the exchange of ATP for ADP by the ADP-ATP translocator electrogenic? Entry field with correct answer Because the concentration of ATP is much greater than that of ADP in the matrix Because the concentration of ATP is much less than that of ADP in the matrix Because the net charge of ATP is more negative than that of ADP Because the net charge of ATP is more positive than that of ADP

Because the net charge of ATP is more negative than that of ADP

Which of the prosthetic groups listed can accept or donate either one or two electrons due to the stability of the semiquinone state? Entry field with correct answer cytochrome c NADH CoQ [2Fe-2S] Rieske center

CoQ

Electrons from FADH2 are delivered to ____ and electrons from NADH are delivered to ____ of the electron transport chain. Entry field with correct answer Complex I; Complex II Complex I; Complex III Complex II; Complex III Complex II; Complex I Complex I; Complex IV

Complex II; Complex I

Which complexes of the electron transport chain have FeS centers? Entry field with correct answer Complexes I, II, and III Complexes I, II, and IV Complexes II, III, and IV Complexes I, III, and IV

Complexes I, II, and III

Which one of the following is FALSE with respect to the chemiosmotic-coupling mechanism of oxidative phosphorylation? Entry field with correct answer Complexes I, II, and IV, pump out electrons during their redox reactions creating an electrochemical potential across the membrane. Coenzyme Q and cytochrome c are mobile electron transport components. The inner mitochondrial membrane is intact and impermeable to most molecules. During electron transport, oxygen is reduced to water in the mitochondrial matrix. The flow back of protons through ATP synthase "drives" the production of ATP.

Complexes I, II, and IV, pump out electrons during their redox reactions creating an electrochemical potential across the membrane.

Which of the following best describes the function of cytochrome c oxidase? Entry field with correct answer Cytochrome c oxidase oxidizes four consecutive cytochrome c molecules, via one-electron transfers, while simultaneously reducing one O2 to two H2O. Cytochrome c oxidase oxidizes two consecutive cytochrome c molecules, via two-electron transfers, while simultaneously reducing one O2 to two H2O. Cytochrome c oxidase oxidizes four consecutive cytochrome c molecules, via one-electron transfers, while simultaneously reducing two O2 to two H2O. Cytochrome c oxidase oxidizes two consecutive cytochrome c molecules, via two- electron transfers, while simultaneously reducing two O2 to two H2O.

Cytochrome c oxidase oxidizes four consecutive cytochrome c molecules, via one-electron transfers, while simultaneously reducing one O2 to two H2O.

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. Entry field with correct answer I, II, III, IV I, II, III II, III, IV III only IV only

I, II, III Blocks electron transport at complex 1

If the transfer of electrons in tightly coupled mitochondria is inhibited between complex III and complex IV which of the following will occur? Entry field with correct answer Electron transfer from NADH will stop. The synthesis of ATP will increase. Oxygen consumption will increase. The H+ ion concentration gradient will be dissipated.

Electron transfer from NADH will stop. If the electron transport chain is inhibited at any point, transfer of electrons between all components of the chain ceases. Under these conditions, the re-oxidation of NADH ceases.

Which of the following statements best describes why electrons from FADH2 moving through the electron transport chain contribute less to the proton gradient than electrons from NADH? Entry field with correct answer FADH2 has a lower reduction potential than NADH and therefore its electrons must enter the electron transport chain downstream of NADH. FADH2 is a prosthetic group. FADH2 has a higher reduction potential than NADH and therefore its electrons must enter the electron transport chain downstream of NADH. FADH2 passes its electrons directly to complex III therefore bypassing a portion of the electron transport chain.

FADH2 has a higher reduction potential than NADH and therefore its electrons must enter the electron transport chain downstream of NADH.

