MCQ Oxidative Phosphorylation and Photophosphorylation Flashcards
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.
E) water.
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.
Cyanide inhibits the respiratory chain, whereas oligomycin and 2,4-dinitrophenol inhibit the synthesis of ATP.
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.
B) cytochrome c is a two-electron acceptor, whereas QH2 is a one-electron donor.
If electron transfer in tightly coupled mitochondria is blocked (with antimycin A) between cytochrome b and cytochrome c1, then:
A) all ATP synthesis will stop.
B) ATP synthesis will continue, but the P/O ratio will drop to one.
C) electron transfer from NADH will cease, but O2 uptake will continue.
D) electron transfer from succinate to O2 will continue unabated.
E) energy diverted from the cytochromes will be used to make ATP, and the P/O ratio will rise.
A) all ATP synthesis will stop.
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 are true.
E) All of the above are true.
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 are correct.
A) Electron transfer in mitochondria is accompanied by an asymmetric release of protons on one side of the inner mitochondrial membrane.
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.
) The membrane ATPase, which plays an important role in other hypotheses for energy coupling,
has no significant role in the chemiosmotic theory.
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.
A) oxygen consumption decreases.
Which of the following statements about energy conservation in the mitochondrion is false?
A) Drug 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.
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.
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 ∆G’°.
C) It consists of F0 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 ∆G’° is actually close to zero.
E) When it catalyzes the ATP synthesis reaction, the ∆G’° is actually close to zero.
When the ∆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.
D) stabilization of ATP relative to ADP by enzyme binding.
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 Pi) for the ATP synthase.
C) induce a conformational change in the ATP synthase.
D) oxidize NADH to NAD+.
E) reduce O2 to H2O.
) induce a conformational change in the ATP synthase.
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.
C) reduction of a flavoprotein.
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?C) Both use oxygen as a terminal electron acceptor.A) Bothcontaincytochromesandflavinsintheirelectroncarrierchains.
B) Both processes are associated with membranous elements of the cell.
C) Both use oxygen as a terminal electron acceptor.
D) EachrepresentsthemajorrouteofATPsynthesisinthosecellsinwhichitisfound.
E) Protons are pumped from the inside to the outside of both mitochondria and chloroplast
membranes
C) Both use oxygen as a terminal electron acceptor.
The relative concentrations of ATP and ADP control the cellular rates of: A) glycolysis. B) oxidative phosphorylation. C) pyruvate oxidation. D) thecitricacidcycle. E) all of the above.
E) all of the above.
