14

Front 1

14-1 The link between bond-forming reactions and membrane transport processes in the mitochondria is called __________________.

Back 1

(a) chemiosmotic coupling.

Hint 1

(a) chemiosmotic coupling.
(b) proton pumping.
(c) electron transfer.
(d) ATP synthesis.

Front 2

14-4 Which of the following is not part of the process known as oxidative phosphorylation?

Back 2

(d) ATP molecules are produced in the cytosol as glucose is converted into pyruvate.

Hint 2

(a) Molecular oxygen serves as a final electron acceptor.
(b) FADH2 and NADH become oxidized as they transfer a pair of electrons to the electron-transport chain.
(c) The electron carriers in the electron-transport chain toggle between reduced and oxidized states as electrons are passed along.
(d) ATP molecules are produced in the cytosol as glucose is converted into pyruvate.

Front 3

14-5 Which of the following statements describes the phosphorylation event that occurs during the process known as oxidative phosphorylation?

Back 3

(a) A phosphate group is added to ADP.

Hint 3

(a) A phosphate group is added to ADP.
(b) ATP is hydrolyzed in order to add phosphate groups to protein substrates.
(c) A phosphate group is added to molecular oxygen.
(d) Inorganic phosphate is transported into the mitochondrial matrix, increasing the local phosphate concentration.

Front 4

14-6 Modern eukaryotes depend on mitochondria to generate most of the cell’s ATP. How many molecules of ATP can a single molecule of glucose generate?

Back 4

(a) 30

Hint 4

(a) 30
(b) 2
(c) 20
(d) 36

Front 5

14-10 Which of the following statements about mitochondrial division is true?

Back 5

(c) Mitochondrial division is mechanistically similar to prokaryotic cell division.

Hint 5

(a) Mitochondria divide in synchrony with the cell.
(b) The rate of mitochondrial division is the same in all cell types.
(c) Mitochondrial division is mechanistically similar to prokaryotic cell division.
(d) Mitochondria cannot divide and produce energy for the cell at the same time.

Front 6

14-11 Which of the following statements describes the mitochondrial outer membrane?

Back 6

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.

Hint 6

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.
(b) It contains transporters for ATP molecules.
(c) It contains proteins that are released during apoptosis.
(d) It contains enzymes required for the oxidation of fatty acids.

Front 7

14-12 Which of the following statements describes the mitochondrial inner membrane?

Back 7

(b) It contains transporters for ATP molecules.

Hint 7

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.
(b) It contains transporters for ATP molecules.
(c) It contains proteins that are released during apoptosis.
(d) It contains enzymes required for the oxidation of fatty acids.

Front 8

14-13 Which of the following statements describes the mitochondrial intermembrane space?

Back 8

(c) It contains proteins that are released during apoptosis.

Hint 8

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.
(b) It contains transporters for ATP molecules.
(c) It contains proteins that are released during apoptosis.
(d) It contains enzymes required for the oxidation of fatty acids.

Front 9

14-14 Which of the following statements describes the mitochondrial matrix?

Back 9

(d) It contains enzymes required for the oxidation of fatty acids.

Hint 9

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.
(b) It contains transporters for ATP molecules.
(c) It contains proteins that are released during apoptosis.
(d) It contains enzymes required for the oxidation of fatty acids.

Front 10

14-15 NADH contains a high-energy bond that, when cleaved, donates a pair of electrons to the electron-transport chain. What are the immediate products of this bond cleavage?

Back 10

(b) NAD+ + H–

Hint 10

(a) NAD+ + OH–
(b) NAD+ + H–
(c) NAD– + H+
(d) NAD + H

Front 11

14-17 Electron transport is coupled to ATP synthesis in mitochondria, in chloroplasts, and in the thermophilic bacterium Methanococcus. Which of the following is likely to affect the coupling of electron transport to ATP synthesis in all of these systems?

Back 11

(d) an ADP analog that inhibits ATP synthase

Hint 11

(a) a potent inhibitor of cytochrome c oxidase
(b) the removal of oxygen
(c) the absence of light
(d) an ADP analog that inhibits ATP synthase

Front 12

14-18 Stage 1 of oxidative phosphorylation requires the movement of electrons along the electron-transport chain coupled to the pumping of protons into the intermembrane space. What is the final result of these electron transfers?

Back 12

(c) O2 is reduced to H2O

Hint 12

(a) OH– is oxidized to O2
(b) pyruvate is oxidized to CO2
(c) O2 is reduced to H2O
(d) H– is converted to H2

Front 13

14-19 Osmosis describes the movement of water across a biological membrane and down its concentration gradient. In chemiosmosis, useful energy is harnessed by the cell from the movement of _______________ across the inner mitochondrial membrane into the matrix _________________ a concentration gradient.

Back 13

(b) protons, down

Hint 13

(a) ATP, against
(b) protons, down
(c) electrons, down
(d) ADP, against

Front 14

14-20 Which of the following components of the electron-transport chain does not act as a proton pump?

Back 14

(b) cytochrome c

Hint 14

(a) NADH dehydrogenase
(b) cytochrome c
(c) cytochrome c reductase
(d) cytochrome c oxidase

Front 15

14-21 Which component of the electron-transport chain is required to combine the pair of electrons with molecular oxygen?