Which of the following correctly ranks redox centers found in Complex I from lower to higher potential? A correct answer will contain redox centers which are found in only Complex I and will also rank those redox centers in order of lower to higher reduction potential. Entry field with correct answer FMN, Heme b560, [2Fe-2S], CoQ ubiquinone, [4Fe-4S], [2Fe-2S], FMN FMN, [2Fe-2S], [4Fe-4S] Heme b560, [2Fe-2S], [4Fe-4S], FAD FAD, [2Fe-2S], [4Fe-4S], Heme b560

FMN, [2Fe-2S], [4Fe-4S]

Which statement(s) concerning the mitochondrial F0F1 ATP synthase is FALSE? I. The F1 subunit includes rotating sets of 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. Entry field with correct answer I, II, III II, III I only III only None of the options (I - III) is false.

I only

The electrons formed from the aerobic oxidation of glucose are I. ultimately transferred to O2 after several other transfer reactions. II. transferred to the coenzymes NAD+ and FAD. III. directly transferred to O2 during the citric acid cycle. IV. transferred to succinate and arachidonic acid. Entry field with correct answer I only II only I, II II, III, IV I, II, III

I, II

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. Entry field with correct answer I, II, III, IV I, II II, III, IV I, IV II, IV

I, II

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. Entry field with correct answer I, II, III, IV I, II, III II, III, IV II, III III only

I, II, III

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. Entry field with correct answer I, III I, III, IV. I, II II, IV I, II, III, IV

I, II, III, IV

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. Entry field with correct answer I, II, IV II, III, IV II, III I, III, IV II, IV

I, III, IV

An animal with the UCP-1 protein would I. generate excess heat. II. have lower energy levels. III. generate ATP efficiently via oxidative phosphorylation. Entry field with correct answer I I, II I, II, III I, III II, III

I. generate excess heat. II. have lower energy levels.

ATP forms (is produced) I. upon transition from the loose to the tight form of the and subunit complex of ATP synthase. II. as a result of the flux of electrons through the channel formed by Fo III. as a result of the positive ions pumped into the matrix of the mitochondrion. Entry field with correct answer I, II, III II, III I, III I only II only

I. upon transition from the loose to the tight form of the and subunit complex of ATP synthase.

Which of the following is TRUE regarding the complexes within the electron transport system? I. Complex II contributes twice as many protons to the gradient than Complex I II. Inhibition of Complex II would decrease the total number of electrons moving through the electron transport chain. III. Inhibition of Complex II would not alter the amount of free energy generated from electrons originating from NADH. IV. Complex I can accept electrons with higher potential than Complex II is able to accept. Entry field with correct answer I, II, III, IV I, II, III II only II, III III, IV

II, III

___ the gradient with the synthesis of ATP via oxidative phosphorylation. I. The Fo portion of ATP synthase II. Thermogenin uncouples III. 2,4-dinitrophenol (DNP) dissipates IV. An ionophore capable of transporting potassium ions across the membrane Entry field with correct answer I, II, III, IV II, III, IV II, III II only I, IV

II, III

Which of the following statements about the mitochondrial inner membrane is TRUE? I. The inner membrane is permeable to CO2, H2O, and small ions. II. The inner membrane contains several transport proteins and membrane bound enzymes. III. In general, a higher inner membrane surface area correlates to a higher rate of respiration. IV. The number of cristae reflects the respiratory activity of the cell. Entry field with correct answer I, II, III, IV I, II, III II only II, III, IV III, IV

II, III, IV

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.-. Entry field with correct answer I only I, II III only III, IV I, III, IV

III only

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. Entry field with correct answer I, II II only II, III III only IV only

III. This complex pumps protons from the matrix to the intermembrane space.

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. Entry field with correct answer I, III, IV I, III II, III, IV I only III only

III.inhibits electron transport which stops consumption of oxygen Cyanide stops electron transport at complex 4

Complexes I and II each transfer electrons to ______.

coenzyme Q

Which property is necessary for a molecule such as DNP to function as a typical uncoupler of oxidative phosphorylation? Entry field with correct answer Hydrophilic weak acid Hydrophilic strong acid Lipophilic alcohol Lipophilic weak acid

