Berg 8e testbank chapter 18 PDF

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Berg 8e testbank chapter 18...

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Chapter 18 Oxidative Phosphorylation Multiple-Choice Questions

1)

What organelle is the site of oxidative phosphorylation in eukaryotes?

A) B) C) D) E)

mitochondria chloroplast lysosome endoplasmic reticulum Golgi apparatus

Answer: A Section: Introduction

2) What term is used to describe an ATP-generating process in which an inorganic substance such as oxygen serves as the ultimate electron acceptor? A) B) C) D) E)

electron transport respiration fermentation anaerobic phosphorylation None of the answers is correct.

Answer: B Section: Introduction

3)

What type of protein makes the outer mitochondrial membrane relatively permeable?

A) B) C) D) E)

proton pump voltage gated transporter ATP-powered pump porin None of the answers is correct.

Answer: D

Section: 18.1

4)

What type of enzyme plays a key role in apoptosis?

A) B) C) D) E)

cytochrome P450 electron-transport complexes caspase enzymes of the citric acid cycle None of the answers is correct.

Answer: C Section: 18.6

5)

Which enzyme catalyzes the reduction of oxygen to water?

A) B) C) D) E)

ATP synthase cytochrome c oxidase NADH-Q oxidoreductase Q-cytochrome c oxidoreductase succinate-Q reductase

Answer: B Section: 18.3

6)

What prosthetic group is present in complexes I, II, and III of electron transport?

A) B) C) D) E)

semiquinone flavin mononucleotide coenzyme Q heme group iron-sulfur cluster

Answer: E Section: 18.3

7)

Which of the citric acid cycle enzymes is also part of an electron-transport complex?

A) B) C) D) E)

isocitrate dehydrogenase -ketoglutarate dehydrogenase succinate dehydrogenase malate dehydrogenase None of the answers is correct.

Answer: C Section: 18.3

8) What name is given to the hypothesis proposed by Peter Mitchell that explains how ATP synthesis is coupled to electron transport? A) B) C) D) E)

chemiosmotic hypothesis oxidative phosphorylation hypothesis electron transport hypothesis proton-motive force hypothesis None of the answers is correct.

Answer: A Section: 18.4

9) Which enzyme transfers electrons from a membrane-soluble carrier to a water-soluble carrier in the electron-transport process? A) B) C) D) E)

ATP synthase cytochrome c oxidase NADH-Q oxidoreductase Q-cytochrome c oxidoreductase succinate-Q reductase

Answer: D Section: 18.3

10) What process allows cytoplasmic NADH to be reoxidized by O2 using the electrontransport system? A) B)

glycerol 3-phosphate shuttle cytochrome c shuttle

C) D) E)

malate-aspartate shuttle quinone shuttle glycerol 3-phosphate shuttle and malate-aspartate shuttle

Answer: E Section: 18.5

Fill-in-the-Blank Questions 11. The unequal distribution of H+ across the inner mitochondrial membrane creates a ________________ force. Ans: proton-motive Section: Introduction and 18.4 12. In the initial step of Complex I, two high-potential electrons are transferred from NADH to the ___________ prosthetic group of this complex. Ans: FMN Section: 18.3 13. Cytochrome ________ is the only water-soluble cytochrome of the electron-transport chain. Ans: c Section: 18.3 14. Cytochrome c oxidase contains two heme A groups and three ______________ ions. Ans: copper Section: 18.3 15. ________________ carries electrons from Complex III to Complex IV. Ans: Cytochrome c Section: 18.3 16. The transfer of a single electron to O2 forms the reactive _______________ ion. Ans: superoxide Section: 18.3 17. _______________ is a molecular assembly in the inner mitochondrial membrane that carries out the synthesis of ATP. Ans: F1F0 ATPase, or ATP synthase, Section: 18.3 18. In the glycerol phosphate shuttle, cytoplasmic glycerol phosphate dehydrogenase uses cytoplasmic NADH to reduce _________________ to glycerol-3-phosphate. Ans: dihydroxyacetone phosphate Section: 18.5

19. Acceptor control of oxidative phosphorylation means that the rate of respiration depends upon the level of __________. Ans: ADP Section: 18.6 20. _________________ is a poison because it blocks the flow of electrons from cytochrome c to oxygen. Ans: Carbon monoxide (CO) or cyanide (CN) or azide (N3) Section: 18.6

Multiple-Choice Questions 21) What type of gradient is critical to ATP formation by oxidative phosphorylation? A) B) C) D) E)

sodium ion chloride ion proton potassium ion None of the answers is correct.

Ans: C Section: Introduction and 18.4 22) When glucose is totally oxidized to CO2 and H2O and the glycerol 3-phosphate shuttle is used, how many ATP molecules are made by oxidative phosphorylation (nonsubstrate-level phosphorylation) relative to the maximum yield? A) B) C) D) E)

12 out of 30 26 out of 30 26 out of 32 12 out of 32 None of the answers is correct.

