Deck 19: Oxidative Phosphorylation and Photophosphorylation

Question 1

Upon the addition of 2,4-dinitrophenol (DNP)to a suspension of mitochondria carrying out oxidative phosphorylation linked to the oxidation of malate,all of the following occur except:

A)oxygen consumption decreases.
B)oxygen consumption increases.
C)the P/O ratio drops from a value of approximately 2.5 to 0.
D)the proton gradient dissipates.
E)the rate of transport of electrons from NADH to O₂ becomes maximal.

Answer 1

oxygen consumption decreases.

Question 2

Antimycin A blocks electron transfer between cytochromes b and c₁.If intact mitochondria were incubated with antimycin A,excess NADH,and an adequate supply of O₂,which of the following would be found in the oxidized state?

A)Coenzyme Q
B)Cytochrome a₃
C)Cytochrome b
D)Cytochrome e
E)Cytochrome f

Answer 2

Cytochrome a₃

Question 3

Which of the following statements about the chemiosmotic theory is correct?

A)Electron transfer in mitochondria is accompanied by an asymmetric release of protons on one side of the inner mitochondrial membrane.
B)It predicts that oxidative phosphorylation can occur,even in the absence of an intact inner mitochondrial membrance.
C)The effect of uncoupling reagents is a consequence of their ability to carry electrons through membranes.
D)The membrane ATP synthase has no significant role in the chemiosmotic theory.
E)All of the above

Answer 3

Electron transfer in mitochondria is accompanied by an asymmetric release of protons on one side of the inner mitochondrial membrane.

Question 4

In normal mitochondria,the rate of NADH consumption (oxidation)will:

A)be increased in active muscle,decreased in inactive muscle.
B)be very low if the ATP synthase is inhibited,but increase when an uncoupler is added.
C)decrease if mitochondrial ADP is depleted.
D)decrease when cyanide is used to prevent electron transfer through the cytochrome a + a₃ complex.
E)All of the above

Question 5

Cyanide,oligomycin,and 2,4-dinitrophenol (DNP)are inhibitors of mitochondrial aerobic phosphorylation.Which of the following statements correctly describes the mode of action of the three inhibitors?

A)Cyanide and 2,4-dinitrophenol inhibit the respiratory chain,and oligomycin inhibits the synthesis of ATP.
B)Cyanide inhibits the respiratory chain,whereas oligomycin and 2,4-dinitrophenol inhibit the synthesis of ATP.
C)Cyanide,oligomycin,and 2,4-dinitrophenol compete with O₂ for cytochrome oxidase (complex IV).
D)Oligomycin and cyanide inhibit synthesis of ATP;2,4-dinitrophenol inhibits the respiratory chain.
E)Oligomycin inhibits the respiratory chain,whereas cyanide and 2,4-dinitrophenol prevent the synthesis of ATP.

Question 6

Which of the following statements about energy conservation in the mitochondrion is false?

A)Drugs that inhibits the ATP synthase will also inhibit the flow of electrons down the chain of carriers.
B)For oxidative phosphorylation to occur,it is essential to have a closed membranous structure with an inside and an outside.
C)The yield of ATP per mole of oxidizable substrate depends on the substrate.
D)Uncouplers (such as dinitrophenol)have exactly the same effect on electron transfer as inhibitors such as cyanide;both block further electron transfer to oxygen.
E)Uncouplers "short circuit" the proton gradient,thereby dissipating the proton motive force as heat.

Question 7

In the reoxidation of QH₂ by purified ubiquinone-cytochrome c reductase (Complex III)from heart muscle,the overall stoichiometry of the reaction requires 2 mol of cytochrome c per mole of QH₂ because:

A)cytochrome c is a one-electron acceptor,whereas QH₂ is a two-electron donor.
B)cytochrome c is a two-electron acceptor,whereas QH₂ is a one-electron donor.
C)cytochrome c is water soluble and operates between the inner and outer mitochondrial membranes
D)heart muscle has a high rate of oxidative metabolism,and therefore requires twice as much cytochrome c as QH₂ for electron transfer to proceed normally.
E)two molecules of cytochrome c must first combine physically before they are catalytically active.