Back 15

(d) cytochrome c oxidase

Hint 15

(a) cytochrome c
(b) cytochrome b-c1 complex
(c) ubiquinone
(d) cytochrome c oxidase

Front 16

14-23 In oxidative phosphorylation, ATP production is coupled to the events in the electron-transport chain. What is accomplished in the final electron-transfer event in the electron-transport chain?

Back 16

(c) O2 is reduced to H2O

Hint 16

(a) OH– is oxidized to O2
(b) pyruvate is oxidized to CO2
(c) O2 is reduced to H2O
(d) NAD+ is reduced to NADH

Front 17

14-24 Which of the following statements is true?

Back 17

(b) The pH in the mitochondrial matrix is higher than the pH in the intermembrane space.

Hint 17

(a) The NADH dehydrogenase complex can pump more protons than can the cytochrome b-c1 complex.
(b) The pH in the mitochondrial matrix is higher than the pH in the intermembrane space.
(c) The proton concentration gradient and the membrane potential across the inner mitochondrial membrane tend to work against each other in driving protons from the intermembrane space into the matrix.
(d) The difference in proton concentration across the inner mitochondrial membrane has a much larger effect than the membrane potential on the total proton-motive force.

Front 18

14-26 Which of the following types of ion movement might be expected to require co-transport of protons from the mitochondrial intermembrane space to the matrix, inasmuch as it could not be driven by the membrane potential across the inner membrane? (Assume that each ion being moved is moving against its concentration gradient.)

Back 18

(b) import of acetate ions into the matrix from the intermembrane space

Hint 18

(a) import of Ca2+ into the matrix from the intermembrane space
(b) import of acetate ions into the matrix from the intermembrane space
(c) exchange of Fe2+ in the matrix for Fe3+ in the intermembrane space
(d) exchange of ATP from the matrix for ADP in the intermembrane space

Front 19

14-27 The mitochondrial ATP synthase consists of several different protein subunits. Which subunit binds to ADP + Pi and catalyzes the synthesis of ATP as a result of a conformational change?

Back 19

(b) F1 ATPase head

Hint 19

(a) transmembrane H+ carrier
(b) F1 ATPase head
(c) peripheral stalk
(d) central stalk

Front 20

14-34 NADH and FADH2 carry high-energy electrons that are used to power the production of ATP in the mitochondria. These cofactors are generated during glycolysis, the citric acid cycle, and the fatty acid oxidation cycle. Which molecule below can produce the most ATP? Explain your answer.

Back 20

(c) NADH from the citric acid cycle

Hint 20

(a) NADH from glycolysis
(b) FADH2 from the fatty acid cycle
(c) NADH from the citric acid cycle
(d) FADH2 from the citric acid cycle

Front 21

14-36 Experimental evidence supporting the chemiosmotic hypothesis was gathered by using artificial vesicles containing a protein that can pump protons in one direction across the vesicle membrane to create a proton gradient. Which protein was used to generate the gradient in a highly controlled manner?

Back 21

(d) bacteriorhodopsin

Hint 21

(a) cytochrome c oxidase
(b) NADH dehydrogenase
(c) cytochrome c
(d) bacteriorhodopsin

Front 22

14-40 Which of the following statements about “redox potential” is true?

Back 22

(b) For molecules that have a strong tendency to pass along their electrons, the standard redox potential is negative.

Hint 22

(a) Redox potential is a measure of a molecule’s capacity to strip electrons from oxygen.
(b) For molecules that have a strong tendency to pass along their electrons, the standard redox potential is negative.
(c) The transfer of electrons from cytochrome c oxidase to oxygen has a negative redox potential.
(d) A molecule’s redox potential is a measure of the molecule’s capacity to pass along electrons to oxygen.

Front 23

14-41 Which of the following statements is true?

Back 23

(c) The ΔE0′ of a redox pair does not depend on the concentration of each member of the pair.

Hint 23

(a) Only compounds with negative redox potentials can donate electrons to other compounds under standard conditions.
(b) Compounds that donate one electron have higher redox potentials than those compounds that donate two electrons.
(c) The ΔE0′ of a redox pair does not depend on the concentration of each member of the pair.
(d) The free-energy change, ΔG, for an electron-transfer reaction does not depend on the concentration of each member of a redox pair.

Front 24

14-43 Which ratio of NADH to NAD+ in solution will generate the largest positive redox potential?

Back 24

(a) 1:10

Hint 24

(a) 1:10
(b) 10:1
(c) 1:1
(d) 5:1

14-45 Ubiquinone is one of two mobile electron carriers in the electron-transport chain. Where does the additional pair of electrons reside in the reduced ubiquinone molecule?

Front 25

14-46 Electron-transfer reactions occur rapidly. Which of the following statements best describes how the diffusion of ubiquinone is controlled in order to ensure its proximity to the other enzyme complexes?

Back 25

(a) Ubiquinone is anchored directly in the inner mitochondrial membrane via its hydrocarbon tail, and can only diffuse laterally.