Ans: B Section: 18.6 23) What is the chemical effect of oligomycin on aerobic metabolism? A) The flow of electrons from NADH to CoQ is blocked. B) The flow of electrons from Cyt a-a3 to oxygen is blocked. C) Oligomycin blocks the proton transfer through F0 of ATP synthase and therefore blocks the phosphorylation of ADP to form ATP.

D) The transport of ATP out of and ADP into the mitochondria is blocked. E) Oxidative phosphorylation is uncoupled from electron transport and all the energy is lost as heat. Ans: C Section: 18.6 24) Choose the correct path taken by a pair of electrons as it travels down the electron-transport chain. A) B)

NADH  Complex I  CoQ  Complex III  Cyt c  Complex IV  O2 FADH2  Complex I  CoQ  Complex III  Cyt c  Complex IV  O2

C) D)

NADH  Complex I  Complex II Complex III  Cyt c  Complex IV  O2 FADH2  Complex III  CoQ  Complex II  Cyt c  Complex IV  O2

E)

None of the answers is correct.

Ans: A Section: 18.3 25) Which of the following does NOT participate in, nor is a component of, the electrontransport chain? A) B) C) D) E)

lipoic acid nonheme, iron-sulfur proteins FADH2 cytochrome c1 NADH

Ans: A Section: 18.3 26) In prokaryotes the site of ATP-synthesizing machinery is A) B) C) D) E)

the mitochondrial matrix. the outer cell wall. the cytoplasmic membrane. the nucleolus. None of the answers is correct.

Ans: C

Section: 18.1 27) Electron flow down the electron-transport chain leads to the A) transport of protons across the inner mitochondrial membrane from inside the matrix to the intermembrane space. B) transport of protons across the inner mitochondrial membrane from the intermembrane space into the matrix. C) coupled synthesis of GTP. D) a dangerous imbalance of K+ ions across the mitochondrial membrane. E) None of the answers is correct. Ans: A Section: 18.3 28) Which electron carrier has an isoprenoid tail? A) B) C) D) E)

NADH cytochrome c coenzyme Q FADH2 None of the answers is correct.

Ans: C Section: 18.3 29) Which of the following does not pump protons? A) B) C) D) E)

Complex I Complex II Complex III Complex IV All of the answers are correct.

Ans: B Section: 18.3 30) The energy for ATP synthesis is generated by the movement of protons from the ______________ side of the inner mitochondrial membrane establishing a(an) _____________ gradient.

A) intermembrane; pH B) intermembrane; electrical potential C) matrix; sodium ion D) matrix; pH E) None of the answers is correct. Ans: D Section: 18.4 31) What is a cytochrome? A) a protein that transfers electrons and that also contains a heme prosthetic group B) a chloroplast protein that transfers electrons and that also contains an iron sulfur prosthetic group C) a protein that pumps ATP and that also contains iron D) an enzyme that reduces oxygen to water E) None of the answers is correct. Ans: A Section: 18.3 32) In the Rieske center, the iron-sulfur center is coordinated to the amino acid(s) _______. A) His B) Cys C) His and Cys D) Cys and Met E) None of the answers is correct. Ans: A Section: 18.3 33) What is the reaction of ATP synthase? A) B) C) D) E)

AMP3– + 2 HPO42– + H+  ATP4– + H2O ADP3– + HPO42–+ H+  ATP4–+ H2O ADP3– + HPO42– + 2 H+  ATP4– + H2O AMP3– + 2 HPO42– + 2 H+  ATP4– + H2O None of the answers is correct.

Ans: B

Section: 18.4 34) What is the net ATP obtained from one cytoplasmic NADH when it is reoxidized by the electron-transport chain using the glycerol 3-phosphate shuttle? A) B) C) D) E)

2.5 1.5 2.0 1.0 None of the answers is correct.

Ans: B Section: 18.5 35) In the malate-aspartate shuttle, electrons from NADH are transferred to ________, forming malate. A) B) C) D) E)

oxaloacetate aspartate acetate glutamate None of the answers is correct.

Ans: A Section: 18.5

Short-Answer Questions 36) Provide a brief description of oxidative phosphorylation. Ans: It is the process in which ATP is formed, due to the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers in the inner membrane of the mitochondria. Section: Introduction 37) Draw the structure of a mitochondrion and indicate the sites of oxidative phosphorylation and the citric acid cycle. Be sure to label your figure to clearly denote where these processes take place. Ans: The drawing should include the overall shape with the outer membrane and the inner membrane, the inner-membrane space, matrix, and cristae labeled. Most of the TCA cycle takes place in the matrix, while oxidative phosphorylation occurs in the inner mitochondrial membrane. It should closely resemble text Figure 18.2.

