Deck 14: Electron Transport and Oxidative Phosphorylation

Question 1

ATP synthase is located in the of the mitochondrion.

A) outer membrane
B) inner membrane
C) matrix
D) intermembrane space

Answer 1

inner membrane

Question 2

The inner mitochondrial membrane contributes to the formation of a proton gradient mainly because it

A) contains ATP synthase complex.
B) is the location of specific transporter proteins.
C) is a barrier to protons.
D) is not rich in proteins.
E) is rich in proteins.

Answer 2

is a barrier to protons.

Question 3

What is the Gibbs free energy change, △G, across a membrane with a pH difference of 0.50 and a membrane potential of -0.10 V at 310 K? R = 8.315 J K^-1 mol^-1; F = 96,485 J V^-1 mol^-1)

A) -6.85 kJ mol^-1
B) -12.6 kJ mol^-1
C) 38.6 kJ mol^-1
D) 57.9 kJ mol^-1

Answer 3

-12.6 kJ mol^-1

Question 4

In the respiratory electron transport chain electrons are passed from .

A) NADH and QH₂ to O₂
B) O₂ to NAD⁺ and Q
C) O₂ to NADH
D) ATP to O₂

Question 5

Which of the following substances can freely pass through the inner mitochondrial matrix?

A) H⁺
B) acetate
C) CO₂
D) ATP

Question 6

Oxidative phosphorylation requires all of the items listed below except

A) ATP synthase in the correct position in the membrane.
B) enzyme complexes embedded in a membrane.
C) the flow of electrons from NADH and QH₂ in the membrane.
D) a matrix more positively charged than the intermembrane space.
E) a terminal electron acceptor which is H₂O in mitochondria.

Question 7

At one time the uncoupler 2,4-dinitrophenol was used as a weight reducing drug. Its side-effects, including death, resulted in its discontinued use. How could this drug cause weight loss?

A) The uncoupler allows the oxidation of fats from adipose tissue without the production of ATP. This allows the oxidation to proceed continuously and use up the fats.
B) The uncoupler causes ATP to be produced at a much higher rate than normal and this causes weight loss.
C) The uncoupler inhibits the transport of pyruvate into the matrix of the mitochondria. Fats are then degraded to glycerol and subsequently to pyruvate to provide the necessary energy. Thereby depleting fat stores.
D) The uncoupler is an allosteric activator of ATP synthase. This increases the rate of translocation of H⁺ and the oxidation of fuels, including fats.

Question 8

Which statement is true about two reactions that are coupled?

A) One reaction will normally not occur without the other.
B) One is always exergonic and the other is always endergonic.
C) Only oxidation-reduction reactions can be coupled.
D) Coupled reactions are always driven by the ATP to ADP conversion.

Question 9

The chemiosmotic theory explains

A) the phosphorylation of ADP.
B) the electron transport chain.
C) the differences between inner and outer mitochondrial membranes.
D) the source of energy for formation of mitochondrial ATP.
E) aerobic respiration.

Question 10

The is between the inner and outer membranes of the mitochondria.

A) matrix
B) intermembrane space
C) intracellular fluid
D) ATP synthase complex

Question 11

The chemiosmotic theory is a concept that .

A) the transport of Na⁺ and K⁺ across cell membranes is by active transport
B) explains how transport by facilitated diffusion reaches a saturation limit
C) explains the blood-brain barrier
D) a proton gradient that drives the formation of ATP

Question 12

Which of the following is mismatched?

A) outer mitochondrial membrane - permeable to ions and water
B) inner mitochondrial membrane - permeable to O₂ and CO₂
C) outer mitochondrial membrane - folded into cristae
D) inner mitochondrial membrane - location of ATP synthase
E) matrix - some ATP synthase subunits extend here

Question 13

In the presence of oxygen and in the absence of ADP, what occurs if the uncoupler 2,4-dinitrophenol is added to a suspension of normal mitochondria five minutes after an oxidizable substrate has been added?

A) The substrate will be oxidized until the addition of the 2,4-dinitrophenol, which blocks further oxidation.
B) There is no effect; oxidation of the substrate continues at the same rate before and after the addition of 2,4-dinitrophenol.
C) The substrate cannot be oxidized either with or without 2,4-dinitrophenol unless ADP is also present.
D) Oxidation of the substrate does not occur until the 2,4-dinitrophenol is added. Afterward, oxidation proceeds rapidly until all of the substrate is consumed.

Question 14

The inner membrane of mitochondria is permeable to , but not to .

A) protons; water
B) cations; anions
C) charged molecules; uncharged molecules
D) uncharged molecules; charged molecules

Question 15

In the mitochondria NADH and QH₂ are essentially oxidized by since it is the terminal electron acceptor.

A) carbon dioxide
B) hydrogen peroxide
C) ozone
D) oxygen

Question 16

The enzyme complexes associated with oxidative phosphorylation and the electron transport chain can be classified as proteins.

A) integral membrane
B) peripheral membrane
C) lipid-anchored membrane
D) water-soluble
E) Both A and C

Question 17

For normal mitochondria in the presence of an oxidizable substrate and an uncoupler such as 2,4-dinitrophenol which do you expect?