Hint 25

(a) Ubiquinone is anchored directly in the inner mitochondrial membrane via its hydrocarbon tail, and can only diffuse laterally.
(b) Ubiquinone is present at high concentrations, minimizing the impact of diffusion on the electron-transport chain.
(c) Ubiquinone becomes covalently attached to the other enzyme complexes.
(d) The intermembrane space in the mitochondrion is relatively small, and therefore the random diffusion of these molecules is not a problem.

Front 26

14-47 Which of the following reactions has a sufficiently large free-energy change to enable it to be used, in principle, to provide the energy needed to synthesize one molecule of ATP from ADP and Pi under standard conditions? See Table Q14-47. Recall that

ΔG° = –n (0.023) ΔE0′, and
ΔE0′ = E0′ (acceptor) – E0′ (donor).

Back 26

(b) the reduction of a molecule of cytochrome b by NADH

Hint 26

(a) the reduction of a molecule of pyruvate by NADH
(b) the reduction of a molecule of cytochrome b by NADH
(c) the reduction of a molecule of cytochrome b by reduced ubiquinone
(d) the oxidation of a molecule of reduced ubiquinone by cytochrome c

Front 27

Table Q14-47

14-48 Cytochrome c oxidase is an enzyme complex that uses metal ions to help coordinate the transfer of four electrons to O2. Which metal atoms are found in the active site of this complex?

Back 27

(b) one iron atom and one copper atom

Hint 27

(a) two iron atoms
(b) one iron atom and one copper atom
(c) one iron atom and one zinc atom
(d) one zinc atom and one copper atom

Front 28

14-51 Which of the following statements is true?

Back 28

(d) Mitochondrial electron carriers with the highest redox potential generally contain copper ions and(or) heme groups.

Hint 28

(a) Ubiquinone is a small, hydrophobic protein containing a metal group that acts as an electron carrier.
(b) A 2Fe2S iron–sulfur center carries one electron, whereas a 4Fe4S center carries two.
(c) Iron–sulfur centers generally have a higher redox potential than do cytochromes.
(d) Mitochondrial electron carriers with the highest redox potential generally contain copper ions and(or) heme groups.

Front 29

14-52 Which of the following is not an electron carrier that participates in the electron-transport chain?

Back 29

(c) rhodopsin

Hint 29

(a) cytochrome
(b) quinone
(c) rhodopsin
(d) copper ion

Front 30

14-53 Which of the following statements about cytochrome c is true?

Back 30

(c) The pair of electrons accepted by cytochrome c are added to the porphyrin ring of the bound heme group.

Hint 30

(a) Cytochrome c shuttles electrons between the NADH dehydrogenase complex and cytochrome c reductase complex.
(b) When cytochrome c becomes reduced, two cysteines (sulfur-containing amino acids) become covalently bound to a heme group.
(c) The pair of electrons accepted by cytochrome c are added to the porphyrin ring of the bound heme group.
(d) Cytochrome c is the last protein in the electron-transport chain, passing its electrons directly to molecular oxygen, a process that reduces O2 to H2O.

Front 31

14-54 Photosynthesis is a process that takes place in chloroplasts and uses light energy to generate high-energy electrons, which are passed along an electron-transport chain. Where are the proteins of the electron-transport chain located in chloroplasts?

Back 31

(d) thylakoid membrane

Hint 31

(a) thylakoid space
(b) stroma
(c) inner membrane
(d) thylakoid membrane

Front 32

14-55 In stage 1 of photosynthesis, a proton gradient is generated and ATP is synthesized. Where do protons become concentrated in the chloroplast?

Back 32

(a) thylakoid space

Hint 32

(a) thylakoid space
(b) stroma
(c) inner membrane
(d) thylakoid membrane

Front 33

14-57 The ATP synthase found in chloroplasts is structurally similar to the ATP synthase in mitochondria. Given that ATP is being synthesized in the stroma, where will the F0 portion of the ATP synthase be located?

Back 33

(d) thylakoid membrane

Hint 33

(a) thylakoid space
(b) stroma
(c) inner membrane
(d) thylakoid membrane

Front 34

14-58 Stage 2 of photosynthesis, sometimes referred to as the dark reactions, involves the reduction of CO2 to produce organic compounds such as sucrose. What cofactor is the electron donor for carbon fixation?

Back 34

(d) NADPH

Hint 34

(a) H2O
(b) NADH
(c) FADH2
(d) NADPH

Front 35

14-59 In the electron-transport chain in chloroplasts, ________-energy electrons are taken from __________.

Back 35

(b) low; H2O.

Hint 35

(a) high; H2O.
(b) low; H2O.
(c) high; NADPH.
(d) low; NADPH.

Front 36

14-60 The photosystems in chloroplasts contain hundreds of chlorophyll molecules, most of which are part of _______________.

Back 36

(b) the antenna complex.

Hint 36

(a) plastoquinone.
(b) the antenna complex.
(c) the reaction center.
(d) the ferredoxin complex.

Front 37

14-62 If you shine light on chloroplasts and measure the rate of photosynthesis as a function of light intensity, you get a curve that reaches a plateau at a fixed rate of photosynthesis, x, as shown in Figure Q14-62.


