Chapter 18 ETC

Cytochrome c oxidase contains four redox centers: two heme groups and two redox centers containing_______.

copper

In a newly discovered electron transport complex a researcher has identified the redox center Fe-S, cytochrome c, and coenzyme Q. The researcher also knows that this complex ultimately passes its electrons to oxygen. What is most likely the redox center which completes this task?

cytochrome c

12. ATP forms (is produced) I. upon transition from the loose to the tight form of the α and β subunit complex of ATP synthase. II. as a result of the flux of electrons through the channel formed by Fo III. as a result of the positive ions pumped into the matrix of the mitochondrion.

I only

17. Which statement(s) concerning the mitochondrial F0F1 ATP synthase is FALSE? I. The F1 subunit includes rotating sets of αβ dimers. II. The F0 subunit includes a ring of between 9 and 12 proton-carrying polypeptides. III. The F1 subunit undergoes a series of conformational changes throughout the course of reaction.

I only

In the electron transport chain, electrons are passed from redox center to redox center ____.

spontaneously due to the redox potential gradient.

37. One method used by newborn mammals to generate heat is referred to as nonshivering thermogenesis. This method utilizes a protein channel called ________ which is present in high levels inside the mitochondria of _____tissue.

thermogenin; brown adipose

38. Approximately how many ATP molecules are synthesized from the oxidation of 1 NADH?

2.5

39. A typical eukaryotic cell contains up to ____ mitochondria each bound by a smooth outer membrane.

2000

15. The effects of a poison on actively respiring mitochondria are being studied to determine its mode of action. When the poison is added, every component of the electron transport chain is found to be in its reduced form based on spectroscopic analysis, and ATP production ceases entirely. It is reasoned that the poison is either blocking the final transfer of electrons to oxygen or is blocking the ATP synthase. Which of the following experiments will help unravel this dilemma?

Add an uncoupling agent along with the poison.

Electrons from FADH2 are delivered to ____ and electrons from NADH are delivered to ____ of the electron transport chain.

Complex II; Complex I

19. Which of the following best describes the function of cytochrome c oxidase?

Cytochrome c oxidase oxidizes four consecutive cytochrome c molecules, via one-electron transfers, while simultaneously reducing one O2 to two H2O.

14. Which statement concerning Complex II of the electron transport chain is FALSE? I. This complex oxidizes FADH2 and reduces coenzyme Q. II. This complex includes the covalently bound enzyme succinate dehydrogenase. III. This complex pumps protons from the matrix to the intermembrane space. IV. This complex also oxidizes succinate to fumarate in the citric acid cycle.

III only

27. Which of the following are TRUE statements regarding the structure of ATP synthase?

It has a membrane-embedded component called F0 and a component found in the matrix referred to as F1.

Which conformation of the active sites in ATP synthase allows binding of substrates?

L state

Use the table below to rank the redox centers in order to produce a favorable electron flow. Redox Center ℰ°' D - 0.002 F - 0.198 Q - 0.225 C - 0.053 Z + 0.002

Q, F, C, D, Z

13. In theory how many protons could be pumped under standard state conditions by Complex III per mol of CoQ oxidized, considering the following information? (NOTE: mt = mitochondria) coenzyme Q + 2H+ + 2 e- → coenzyme QH2 ℰ°' ≈ 0.040 V cytochrome c (Fe3+) + e- → cytochrome c (Fe2+) ℰ° ≈ 0.270 V H+ (outside mt) → H+ (inside mt) ΔG ≈ -20 kJ/mol Faraday constant (F) ≈ 100 kJ/V mol ∆Gº' = -nF∆E0'

greater than four protons but less than or equal to six protons

The cytochromes within complex III all contain _____ groups.

heme

32. The inner mitochondrial membrane divides the mitochondrion into the inner membrane space and the ______.

matrix

All of the following inhibit electron transport EXCEPT

oxaloacetate

Bacteria carry out electron transport in the _____.

plasma membrane

The stoichiometric relationship of ATP synthesis to ______ is referred to as the P/O ratio.

respiration

23. Electrons from cytosolic NADH are transferred to the matrix via electron ______ systems.

shuttle

25. Phosphate (Pi) is transported into the mitochondria from the cytosol by a phosphate carrier which is driven by the

simultaneous transport of H+ into the mitochondrion.