Lipophilic weak acid

What is the path of electrons from NADH through the electron transport chain? Entry field with correct answer NADH, Complex II, Q, Complex III, CytC, Complex IV, O2 NADH, Complex I, Q, Complex III, CytC, Complex IV, O2 NADH, Complex I, Q, Complex II, CytC, Complex IV, O2 NADH, Complex I, Q, Complex III, CytB, Complex IV, O2

NADH, Complex I, Q, Complex III, CytC, Complex IV, O2

Why are P/O ratios not necessarily integral? Entry field with correct answer P/O ratios depend upon the source of the mitochondria. Under some circumstances more protons are necessary for ATP synthesis. P/O ratios depend upon the ratios of the individual complexes. Not all of the protons translocated will be used for ATP synthesis, in part due to proton leakage.

Not all of the protons translocated will be used for ATP synthesis, in part due to proton leakage.

What is the correct order for the following substances in terms of reduction potential, greatest to least? Entry field with correct answer NAD+ > CoQ >FAD > O2 O2 > CoQ >FAD > NAD+ NAD+ > FAD > CoQ > O2 O2 > NAD+ > CoQ >FAD

O2 > CoQ >FAD > NAD+

Oligomycin is a substance that prevents the ATP synthesis reaction in oxidative phosphorylation, and 2,4-dinitrophenol is an uncoupling agent. In the presence of oligomycin, what would be the effect of adding 2,4-dinitrophenol? Entry field with correct answer Electron transfer will be blocked. O2 consumption will increase. Production of water will decrease. Oxidative phosphorylation will occur.

O2 consumption will increase.

Which of the following molecules can reduce the proton electrochemical gradient in mitochondria? Entry field with correct answer O2 Succinate dehydrogenase. NADH Cytochrome C. Pi-H+ symporter.

Pi-H+ symporter.

What is the net result of the successive reactions catalyzed by superoxide dismutase and catalase? Entry field with correct answer conversion of the free radical O2· to H2O2, which is converted to water and O2 conversion of the free radical O2· to H2O2, which is converted to water and GSSG and water conversion of the free radical O2· to peroxide, which is converted to CO2 and water conversion of the free radical O2· to carbon dioxide and water none of the above

conversion of the free radical O2· to H2O2, which is converted to water and O2

Cytochrome c oxidase contains four redox centers: two heme groups and two redox centers containing_______.

copper

Which of the following statements regarding oxidative phosphorylation is TRUE? Entry field with correct answer The addition of an uncoupler decreases the rate of reoxidation of NADH and FADH2, therefore decreasing the rate of the citric acid cycle. The smaller the electrochemical gradient, the faster the Pi- H+ symporter works. Proton transfer through the Fo subunit of ATP synthase is required in order for ATP synthesis to occur. The rate of ATP synthesis depends on the magnitude of the proton electrochemical gradient.

Proton transfer through the Fo subunit of ATP synthase is required in order for ATP synthesis to occur.

In a newly discovered electron transport complex a researcher has identified the redox center Fe-S, cytochrome c, and coenzyme Q. The researcher also knows that this complex ultimately passes its electrons to oxygen. What is most likely the redox center which completes this task? Entry field with correct answer Fe-S 2Fe-2S coenzyme Q cytochrome c None of the above

cytochrome c

The electron transport chain and the ATP synthase are effectively coupled. Which of the following statements best describes how this occurs? Entry field with correct answer The electron transport chain re-oxidizes reduced cofactors. The electron transport chain generates an electrochemical gradient that drives the production of ATP. ATP synthase utilizes oxidized cofactors. Through a series of conformational changes, ATP synthase generates ATP.

The electron transport chain generates an electrochemical gradient that drives the production of ATP.

The consumption of acetyl-CoA by the citric acid cycle is DECREASED under which of the following conditions? Entry field with correct answer The concentration of oxaloacetate is high. NADH is rapidly re-oxidized via the electron transport chain. The concentration of NAD+ is high. The mitochondrial ATP synthase is inactive.

