quiz lehninger ch 19 final

8/17/2019 Quiz Lehninger Ch 19 Final

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Chapter 19 Oxidative Phosphorylation and Photophosphorylation

Multiple Choice Questions

1. Almost all of the oxygen (O 2) one consumes in breathing is converted to:

A) acetyl-CoA.B) carbon dioxide (CO 2).C) carbon monoxide and then to carbon dioxide.D) None of the aboveE) ater.

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2. !hich of the follo ing electron carriers is not able to transfer one electron at a time"

A) NA#$B) %&NC) %A#D) 'bi uinoneE) $eme

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3. A ne com ound isolated from mitochondria is claimed to re resent a reviously unrecogni*edcarrier in the electron transfer chain. +t is given the name coen*yme ,. !hich line of evidence doyou feel is the least conclusive in assigning this com ound a osition in the electron transfer chain"

A) Alternate oxidation and reduction of the mitochondrion-bound coen*yme , can be readilydemonstrated.

B) emoval of coen*yme , from the mitochondria results in a decreased rate of oxygenconsum tion.

C) he rate of oxidation and reduction of mitochondrion-bound coen*yme is of the same order ofmagnitude as the overall rate of electron transfer in mitochondria as measured by oxygenconsum tion.

D) he reduction otential of , is bet een that of t o com ounds /no n to artici ate in theelectron trans ort chain

E) !hen added to a mitochondrial sus ension0 coen*yme , is ta/en u very ra idly and s ecifically by the mitochondria.

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4. Antimycin A bloc/s electron transfer bet een cytochromes b and c1. +f intact mitochondria ereincubated ith antimycin A0 excess NA#$0 and an ade uate su ly of O 20 hich of the follo ing

ould be found in the oxidi*ed state"

A) Coen*yme B) Cytochrome a 3

C) Cytochrome bD) Cytochrome eE) Cytochrome f

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5. educed $ 2 is not formed by hich of the follo ing"

A) Com lex + and NA#$

B) Com lex ++ and succinateC) Com lex +++ and cytochrome c#) %atty acid oxidationE) Oxidation of glycerol-3- hos hate

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6. +n the reoxidation of $ 2 by urified ubi uinone-cytochrome c reductase (Com lex +++) from heartmuscle0 the overall stoichiometry of the reaction re uires 2 mol of cytochrome c er mole of $ 2

because:

A) cytochrome c is a one-electron acce tor0 hereas $ 2 is a t o-electron donor.B) cytochrome c is a t o-electron acce tor0 hereas $ 2 is a one-electron donor.C) cytochrome c is ater soluble and o erates bet een the inner and outer mitochondrial

membranesD) heart muscle has a high rate of oxidative metabolism0 and therefore re uires t ice as much

cytochrome c as $ 2 for electron transfer to roceed normally.E) t o molecules of cytochrome c must first combine hysically before they are catalytically

active.

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7. !hich of the follo ing is not a feature of com lex +4"

A) Cytochrome c is a one-electron donor.B) Oxygen is a substrate.C) Co er is an essential metal for the reaction.D) %or every electron assed to com lex +40 t o rotons are consumed from the matrix (N) side.E) +n order to generate t o ater molecules0 com lex +4 must go through the catalytic cycle t o

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times.

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8. !hich of the follo ing is not true of the roton motive force ( mf)"

A) One com onent of the mf is the chemical gradient of rotons.B) One com onent of the mf is the charge gradient of rotons.C) 5eneration of the mf in mitochondria re uires succinate.#) he mf is generated by the electron trans ort chain in mitochondria.E) he mf drives A 6 synthesis in mitochondria.

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9. Cyanide0 oligomycin0 and 207-dinitro henol (#N6) are inhibitors of mitochondrial aerobic hos horylation. !hich of the follo ing statements correctly describes the mode of action of thethree inhibitors"

A) Cyanide and 207-dinitro henol inhibit the res iratory chain0 and oligomycin inhibits thesynthesis of A 6.

B) Cyanide inhibits the res iratory chain0 hereas oligomycin and 207-dinitro henol inhibit thesynthesis of A 6.

C) Cyanide0 oligomycin0 and 207-dinitro henol com ete ith O 2 for cytochrome oxidase (com lex+4).

#) Oligomycin and cyanide inhibit synthesis of A 68 207-dinitro henol inhibits the res iratorychain.

E) Oligomycin inhibits the res iratory chain0 hereas cyanide and 207-dinitro henol revent thesynthesis of A 6.

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10. +f electron transfer in tightly cou led mitochondria is bloc/ed ( ith antimycin A) bet eencytochrome b and cytochrome c10 then:

A) all A 6 synthesis ill sto .B) A 6 synthesis ill continue0 but the 69O ratio ill dro to one.C) electron transfer from NA#$ ill cease0 but O 2 u ta/e ill continue.D) electron transfer from succinate to O 2 ill continue unabated.

E) energy diverted from the cytochromes ill be used to ma/e A 60 and the 69O ratio ill rise.

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11. +n normal mitochondria0 the rate of NA#$ consum tion (oxidation) ill:

A) be increased in active muscle0 decreased in inactive muscle.B) be very lo if the A 6 synthase is inhibited0 but increase hen an uncou ler is added.

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C) decrease if mitochondrial A#6 is de leted.D) decrease hen cyanide is used to revent electron transfer through the cytochrome a a 3

com lex.E) All of the above

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12. !hich of the follo ing statements about the chemiosmotic theory is correct "

A) ;lectron transfer in mitochondria is accom anied by an asymmetric release of rotons on one side of the inner mitochondrial membrane.

B) +t redicts that oxidative hos horylation can occur0 even in the absence of an intact innermitochondrial membrance.

