Chapter 14 Molec Cell Bio

The overall relationship that links high-energy bond-forming reactions to proton transport processes in the mitochondria is called

a. chemiosmotic coupling.

b. proton pumping.

c. electron transfer.

d. ATP synthesis

a. chemiosmotic coupling.

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.

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. A phosphate group is transported into the mitochondrial matrix, increasing the local phosphate concentration.

a. A phosphate group is added to ADP.

Modern eukaryotes depend on mitochondria to generate most of the cell's ATP. What is the approximate number of ATP molecules that can be generated from a single molecule of glucose?

a. 30

b. 2

c. 20

d. 40

a. 30

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 like prokaryotic cell division.

d. Mitochondria cannot divide and produce energy for the cell at the same time.

c. Mitochondrial division is mechanistically like prokaryotic cell division.

The generation of ATP from the proton gradient is a wonderful application of the first law of thermodynamics. What forms of energy are used to generate ATP during oxidative phosphorylation in mitochondria?

a. potential energy to vibrational (heat) energy to chemical bond energy in ATP

b. mechanical energy of the proton pumping to proton motive force to mechanical energy of ATP synthase to chemical bond energy in ATP

c. heat energy to mechanical energy of proton pumps to proton motive force to chemical bond energy

d. chemical bond energy to mechanical energy of ATP synthase to chemical bond energy in ATP

b. mechanical energy of the proton pumping to proton motive force to mechanical energy of ATP synthase to chemical bond energy in ATP

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.

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.

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.

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.

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

What does it mean that electrons are high energy? Compare NADH or complex I of the electron transport chain to low energy electrons in complex IV or H2O.

a. Low-energy electrons are in a stable noncovalent bond, such as the bonds in water.

b. Electrons that are prevented from joining the valence electrons in certain atoms, such as carbon in NADH and complex I, give the electrons a high energy status.

c. In the presence of oxygen, the electrons are likely to transform into neutrons due to the electronegativity of oxygen.

d. High-energy electrons are not in the most stable polar covalent bond and can thus be attracted to other elements with a higher redox potential or higher electronegativity value, like oxygen.

d. High-energy electrons are not in the most stable polar covalent bond and can thus be attracted to other elements with a higher redox potential or higher electronegativity value, like oxygen.

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 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

What is the source of protons that are pumped out of the mitochondrial matrix in stage 1 of oxidative phosphorylation?

a. NADH

b. H2O

c. FADH

d. H2S

b. H2O

What is the result of the electron transfers in stage 1 of the membrane-based processes that drive ATP synthesis in mitochondria?

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.

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

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

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

During stage 2 of oxidative phosphorylation, ATP synthesis is powered by movement of __________ ions through the __________.

a. H+; H+ pump

b. OH- ; porin complex

c. H+; ATP synthase

d. elections; electron-transport chain

c. H+; ATP synthase

Which of the following statements is true?

a. The NADH dehydrogenase complex does not pump protons across the membrane.

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.

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

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 ATPase head

c. peripheral stalk

d. central stalk

b. F1 ATPase head

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 phosphate, 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] [phosphate]/[ATP]) In a resting muscle, the concentrations of ATP, ADP, and phosphate 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

b. -8.72 kcal/mole

c. 6.01 kcal/mole

d. -5.88 kcal/mole

a. -11.1 kcal/mole

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

a. -6.01 kcal/mole

b. 5.88 kcal/mole

c. 8.72 kcal/mole

d. 11.1 kcal/mole

d. 11.1 kcal/mole

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, and from which biochemical pathway stated below, can produce the most ATP?

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

Below is a picture of a mitochondrion located in a cell. The letter A represents what region?

a. nucleoplasma

b. rough endoplasmic reticulum

c. cytoplasm

d. extracellular space

c. cytoplasm

Below is a picture of a mitochondrion located in a cell. Which mitochondrial space or region has the lowest H+ concentration?

a. A

b. B

c. C

d. D

c. C

Below is a picture of a mitochondrion located in a cell. Which two regions or spaces have nearly identical pH levels and, therefore, no proton motive force?

a. C and D

b. B and C

c. A and B

d. A and C

c. A and B

Below is a picture of a mitochondrion located in a cell. The letter that best represents where the Fo region of ATP synthase is located is C, the matrix.

a. True

b. False

b. False

What is the function of the heme groups in the complexes of the electron transport chain?

a. to reduce NADH and FADH2

b. to transport protons across the inner membrane

c. to bind other intermembrane proteins and release heat energy as the electrons pass through the inner membrane

d. to provide a pathway for electrons to flow through the complex to reaction centers of higher redox potentials

d. to provide a pathway for electrons to flow through the complex to reaction centers of higher redox potentials

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.

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 depend on the concentration of each member of a redox pair.

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

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

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.

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

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 ironsulfur center carries two electrons.

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 or heme groups.

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

Which of the following is NOT an electron carrier that participates in the electrontransport chain?

a. cytochrome

b. quinone

c. rhodopsin

d. copper ion

c. rhodopsin

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.

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

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

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

The ATP synthase found in chloroplasts is structurally like 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 membrane

d. thylakoid membrane

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

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

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.

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 14-2. Which of the following conditions will increase the value of x?

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

b. increasing the number of reaction centers

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. ATP 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.

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

Which of the following statements about the possible fates of glyceraldehyde 3- phosphate is FALSE?

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.

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

51. 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

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

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

a. True

b. False

a. True

ATP is synthesized in the thylakoid space of chloroplasts.

a. True

b. False

b. False

Much of the glyceraldehyde 3-phosphate made in the chloroplast ends up producing the molecules needed by the mitochondria to produce ATP.

a. True

b. False

a. True

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.

a. True

b. False

a. True

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.

a. True

b. False

b. False

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

a. True

b. False

b. False

Ubiquinone can transfer only one electron in each cycle.

a. True

b. False

b. False

Cytochrome c oxidase binds O2 by using an iron-heme group, where four electrons are shuttled one at a time.

a. True

b. False

a. True

The electron-transport proteins, utilized in stage 1 of photosynthesis, reside in the inner membrane of the chloroplast.

a. True

b. False

b. False

Like oxidative phosphorylation, the electrons passed along the chloroplast electron-transport chain are ultimately passed on to a molecule of O2 , to produce H2O.

a. True

b. False

b. False