生物化学英文版习题.docx

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生物化学英文版习题

I.FuelMetabolism

PART1:

StructureandFunctionofProtein

Directions:

Eachofthenumbereditemsorincompletestatementsinthissectionisfollowedbyanswersorbycompletionsofthestatement.Selecttheoneletteredanswerorcompletionthatisbestineachcase.

Questions9and10

Usethestructuretoanswerquestions9and10：

Asp-Ala-Ser-Glu-Val-Arg

9.TheC-terminalaminoacidofthehexapeptideshownis

（A）alanine（B）asparagine（C）aspartate（D）arginine

10.AtphysiologicpH（7.4）,thishexapeptidewillcontainanetchargeof

（A）-2（B）-1（C）0（D）+1（E）+2

11.Whichoneofthefollowingtypesofbondsiscovalent?

（A）Hydrophobic（B）Hydrogen（C）Disulfide（D）Electrostatic

13.Whichoneofthefollowingconditionscauseshemoglobintoreleaseoxygenmore

readily?

（A）Metabolicalkalosis

（B）Increasedproductionof2,3-bisphosphoglycerate（BPG）

（C）Hyperventilation,leadingtodecreasedlevelsofCO2intheblood

（D）Replacementoftheβsubunitswithγsubunits

14.Productionofwhichofthefollowingproreinswouldbemostdirectlyaffectedin

scurvy?

（A）Myoglobin（B）Collagen（C）Insulin（D）Hemoglobin

15.Theactivesiteofanenzyme

（A）isformedonlyafteradditionofaspecificsubstrate

（B）isdirectlyinvolvedinbindingofallostericinhibitors

（C）residesinafewadjacentaminoacidresiduesintheprimarysequenceofthe

polypeptidechain

（D）bindscompetitiveinhibitors

16.AnenzymecatalyzingthereactionE+S=ES→E+Pwasmixedwith4mMsubstrate.Theinitialrateofproductformationwas25%ofVm.TheKmfortheenzymeis

（A）2mM（B）4mM（C）9mM（D）12mM（E）25mM

17.Thevelocity（v）ofanenzyme-catalyzedreaction

（A）decreasesasthesubstrateconcentrationincreases

（B）islowestwhentheenzymeissaturatedwithsubstrate

（C）isrelatedtothesubstrateconcentrationatlhVm

（D）isindependentofthepHofthesolution

Questions18and19

Refertothefollowingreactionwhenansweringquestions18and19.

Fumarate+H20↔malate

fumarase

18.Fumarasecatalyzestheconversionoffumaratetomalate.IthasaKmof5μMfor

fumarateandaVmaxof50μmol/min/mgofproteinwhenmeasuredinthedirectionofmalateformation.Theconcentrationoffumaraterequiredtogiveavelocityof25μmol/min/mgproteinis

（A）2μM（B）5μM（C）10μM（D）20μM（E）50μM

19.TheKmforfumaraseisapproximately5μMforfumarate.Thefumarateconcentrationinmitochondriaisapproximately2mM.Ifthefumarateconcentrationdroppedto1mM,thereactionratewould

（A）increaseslightly（B）decreaseslightly

（C）decreasebyonehalf（D）stayexactlythesame

20.Hexokinaseandglucokinasebothcatalyzethephosphorylationofglucosetoglucose6-phosphate.ThevaluesofKmfortheenzymesare10μMand0.02M,respectively.Ifbloodglucoseis5mMunderfastingconditionsand20mMafterahigh-carbohydratemeal

（A）hexokinasewillfunctionnearitsVmaxunderfastingconditions

（B）glucokinasewillfunctionnearitsVmaxunderfastingconditions

（C）hexokinasewillfunctionatlessthanone-halfVmaxafterahigh-carbohydratemeal

（D）glucokinasewillfunctionatlessthanone-halfVmaxafterahigh-carbohydratemeal

21.Acompetitiveinhibitorofanenzyme

（A）increasesKmbutdoesnotaffectVmax

（B）decreasesKmbutdoesnotaffectVmax

（C）increasesVmaxbutdoesnotaffectKm

（D）decreasesVmaxbutdoesnotaffectKm

（E）decreasesbothVmaxandKm

Questions22-25

Refertothegraphwhenansweringquestions22-25.