The mitochondrial ATP synthase is inactive. Oxidative phosphorylation is coupled. This means that when ATP synthase is inactive, the rate of electron transport decreases and the concentration of NADH and FADH2 increases. The citric acid cycle is inhibited by NADH and FADH2.

Relative to the electron transport chain, which best describes the reduction of one molecule of oxygen to two molecules of water? Entry field with correct answer This process requires input of four electrons and four protons, and takes place at a binuclear center, cytochrome a3-Cu_B. This process requires input of two electrons and two protons, and takes place at a binuclear center, cytochrome a3-Cu_B. This process requires input of two electrons and two protons, and takes place at a single metal center, cytochrome a3. This process requires input of four electrons and four protons, and takes place at a single metal center, cytochrome a3.

This process requires input of four electrons and four protons, and takes place at a binuclear center, cytochrome a3-Cu_B.

Which one of the following is NOT associated with electron transport? Entry field with correct answer heme group flavin mononucleotide iron-sulfur clusters coenzyme A coenzyme Q

coenzyme A

The inner mitochondrial membrane divides the mitochondrion into the inner membrane space and the ______.

matrix

All of the following inhibit electron transport EXCEPT Entry field with correct answer oxaloacetate rotenone anitimycin A cyanide All of the above inhibit electron transport

oxaloacetate

Some degenerative diseases, such as Parkinson's disease, are associated with ______ damage to ______. Entry field with correct answer oxidative; mitochondria thermogenic; mitochondria free radical; nuclei oxidative; nuclei thermogenic; nuclei

oxidative; mitochondria

Bacteria carry out electron transport in the _____.

plasma membrane

Bacteriorhodopsin is an example of a light-driven ______

proton pump

Phosphate (Pi) is transported into the mitochondria from the cytosol by a phosphate carrier which is driven by the Entry field with correct answer hydrolysis of ATP. simultaneous transport of H+ into the mitochondrion. simultaneous transport of ADP into the mitochondrion. simultaneous transport of H+ out of the mitochondrion. simultaneous transport of ATP out of the mitochondrion.

simultaneous transport of H+ into the mitochondrion.

In the electron transport chain, electrons are passed from redox center to redox center ____. Entry field with correct answer spontaneously due to the redox potential gradient. in an ATP dependent fashion. as a result of the addition of free energy. as a result of the proton gradient. with the assistance of a carrier protein.

spontaneously due to the redox potential gradient.

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, Entry field with correct answer the coenzyme Q pool will be found in the reduced state, and cytochrome c will be found in the oxidized state. the coenzyme Q pool will be found in the oxidized state, and cytochrome c will be found in the reduced state. the coenzyme Q pool will be found in both oxidized & reduced states, and cytochrome c will be found in only one state. the coenzyme Q pool will be found in only one state, and cytochrome c will be found in both oxidized & reduced states. both the coenzyme Q pool and cytochrome c will be found in both oxidized & reduced states.

the coenzyme Q pool will be found in the reduced state, and cytochrome c will be found in the oxidized state.

The structure of ATP synthase changes in conformation as a result of Entry field with correct answer the rotation of the a and B subunits. the rotation of the B subunit. the rotation of ATP. the rotation of the gamma subunit. all of the above.

the rotation of the gamma subunit.

One method used by newborn mammals to generate heat is referred to as nonshivering thermogenesis. This method utilizes a protein channel called ________ which is present in high levels inside the mitochondria of _____tissue. Entry field with correct answer thermogenin; muscle UCP-1; muscle thermogenin; brown adipose UCP-1; white adipose UCP-2; brown adipose

thermogenin; brown adipose

According to the proposed reaction sequence presented in the chapter, cytochrome c oxidase obtains a fourth electron from a ____ residue adjacent to the heme a3-ligated O2, thus forming a transient radical. Entry field with correct answer serine threonine tyrosine phenylalanine tryptophan

tyrosine

Protons moving through a transmembrane channel by "jumping" through an arrangement of hydrogen-bonded groups are described as moving through a proton ______.

wire