C) he effect of uncou ling reagents is a conse uence of their ability to carry electrons throughmembranes.

D) he membrane A 6 synthase has no significant role in the chemiosmotic theory.E) All of the above

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13. !hich of the follo ing statements about the chemiosmotic theory is false "

A) ;lectron transfer in mitochondria is accom anied by an asymmetric release of rotons on one side of the inner mitochondrial membrane.

B) ;nergy is conserved as a transmembrane $ gradient.C) Oxidative hos horylation cannot occur in membrane-free re arations.D) he effect of uncou ling reagents is a conse uence of their ability to carry rotons through

membranes.E) he membrane A 6ase0 hich lays an im ortant role in other hy otheses for energy cou ling0

has no significant role in the chemiosmotic theory.

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14. ' on the addition of 207-dinitro henol (#N6) to a sus ension of mitochondria carrying out oxidative hos horylation lin/ed to the oxidation of malate0 all of the follo ing occur except :

A) oxygen consum tion decreases.B) oxygen consum tion increases.C) the 69O ratio dro s from a value of a roximately 2.< to =.D) the roton gradient dissi ates.;) the rate of trans ort of electrons from NA#$ to O 2 becomes maximal.

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15. 'ncou ling of mitochondrial oxidative hos horylation:

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A) allo s continued mitochondrial A 6 formation but halts O 2 consum tion.B) halts all mitochondrial metabolism.C) halts mitochondrial A 6 formation but allo s continued O 2 consum tion.D) slo s do n the citric acid cycle.;) slo s the conversion of glucose to yruvate by glycolysis.

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16. 207-#initro henol and oligomycin inhibit mitochondrial oxidative hos horylation. 207-#initro henol is an uncou ling agent8 oligomycin bloc/s the A 6 synthesis reaction itself. herefore0207-dinitro henol ill:

A) allo electron transfer in the resence of oligomycin.B) allo oxidative hos horylation in the resence of oligomycin.C) bloc/ electron transfer in the resence of oligomycin.

#) diminish O 2 consum tion in the resence of oligomycin.E) None of the above

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17. !hich of the follo ing statements about energy conservation in the mitochondrion is false "

A) #rugs that inhibits the A 6 synthase ill also inhibit the flo of electrons do n the chain ofcarriers.

B) %or oxidative hos horylation to occur0 it is essential to have a closed membranous structureith an inside and an outside.

C) he yield of A 6 er mole of oxidi*able substrate de ends on the substrate.D) 'ncou lers (such as dinitro henol) have exactly the same effect on electron transfer as inhibitorssuch as cyanide8 both bloc/ further electron transfer to oxygen.

;) 'ncou lers >short circuit? the roton gradient0 thereby dissi ating the roton motive force asheat.

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18. !hich of the follo ing is correct concerning the mitochondrial A 6 synthase"

A) +t can synthesi*e A 6 after it is extracted from bro/en mitochondria.

B) +t cataly*es the formation of A 6 even though the reaction has a large ositive∆

G' @.C) +t consists of % o and %1 subunits0 hich are transmembrane (integral) oly e tides.D) +t is actually an A 6ase and only cataly*es the hydrolysis of A 6.E) !hen it cataly*es the A 6 synthesis reaction0 the ∆ G' @ is actually close to *ero.

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19. !hen the ∆ G' @ of the A 6 synthesis reaction is measured on the surface of the A 6 synthase en*yme0

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it is found to be close to *ero. his is thought to be due to:

A) a very lo energy of activation.B) en*yme-induced oxygen exchange.C) stabili*ation of A#6 relative to A 6 by en*yme binding.D) stabili*ation of A 6 relative to A#6 by en*yme binding.;) None of the above

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20. #uring oxidative hos horylation0 the roton motive force that is generated by electron trans ort isused to:

A) create a ore in the inner mitochondrial membrane.B) generate the substrates (A#6 and 6 i) for the A 6 synthase.C) induce a conformational change in the A 6 synthase.D) oxidi*e NA#$ to NA# .E) reduce O 2 to $ 2O.

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21. he oxidation of a articular hydroxy substrate to a /eto roduct by mitochondria has a 69O ratio ofless than 2. he initial oxidation ste is very li/ely directly cou led to the:

A) oxidation of a flavo rotein.B) oxidation of a yridine nucleotide.

C) reduction of a flavo rotein.D) reduction of a yridine nucleotide.E) reduction of cytochrome a 3.

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22. he relative concentrations of A 6 and A#6 control the cellular rates of:

A) glycolysis.B) oxidative hos horylation.C) yruvate oxidation.

#) the citric acid cycle.;) All of the above

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23. he rate of oxidative hos horylation in mitochondria is controlled rimarily by:

A) feedbac/ inhibition by CO 2.

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B) the availability of NA#$ from the CA cycle.C) the concentration of citrate (or) the glycerol-3- hos hate shuttle.#) the mass-action ratio of the A #-A#6 system.;) the resence of thermogenin.

.egulation of oxidative phosphorylationPage: '* #ifficulty: " $ns: #

27. !hich of the follo ing is not controlled by hy oxia-inducible factor ($+%-1)"

A) 5lucose trans ortB) 5lycolysisC) Citric acid cycle#) Com ex + of the res iratory chain;) Com lex +4 of the res iratory chain

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2<. &ammals roduce heat by using the endogenous uncou ling agent:

A) the small molecule 2-7-#initro henol synthesi*ed by the cell.B) the rotein thermogenin.C) the rotein thioredoxin.#) the rotein cytochrome c.;) a modified form of the % o%1 A 6ase.