22.ThevalueofKmfortheenzymedepictedbycurveAis

（A）0.5mM（B）1mM（C）2mM（D）1μmol/min/mg（E）10μmol/min/mg

23.ThevalueofVmfortheenzymedepictedbycurveAis

（A）0.1μmol/min/mg（B）1μmol/min/mg

（C）10μmol/min/mg（D）0.5mM（E）2mM

24.CurveBdepictstheeffectofaninhibitoronthesystemdescribedbycurveA.Thisinhibitor

（A）isacompetitiveinhibitor（B）isanoncompetitiveinhibitor

（C）increasestheVmax（D）decreasestheKm

25.CurveCdepictstheeffectofadifferentinhibitorofthesystemdescribedbycurveA.Thissecondinhibitor

（A）isacompetitiveinhibitor

（B）isanoncompetitiveinhibitor

（C）increasestheVmax

（D）decreasestheKm

answer：

DBCBBDDCBBAAACAB

Directions:

Eachgroupofitemsinthissectionconsistsofletteredoptionsfollowedbyasetofnumbereditems.Foreachitem,selecttheoneletteredoptionthatismostcloselyassociatedwithit.Eachletteredoptionmaybeselectedonce,morethanonce,ornotatall.

Questions33-37

Matcheachcharacteristicbelowwiththeproteinitbestdescribes.

（A）Hemoglobin（B）Myoglobin（C）Collagen（D）Insulin

33.RequiresvitaminCforitssynthesis

34.Hasoneoxygenbindingsiteandonepolypeptidechain

35.Containsfourmoleculesofheinepermoleculeofprotein

36.Isconvertedintoatriplehelixduringitssynthesis

37.Iscomposedoftwopolypeptidechainsjoinedbydisulfidebonds

answer：

CBACD

9-D.Byconvention,peptidesaredrawnwiththeN-terminalaminoacidontheleftandtheC-

terminalaminoacidontheright.Therefore,thispeptidecontainsarginineatitsC-terminus.

10-B.TheN-terminalaspartatecontainsapositivechargeonitsN-terminalaminogroupanda

negativechargeonthecarboxylgroupofitssidechain.Glutamatecontainsanegativechargeon

thecarboxylgroupofitssidechain.TheC-terminalargininecontainsanegativechargeonitsC-

terminalcarboxylgroupandapositivechargeonitssidechain.Thus,theoverallchargesare+2

and-3,whichgivesanetchargeof-1.

11-C.Disulfidebondsarecovalent.

13-B.Increased[H+],BPG,andCO2decreasetheaffinityofHbAforO2.Fetalhemoglobin（HbF

=（α2Y2）hasagreateraffinityforO2thanHbA（α2β2）.IncreasedBPGwouldcauseO2tobemore

readilyreleased.

14-B.ScurvyiscausedbyadeficiencyofvitaminC.Thehydroxylationofprolineandlysine

residuesincollagenrequiresvitaminCandoxygen.Globinsynthesismightbeindirectly

affectedbecauseabsorptionofironfromtheintestineisstimulatedbyvitaminC.Ironis

involvedinheinesynthesis,whichregulatesglobinsynthesis.

15-D.Theactivesiteisformedwhentheenzymefoldsintoitsthree-dimensionalconfiguration

andmayinvolveaminoacidresiduesthatarefarapartintheprimarysequence.Substratemol-

eculesbindattheactivesite.Competitiveinhibitorscompetewiththesubstrate.（Bothbindat

theactivesite.）Allostericinhibitorsbindatasiteotherthantheactivesite.

