fosf.oxi

Chapter 18 Oxidative Phosphorylation

Matching Questions Use the following to answer questions 1-10:

Choose the correct answer from the list below. Not all of the answers will be used.

a) mitochondria

b) chemiosmotic theory

c) coenzyme Q

d) FMN

e) iron-sulfur clusters

f) respiration

g) transporters

h) porins

i) succinate dehydrogenase

j) cytochrome c oxidase

k) ATP-ADP translocase

l) malate-aspartate shuttle

1. ____________ This is where oxidative phosphorylation occurs in eukaryotes.

Ans: a

Section: Introduction

2. ____________ An ATP-generating process in which an inorganic substance such as oxygen

serves as the ultimate electron acceptor.

Ans: f


3. ____________ The permeability of the outer mitochondrial membrane is primarily due to the

presence of these substances.

Ans: h

Section: 18.1

4. ____________ This electron carrier is a derivative of quinone and has an isoprenoid tail.

Ans: c

Section: 18.3

5. ____________ This enzyme catalyzes the reduction of O2.

Ans: j

Section: 18.3


2

6. ____________ This prosthetic group is present in complexes I, II, and III of electron

transport.

Ans: e

Section: 18.3

7. ____________ This citric acid cycle enzyme is also part of an electron-transport complex.

Ans: i

Section: 18.3

8. ____________ This is the name given to the hypothesis proposed by Peter Mitchell to explain

how ATP synthesis is coupled to electron transport.

Ans: b

Section: 18.4

9. ____________ Atractyloside inhibits this mitochondrial protein.

Ans: k

Section: 18.6

10. ____________ This is a process by which cytoplasmic NADH can be re-oxidized by O2 using

the electron-transport system.

Ans: l

Section: 18.5

Fill in the Blank Questions

11. A strong oxidizing agent has a strong tendency to ____________ (accept, donate) electron(s).

Ans: accept Section: 18.2

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


3

17. _______________ is a molecular assembly in the inner mitochondrial membrane that carries out

the synthesis of ATP.

Ans: F1Fo 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) sodium ion D) potassium ion

B) chloride ion E) None of the above.

C) proton

Ans: C Section: Introduction

22. When glucose is totally oxidized to CO2 and H2O, how many ATP molecules are made by

oxidative phosphorylation relative to the maximum yield?

A) 12 out of 30

B) 26 out of 30

C) 26 out of 32

D) 12 out of 38

E) None of the above.

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 Fo 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


4

24. Choose the correct path taken by a pair of electrons as it travels down the electron-transport

chain.

A) NADH complex I CoQ Complex III Cyt c complex IV O2

B) FADH2 complex I CoQ Complex III Cyt c complex IV O2

C) NADH complex I complex II Complex III Cyt c complex IV O2

D) FADH2 complex II CoQ Complex III Cyt c complex IV O2

E) a and d

Ans: E Section: 18.3

25. Which of the following does not participate in, nor is a component of, the electron-transport

chain?

A) coenzyme A

B) non-heme, iron-sulfur proteins

C) coenzyme Q

D) cytochrome c1

E) NADH

Ans: A Section: 18.3

26. In prokaryotes the site of ATP-synthesizing machinery is

A) the mitochondrial matrix. D) the nucleolus.

B) the outer cell wall. E) none of the above.

C) the cytoplasmic membrane.


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 mitochondiral membrane.

E) none of the above.


28. Coenzyme Q is also called

A) NADH. D) all of the above.

B) oxidoreductase. E) none of the above.

C) ubiquinone.


29. Which of the following does not pump protons?

A) Complex I D) Complex IV

B) Complex II E) All of the above.

C) Complex III


30. In proteins these amino acid residues usually complex to the iron-sulfur clusters.

A) Gly B) Arg C) Cys D) All of the above. E) None of the above.



5

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) All of the above.

E) None of the above.


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 these


33. What is the reaction of ATP synthase?

A) AMP3

+ 2 HPO42

+ H+

ATP4

+ H2O

B) ADP3

+ HPO42

+ H+ ATP

4 + H2O

C) ADP3

+ HPO42

+ 2H+

ATP4

+ H2O

D) AMP3

+ 2 HPO42

+ 2H+ ATP

4 + H2O

E) None of the above


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) 2.5. B) 1.5. C) 2.0. D) 1.0. E) None of the above.


35. In the malate-aspartate shuttle, electrons from NADH are transferred to ________, forming

malate.

A) oxaloacetate D) glutamate

B) aspartate E) none of the above

C) acetate


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.


37. Draw the structure of a mitochondrion and indicate the sites of oxidative phosphorylation and

the citric acid cycle.

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


6

38. What is the current belief for the presence of mitochondria in eukaryotic cells? What is the

proof?

Ans: It is believed that the organelles are the result of an endosymbiotic event. The structure of

mitochondria is consistent with this theory. Furthermore, DNA sequence analysis

suggests that an ancestor of an existing bacterium is the source for extant mitochondria.

Section: 18.2

39. Describe the path by which electrons from FADH2 enter the electron transport chain.

Ans: Succinate dehydrogenase, which forms FADH2, is part of the succinate-Q reductase

complex. The FADH2 does not leave this complex, but transfers electrons to the iron

sulfur centers of the complex, and then to Q.

Section: 18.3

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 oxido-reducatase.

Ans: QH2 + 2Cyt cox + 2H+

matrix Q + 2Cyt cred + 4H+

cytosol

Section: 18.3

42. What is a major defense strategy against oxidative damage caused by reactive oxygen species

(ROS)?

Ans: Superoxide dismutase converts superoxide radicals to peroxide and oxygen (requires

protons), and catalase converts hydrogen peroxide to water and oxygen.

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 the many different organisms

can react with the cytochrome c oxidase, 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. What is the actual function of the protons in the synthesis of ATP by FoF1 ATP synthase?

Ans: 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. The role of the proton

gradient is not to form ATP but to release it from the synthase.

Section: 18.4

45. What was the proof that the ATP synthase was rotating?

Ans: Using cloned 3 3 subunits, with the subunits tagged with a histidine that attached it to

a nickel coated slide, and using another fluorescent tag linked to the subunit, the

rotation could be observed using a fluorescent microscope.

Section: 18.4. and Figure 18.30


7

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 of 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: Inside the mitochondria, the malate is converted to OAA by malate dehydrogenase. The

OAA is converted to aspartate, which can be transported out of the mitochondria. The

aspartate can then be converted to oxaloacetate. The aspartate-oxaloacetate reactions

require glutamate and -ketoglutarate.

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 uncouplers? Provide an example of when this might be useful.

Ans: Uncouplers 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. Non-shivering thermogenesis, to generate heat for newborns, is

one example provided (due to the uncoupler UCP-1).

Section: 18.6

50. Explain why carbon monoxide is toxic.

Ans: Carbon monoxide bond 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 cannot occur. Thus

energy production ceases.

Section: 18.6

fosf.oxi

Documents