Question 8

Which of the following electron carriers is not able to transfer one electron at a time?

A)NADH
B)FMN
C)FAD
D)Ubiquinone
E)Heme

Question 9

Which of the following statements about the chemiosmotic theory is false?

A)Electron transfer in mitochondria is accompanied by an asymmetric release of protons on one side of the inner mitochondrial membrane.
B)Energy is conserved as a transmembrane pH gradient.
C)Oxidative phosphorylation cannot occur in membrane-free preparations.
D)The effect of uncoupling reagents is a consequence of their ability to carry protons through membranes.
E)The membrane ATPase,which plays an important role in other hypotheses for energy coupling,has no significant role in the chemiosmotic theory.

Question 10

Which of the following is not true of the proton motive force (pmf)?

A)One component of the pmf is the chemical gradient of protons.
B)One component of the pmf is the charge gradient of protons.
C)Generation of the pmf in mitochondria requires succinate.
D)The pmf is generated by the electron transport chain in mitochondria.
E)The pmf drives ATP synthesis in mitochondria.

Question 11

Which of the following is correct concerning the mitochondrial ATP synthase?

A)It can synthesize ATP after it is extracted from broken mitochondria.
B)It catalyzes the formation of ATP even though the reaction has a large positive $\Delta$ G'°.
C)It consists of F_o and F₁ subunits,which are transmembrane (integral)polypeptides.
D)It is actually an ATPase and only catalyzes the hydrolysis of ATP.
E)When it catalyzes the ATP synthesis reaction,the $\Delta$ G'° is actually close to zero.

Question 12

The oxidation of a particular hydroxy substrate to a keto product by mitochondria has a P/O ratio of less than 2.The initial oxidation step is very likely directly coupled to the:

A)oxidation of a flavoprotein.
B)oxidation of a pyridine nucleotide.
C)reduction of a flavoprotein.
D)reduction of a pyridine nucleotide.
E)reduction of cytochrome a₃.

Question 13

During oxidative phosphorylation,the proton motive force that is generated by electron transport is used to:

A)create a pore in the inner mitochondrial membrane.
B)generate the substrates (ADP and P_i)for the ATP synthase.
C)induce a conformational change in the ATP synthase.
D)oxidize NADH to NAD⁺.
E)reduce O₂ to H₂O.

Question 14

Almost all of the oxygen (O₂)one consumes in breathing is converted to:

A)acetyl-CoA.
B)carbon dioxide (CO₂).
C)carbon monoxide and then to carbon dioxide.
D)None of the above
E)water.

Question 15

The rate of oxidative phosphorylation in mitochondria is controlled primarily by:

A)feedback inhibition by CO₂.
B)the availability of NADH from the TCA cycle.
C)the concentration of citrate (or)the glycerol-3-phosphate shuttle.
D)the mass-action ratio of the ATD-ADP system.
E)the presence of thermogenin.

Question 16

A new compound isolated from mitochondria is claimed to represent a previously unrecognized carrier in the electron transfer chain.It is given the name coenzyme Z.Which line of evidence do you feel is the least conclusive in assigning this compound a position in the electron transfer chain?

A)Alternate oxidation and reduction of the mitochondrion-bound coenzyme Z can be readily demonstrated.
B)Removal of coenzyme Z from the mitochondria results in a decreased rate of oxygen consumption.
C)The rate of oxidation and reduction of mitochondrion-bound coenzyme is of the same order of magnitude as the overall rate of electron transfer in mitochondria as measured by oxygen consumption.
D)The reduction potential of Z is between that of two compounds known to participate in the electron transport chain
E)When added to a mitochondrial suspension,coenzyme Z is taken up very rapidly and specifically by the mitochondria.

Question 17

Which of the following is not a feature of complex IV?