16-D.IntheMichaelis-Mentenequation,v=（Vmx[S]）/（Km+[S]）.Inthiscase,1/4Vm=（Vmx

4）/（Km+4）,orKm=12mM.

17-C.Thevelocityofanenzyme-catalyzedreactionincreasesasthesubstrateconcentration

increases.Itishighestwhentheenzymeissaturatedwithsubstrate.Then,vequalsVm,the

maximumvelocity.ThevelocitydependsonKm.EnzymeshaveanoptimalpHatwhichtheir

activityismaximal.

18-B.Avelocityof25is1/2Vm,whichis50.Km=[S]at1/2Vm.Km.=5μM.

19-B.Thevelocitydecreasesslightlywhentheconcentrationofthesubstratedropsfrom2mM

to1mM.At2mM,v=（Vmaxx2,000μM）/（5μM+2,000μM）=99.8%Vmax.At1mM,v=（Vmaxx1,000μM）/（5μpM+1,000μM）=99.5%Vmax.

20-A.Duringfasting,forhexokinase,v=（5xVm）/（0.01+5）=99.8%Vm;forglucokinase,v=

（5xVm）/（20+5）=20%Vm.Inthefedstate,forhexokinase,v=（20xVm）/（0.01+20）=99.9%Vm;forglucokinase,v=（20xVm）/（20+20）=50%Vm.HexokinasewillfunctionnearitsVminboth

thefedandfastingstates.Glucokinase（aliverenzyme）ismoreactiveinthefedthanthefastingstate.At20mMglucose,itsvelocityis50%Vm.

21-A.Acompetitiveinhibitorcompeteswiththesubstratefortheactivesiteoftheenzyme,ineffect

increasingtheKm.Asthesubstrateconcentrationisincreased,thesubstrate,bycompetingwiththe

inhibitor,canovercomeitsinhibitoryeffects,andeventuallythenormalVisreached.

22-A.Theinterceptonthexaxisis-1/Km=-2.Therefore,Km=0.5mM.

23-C.Theinterceptontheyaxisis1/Vm=0.1.Therefore,V=10μmol/min/mg.

24-A.Withthisinhibitor,Visthesame（theyinterceptisthesame）,butKmislarger（thex

interceptislessnegative）.Therefore,thisisacompetitiveinhibitor.

25-B.Withthisinhibitor,VmislowerbutKmisthesame.Itisanoncompetitiveinhibitor.

33-C.ProlineandlysineresiduesincollagenarehydroxylatedinareactionthatrequirestaminC.

34-B.Eachmyoglobinmoleculecontainsonepolypeptidechainandoneheinemoleculethat

bindsoneO2molecule.Eachhemoglobinmoleculecontainsfourpolypeptidechains,fourmole-

culesofheine,andfourmoleculesofoxygen.

35-A.Eachmoleculeofhemoglobincontainsfourmoleculesofheine.Eachmyoglobinmolecule

containsonemoleculeofheine.

36-C.Collagenformsatriplehelixduringitssynthesis.

37-D.InsuliniscomposedofanAchainandaBchain,whicharelinkedbydisulfidebonds.

PART2:

nucleicacid

Directions:

Eachofthenumbereditemsorincompletestatementsinthissectionisfollowed

byanswersorbycompletionsofthestatement.Selecttheoneletteredanswerorcompletion

thatisbestineachcase.

1.InDNA,onamolarbasis

（A）adenineequalsthymine（B）adenineequalsuracil（C）guanineequalsadenine

（D）cytosineequalsthymine（E）cytosineequalsuracil

2.WhichofthefollowingsequencesiscomplementarytotheDNAsequence5'-AAGTCCGA-3'?

（A）5'-AAGUCCGA-3'（B）3'-TTCAGGCT-5'（C）5'-TTCAGGCT-3'（D）3'-TCGGACTT-5'

3.DNAcontainswhichoneofthefollowingcomponents?

（A）Nitrogenousbasesjoinedbyphosphodiesterbonds

（B）