Figure Q14-62

Which of the following conditions will increase the value of x?

Back 37

(b) increasing the number of reaction centers

Hint 37

(a) increasing the number of chlorophyll molecules in the antenna complexes
(b) increasing the number of reaction centers
(c) adding a powerful oxidizing agent
(d) decreasing the wavelength of light used

Front 38

14-63 If you add a compound to illuminated chloroplasts that inhibits the NADP+ reductase, NADPH generation ceases, as expected. However, ferredoxin does not accumulate in the reduced form because it is able to donate its electrons not only to NADP+ (via NADP+ reductase) but also back to the cytochrome b6-f complex. Thus, in the presence of the compound, a “cyclic” form of photosynthesis occurs in which electrons flow in a circle from ferredoxin, to the cytochrome b6-f complex, to plastocyanin, to photosystem I, to ferredoxin. What will happen if you now also inhibit photosystem II?

Back 38

(c) Plastoquinone will accumulate in the oxidized form.

Hint 38

(a) Less ATP will be generated per photon absorbed.
(b) ATP synthesis will cease.
(c) Plastoquinone will accumulate in the oxidized form.
(d) Plastocyanin will accumulate in the oxidized form.

Front 39

14-64 The enzyme ribulose bisphosphate carboxylase (Rubisco) normally adds carbon dioxide to ribulose 1,5-bisphosphate. However, it will also catalyze a competing reaction in which O2 is added to ribulose 1,5-bisphosphate to form 3-phosphoglycerate and phosphoglycolate. Assume that phosphoglycolate is a compound that cannot be used in any further reactions. If O2 and CO2 have the same affinity for Rubisco, which of the following is the lowest ratio of CO2 to O2 at which a net synthesis of sugar can occur?

Back 39

(c) 3:1

Hint 39

(a) 1:3
(b) 1:2
(c) 3:1
(d) 2:1

Front 40

14-65 Which of the following statements is not true about the possible fates of glyceraldehyde 3-phosphate?

Back 40

(d) It can be transported into the thylakoid space for use as a secondary electron acceptor downstream of the electron-transport chain.

Hint 40

(a) It can be exported from the chloroplast to the cytosol for conversion into sucrose.
(b) It can be used to make starch, which is stored inside the stroma of the chloroplast.
(c) It can be used as a precursor for fatty acid synthesis and stored as fat droplets in the stroma.
(d) It can be transported into the thylakoid space for use as a secondary electron acceptor downstream of the electron-transport chain.

Front 41

14-69 Oxidative phosphorylation, as it occurs in modern eukaryotes, is a complex process that probably arose in simple stages in primitive bacteria. Which mechanism is proposed to have arisen first as this complex system evolved?

Back 41

(c) ATP-driven proton pumps

Hint 41

(a) electron transfers coupled to a proton pump
(b) the reaction of oxygen with an ancestor of cytochrome c oxidase
(c) ATP-driven proton pumps
(d) the generation of ATP from the energy of a proton gradient

Front 42

14-70 Below is a list of breakthroughs in energy metabolism in living systems. Which is the correct order in which they are thought to have evolved?
A. H2O-splitting enzyme activity
B. light-dependent transfer of electrons from H2S to NADPH
C. the consumption of fermentable organic acids
D. oxygen-dependent ATP synthesis

Back 42

(d) C, B, A, D

Hint 42

(a) A, C, D, B
(b) C, A, B, D
(c) B, C, A, D
(d) C, B, A, D

Front 43

14-1 The link between bond-forming reactions and membrane transport processes in the mitochondria is called __________________.

Back 43

(a) chemiosmotic coupling.

Hint 43

(a) chemiosmotic coupling.
(b) proton pumping.
(c) electron transfer.
(d) ATP synthesis.

Front 44

14-4 Which of the following is not part of the process known as oxidative phosphorylation?

Back 44

(d) ATP molecules are produced in the cytosol as glucose is converted into pyruvate.

Hint 44

(a) Molecular oxygen serves as a final electron acceptor.
(b) FADH2 and NADH become oxidized as they transfer a pair of electrons to the electron-transport chain.
(c) The electron carriers in the electron-transport chain toggle between reduced and oxidized states as electrons are passed along.
(d) ATP molecules are produced in the cytosol as glucose is converted into pyruvate.

Front 45

14-5 Which of the following statements describes the phosphorylation event that occurs during the process known as oxidative phosphorylation?

Back 45

(a) A phosphate group is added to ADP.

Hint 45

(a) A phosphate group is added to ADP.
(b) ATP is hydrolyzed in order to add phosphate groups to protein substrates.
(c) A phosphate group is added to molecular oxygen.
(d) Inorganic phosphate is transported into the mitochondrial matrix, increasing the local phosphate concentration.

Front 46

14-6 Modern eukaryotes depend on mitochondria to generate most of the cell’s ATP. How many molecules of ATP can a single molecule of glucose generate?

Back 46

(a) 30

Hint 46

(a) 30
(b) 2
(c) 20
(d) 36

Front 47

14-10 Which of the following statements about mitochondrial division is true?