A)Cytochrome c is a one-electron donor.
B)Oxygen is a substrate.
C)Copper is an essential metal for the reaction.
D)For every electron passed to complex IV,two protons are consumed from the matrix (N)side.
E)In order to generate two water molecules,complex IV must go through the catalytic cycle two times.

Question 18

Reduced QH₂ is not formed by which of the following?

A)Complex I and NADH
B)Complex II and succinate
C)Complex III and cytochrome c
D)Fatty acid oxidation
E)Oxidation of glycerol-3-phosphate

Question 19

When the $\Delta$ G'° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme,it is found to be close to zero.This is thought to be due to:

A)a very low energy of activation.
B)enzyme-induced oxygen exchange.
C)stabilization of ADP relative to ATP by enzyme binding.
D)stabilization of ATP relative to ADP by enzyme binding.
E)None of the above

Question 20

The relative concentrations of ATP and ADP control the cellular rates of:

A)glycolysis.
B)oxidative phosphorylation.
C)pyruvate oxidation.
D)the citric acid cycle.
E)All of the above

Question 21

Which of the following is not controlled by hypoxia-inducible factor (HIF-1)?

A)Glucose transport
B)Glycolysis
C)Citric acid cycle
D)Compex I of the respiratory chain
E)Complex IV of the respiratory chain

Question 22

The light reactions in photosynthetic higher plants:

A)do not require chlorophyll.
B)produce ATP and consume NADH.
C)require the action of a single reaction center.
D)result in the splitting of H₂O,yielding O₂.
E)serve to produce light so that plants can see underground.

Question 23

Cyclic electron flow in chloroplasts produces:

A)ATP and O₂,but not NADPH.
B)ATP,but not NADPH or O₂.
C)NADPH and ATP,but not O₂.
D)NADPH,but not ATP or O₂.
E)O₂,but not ATP or NADPH.

Question 24

Which one of the following best describes the role of mitochondria in apoptosis?

A)Escape of cytochrome c into the cytoplasm
B)Increased rate of fatty acid $\beta$ -oxidation
C)Increase in permeability of outer membrane
D)Uncoupling of oxidative phosphorylation
E)Both A and C are correct.

Question 25

In what order do the following five steps occur in the photochemical reaction centers?
1)Excitation of the chlorophyll a molecule at the reaction center
2)Replacement of the electron in the reaction center chlorophyll
3)Light excitation of antenna chlorophyll molecule
4)Passage of excited electron to electron-transfer chain
5)Exiton transfer to neighboring chlorophyll

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

Question 26

Photosynthetic phosphorylation and oxidative phosphorylation appear to be generally similar processes,both consisting of ATP synthesis coupled to the transfer of electrons along an electron carrier chain.Which of the following is not true of both processes?

A)Both contain cytochromes and flavins in their electron carrier chains.
B)Both processes are associated with membranous elements of the cell.
C)Both use oxygen as a terminal electron acceptor.
D)Each represents the major route of ATP synthesis in those cells in which it is found.
E)Protons are pumped from the inside to the outside of both mitochondria and chloroplast membranes

Question 27

In photophosphorylation,absorption of light energy in chloroplast "light reactions" leads to:

A)absorption of CO₂ and release of O₂.
B)absorption of O₂ and release of CO₂.
C)hydrolysis of ATP and reduction of NADP⁺.
D)synthesis of ATP and oxidation of NADPH.
E)use of iron-sulfur proteins.

Question 28

In the photolytic cleavage of water by the oxygen-evolving complex [2H₂O $\rightarrow$ 4 H⁺ + 4e^- + O₂],how many photons of light at a wavelength of 680 nm are required?

A)1
B)2
C)4
D)6
E)8

Question 29

Mutations in mitochondrial genes play a role in each of the following diseases except:

A)adult onset diabetes.
B)cystic fibrosis.
C)hypertrophic cardiomyopathy.
D)Leber's hereditary optic neuropathy.
E)myoclonic epilepsy.

Question 30

Which of the following is not true about cyclic electron flow?