Mitochondria in thermogenesis, steroid synthesis, and apoptosisPage: '! #ifficulty: " $ns: )

2 . !hich one of the follo ing best describes the role of mitochondria in a o tosis"

A) ;sca e of cytochrome c into the cyto lasmB) +ncreased rate of fatty acid β -oxidationC) +ncrease in ermeability of outer membrane#) 'ncou ling of oxidative hos horylation;) Both A and C are correct.

Mitochondria in thermogenesis, steroid synthesis, and apoptosisPage: '% #ifficulty: " $ns: E

2D. &utations in mitochondrial genes lay a role in each of the follo ing diseases except :

A) adult onset diabetes.B) cystic fibrosis.C) hy ertro hic cardiomyo athy.#) EeberFs hereditary o tic neuro athy.;) myoclonic e ile sy.

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Mitochondrial genes: their origin and the effects of mutationPages: ' & ' #ifficulty: " $ns: )

2G. !hich one of the follo ing statements about human mitochondria is true "

A) About H== mitochondrial roteins are encoded by nuclear genes.B) &itochondrial genes are inherited from both maternal and aternal sources.C) r NA and t NA are im orted from the cyto lasm and used in mitochondrial rotein synthesis.#) he mitochondrial genome codes for all roteins found in mitochondria.;) he mitochondrial genome is not subIect to mutations.

Mitochondrial genes: their origin and the effects of mutationPages: '(& ' #ifficulty: " $ns: $

2H. +n hoto hos horylation0 absor tion of light energy in chloro last >light reactions? leads to:

A) absor tion of CO 2 and release of O 2.B) absor tion of O 2 and release of CO 2.C) hydrolysis of A 6 and reduction of NA#6 .#) synthesis of A 6 and oxidation of NA#6$.;) use of iron-sulfur roteins.

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30. !hich of the follo ing statements about the light reactions in hotosynthetic lants is false "

A) A membrane-bound A 6ase cou les A 6 synthesis to electron transfer.B) No CO 2 is fixed in the light reactions.C) he ultimate electron acce tor is O 2.

D) he ultimate source of electrons for the rocess is $ 2O.E) here are t o distinct hotosystems0 lin/ed together by an electron transfer chain.

/eneral features of photophosphorylationPages: '9& * #ifficulty: " $ns: )

31. he light reactions in hotosynthetic higher lants:

A) do not re uire chloro hyll.B) roduce A 6 and consume NA#$.C) re uire the action of a single reaction center.D) result in the s litting of $ 2O0 yielding O 2.

E) serve to roduce light so that lants can see underground.

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32. 6hotosynthetic hos horylation and oxidative hos horylation a ear to be generally similar rocesses0 both consisting of A 6 synthesis cou led to the transfer of electrons along an electroncarrier chain. !hich of the follo ing is not true of both rocesses"

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A) Both contain cytochromes and flavins in their electron carrier chains.B) Both rocesses are associated ith membranous elements of the cell.C) Both use oxygen as a terminal electron acce tor.D) ;ach re resents the maIor route of A 6 synthesis in those cells in hich it is found.;) 6rotons are um ed from the inside to the outside of both mitochondria and chloro last

membranes

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33. Oxidative hos horylation and hoto hos horylation share all of the follo ing except :

A) chloro hyll.B) involvement of cytochromes.C) artici ation of uinones.#) roton um ing across a membrane to create electrochemical otential.;) use of iron-sulfur roteins.

/eneral features of photophosphorylationPages: '9 * #ifficulty: " $ns: $

37. he ex erimental determination of the effectiveness of light of different colors in romoting hotosynthesis is called the:

A) absor tion s ectrum.B) action s ectrum.C) difference s ectrum.#) reflectance s ectrum.;) refraction s ectrum.

0ight a sorptionPages: ! % #ifficulty: " $ns: )

3<. +n hat order do the follo ing five ste s occur in the hotochemical reaction centers"

1) ;xcitation of the chloro hyll a molecule at the reaction center 2) e lacement of the electron in the reaction center chloro hyll3) Eight excitation of antenna chloro hyll molecule7) 6assage of excited electron to electron-transfer chain<) ;xiton transfer to neighboring chloro hyll

A) 1-2-3-7-<B) 3-2-<-7-1C) 3-<-1-7-2#) 7-2-3-<-1;) <-7-3-2-1

0ight a sorptionPages: % ( #ifficulty: " $ns: C

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3 . !hich one of the follo ing is true about reaction centers"

A) Cyanobacteria and lants have t o reaction centers arranged in tandem.B) Cyanobacteria contain a single reaction center of the %e-J ty e.C) 5reen sulfur bacteria have t o reaction centers arranged in tandem.#) 6lant hotosystems have a single reaction center of the heo hytin- uinone ty e.;) 6ur le bacteria contain a single reaction center of the %e-J ty e.

+he central photochemical event: light-driven electron flo2Pages: '& 9 #ifficulty: " $ns: $

3D. +n the hotolytic cleavage of ater by the oxygen-evolving com lex K2$ 2O → 7 $ 7e O 2L0 homany hotons of light at a avelength of G= nm are re uired"

A) 1B) 2C) 7#);) G

+he central photochemical event: light-driven electron flo2Page: * #ifficulty: " $ns: C

3G. 6lace the follo ing electron-carriers into the ro er order as found in lant chloro lasts.

1) Cytochrome b f com lex2) 6 G=3) 6D==7) 6lastocyanin<) NA#6$

A) 20 10 30 70 <B) 20 70 30 10 <C) 30 10 70 20 <#) 20 10 70 30 <;) 30 70 20 10 <

+he central photochemical event: light-driven electron flo2Page: 9 #ifficulty: ! $ns: #

3H. !hich of the follo ing is not true about cyclic electron flo "

A) Cyclic electron flo roduces more NA#6$ er hoton than noncyclic electron flo .B) Cyclic electron flo involves only 6J+.C) 6lastocyanin is re uired for cyclic electron flo .#) Cyclic electron flo leads to the build-u of a roton gradient.;) Cyclic electron flo does not roduce O 2.