Back 47

(c) Mitochondrial division is mechanistically similar to prokaryotic cell division.

Hint 47

(a) Mitochondria divide in synchrony with the cell.
(b) The rate of mitochondrial division is the same in all cell types.
(c) Mitochondrial division is mechanistically similar to prokaryotic cell division.
(d) Mitochondria cannot divide and produce energy for the cell at the same time.

Front 48

14-11 Which of the following statements describes the mitochondrial outer membrane?

Back 48

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.

Hint 48

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.
(b) It contains transporters for ATP molecules.
(c) It contains proteins that are released during apoptosis.
(d) It contains enzymes required for the oxidation of fatty acids.

Front 49

14-12 Which of the following statements describes the mitochondrial inner membrane?

Back 49

(b) It contains transporters for ATP molecules.

Hint 49

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.
(b) It contains transporters for ATP molecules.
(c) It contains proteins that are released during apoptosis.
(d) It contains enzymes required for the oxidation of fatty acids.

Front 50

14-13 Which of the following statements describes the mitochondrial intermembrane space?

Back 50

(c) It contains proteins that are released during apoptosis.

Hint 50

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.
(b) It contains transporters for ATP molecules.
(c) It contains proteins that are released during apoptosis.
(d) It contains enzymes required for the oxidation of fatty acids.

Front 51

14-14 Which of the following statements describes the mitochondrial matrix?

Back 51

(d) It contains enzymes required for the oxidation of fatty acids.

Hint 51

(a) It is permeable to molecules with molecular mass as high as 5000 daltons.
(b) It contains transporters for ATP molecules.
(c) It contains proteins that are released during apoptosis.
(d) It contains enzymes required for the oxidation of fatty acids.

Front 52

14-15 NADH contains a high-energy bond that, when cleaved, donates a pair of electrons to the electron-transport chain. What are the immediate products of this bond cleavage?

Back 52

(b) NAD+ + H–

Hint 52

(a) NAD+ + OH–
(b) NAD+ + H–
(c) NAD– + H+
(d) NAD + H

Front 53

14-17 Electron transport is coupled to ATP synthesis in mitochondria, in chloroplasts, and in the thermophilic bacterium Methanococcus. Which of the following is likely to affect the coupling of electron transport to ATP synthesis in all of these systems?

Back 53

(d) an ADP analog that inhibits ATP synthase

Hint 53

(a) a potent inhibitor of cytochrome c oxidase
(b) the removal of oxygen
(c) the absence of light
(d) an ADP analog that inhibits ATP synthase

Front 54

14-18 Stage 1 of oxidative phosphorylation requires the movement of electrons along the electron-transport chain coupled to the pumping of protons into the intermembrane space. What is the final result of these electron transfers?

Back 54

(c) O2 is reduced to H2O

Hint 54

(a) OH– is oxidized to O2
(b) pyruvate is oxidized to CO2
(c) O2 is reduced to H2O
(d) H– is converted to H2

Front 55

14-19 Osmosis describes the movement of water across a biological membrane and down its concentration gradient. In chemiosmosis, useful energy is harnessed by the cell from the movement of _______________ across the inner mitochondrial membrane into the matrix _________________ a concentration gradient.

Back 55

(b) protons, down

Hint 55

(a) ATP, against
(b) protons, down
(c) electrons, down
(d) ADP, against

Front 56

14-20 Which of the following components of the electron-transport chain does not act as a proton pump?

Back 56

(b) cytochrome c

Hint 56

(a) NADH dehydrogenase
(b) cytochrome c
(c) cytochrome c reductase
(d) cytochrome c oxidase

Front 57

14-21 Which component of the electron-transport chain is required to combine the pair of electrons with molecular oxygen?

Back 57

(d) cytochrome c oxidase

Hint 57

(a) cytochrome c
(b) cytochrome b-c1 complex
(c) ubiquinone
(d) cytochrome c oxidase

Front 58

14-23 In oxidative phosphorylation, ATP production is coupled to the events in the electron-transport chain. What is accomplished in the final electron-transfer event in the electron-transport chain?

Back 58

(c) O2 is reduced to H2O

Hint 58

(a) OH– is oxidized to O2
(b) pyruvate is oxidized to CO2
(c) O2 is reduced to H2O
(d) NAD+ is reduced to NADH

Front 59

14-24 Which of the following statements is true?

Back 59

(b) The pH in the mitochondrial matrix is higher than the pH in the intermembrane space.

Hint 59

(a) The NADH dehydrogenase complex can pump more protons than can the cytochrome b-c1 complex.
(b) The pH in the mitochondrial matrix is higher than the pH in the intermembrane space.
(c) The proton concentration gradient and the membrane potential across the inner mitochondrial membrane tend to work against each other in driving protons from the intermembrane space into the matrix.
(d) The difference in proton concentration across the inner mitochondrial membrane has a much larger effect than the membrane potential on the total proton-motive force.

Front 60

14-26 Which of the following types of ion movement might be expected to require co-transport of protons from the mitochondrial intermembrane space to the matrix, inasmuch as it could not be driven by the membrane potential across the inner membrane? (Assume that each ion being moved is moving against its concentration gradient.)