A)Cyclic electron flow produces more NADPH per photon than noncyclic electron flow.
B)Cyclic electron flow involves only PSI.
C)Plastocyanin is required for cyclic electron flow.
D)Cyclic electron flow leads to the build-up of a proton gradient.
E)Cyclic electron flow does not produce O₂.

Question 31

Which one of the following statements about photophosphorylation is false?

A)It can be uncoupled from electron flow by agents that dissipate the proton gradient.
B)The difference in pH between the luminal and stromal side of the thylakoid membrane is 3 pH units.
C)The luminal side of the thylakoid membrane has a higher pH than the stromal side.
D)The number of ATPs formed per oxygen molecule is about three.
E)The reaction centers,electron carriers,and ATP-forming enzymes are located in the thylakoid membrane.

Question 32

The experimental determination of the effectiveness of light of different colors in promoting photosynthesis is called the:

A)absorption spectrum.
B)action spectrum.
C)difference spectrum.
D)reflectance spectrum.
E)refraction spectrum.

Question 33

Oxidative phosphorylation and photophosphorylation share all of the following except:

A)chlorophyll.
B)involvement of cytochromes.
C)participation of quinones.
D)proton pumping across a membrane to create electrochemical potential.
E)use of iron-sulfur proteins.

Question 34

Which one of the following is true about reaction centers?

A)Cyanobacteria and plants have two reaction centers arranged in tandem.
B)Cyanobacteria contain a single reaction center of the Fe-S type.
C)Green sulfur bacteria have two reaction centers arranged in tandem.
D)Plant photosystems have a single reaction center of the pheophytin-quinone type.
E)Purple bacteria contain a single reaction center of the Fe-S type.

Question 35

Place the following electron-carriers into the proper order as found in plant chloroplasts.
1)Cytochrome b₆f complex
2)P680
3)P700
4)Plastocyanin
5)NADPH

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

Question 36

Mammals produce heat by using the endogenous uncoupling agent:

A)the small molecule 2-4-Dinitrophenol synthesized by the cell.
B)the protein thermogenin.
C)the protein thioredoxin.
D)the protein cytochrome c.
E)a modified form of the F_oF₁ ATPase.

Question 37

Cyclic electron flow in chloroplasts produces:

A)ATP and O₂,but not NADPH.
B)ATP,but not NADPH or O₂.
C)NADPH and ATP,but not O₂.
D)NADPH,but not ATP or O₂.
E)O₂,but not ATP or NADPH.

Question 38

Which one of the following statements about human mitochondria is true?

A)About 900 mitochondrial proteins are encoded by nuclear genes.
B)Mitochondrial genes are inherited from both maternal and paternal sources.
C)rRNA and tRNA are imported from the cytoplasm and used in mitochondrial
D)The mitochondrial genome codes for all proteins found in mitochondria.
E)The mitochondrial genome is not subject to mutations.

Question 39

Which of the following statements about the light reactions in photosynthetic plants is false?

A)A membrane-bound ATPase couples ATP synthesis to electron transfer.
B)No CO₂ is fixed in the light reactions.
C)The ultimate electron acceptor is O₂.
D)The ultimate source of electrons for the process is H₂O.
E)There are two distinct photosystems,linked together by an electron transfer chain.

Question 40

Which of the following is not found in modern cyanobacteria?

A)PSI
B)PSII
C)NADH dehydrogenase complex I
D)Oxygen-reducing complex IV
E)Mitochondria

Question 41

The compound 2,4-dinitrophenol (DNP),an uncoupler,was briefly used as a weight-loss drug.Some of its effects in people who took the drug included weight loss and higher than normal body temperature.Some people even died.Explain the first two effects of the compound in biochemical terms.

Question 42

Explain briefly the current model for how the proton motive force that is generated by electron transport is used to drive the ATP synthesis reaction.

Question 43

Show the path of electrons from ubiquinone (Q or coenzyme Q)to oxygen in the mitochondrial respiratory chain.One of the two compounds (Q and O₂)has a standard reduction potential (E'°)of 0.82 V,and the other,0.045 V.Which value belongs to each compound? How did you deduce this?