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+he central photochemical event: light-driven electron flo26age: DG3 #ifficulty: 2 Ans: A

7=. Cyclic electron flo in chloro lasts roduces:

A) A 6 and O 20 but not NA#6$.B) A 60 but not NA#6$ or O 2.C) NA#6$ and A 60 but not O 2.#) NA#6$0 but not A 6 or O 2.;) O 20 but not A 6 or NA#6$.

+he central photochemical event: light-driven electron flo2Page: ! #ifficulty: ! $ns: )

71. !hich one of the follo ing statements about hoto hos horylation is false "

A) +t can be uncou led from electron flo by agents that dissi ate the roton gradient.B) he difference in $ bet een the luminal and stromal side of the thyla/oid membrane is 3 $

units.C) he luminal side of the thyla/oid membrane has a higher $ than the stromal side.#) he number of A 6s formed er oxygen molecule is about three.;) he reaction centers0 electron carriers0 and A 6-forming en*ymes are located in the thyla/oid

membrane.

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72. Cyclic electron flo in chloro lasts roduces:

A) A 6 and O 20 but not NA#6$.B) A 60 but not NA#6$ or O 2.C) NA#6$ and A 60 but not O 2.#) NA#6$0 but not A 6 or O 2.;) O 20 but not A 6 or NA#6$.

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73. !hich of the follo ing is not found in modern cyanobacteria"

A) 6J+

B) 6J++C) NA#$ dehydrogenase com lex +#) Oxygen-reducing com lex +4;) &itochondria

+he evolution of oxygenic photosynthesisPage: (9 #ifficulty: 1 $ns: E

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3hort $ns2er Questions

44. As you read and ans er this uestion0 you are ( resumably) consuming oxygen. !hat single reactionaccounts for most of your oxygen consum tion"

$ns: O2 is converted to $ 2O by electrons from the res iratory chain. he final ste is the onecataly*ed by cytochrome oxidase (com lex +4).

Electron-transfer reactions in mitochondriaPage: !" #ifficulty: 1

45. Jho the ath of electrons from ubi uinone ( or coen*yme ) to oxygen in the mitochondrialres iratory chain. One of the t o com ounds ( and O 2) has a standard reduction otential ( E' @) of=.G2 40 and the other0 =.=7< 4. !hich value belongs to each com ound" $o did you deduce this"

$ns: $ 2 → cyt b → cyt c1 → cyt c → cyt ( a a 3) → O 2

E' @ for O2 must be the larger ositive value ( =.G2) because electron flo occurs s ontaneously to theelectron acce tor ith the more ositive E' @.

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46. #iagram the ath of electron flo from NA#$ to the final electron acce tor during electron trans ortin mitochondria. %or each electron carrier0 indicate hether only electrons0 or both electrons and

rotons0 are acce ted9donated by that carrier. Also0 indicate here electrons from succinate oxidationenter the chain of carriers.

$ns: NA#$ (both) → %6 (both) → (both) → cyt b (e only) → cyt c1 (e only) → cyt c (e only)→ cyt ( a a 3) (e only) → O 2 (both)

;lectrons from succinate enter at .

Electron-transfer reactions in mitochondriaPages: ! #ifficulty: !

47. #uring electron transfer through the mitochondrial res iratory chain0 the overall reaction is: NA#$ 192 O 2 $ → NA# $ 2O. he difference in reduction otentials for the t o half-reactions ( ∆ E' @) is 1.17 4. Jho ho you ould calculate the standard free-energy change0 ∆ G' @0 for the reaction as ritten above. ( he %araday constant0 0 is H .7G /M94 mol.)

$ns: ∆ G' @ n ∆ E' @ ( 2)(H .7G /M94 mol)(1.174) 22= /M9mol

Electron-transfer reactions in mitochondriaPage: ! #ifficulty: "

48. he standard reduction otential for ubi uinone ( or coen*yme ) is =.=7< 40 and the standardreduction otential ( E' @) for %A# is =.21H 4. 'sing these values0 sho that the oxidation of %A#$ 2

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by ubi uinone theoretically liberates enough energy to drive the synthesis of A 6. he %aradayconstant0 0 is H .7G /M94 mol.∆ G' @ for A 6 synthesis is 3=.< /M9mol.

$ns: ∆ E' @ E' @(oxidant) E' @(reductant) =.=7< ( =.21H) =.2 7 4∆ G' @ n ∆ E' @ ( 2)(H .7G /M94.mol)(=.2 7 4) <1.= /M9mol.

6assage of t o electrons from %A#$ 2 to can0 in rinci le0 rovide sufficient energy forsynthesi*ing 1 A 6.

Electron-transfer reactions in mitochondriaPage: ! #ifficulty: "

49. A recently discovered bacterium carries out A 6 synthesis cou led to the flo of electrons through achain of carriers to some electron acce tor. he com onents of its electron transfer chain differ fromthose found in mitochondria8 they are listed belo ith their standard reduction otentials.