A) oxygen consumption even in the absence of ADP
B) a rise in temperature to dissipate energy that would otherwise have been used to generate ATP
C) the flow of protons into the mitochondria matrix
D) All of the above
E) None of the above

Question 18

Compare the pH of the mitochondrial matrix and the inner membrane space.

A) The pH is lower in the matrix.
B) The pH in both regions is the same.
C) The pH is lower in the inner membrane space.
D) The comparison of pH varies from moment to moment depending on energy needs of the cell.

Question 19

The protonmotive force is a result of .

A) the flow of electrons from the matrix to the inner membrane space
B) a combination of an electrical potential and a chemical potential
C) the flow of protons within the inner mitochondrial membrane
D) All of the above

Question 20

If the difference in pH across a membrane is 0.60 and the membrane potential is -0.10 V, about what percent of the Gibbs free energy change, △G, is from the pH difference at 37 ^oC? R = 8.315 J K^-1 mol^-1; F = 96,485 J V^-1 mol^-1)

A) 15%
B) 27%
C) 73%
D) 85%

Question 21

The terminal electron acceptor for complex III of the electron transport chain is .

A) Q
B) Fe-S
C) FAD
D) cytochrome c

Question 22

In a series of oxidation-reduction agents, the strongest, weakest) reducing agent has the highest, lowest) reduction potential.

A) strongest; highest
B) strongest; lowest
C) weakest; highest
D) weakest; lowest

Question 23

How many protons are translocated across the inner mitochondrial membrane by complex III for each pair of electrons passing through the electron transport chain?

A) 0
B) 1
C) 2
D) 4

Question 24

Which has the highest reduction potential?

A) NADH
B) complex I
C) complex II
D) O₂

Question 25

Which complex in the electron transport chain does not contribute to the proton gradient?

A) I
B) II
C) III
D) IV
E) V

Question 26

Which complex in the electron transport chain carries electrons from cytochrome c to molecular oxygen, reducing it to water?

A) I
B) II
C) III
D) IV
E) V

Question 27

The ultimate electron acceptor from complex II is .

A) Q
B) QH₂
C) cytochrome c
D) O₂
E) FMN

Question 28

Complex II in the electron transport chain supplies electrons as to the rest of the chain complexes III and IV).

A) FADH₂
B) Fe-S
C) succinate
D) QH₂

Question 29

What is the role of FMN in complex I?

A) Converts a two-electron transfer to a one-electron transfer.
B) Converts a one-electron transfer to a two-electron transfer.
C) Transports four H⁺ across the membrane.
D) None, there is no FMN in complex I.

Question 30

Which statement is false about complex IV?

A) A binuclear center that contains an iron ion and heme-a₃ is the site of the reduction of molecular oxygen to water.
B) Bacterial and eukaryotic forms of complex IV have very similar structures and number of subunits per functional unit.
C) The core structure of the cytochrome c oxidase in complex IV has three conserved subunits.
D) Copper ions shift from a +2 oxidation state to a +1 oxidation state as electrons are passed through the complex.

Question 31

Which is a component of complex I?

A) FAD
B) FMN
C) Q
D) TPP

Question 32

Iron sulfur clusters Fs-S) that can accept or donate one electron are found in which complexes of the electron transport chain?

A) I
B) II and III
C) I, II and III
D) I, II, III and IV

Question 33

A lipid-soluble cofactor that can diffuse freely in the membrane of the electron transport chain and carry electrons across the membrane is .

A) ubiquinone Q)
B) Fe-S
C) cytochrome c
D) FADH₂

Question 34

How many protons are translocated across the inner mitochondrial membrane by complex IV for every pair of electrons passing through the electron transport chain?

A) 0
B) 1
C) 2
D) 3
E) 4

Question 35

During the Q-cycle molecules) of QH₂ isare) oxidized and molecules) of Q isare) produced.

A) 1; 1
B) 1; 2
C) 2; 1
D) 2; 2

Question 36

Which best describe the structure of complex II?

A) An L-shaped structure that spans the membrane and partially extends into the mitochondrial matrix.
B) A structure firmly anchored to the membrane by many a-helices that span the lipid-bilayer.
C) Three identical multisubunit enzymes that associate to form a mushroom-shaped structure.
D) Has a core structure of three conserved subunits, one of which forms a b-barrel on the exterior surface of the membrane.

Question 37

Which is not a component of complex II?

A) Fe-S clusters
B) FAD
C) heme
D) cytochrome b
E) All of the above are components of complex II.

Question 38

To reduce one molecule of O₂, electrons) must be passed through the electron transport chain and molecules) of NADH isare) oxidized.

A) 4; 2
B) 2; 1
C) 1; 1
D) 1; 2
E) 4; 4

Question 39

What feature of cytochromes makes them valuable in electron transport systems?

A) aspartate residues in the active site
B) the porphyrin ring
C) the multiple α-helices
D) the iron ion

Question 40

How many protons are translocated across the membrane by complex I for every pair of electrons that are passed from NADH to QH₂?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 41

The number of mitochondria per cell is relatively constant among cell types and species.