Back 60

(b) import of acetate ions into the matrix from the intermembrane space

Hint 60

(a) import of Ca2+ into the matrix from the intermembrane space
(b) import of acetate ions into the matrix from the intermembrane space
(c) exchange of Fe2+ in the matrix for Fe3+ in the intermembrane space
(d) exchange of ATP from the matrix for ADP in the intermembrane space

Front 61

14-27 The mitochondrial ATP synthase consists of several different protein subunits. Which subunit binds to ADP + Pi and catalyzes the synthesis of ATP as a result of a conformational change?

Back 61

(b) F1 ATPase head

Hint 61

(a) transmembrane H+ carrier
(b) F1 ATPase head
(c) peripheral stalk
(d) central stalk

Front 62

14-34 NADH and FADH2 carry high-energy electrons that are used to power the production of ATP in the mitochondria. These cofactors are generated during glycolysis, the citric acid cycle, and the fatty acid oxidation cycle. Which molecule below can produce the most ATP? Explain your answer.

Back 62

(c) NADH from the citric acid cycle

Hint 62

(a) NADH from glycolysis
(b) FADH2 from the fatty acid cycle
(c) NADH from the citric acid cycle
(d) FADH2 from the citric acid cycle

Front 63

14-36 Experimental evidence supporting the chemiosmotic hypothesis was gathered by using artificial vesicles containing a protein that can pump protons in one direction across the vesicle membrane to create a proton gradient. Which protein was used to generate the gradient in a highly controlled manner?

Back 63

(d) bacteriorhodopsin

Hint 63

(a) cytochrome c oxidase
(b) NADH dehydrogenase
(c) cytochrome c
(d) bacteriorhodopsin

Front 64

14-40 Which of the following statements about “redox potential” is true?

Back 64

(b) For molecules that have a strong tendency to pass along their electrons, the standard redox potential is negative.

Hint 64

(a) Redox potential is a measure of a molecule’s capacity to strip electrons from oxygen.
(b) For molecules that have a strong tendency to pass along their electrons, the standard redox potential is negative.
(c) The transfer of electrons from cytochrome c oxidase to oxygen has a negative redox potential.
(d) A molecule’s redox potential is a measure of the molecule’s capacity to pass along electrons to oxygen.

Front 65

14-41 Which of the following statements is true?

Back 65

(c) The ΔE0′ of a redox pair does not depend on the concentration of each member of the pair.

Hint 65

(a) Only compounds with negative redox potentials can donate electrons to other compounds under standard conditions.
(b) Compounds that donate one electron have higher redox potentials than those compounds that donate two electrons.
(c) The ΔE0′ of a redox pair does not depend on the concentration of each member of the pair.
(d) The free-energy change, ΔG, for an electron-transfer reaction does not depend on the concentration of each member of a redox pair.

Front 66

14-43 Which ratio of NADH to NAD+ in solution will generate the largest positive redox potential?

Back 66

(a) 1:10

Hint 66

(a) 1:10
(b) 10:1
(c) 1:1
(d) 5:1

14-45 Ubiquinone is one of two mobile electron carriers in the electron-transport chain. Where does the additional pair of electrons reside in the reduced ubiquinone molecule?

Front 67

14-46 Electron-transfer reactions occur rapidly. Which of the following statements best describes how the diffusion of ubiquinone is controlled in order to ensure its proximity to the other enzyme complexes?

Back 67

(a) Ubiquinone is anchored directly in the inner mitochondrial membrane via its hydrocarbon tail, and can only diffuse laterally.

Hint 67

(a) Ubiquinone is anchored directly in the inner mitochondrial membrane via its hydrocarbon tail, and can only diffuse laterally.
(b) Ubiquinone is present at high concentrations, minimizing the impact of diffusion on the electron-transport chain.
(c) Ubiquinone becomes covalently attached to the other enzyme complexes.
(d) The intermembrane space in the mitochondrion is relatively small, and therefore the random diffusion of these molecules is not a problem.

Front 68

14-47 Which of the following reactions has a sufficiently large free-energy change to enable it to be used, in principle, to provide the energy needed to synthesize one molecule of ATP from ADP and Pi under standard conditions? See Table Q14-47. Recall that

ΔG° = –n (0.023) ΔE0′, and
ΔE0′ = E0′ (acceptor) – E0′ (donor).

Back 68

(b) the reduction of a molecule of cytochrome b by NADH

Hint 68

(a) the reduction of a molecule of pyruvate by NADH
(b) the reduction of a molecule of cytochrome b by NADH
(c) the reduction of a molecule of cytochrome b by reduced ubiquinone
(d) the oxidation of a molecule of reduced ubiquinone by cytochrome c

Front 69

14-48 Cytochrome c oxidase is an enzyme complex that uses metal ions to help coordinate the transfer of four electrons to O2. Which metal atoms are found in the active site of this complex?

Back 69

(b) one iron atom and one copper atom

Hint 69

(a) two iron atoms
(b) one iron atom and one copper atom
(c) one iron atom and one zinc atom
(d) one zinc atom and one copper atom

Front 70

14-51 Which of the following statements is true?