;lectron carriers in the ne ly discovered bacterium:

PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP ;lectrons E' @

Oxidant eductant transferred (4) PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP NA# NA#$ 2 =.32flavo rotein b (%6b) flavo rotein b 2 =. 2

(oxidi*ed) (reduced)cytochrome c (%e3 ) cytochrome c (%e2 ) 1 =.22%e-J rotein %e-J rotein 2 =.GH

(oxidi*ed) (reduced)flavo rotein a (%6a) flavo rotein a 2 =.DD

(oxidi*ed) (reduced) PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP

(a) 6lace the electron carriers in the order in hich they are most li/ely to act in carrying electrons.(b) +s it li/ely that O 2 (for hich E' @ =.G2 4) is the final electron acce tor in this organism" !hyor hy not" (c) $o ould you calculate the maximum number of A 6 molecules that couldtheoretically be synthesi*ed0 under standard conditions0 er air of electrons transfered through thischain of carriers" ( he %araday constant0 0 is H .7G /M94 mol.) ∆ G' @ for A 6 synthesis is 3=.</M9mol.

$ns: (a) %6b→ NA# → cyt c → %6a → %e-J(b) No8 %e-J has a larger E' @0 so ill robably be the terminal acce tor.(c) %irst0 calculate ∆ G' @ for e flo from %6 b to %e-J:∆ E' @ E' @(oxidant) E' @(reductant) =.GH ( =. 2) 1.<1 4∆ G' @ n ∆ E' @ ( 2)(H .7G /M94 mol)(1.<1 4) 2H1 /M92e

heoretically0 the flo of t o electrons from %6 b to %e-J could drive the synthesis of 2H1 /M93=.</M9mol H.< mol A 6. Because only hole numbers of molecules can be made0 the correct ans er isH mol A 6 er electron air.

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Electron-transfer reactions in mitochondriaPages: ! #ifficulty: !

50. #escribe0 in sim le diagrams and a fe ords0 the chemiosmotic theory for cou ling oxidation to hos horylation in mitochondria.

$ns: here are t o central elements in the chemiosmotic model:(1) ;nergetically favorable electron flo through asymmetrically arranged membrane-bound carrierscauses transmembrane flo of $ 0 creating a roton gradient (a roton motive force).(2) he energy released by >do nhill? movement of rotons is ca tured hen A#6 and 6 i arecondensed by A 6 synthase (% o%1). (Jee %ig. 1H-1H.)

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51. Com ound Q is an inhibitor of mitochondrial A 6 synthesis. +t as observed that hen com ound Qas added to cells0 the NA# 9NA#$ ratio decreased. !ould you ex ect Q to be an uncou ling agent

or an inhibitor of res iratory electron transfer" ;x lain.

$ns: +t is an inhibitor of electron transfer8 its addition lo ers the NA# 9NA#$ ratio because NA#$ roduced by oxidative reactions in mitochondria can no longer be reoxidi*ed by electron flo to O 2.+f it had been an uncou ling agent0 the NA#$ could be reoxidi*ed0 the ratio of NA# 9NA#$ ould

be unchanged0 but there ould be no build-u of a roton gradient (i.e.0 no synthesis of A 6).

$+P synthesisPages: % & %9 #ifficulty: !

52. Cyanide ion (CN ) bloc/s electron transfer in mitochondria at the level of cytochrome a a3. 207-#initro henol (#N6) is an uncou ler of mitochondrial oxidative hos horylation. #ra gra hs (A 6

synthesi*ed vs. time and O 2 consumed vs. time) ith labeled curves to sho the effects of addingeach of these com ounds separately to a sus ension of mitochondria su lied ith O 20 succinate0A#60 and 6 i. 'se an arro to indicate the time of drug addition.

$ns:


53. 5ive an exam le of (a) an uncou ler of oxidative hos horylation0 and (b) an inhibitor of res iration.

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(c) #escribe the difference in the effects of such uncou lers and inhibitors on mitochondrial function.

$ns: (a) 'ncou lers include #N60 valinomycin0 and CCC6. (b) es iration inhibitors includeantimycin A0 iericidin A0 CN 0 rotenone0 and amytal. (c) 'ncou lers sto formation of A 6 hileallo ing electron transfer to continue. +nhibitors of res iration bloc/ both electron transfer and

hos horylation.


54. &itochondria carrying out oxidative hos horylation consume oxygen. ;x lain hat ha ens to thisoxygen0 and describe the effect of an uncou ling agent such as 207-dinitro henol on the rate ofoxygen consum tion. Assume there is a sufficient su ly of oxidi*able substrate0 A#60 and 6 i.

$ns: O2 is reduced to $ 2O by electrons assed through the res iratory chain. Addition of 207-dinitro henol0 hich uncou les hos horylation (A 6 synthesis) from electron flo 0 actuallystimulates O 2 consum tion slightly by removing the >drag? of A 6 synthesis.


55. he com ound 207-dinitro henol (#N6)0 an uncou ler0 as briefly used as a eight-loss drug. Jomeof its effects in eo le ho too/ the drug included eight loss and higher than normal bodytem erature. Jome eo le even died. ;x lain the first t o effects of the com ound in biochemicalterms.

$ns: he uncou ler allo s continuous oxidation of fuels (li/e fatty acids from adi ose tissue).Because little or no A 6 synthesis occurs0 the res iratory control that normally limits fuel oxidation

hen A 6 levels are high does not o erate. he energy of fuel oxidation is dissi ated as heat0accounting for the elevated body tem erature.


56. Although molecular oxygen (O 2) does not artici ate directly in any of the reactions of the citric acidcycle0 the cycle o erates only hen O 2 is resent. ;x lain this observation.

$ns: he citric acid cycle roduces NA#$0 hich is normally reoxidi*ed to NA# by the assage of electrons through the res iratory chain to O 2. !ith no O 2 to acce t electrons0 NA#$ accumulates0

NA# is de leted0 and the citric acid cycle slo s for lac/ of NA# .


57. he s/un/ cabbage ( Symphocarpus foetidus ) can maintain a tem erature of 1= 2< @C higher than thetem erature of the surrounding air. Juggest a mechanism for this.