Question 44

Compound X is an inhibitor of mitochondrial ATP synthesis.It was observed that when compound X was added to cells,the NAD⁺/NADH ratio decreased.Would you expect X to be an uncoupling agent or an inhibitor of respiratory electron transfer? Explain.

Question 45

When the $\Delta$ G'° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme,it was found to be close to zero.Describe briefly why this is so.

Question 46

Diagram the path of electron flow from NADH to the final electron acceptor during electron transport in mitochondria.For each electron carrier,indicate whether only electrons,or both electrons and protons,are accepted/donated by that carrier.Also,indicate where electrons from succinate oxidation enter the chain of carriers.

Question 47

The standard reduction potential for ubiquinone (Q or coenzyme Q)is 0.045 V,and the standard reduction potential (E'°)for FAD is -0.219 V.Using these values,show that the oxidation of FADH₂ by ubiquinone theoretically liberates enough energy to drive the synthesis of ATP.The Faraday constant,,is 96.48 kJ/V·mol. $\Delta$ G'° for ATP synthesis is +30.5 kJ/mol.

Question 48

During electron transfer through the mitochondrial respiratory chain,the overall reaction is:
NADH + 1/2 O₂ + H⁺ $\rightarrow$ NAD⁺ + H₂O.The difference in reduction potentials for the two half-reactions ( $\Delta$ E'°)is +1.14 V.Show how you would calculate the standard free-energy change, $\Delta$ G'°,for the reaction as written above.(The Faraday constant,,is 96.48 kJ/V·mol. )

Question 49

The skunk cabbage (Symphocarpus foetidus)can maintain a temperature of 10-25 °C higher than the temperature of the surrounding air.Suggest a mechanism for this.

Question 50

When the F₁ portion of the ATP synthetase complex is removed from the mitochondrial membrane and studied in solution,it functions as an ATPase.Why does it not function as an ATP synthetase?

Question 51

As you read and answer this question,you are (presumably)consuming oxygen.What single reaction accounts for most of your oxygen consumption?

Question 52

Consider a liver cell carrying out the oxidation of glucose under aerobic conditions.Suppose that we added a very potent and specific inhibitor of the mitochondrial ATP synthase,completely inhibiting this enzyme.Indicate whether each of the following statements about the effect of this inhibitor is true or false;if false,explain in a sentence or two why it is false.
____ (a)ATP production in the cell will quickly drop to zero.
____ (b)The rate of glucose consumption by this cell will decrease sharply.
____ (c)The rate of oxygen consumption will increase.
____ (d)The citric acid cycle will speed up to compensate.
____ (e)The cell will switch to fatty acid oxidation as an alternative to glucose oxidation,and the inhibitor will therefore have no effect on ATP production.

Question 53

Describe,in simple diagrams and a few words,the chemiosmotic theory for coupling oxidation to phosphorylation in mitochondria.

Question 54

Describe and explain the two different ratios that affect the rate of respiration in mitochondria.What is accomplished by these control mechanisms?

Question 55

Give an example of (a)an uncoupler of oxidative phosphorylation,and (b)an inhibitor of respiration.(c)Describe the difference in the effects of such uncouplers and inhibitors on mitochondrial function.

Question 56

Mitochondria carrying out oxidative phosphorylation consume oxygen.Explain what happens to this oxygen,and describe the effect of an uncoupling agent such as 2,4-dinitrophenol on the rate of oxygen consumption.Assume there is a sufficient supply of oxidizable substrate,ADP,and P_i.

Question 57

Although molecular oxygen (O₂)does not participate directly in any of the reactions of the citric acid cycle,the cycle operates only when O₂ is present.Explain this observation.

Question 58

Cyanide ion (CN^-)blocks electron transfer in mitochondria at the level of cytochrome a + a₃.2,4-Dinitrophenol (DNP)is an uncoupler of mitochondrial oxidative phosphorylation.Draw graphs (ATP synthesized vs.time and O₂ consumed vs.time)with labeled curves to show the effects of adding each of these compounds separately to a suspension of mitochondria supplied with O₂,succinate,ADP,and P_i.Use an arrow to indicate the time of drug addition.

