Cell Bio Ch. 14

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

(a) chemiosmotic coupling.

(b) proton pumping.

(c) electron transfer.

(d) A TP synthesis.

(a) chemiosmotic coupling.

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

(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.

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

pyruvate.

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

(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.

(a) A phosphate group is added to ADP.

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?

(a) 30

(b) 2

(c) 20

(d) 36

(a) 30

14-8 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

A. The number and location of mitochondria within a cell can change, depending on both the cell type and the amount of energy required.

true

14-8 t or f

B. The inner mitochondrial membrane contains porins, which allow pyruvate to enter for use in the citric acid cycle.

false

14-8 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

C. The inner mitochondrial membrane is actually a series of discrete, flattened, membrane-enclosed compartments called cristae, similar to what is seen in the Golgi apparatus.

false

14-8 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

D. The intermembrane space of the mitochondria is chemically equivalent to the cytosol with respect to pH and the small molecules present.

true

14-9 In which of the four compartments of a mitochondrion are each of the following located?

A. porin

B. the mitochondrial genome

C. citric acid cycle enzymes

D. proteins of the electron-transport chain

E. A TP synthase

F. membrane transport protein for pyruvate

***14-9 A.

B. The mitochondrial genome is in the matrix.

C. The citric acid cycle enzymes are in the matrix.

D. The proteins of the electron-transport chain are in the inner membrane.

E. ATP synthase is in the inner membrane.

F. The transport protein for pyruvate is in the inner membrane.

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

(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.

(c) Mitochondrial division is mechanistically similar to prokaryotic cell

division.

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

(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.

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

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

(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.

(b) It contains transporters for ATP molecules.

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

(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.

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

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

(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.

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

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?

(a) NAD+ + OH-

(b) NAD+ + H-

(c) NAD- + H+

(d) NAD + H

(b) NAD+ + H-

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?

(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

(d) an ADP analog that inhibits ATP synthase

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?

(a) OH- is oxidized to O2

(b) pyruvate is oxidized to CO2

(c) O2 is reduced to H2O

(d) H- is converted to H2

(c) O2 is reduced to H2O

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.

(a) ATP, against

(b) protons, down

(c) electrons, down

(d) ADP, against

(b) protons, down

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

(a) NADH dehydrogenase

(b) cytochrome c

(c) cytochrome c reductase

(d) cytochrome c oxidase

(b) cytochrome c

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

(a) cytochrome c

(b) cytochrome b-c1 complex

(c) ubiquinone

(d) cytochrome c oxidase

(d) cytochrome c oxidase

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?

(a) OH- is oxidized to O2

(b) pyruvate is oxidized to CO2

(c) O2 is reduced to H2O

(d) NAD+ is reduced to NADH

(c) O2 is reduced to H2O

14-24 Which of the following statements is true?

(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.

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

intermembrane space.

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.)

(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

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

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?

(a) transmembrane H+ carrier

(b) F1 A TPase head

(c) peripheral stalk

(d) central stalk

(b) F1 A TPase head

14-29 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

A. The driving force that pulls protons into the matrix is called the proton- motive force, which is a combination of the large force due to the pH gradient and the smaller force that results from the voltage gradient across the inner mitochondrial membrane.

false

14-29 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

B. Under anaerobic conditions, the ATP synthase can hydrolyze ATP instead of synthesizing it.

true

14-29 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

C. ATP is moved out of the matrix, across the inner mitochondrial membrane, in a co-transporter that also brings ADP into the matrix.

true

14-29 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

D. Brown fat cells make less ATP because they have an inefficient ATP synthase.

false

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?

(a) placing the mitochondria in anaerobic conditions

(b) adding FADH2

(c) making the inner membrane permeable to protons

(d) inhibiting the ATP synthase

(c) making the inner membrane permeable to protons

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.

(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

(c) NADH from the citric acid cycle

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?

(a) cytochrome c oxidase

(b) NADH dehydrogenase

(c) cytochrome c

(d) bacteriorhodopsin

(d) bacteriorhodopsin

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

(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.

(b) For molecules that have a strong tendency to pass along their electrons,

the standard redox potential is negative.

14-41 Which of the following statements is true?