$ns: One ossible heat-generating mechanism is artially uncou led mitochondria in hich some ofthe energy of electron flo is dissi ated as heat. his is most easily achieved using by asses of someof the mitochondrial com lexes that normally ca ture favorable electron flo to ards ma/ing a

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roton gradient that then drives A 6 synthesis. +f some of these com lexes are omitted0 then largerdo nhill ste s by electrons that do not drive roton flo ill instead generate heat. (Jee Box 1H-1.)

$+P synthesisPage: % #ifficulty: "

<G. Consider a liver cell carrying out the oxidation of glucose under aerobic conditions. Ju ose that eadded a very otent and s ecific inhibitor of the mitochondrial A 6 synthase0 com letely inhibitingthis en*yme. +ndicate hether each of the follo ing statements about the effect of this inhibitor istrue or false8 if false0 ex lain in a sentence or t o hy it is false.

RRRR (a) A 6 roduction in the cell ill uic/ly dro to *ero. RRRR (b) he rate of glucose consum tion by this cell ill decrease shar ly. RRRR (c) he rate of oxygen consum tion ill increase. RRRR (d) he citric acid cycle ill s eed u to com ensate. RRRR (e) he cell ill s itch to fatty acid oxidation as an alternative to glucose oxidation0 and theinhibitor ill therefore have no effect on A 6 roduction.

$ns: (a) %alse. &itochondrial A 6 synthesis ill cease0 but to com ensate0 cells ill accelerate the roduction of A 6 by glycolysis0 reventing A 6 levels from dro ing to *ero.(b) %alse. he acceleration of glycolysis noted above ill actually increase the rate of glucoseconsum tion.(c) %alse. Because electron transfer through the res iratory chain is tightly cou led to A 6 synthesis0

bloc/ing A 6 synthase bloc/s electron flo and oxygen consum tion.(d) %alse. he citric acid cycle is an oxidative ath ay0 roducing NA#$. !hen electron flo from

NA#$ to O 2 is bloc/ed0 NA#$ accumulates0 NA# is de leted0 and the citric acid cycle slo s forlac/ of an electron acce tor (NA# ).(e) %alse. Oxidation of fats roduces NA#$0 %A#$ 20 and acetyl-CoA0 hich is further oxidi*ed viathe citric acid cycle. %or the reasons noted above0 bloc/ing electron flo through the res iratorychain revents A 6 synthesis ith energy from fatty acid oxidation.


<H. !hen the % 1 ortion of the A 6 synthetase com lex is removed from the mitochondrial membraneand studied in solution0 it functions as an A 6ase. !hy does it not function as an A 6 synthetase"

$ns: Ei/e all en*ymes0 the % 1 subunit of the A 6 synthase cataly*es a reaction in both directions:

A#6 6 i ↔ A 6 $ 2O

he standard free-energy change (∆

G' @) for A 6 hydrolysis is 3=.< /M9mol. !ith no roton motiveforce to drive the reaction to ard A 6 synthesis0 the hydrolysis (A 6ase activity) occurss ontaneously.

$+P synthesisPages: (*& (" #ifficulty: "

60. !hen the ∆ G' @ of the A 6 synthesis reaction is measured on the surface of the A 6 synthase en*yme0it as found to be close to *ero. #escribe briefly hy this is so.

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$ns: he en*yme binds A 6 more tightly than A#6 thus stabili*ing the former (i.e.0 the roduct ofthe synthesis reaction) relative to the latter (i.e.0 the reactant in the synthesis reaction).

$+P synthesisPage: (1 #ifficulty: "

61. ;x lain briefly the current model for ho the roton motive force that is generated by electrontrans ort is used to drive the A 6 synthesis reaction.

$ns: he en*yme binds A 6 more tightly than A#6 thus stabili*ing the former0 ma/ing the ∆ G' @ ofthe synthetic reaction more favorable. Once the reaction has occurred0 the A 6 roduct must bereleased from the en*yme ( hich is unfavorable). he roton motive force causes rotons to moveacross the inner mitochondrial membrane through the ore in the % o com lex. his movement leadsto conformational changes that decrease the affinity of the % 1 ortion of the synthase for A 60resulting in its release from the en*yme.

$+P synthesisPages: (*& (( #ifficulty: !

2. %or each of the follo ing ex lain hether they are trans orted into or out of the mitochondrion andcomment briefly on the mechanism for each:

(1) NA#$(2) +norganic hos hate(3) A#6

$ns: NA#$ roduced by glycolysis is indirectly transferred into the mitochondrion via the as arate-malate shuttle. (Only NA#$ e uivalents are moved in0 not the actual NA#$ molecule itself.)+norganic hos hate is moved into the mitochondrion via the hos hate translocon0 hichaccom anied by anti- ort of a roton and is driven by the roton motive force. A#6 is trans ortedinto the mitochondrion by the adenine nucleotide translocase that simultaneously moves an A 6 outof the mitochondrion and is driven by the roton motive force.

$+P synthesisPages: ( & (9 #ifficulty: "

3. #escribe and ex lain the t o different ratios that affect the rate of res iration in mitochondria. !hatis accom lished by these control mechanisms"

$ns: he acceptor control ratio describes ho much res iration ta/es lace in the resence of A#6vs. the absence of A#6. ( he availability of A#6 to form A 6 limits res iration.) he mass-actionratio relates the relative concentration of A 6 to A#6. %or both ratios0 high A#6 levels lead toincreases in O 2 consum tion. he overall effect is to /ee the level of A 6 nearly constant and to

revent oxidation of fuels hen the demand for A 6 is lo .