Question 59

In his studies of alcoholic fermentation by yeast,Louis Pasteur noted that the sudden addition of oxygen (O₂)to a previously anaerobic culture of fermenting grape juice resulted in a dramatic decrease in the rate of glucose consumption.This "Pasteur effect" can be counteracted by the addition of 2,4-dinitrophenol (DNP),an uncoupler of oxidative phosphorylation.
(a)Why would the yeast cells consume less glucose in the presence of oxygen? Can you estimate how much less glucose they would use?
(b)Why would DNP counteract or prevent the Pasteur effect?

Question 60

For each of the following explain whether they are transported into or out of the mitochondrion and comment briefly on the mechanism for each:
(1)NADH
(2)Inorganic phosphate
(3)ADP

Question 61

Some photosynthetic bacteria contain the protein bacteriorhodopsin,which absorbs light and pumps protons out of the cell directly.Briefly describe how such a cell could use bacteriorhodopsin and an H⁺ATPase to make ATP using light.

Question 62

DCMU is an herbicide that acts by blocking photosynthetic electron flow from photosystem II (PSII)to the cytochrome b₆f complex.Predict the effect of DCMU on O₂ production and on ATP synthesis in the chloroplasts of plants sensitive to DCMU.

Question 63

Discuss three lines of evidence that support the theory that mitochondria evolved from endosymbiontic bacteria.

Question 64

The processes of oxidative phosphorylation coupled with electron transfer (in mitochondria)and photophosphorylation (in chloroplasts)resemble each other in certain respects.Describe five ways in which the two processes are similar,and describe three significant differences between the two processes.

Question 65

Give five general classes of electron carriers that function in both mitochondrial electron transfer to O₂ and photosynthetic electron transfer.

Question 66

Photophosphorylation differs from oxidative phosphorylation in that the former requires the input of energy in the form of ___________ to create a good electron donor.In photophosphorylation,electrons flow through a series of membrane-bound carriers including ___________ ,___________ ,and ___________ proteins,whereas ___________ are pumped across a membrane to create an ___________ potential.

Question 67

Plants carrying out photosynthesis produce O₂.Describe the source of this O₂,and explain,with chemical equations or schematic diagrams,why O₂ production occurs only during daylight hours.

Question 68

Given that ~8 photons are required to produce one molecule of O₂,roughly how many photons are required to produce one molecule of glucose.

Question 69

Describe what happens at photosystem I from the point where an antenna chlorophyll molecule absorbs a photon of light to the passage of an electron to NADP⁺.

Question 70

Describe the role of hypoxia-inducible factor (HIF-1)in reducing reactive oxygen species (ROS).

Question 71

Describe what happens when a photon is absorbed by photosystem II;end the description of electron flow at plastoquinone.

Question 72

Describe the role of cytochrome c in apoptosis.

Question 73

Describe the effect(s)that a mitochondrial uncoupler such as 2,4-dinitrophenol (DNP)would have on photophosphorylation.

Question 74

What is an action spectrum,and what do peaks in an action spectrum signify? Show a typical action spectrum plot for photosynthesis.

Question 75

Mutations in mitochondrial genes frequently produce diseases that affect the brain and skeletal muscle (mitochondrial encephalomyopathies).Why are these two tissues particularly sensitive to mitochondrial mutations?

Question 76

During photophosphorylation in plants,electrons flow through a series of carriers in the chloroplast.What is the ultimate donor of electrons,and what is the ultimate acceptor? What provides the energy to move those electrons?

Question 77

Show the path of electrons from photosystem II to NADPH in the chloroplast.What is the source of the energy that moves electrons through this path? Show where oxygen is involved in this pathway.

Question 78

Discuss how "accessory pigments" are able to extend the range of light absorption of the chlorophylls.Name some accessory pigments.