Back 70

(d) Mitochondrial electron carriers with the highest redox potential generally contain copper ions and(or) heme groups.

Hint 70

(a) Ubiquinone is a small, hydrophobic protein containing a metal group that acts as an electron carrier.
(b) A 2Fe2S iron–sulfur center carries one electron, whereas a 4Fe4S center carries two.
(c) Iron–sulfur centers generally have a higher redox potential than do cytochromes.
(d) Mitochondrial electron carriers with the highest redox potential generally contain copper ions and(or) heme groups.

Front 71

14-52 Which of the following is not an electron carrier that participates in the electron-transport chain?

Back 71

(c) rhodopsin

Hint 71

(a) cytochrome
(b) quinone
(c) rhodopsin
(d) copper ion

Front 72

14-53 Which of the following statements about cytochrome c is true?

Back 72

(c) The pair of electrons accepted by cytochrome c are added to the porphyrin ring of the bound heme group.

Hint 72

(a) Cytochrome c shuttles electrons between the NADH dehydrogenase complex and cytochrome c reductase complex.
(b) When cytochrome c becomes reduced, two cysteines (sulfur-containing amino acids) become covalently bound to a heme group.
(c) The pair of electrons accepted by cytochrome c are added to the porphyrin ring of the bound heme group.
(d) Cytochrome c is the last protein in the electron-transport chain, passing its electrons directly to molecular oxygen, a process that reduces O2 to H2O.

Front 73

14-54 Photosynthesis is a process that takes place in chloroplasts and uses light energy to generate high-energy electrons, which are passed along an electron-transport chain. Where are the proteins of the electron-transport chain located in chloroplasts?

Back 73

(d) thylakoid membrane

Hint 73

(a) thylakoid space
(b) stroma
(c) inner membrane
(d) thylakoid membrane

Front 74

14-55 In stage 1 of photosynthesis, a proton gradient is generated and ATP is synthesized. Where do protons become concentrated in the chloroplast?

Back 74

(a) thylakoid space

Hint 74

(a) thylakoid space
(b) stroma
(c) inner membrane
(d) thylakoid membrane

Front 75

14-57 The ATP synthase found in chloroplasts is structurally similar to the ATP synthase in mitochondria. Given that ATP is being synthesized in the stroma, where will the F0 portion of the ATP synthase be located?

Back 75

(d) thylakoid membrane

Hint 75

(a) thylakoid space
(b) stroma
(c) inner membrane
(d) thylakoid membrane

Front 76

14-58 Stage 2 of photosynthesis, sometimes referred to as the dark reactions, involves the reduction of CO2 to produce organic compounds such as sucrose. What cofactor is the electron donor for carbon fixation?

Back 76

(d) NADPH

Hint 76

(a) H2O
(b) NADH
(c) FADH2
(d) NADPH

Front 77

14-59 In the electron-transport chain in chloroplasts, ________-energy electrons are taken from __________.

Back 77

(b) low; H2O.

Hint 77

(a) high; H2O.
(b) low; H2O.
(c) high; NADPH.
(d) low; NADPH.

Front 78

14-60 The photosystems in chloroplasts contain hundreds of chlorophyll molecules, most of which are part of _______________.

Back 78

(b) the antenna complex.

Hint 78

(a) plastoquinone.
(b) the antenna complex.
(c) the reaction center.
(d) the ferredoxin complex.

Front 79

14-62 If you shine light on chloroplasts and measure the rate of photosynthesis as a function of light intensity, you get a curve that reaches a plateau at a fixed rate of photosynthesis, x, as shown in Figure Q14-62.


Figure Q14-62

Which of the following conditions will increase the value of x?

Back 79

(b) increasing the number of reaction centers

Hint 79

(a) increasing the number of chlorophyll molecules in the antenna complexes
(b) increasing the number of reaction centers
(c) adding a powerful oxidizing agent
(d) decreasing the wavelength of light used

Front 80

14-63 If you add a compound to illuminated chloroplasts that inhibits the NADP+ reductase, NADPH generation ceases, as expected. However, ferredoxin does not accumulate in the reduced form because it is able to donate its electrons not only to NADP+ (via NADP+ reductase) but also back to the cytochrome b6-f complex. Thus, in the presence of the compound, a “cyclic” form of photosynthesis occurs in which electrons flow in a circle from ferredoxin, to the cytochrome b6-f complex, to plastocyanin, to photosystem I, to ferredoxin. What will happen if you now also inhibit photosystem II?

Back 80

(c) Plastoquinone will accumulate in the oxidized form.

Hint 80

(a) Less ATP will be generated per photon absorbed.
(b) ATP synthesis will cease.
(c) Plastoquinone will accumulate in the oxidized form.
(d) Plastocyanin will accumulate in the oxidized form.

Front 81

14-64 The enzyme ribulose bisphosphate carboxylase (Rubisco) normally adds carbon dioxide to ribulose 1,5-bisphosphate. However, it will also catalyze a competing reaction in which O2 is added to ribulose 1,5-bisphosphate to form 3-phosphoglycerate and phosphoglycolate. Assume that phosphoglycolate is a compound that cannot be used in any further reactions. If O2 and CO2 have the same affinity for Rubisco, which of the following is the lowest ratio of CO2 to O2 at which a net synthesis of sugar can occur?