.egulation of oxidative phosphorylationPage: '* #ifficulty: "

7. +n his studies of alcoholic fermentation by yeast0 Eouis 6asteur noted that the sudden addition ofoxygen (O 2) to a reviously anaerobic culture of fermenting gra e Iuice resulted in a dramatic

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decrease in the rate of glucose consum tion. his >6asteur effect? can be counteracted by theaddition of 207-dinitro henol (#N6)0 an uncou ler of oxidative hos horylation. (a) !hy ould theyeast cells consume less glucose in the resence of oxygen" Can you estimate ho much lessglucose they ould use" (b) !hy ould #N6 counteract or revent the 6asteur effect"

$ns: (a) #uring aerobic oxidation of glucose0 the yield of A 6 is about 3G mol er mole of glucose.'nder anaerobic conditions0 only 2 A 6 are roduced er glucose. hus0 to get the same amount ofA 60 a cell needs to use 1H times more glucose anaerobically. (b) Because #N6 bloc/s the rinci al

ath of aerobic A 6 roduction0 aerobic cells in the resence of #N6 need about the same amount ofglucose as anaerobic cells.

.egulation of oxidative phosphorylationPages: (9 #ifficulty: "

<. #escribe the role of hy oxia-inducible factor ($+%-1) in reducing reactive oxygen s ecies ( OJ).

$ns: 'nder conditions of lo oxygen0 the electron trans ort chain may accidentally generate OJ because of the lo levels of the final electron acce tor (oxygen). herefore0 $+%-1 is induced andserves as a transcri tion factor to increase glycolysis (i.e.0 anaerobic consum tion of glucose). Jomeof the roteins hose transcri tion are turned on to effect this res onse are the glucose trans orter0glycolytic en*ymes0 and lactate dehydrogenase. Additionally0 the activity of yruvate dehydrogenaseis reduced (via hos horylation) to slo the citric acid cycle and the flux of electrons into theelectron trans ort chain.

.egulation of oxidative phosphorylationPages: '*& '1 #ifficulty: !

. #escribe the role of cytochrome c in a o tosis.

$ns: ' on receiving one or more of a variety of signals to trigger a o tosis0 the ermeability of theouter membrane of mitochondria increase0 allo ing the esca e of cytochrome c from theintermembrane s ace. Cytochrome c then associates ith A af-1 to form an a o tosome. hea o otsome rovides the scaffold for the cas ases that initiate a cascade of roteolytic activations0ultimately leading to cell death.

Mitochondria in thermogenesis, steroid synthesis, and apoptosisPages: '%& '( #ifficulty: "

D. &utations in mitochondrial genes fre uently roduce diseases that affect the brain and s/eletalmuscle (mitochondrial ence halomyo athies). !hy are these t o tissues articularly sensitive tomitochondrial mutations"

$ns: Both the brain and s/eletal muscles are heavily de endent on an abundant su ly of A 6 fornormal functioning.

Mitochondrial genes: their origin and the effects of mutationPage: ' #ifficulty: "

G. #iscuss three lines of evidence that su ort the theory that mitochondria evolved fromendosymbiontic bacteria.

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$ns: 1) &odern ro/aryotes have res iratory chains very similar to those in mitochondria. 2)Bacteria translate rotons out ard across their lasma membrane and use this roton gradient to driveA 6 synthesis and other energy-re uiring rocesses such as flagellar motion. 3) 'nli/e most otherorganelles0 mitochondria in eu/aryotic cells retain their o n genome.

Mitochondrial genes: their origin and the effects of mutationPages: '(& '' #ifficulty: "

H. 6hoto hos horylation differs from oxidative hos horylation in that the former re uires the in ut ofenergy in the form of RRRRRRRRRRR to create a good electron donor. +n hoto hos horylation0electrons flo through a series of membrane-bound carriers including RRRRRRRRRRR 0 RRRRRRRRRRR 0and RRRRRRRRRRR roteins0 hereas RRRRRRRRRRR are um ed across a membrane to create an

RRRRRRRRRRR otential.

$ns: Eight8 cytochromes8 uinones8 iron-sulfur8 rotons8 electrochemical

/eneral features of photophosphorylationPages: '9& * #ifficulty: "

D=. #escribe the effect(s) that a mitochondrial uncou ler such as 207-dinitro henol (#N6) ould have on hoto hos horylation.

$ns: 'ncou lers li/e #N60 hich act by dissi ating transmembrane roton gradients0 oulduncou le hoto hos horylation because it is also de endent on a transmembrane roton gradient to

rovide the energy re uired to synthesi*e A 6 from A#6 and 6 i.

/eneral features of photophosphorylationPages: '9& *#ifficulty: "

D1. #iscuss ho >accessory igments? are able to extend the range of light absor tion of thechloro hylls. Name some accessory igments.

$ns: Accessory igments are able to absorb light and transfer the absorbed energy to thechloro hylls in a rocess /no as >exciton transfer.? o accessory igments are β -carotene andlutein.

0ight a sorptionPage: ! #ifficulty: "

D2. !hat is an action s ectrum0 and hat do ea/s in an action s ectrum signify" Jho a ty ical action

s ectrum lot for hotosynthesis.

$ns: An action s ectrum is a lot of the effectiveness of a rocess (such as hotosynthesis) versusavelength of incident light. +ts ea/s signify the resence of a chromo hore that absorbs light at

that avelength. (Jee %ig. 1H-<3.)

0ight a sorptionPage: % #ifficulty: "

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73. #escribe hat ha ens at hotosystem + from the oint here an antenna chloro hyll moleculeabsorbs a hoton of light to the assage of an electron to NA#6 .