Question 42

In bacteria, oxidative phosphorylation occurs in the mitochondrial membrane.

Question 43

The oxidation-reduction cofactor in the multisubunit enzyme fumarate reductase in E. coli which has the greatest reduction potential is

A) FAD.
B) iron clusters.
C) ubiquinone.
D) menaquinone.
E) NADH.

Question 44

The oxidizing agent in the enzyme superoxide dismutase is

A) superoxide anion ·O₂^-).
B) H₂O_2.
C) Copper.
D) O_2.
E) All of the above

Question 45

Electron transport chains occur only in the inner mitochondrial membrane of animal cells or the plasma membrane of bacteria.

Question 46

Mitochondria are about the size of an E. coli cell.

Question 47

The P/O ratio for passing electrons through complexes I, III and IV is .

A) 1
B) 1.5
C) 2
D) 2.5
E) 3

Question 48

The synthesis of one molecule of ATP from ADP requires to be translocated across the inner mitochondrial membrane.

A) one proton
B) three protons
C) hundreds of protons
D) 1 mole of protons

Question 49

Superoxide dismutase protects cells from damage caused by .

A) ·O₂^-
B) O₃^2-
C) H₂O₂
D) H₃O⁺

Question 50

In mammals the enzyme complexes of oxidative phosphorylation are in the inner mitochondrial matrix.

Question 51

Which component of ATP synthase is the site of the proton channel?

A) F₀
B) F₁
C) F₂
D) b subunit
E) g subunit

Question 52

Most of the free energy needed to drive ATP formation in the mitochondria is the result of an electrical contribution from a charge gradient across the inner mitochondrial membrane.

Question 53

Heat can be generated in the brown adipose tissue of hibernating mammals due to .

A) increased ATP production by ATP synthase
B) uncoupling by thermogenin
C) a greater pH gradient across the inner mitochondrial membrane by complex IV
D) insufficient NADH production during the citric acid cycle due to less active pyruvate translocase.

Question 54

White muscle cells contain fewer mitochondria than red muscle cells, so they rely on anaerobic glycolysis for energy needs.

Question 55

The numbers of mitochondria in cells is closely associated with cell function.

Question 56

Which statement is not true about the transport of ATP across the inner mitochondrial membrane on its way to the cytosol?

A) It is accomplished by adenine nucleotide translocase.
B) The same enzyme that transports ATP also transport ADP in the opposite direction.
C) It is complexed with Mg²⁺ to reduce the draw on the electrical part of the protonmotive force.
D) The transport causes the loss of a net charge of -1 in the matrix.

Question 57

Rotation of the subunit of ATP synthase causes conformational changes in the catalytic sites that produce ATP.

A) a
B) b
C) c
D) e
E) g

Question 58

Oxidative phosphorylation occurs in the mitochondrial membrane in eukaryotes and the plasma membrane in bacteria.

Question 59

A muscle cell from an alligator jaw contains more mitochondria than a wing muscle of a migrating bird such as a goose.

Question 60

The inner mitochondrial membrane is permeable to water but the outer membrane is not.

Question 61

The source of energy to produce ATP in mitochondria is a proton gradient formed across the outer mitochondrial membrane.

Question 62

Mitochondrial electron transport and ATP formation are interdependent.

Question 63

An obligate anaerobe cannot grow in the presence of oxygen.

Question 64

Menaquinone has greater reduction potential than FAD.

Question 65

ATP directly provides the energy to transport protons across the inner membrane from the matrix to the inner-membrane space of mitochondria.

Question 66

E. coli can use electron carriers to grow aerobically or anaerobically.

Question 67

Complex II participates in both the electron transport chain and the citric acid cycle.

Question 68

In the presence of an uncoupler, more substrate can be oxidized.

Question 69

Complex I contains a porin protein subunit that transports H⁺ across the inner mitochondrial membrane.

Question 70

The enzyme complexes I-IV in the electron transport chain associate with each other by a combination of hydrophobic interactions, disulfide bridges and hydrogen bonding.

Question 71

The protonmotive force is the free energy due to the proton gradient across the inner mitochondrial membrane.

Question 72

Both fumarate reductase and succinate dehydrogenase can function at the same time in E. coli.

Question 73

The P/O ratio is independent of whether electrons originate from complex I or complex II.

Question 74

If an inhibitor disrupts the flow of protons from the matrix into the intermembrane space of mitochondria, no ATP will be formed.

Question 75

The presence of superoxide dismutase (SOD) in mammalian cells can be harmful or beneficial, depending on the location.

Question 76

Fumarate reductase essentially catalyzes the reverse reaction catalyzed by the succinate dehydrogenase.

Question 77

Electron flow to oxidize electron carriers does not occur in anaerobic organisms.

Question 78

NADH and QH₂ for oxidative phosphorylation are produced only through the citric acid cycle under aerobic conditions.

Question 79

The chemiosmotic theory explains that the energy for driving ATP formation in mitochondria comes from a proton concentration gradient.

Question 80

The reduction potential of Complex I is lower than that of Complex III.