(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

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

member of the pair.

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

(a) 1:10

(b) 10:1

(c) 1:1

(d) 5:1

(a) 1:10

14-44 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

A. Ubiquinone is associated with the inner mitochondrial membrane as a protein-bound electron carrier molecule.

false

14-44 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

B. Ubiquinone can transfer only one electron in each cycle.

false

14-44 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

C. The iron-sulfur centers in NADH dehydrogenase are relatively poor

electron acceptors.

true

14-44 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

D. Cytochrome c oxidase binds O2 using an iron-heme group, where four

electrons are shuttled one at a time.

true

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?

(a) The electrons are added directly to the aromatic ring.

(b) The electrons are added to each of two ketone oxygens on the aromatic ring.

(c) The electrons are added to the hydrocarbon tail, which hides them inside the membrane bilayer.

(d) Both electrons, and one proton, are added to a single ketone oxygen bound to the aromatic ring.

(b) The electrons are added to each of two ketone oxygens on the aromatic ring.

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?

(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

(a) Ubiquinone is anchored directly in the inner mitochondrial membrane via

its hydrocarbon tail, and can only diffuse laterally.

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?

(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

(b) one iron atom and one copper atom

14-51 Which of the following statements is true?

(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.

(d) Mitochondrial electron carriers with the highest redox potential generally

contain copper ions and/or heme groups.

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

(a) cytochrome

(b) quinone

(c) rhodopsin

(d) copper ion

(c) rhodopsin

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

(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.

(c) The pair of electrons accepted by cytochrome c are added to the porphyrin

ring of the bound heme group.

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?

(a) thylakoid space

(b) stroma

(c) inner membrane

(d) thylakoid membrane

d) thylakoid membrane

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

(a) thylakoid space

(b) stroma

(c) inner membrane

(d) thylakoid membrane

(a) thylakoid space

14-56 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

A. Carbon fixation can be described as a process by which gaseous carbon-

containing molecules are captured and incorporated into biological

hydrocarbon molecules.

true

14-56 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

B. The electron-transport proteins, utilized in stage 1 of photosynthesis,

reside in the inner membrane of the chloroplast.

false

14-56 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

C. Similar to oxidative phosphorylation, the electrons passed along the

chloroplast electron-transport chain are ultimately passed on to a molecule

of O2, to produce H2O.

false

14-56 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

D. Stage 2 of photosynthesis involves a cycle of reactions that does not

directly depend on energy derived from sunlight.

treue

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?

(a) thylakoid space

(b) stroma

(c) inner membrane

(d) thylakoid membrane1

(d) thylakoid membrane1

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?

(a) H2O

(b) NADH

(c) FADH2

(d) NADPH

(d) NADPH

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

(a) high; H2O.

(b) low; H2O.

(c) high; NADPH.

(d) low; NADPH.

(b) low; H2O.

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

(a) plastoquinone.

(b) the antenna complex.

(c) the reaction center.

(d) the ferredoxin complex.

(b) the antenna complex.

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?

(a) Less ATP will be generated per photon absorbed.

(b) A TP synthesis will cease.

(c) Plastoquinone will accumulate in the oxidized form.

(d) Plastocyanin will accumulate in the oxidized form.

(c) Plastoquinone will accumulate in the oxidized form.

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?

(a) 1:3

(b) 1:2

(c) 3:1

(d) 2:1

(c) 3:1

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

(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.

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

14-66 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

A. The dark reactions of photosynthesis occur only in the absence of light.

false

B. Much of the glyceraldehyde 3-phosphate made in the chloroplast ends up

producing the molecules needed by the mitochondria to produce ATP.

true

C. Ribulose 1,5-bisphosphate is similar to oxaloacetate in the Krebs cycle in

that they are both regenerated at the end of their respective cycles.

true

D. Each round of the Calvin cycle uses five molecules of CO2 to produce one

molecule of glyceraldehyde 3-phosphate and one of pyruvate.

false

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?

(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

(c) ATP-driven proton pumps

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 A TP synthesis

(a) A, C, D, B

(b) C, A, B, D

(c) B, C, A, D

(d) C, B, A, D

(d) C, B, A, D