$ns: he antenna chloro hyll molecule asses the energy of the hoton0 via exciton transfer0 toneighboring chloro hyll molecules and ultimately to reaction center chloro hyll molecules. hisexcites 6D== to 6D==S0 hich donates an electron to A =. %rom A=0 electrons ass to hyllo uinone(A 1)0 through an %e-J rotein0 to ferredoxin0 then through a flavo rotein to NA#6 .

6D==S → A= → A 1 → %e-J → NA#6 (Jee %igs. 1H-<G8 1H- =.)

+he central photochemical event: light-driven electron flo2Pages: 9& 1 #ifficulty: "

74. 5ive five general classes of electron carriers that function in both mitochondrial electron transfer toO2 and hotosynthetic electron transfer.

$ns: Any five of the follo ing: yridine nucleotides (NA#$0 NA#6$)8 flavin nucleotides (%A#$ 20%&N$ 2)8 uinones (ubi uinone0 lasto uinone)8 cytochromes8 %e-J roteins8 flavo roteins.

+he central photochemical event: light-driven electron flo2Pages: '& ! #ifficulty: "

75. he rocesses of oxidative hos horylation cou led ith electron transfer (in mitochondria) and hoto hos horylation (in chloro lasts) resemble each other in certain res ects. #escribe five ays in

hich the t o rocesses are similar0 and describe three significant differences bet een the t o rocesses.

$ns: Jimilarities include: both contain a chain of membrane-bound electron carriers8 electron transfer leads to establishment of a roton gradient8 an A 6ase9A 6 synthase is a cou ling factor8 A 6synthesis is sensitive to uncou lers8 both re uire a system of intact membranes to se arate electronsinside and outside. #ifferences include: source of reducing o er (NA#$ vs. light)0 roduct (A 6 inres iration8 NA#6$ in hotosynthesis)8 source of oxidi*ing o er (O 2 in mitochondria8 light in

hotosynthesis).

+he central photochemical event: light-driven electron flo2Pages: '9& ! #ifficulty: !

76. Jho the ath of electrons from hotosystem ++ to NA#6$ in the chloro last. !hat is the source ofthe energy that moves electrons through this ath" Jho here oxygen is involved in this ath ay.

$ns: $ 2O → 6 G= → 6heo hytin → 6 A → 6 B → cyt b f com lex → 6lastocyanin → 6D== → A=

→ A1 → %e-J → %erredoxin → %erredoxin-NA#6 oxidoreductase → NA#6 .

he energy that drives the electron flo is from light. O 2 is generated from $ 2O hen $ 2O donateselectrons to 6J++.

+he central photochemical event: light-driven electron flo2Pages: '& 9 #ifficulty: "

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77. 6lants carrying out hotosynthesis roduce O 2. #escribe the source of this O 20 and ex lain0 ithchemical e uations or schematic diagrams0 hy O 2 roduction occurs only during daylight hours.

$ns: O2 is generated by the s litting and oxidation of $ 2O0 driven by the absor tion of a hoton by6J++ ( hich occurs only in daylight). (Jee %ig. 1H-<G.)

+he central photochemical event: light-driven electron flo2Page: 9 #ifficulty: "

78. #uring hoto hos horylation in lants0 electrons flo through a series of carriers in the chloro last.!hat is the ultimate donor of electrons0 and hat is the ultimate acce tor" !hat rovides the energyto move those electrons"

$ns: he ultimate donor is $ 2O0 and the acce tor0 NA#6 . he energy that drives this electron flois from light.

+he central photochemical event: light-driven electron flo2Page: 9 #ifficulty: "

DH. #escribe hat ha ens hen a hoton is absorbed by hotosystem ++8 end the descri tion of electronflo at lasto uinone.

$ns: Absor tion of a hoton by 6J++ excites 6 G= to 6 G=S0 hich asses an electron to heo hytin0hich asses the electron to lasto uinone. 6 G=0 no lac/ing an electron0 ta/es one a ay from a

> ater-s litting com lex? of 6J++0 hich in turn ta/es one from $ 2O. (Jee %ig. 1H-<G.)

+he central photochemical event: light-driven electron flo2Page: 9 #ifficulty: !

80. #C&' is an herbicide that acts by bloc/ing hotosynthetic electron flo from hotosystem ++ (6J++)to the cytochrome b f com lex. 6redict the effect of #C&' on O 2 roduction and on A 6 synthesisin the chloro lasts of lants sensitive to #C&'.

$ns: #C&' bloc/s electron flo from 6J++ to 6J+0 reventing generation of O 2 from $ 2O. A 6synthesis ill be inhibited0 but not com letely8 cyclic hoto hos horylation can continue in the

resence of #C&'.

$+P synthesis y photophosphorylationPages: !9, #ifficulty: !

81. 5iven that TG hotons are re uired to roduce one molecule of O 20 roughly ho many hotons arere uired to roduce one molecule of glucose.

$ns: Jince the overall reaction of hotosynthesis is CO 2 $ 2O C $ 12O O 20 six molecules of O2 must be roduced0 re uiring x G or roughly 7G hotons.

$+P synthesis y photophosphorylationPage: #ifficulty: "

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82. Jome hotosynthetic bacteria contain the rotein bacteriorhodo sin0 hich absorbs light and um s rotons out of the cell directly. Briefly describe ho such a cell could use bacteriorhodo sin and an$ A 6ase to ma/e A 6 using light.

$ns: On ex osure to light0 bacteriorhodo sin ould um rotons out of the cell0 establishing a roton gradient. his roton gradient could be used by an $ A 6ase to generate A 6.

+he Evolution of Oxygenic PhotosynthesisPages: 9 & 9* #ifficulty: 1

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quiz lehninger ch 19 final

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