Section: 18.1 38) What is the currently accepted model which explains the presence of mitochondria in eukaryotic cells? What is the best evidence which supports this model? Ans: It is believed that the organelles are the result of a single endosymbiotic event in which one cell engulfed a bacterium. The structure of mitochondria is consistent with this theory in that it has the general size and physical characteristics of a bacterium including a double membrane and a circular (or sometimes linear) genome. Furthermore, DNA sequence analysis suggests that an ancestor of an existing bacterium is the source for extant mitochondria. Section: 18.2 39) What is the driving force for electron transport through the electron-transport chain? Ans: NADH is a strong reducing agent and is poised to donate electrons to a strong oxidizing agent such as O2. Transfer of two electrons from NADH to O2 results in a substantial release of free energy (–220.1 kJ mol–1). Section: 18.2 40) Explain why less ATP is made from the reoxidation of FADH2 as compared to NADH. Ans: Complex II is not a proton pump. When electrons flow from FADH2 to oxygen, as catalyzed by Complex II, Complex III, and Complex IV, fewer protons are pumped out of the matrix as compared to NADH. Thus, fewer ATP molecules are ultimately made. Section: 18.3 41) Give the balanced equation for the net reaction catalyzed by Q-cytochrome c oxidoreducatase. Ans: QH2 + 2 Cyt cox + 2 H+matrix  Q + 2 Cyt cred + 4 H+cytosol Section: 18.3 42) Describe the major defensive strategy that cells employ to prevent the harmful effects of the reactive oxygen species (ROS) that are inevitably produced during respiration. Ans: The enzyme superoxide dismutase converts superoxide radicals to peroxide and oxygen (requires protons), and the enzyme catalase converts hydrogen peroxide to water and oxygen. Both of these enzymes are ubiquitously expressed and operate at near perfect catalytic efficiency. Section: 18.3 43) Discuss the evolution of the cytochrome c protein. Ans: Cytochrome c has been studied in many organisms with mitochondrial respiratory systems and shows little divergence. Cytochrome c, from many different organisms, can react with the cytochrome c oxidase from other organisms, demonstrating little structural difference at their interfaces. The amino acid sequences of the various cytochrome c proteins are similar and, over a billion years of evolution, 25% of the amino acids remained unchanged.

Section: 18.3 44) Describe the function of protons in the mechanism of ATP synthesis by the F1 subunit of ATP synthase. Ans: Recent evidence suggests that the role of the proton gradient is not to form ATP but to release it from the synthase. The proton gradient is necessary for ATP synthesis because the binding of a proton to the enzyme causes a conformational change that releases the bound ATP. Section: 18.4 45) What evidence demonstrated the ATP synthase has components that can actually rotate? Ans: 33 subunits were cloned and expressed with the  subunits bearing a poly-histidine tag which binds nickel ions. This allowed the F1 subunit to be attached to a nickel coated slide. Using fluorescently tagged actin linked to the subunit, the ATP dependent rotation could be observed using a fluorescent microscope. Section: 18.4. and Figure 18.30 46) How does the glycerol 3-phosphate shuttle function? Ans: Electrons from NADH are transferred to DHAP, to form glycerol-3-P, a reaction that occurs in the cytosol. Glycerol-3-P diffuses through the outer membrane and then transfers the electrons to FAD in a reaction catalyzed by glycerol-3-phosphate dehydrogenase located in the inner membrane. The FADH2 then transfers the electrons to Q. Section: 18.5 47) In the malate-aspartate shuttle, how is oxaloacetate regenerated since there is no transporter for oxaloacetate across the inner membrane? Ans: Oxaloacetate is interconverted between malate and α-ketoglutarate, which requires the concomitant interconversion of glutamate and aspartate. Identical sets of reactions take place both inside and outside the mitochondria to accomplish the translocation of NADH reducing equivalents. Section: 18.5 48) How is oxidative phosphorylation regulated? Ans: The electrons do not flow unless ADP is available to be simultaneously phosphorylated to ATP. Thus, the synthesis of ATP does not occur unless ADP levels are high. This is referred to as acceptor control. Section: 18.6 49) What are uncoupling agents? Provide an example of when these might be useful. Ans: Uncoupling agents destroy the proton gradient across the inner membrane by carrying protons back into the matrix. This disrupts the coupling of electron transport to oxidative phosphorylation, and the energy is released as heat instead of being used to drive

phosphorylation of ADP. Brown fat utilizes an uncoupling agent UCP-1 as a means of accomplishing non-shivering thermogenesis to generate heat for newborns. Other examples of the function of brown fat are also acceptable examples. Section: 18.6 50) Explain why carbon monoxide is toxic. Ans: Carbon monoxide binds to the ferrous ion of cytochrome a3 of cytochrome c oxidase. This blocks the electron flow to oxygen and the proton-motive force can no longer be generated. Without the proton gradient, the phosphorylation of ADP ceases. Section: 18.6...