生物化学英文版习题Word文件下载.docx
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(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
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
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
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