Back 81

(c) 3:1

Hint 81

(a) 1:3
(b) 1:2
(c) 3:1
(d) 2:1

Front 82

14-65 Which of the following statements is not true about the possible fates of glyceraldehyde 3-phosphate?

Back 82

(d) It can be transported into the thylakoid space for use as a secondary electron acceptor downstream of the electron-transport chain.

Hint 82

(a) It can be exported from the chloroplast to the cytosol for conversion into sucrose.
(b) It can be used to make starch, which is stored inside the stroma of the chloroplast.
(c) It can be used as a precursor for fatty acid synthesis and stored as fat droplets in the stroma.
(d) It can be transported into the thylakoid space for use as a secondary electron acceptor downstream of the electron-transport chain.

Front 83

14-69 Oxidative phosphorylation, as it occurs in modern eukaryotes, is a complex process that probably arose in simple stages in primitive bacteria. Which mechanism is proposed to have arisen first as this complex system evolved?

Back 83

(c) ATP-driven proton pumps

Hint 83

(a) electron transfers coupled to a proton pump
(b) the reaction of oxygen with an ancestor of cytochrome c oxidase
(c) ATP-driven proton pumps
(d) the generation of ATP from the energy of a proton gradient

Front 84

14-70 Below is a list of breakthroughs in energy metabolism in living systems. Which is the correct order in which they are thought to have evolved?
A. H2O-splitting enzyme activity
B. light-dependent transfer of electrons from H2S to NADPH
C. the consumption of fermentable organic acids
D. oxygen-dependent ATP synthesis

Back 84

(d) C, B, A, D

Hint 84

(a) A, C, D, B
(b) C, A, B, D
(c) B, C, A, D
(d) C, B, A, D

Front 85

14-30 Bongkrekic acid is an antibiotic that inhibits the ATP/ADP transport protein in the inner mitochondrial membrane. Which of the following will allow electron transport to occur in mitochondria treated with bongkrekic acid?

Back 85

(c) making the inner membrane permeable to protons

Hint 85

(a) placing the mitochondria in anaerobic conditions
(b) adding FADH2
(c) making the inner membrane permeable to protons
(d) inhibiting the ATP synthase

Front 86

14-31 The relationship of free-energy change (ΔG) to the concentrations of reactants and products is important because it predicts the direction of spontaneous chemical reactions. In the hydrolysis of ATP to ADP and inorganic phosphate (Pi), the standard free-energy change (ΔG°) is –7.3 kcal/mole. The free-energy change depends on concentrations according to the following equation:

ΔG = ΔG° + 1.42 log10 ([ADP] [Pi]/[ATP])

In a resting muscle, the concentrations of ATP, ADP, and Pi are approximately 0.005 M, 0.001 M, and 0.010 M, respectively. What is the ΔG for ATP hydrolysis in resting muscle?/ (a) –11.1 kcal/mole

Back 86

(a) –11.1 kcal/mole
(b) –8.72 kcal/mole
(c) 6.01 kcal/mole
(d) –5.88 kcal/mole

Front 87

14-32 The relationship of free-energy change (ΔG) to the concentrations of reactants and products is important because it predicts the direction of spontaneous chemical reactions. In the hydrolysis of ATP to ADP and inorganic phosphate (Pi), the standard free-energy change (ΔG°) is –7.3 kcal/mole. The free-energy change depends on concentrations according to the following equation:

ΔG = ΔG° + 1.42 log10 ([ADP] [Pi]/[ATP])

In a resting muscle, the concentrations of ATP, ADP, and Pi are approximately 0.005 M, 0.001 M, and 0.010 M, respectively. What is the ΔG for ATP synthesis in resting muscle?

Back 87

(d) 11.1 kcal/mole

Hint 87

(a) –6.01 kcal/mole
(b) 5.88 kcal/mole
(c) 8.72 kcal/mole
(d) 11.1 kcal/mole

Front 88

14-33 The relationship of free-energy change (ΔG) to the concentrations of reactants and products is important because it predicts the direction of
spontaneous chemical reactions. Consider, for example, the hydrolysis of ATP to ADP and inorganic phosphate (Pi). The standard free-energy change (ΔG°) for this reaction is –7.3 kcal/mole. The free-energy change depends on concentrations according to the following equation:

ΔG = ΔG° + 1.42 log10 ([ADP] [Pi]/[ATP])

In a resting muscle, the concentrations of ATP, ADP, and Pi are approximately 0.005 M, 0.001 M, and 0.010 M, respectively. At [Pi] = 0.010 M, what will be the ratio of [ATP] to [ADP] at equilibrium?

Back 88

(c) 7.2 × 10–8

Hint 88

(a) 1.38 × 106
(b) 1
(c) 7.2 × 10–8
(d) 5.14

Front 89

Which of the phylogenetic trees in Figure Q14-71 is the most accurate? (The mitochondria and chloroplasts are from maize, but they are treated as independent “organisms” for the purposes of this question.)

Back 89

C

Hint 89