18. Cyclonite is a poison that blocks electron transfer between cytochromes bL and bH. When this poison is added to a suspension of isolated mitochondria, and when spectroscopic analysis is performed,

the coenzyme Q pool will be found in the reduced state, and cytochrome c will be found in the oxidized state.

The structure of ATP synthase changes in conformation as a result of

the rotation of the γ subunit.

36. Based on the estimation presented in the chapter, how many ATP per glucose are synthesized by the aerobic metabolism in eukaryotes?

32

16. A poison that prevents the transfer of electrons from the last [Fe-S] cluster of Complex I to coenzyme Q is added to a suspension of actively respiring mitochondria. Which of the following will be observed?

ATP production would be reduced due to a decrease in the number of protons pumped out of the mitochondrial matrix.

29. Which of the prosthetic groups listed can accept or donate either one or two electrons due to the stability of the semiquinone state?

CoQ

28. Which of the following statements is(are) TRUE about oxidative phosphorylation? I. Electron transport provides energy to pump protons into the intermembrane space. II. An electrochemical gradient is formed across the inner mitochondrial membrane. III. Potassium and sodium ions form an ionic gradient across the inner mitochondrial membrane. IV. Complexes I, II, III, IV actively transport protons into the intermembrane space during electron transport.

I, II

35. The electrons formed from the aerobic oxidation of glucose are I. ultimately transferred to O2 after several other transfer reactions. II. transferred to the coenzymes NAD+ and FAD. III. directly transferred to O2 during the citric acid cycle. IV. transferred to succinate and arachidonic acid.

I, II

22. Rotenone and amytal I. inhibition can be restored by addition of succinate. II. inhibition can be restored by addition of cytochrome c. III. blocks consumption of oxygen. IV. blocks transfer of electrons from CoQ to Complex III.

I, II, III

20. Which of the following is TRUE regarding heme proteins? I. Heme groups are capable of transferring electrons across large distances provided that some molecular network exists as a "path." II. Heme groups are often buried in protein structure because the protein protects the heme and prevents it from indiscriminately transferring electrons. III. The rate of electron transfer from a reduced heme is physiologically significant. IV. Heme groups are often differentiated by their absorption spectrum.

I, II, III, IV

26. The rate of oxidative phosphorylation I. is regulated by the availability of ADP and Pi. II. is reduced when the ratio of [NADH]/[NAD+] is high. III. increases with a higher concentration of reduced cytochrome c IV. is regulated by activity of the ADP-ATP translocator.

I, III, IV

33. Which of the following is TRUE regarding the complexes within the electron transport system? I. Complex II contributes twice as many protons to the gradient than Complex I II. Inhibition of Complex II would decrease the total number of electrons moving through the electron transport chain. III. Inhibition of Complex II would not alter the amount of free energy generated from electrons originating from NADH. IV. Complex I can accept electrons with higher potential than Complex II is able to accept.

II, III

21. Antimycin A I. inhibition can be restored by addition of succinate. II. inhibition can be restored by addition of cytochrome c. III. blocks consumption of oxygen. IV. blocks transfer of electrons from CoQ to Complex III.

II, III, IV

34. Which of the following statements about the mitochondrial inner membrane is TRUE? I. The inner membrane is permeable to CO2, H2O, and small ions. II. The inner membrane contains several transport proteins and membrane bound enzymes. III. In general, a higher inner membrane surface area correlates to a higher rate of respiration. IV. The number of cristae reflects the respiratory activity of the cell.

II, III, IV

24. Cyanide (CN-) I. inhibition can be restored by addition of succinate. II. inhibition can be restored by addition of cytochrome c. III.inhibits electron transport which stops consumption of oxygen. IV. blocks transfer of electrons from CoQ to Complex III.

III only

30. Based on the information in the chapter, which of the following is TRUE regarding Complex III? I. A large portion of Complex III dissociates from the membrane bound portion of the complex. II. Complex III contains three identical cytochrome redox centers. III. The Q cycle allows stepwise reoxidation of the two electrons from CoQH2. IV. A change in conformation of iron sulfur protein (ISP) ensures that the Reiske center is reduced preferentially by CoQ.-

III only

40. Molecules that prevent oxidative damage by the superoxide radical possess ______ properties.

antioxidant

31. Complexes I and II each transfer electrons to ______.

coenzyme Q