Biochemistry I Final Exam and Answer fall.docx

Biochemistry I Final Exam and Answer fall.docx

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BiochemistryIFinalExamandAnswerfall

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Biochemistry（I）FinalExam（fall,2004）

NOTE:

Youmustwriteyouranswerontheanswersheet!

PartI:

Forthefollowingmultiplechoicequestions,oneanswerismostappropriate（2.518=45points）.

1.Withregardtoaminoacids,whichstatementisfalse?

A）Aminoacidscanactasprotondonorsandacceptors.

B）AllaminoacidsdiscoveredinorganismareLenantiomers.

C）AnLaminoacidcanbeDextrorotary.

D）Aconjugateacid/basepairisatitsgreatestbufferingcapacitywhenthepHequalsitspK.

E）Non-standardaminoacidscanbefoundinthehydrolysisproductofaprotein.

2.AmixtureofAla,Arg,andAspinapH5.5bufferwasplacedonacationexchangecolumn（thecolumnisnegativelycharged）andelutedwiththesamebuffer.Whatistheorderofelutionfromthecolumn?

UsethesepKavalues:

terminalCOOH-2,terminalNH3+-9,R-amino-10,R-COOH-3

A）Arg,AlathenAsp

B）Arg,AspthenAla

C）Asp,AlathenArg

D）Asp,ArgthenAsp

E）Ala,AspthenArg

3.Proteinscanbechromatographicallyseparatedbytheirdifferent

A）Charge.

B）Molecularweight.

C）Hydrophobicity.

D）Affinityforothermolecules.

E）Allofabove.

4.Apeptidewasfoundtohaveamolecularmassofabout650anduponhydrolysisproducedAla,Cys,Lys,Phe,andValina1:

1:

1:

1:

1ratio.ThepeptideupontreatmentwithSanger'sreagent（FDNB）producedNP-Cysandexposuretocarboxypeptidaseproducedvaline.ChymotrypsintreatmentofthepeptideproducedadipeptidethatcontainedsulfurandhasaUVabsorbance,andatripeptide.Exposureofthepeptidetotrypsinproducedadipeptideandatripeptide.Thesequenceofthepeptideis

A）val-ala-lys-phe-cys

B）cys-lys-phe-ala-val

C）cys-ala-lys-phe-val

D）cys-phe-lys-ala-val

E）val-phe-lys-ala-cys

5.Withregardtoproteinstructure,whichstatementisfalse?

A）Thedominantforcethatdrivesawater-solubleproteintofoldishydrophobicinteraction.

B）Thenumberofhydrogenbondswithinaproteinintendstobeminimized.

C）Theconformationsofanativeproteinarepossiblythelowestenergystate.

D）Theconformationsofanativeproteinarecountless.

E）Disulfdebridgescanincreasethestabilityofaprotein.

6.Whichstructureisuniquetocollagen?

A）Thealphahelix.

B）Thedoublehelix.

C）Thetriplehelix.

D）Thebetastructure.

E）Thebetabarrel.

7.Whichproteinhasquaternarystructure?

A）Insulin.

B）Anaturalantibody.

C）Chymotrypsin.

D）Aspartatetranscarbamoylase（ATCase）.

E）Myoglobin.

8.Whichofthefollowingare"broadthemesusedindiscussingenzymereactionmechanisms"?

A）Proximitystabilization

B）Transitionstatestabilization

C）Acid-basecatalysis

D）Covalentcatalysis

E）Alloftheabove

9.Underphysiologicalconditions,whichofthefollowingprocessesisnotanimportantmethodforregulatingtheactivityofenzymes?

A）Phosphorylation

B）Temperaturechanges

C）Adenylation

D）Allostericregulation

E）Proteinprocessing

10.Theconversionofglucosetopyruvateisamultistepprocessrequiringtenenzymes.Ifamutationoccursresultinginalackofactivityforoneoftheseenzymes,whichofthefollowinghappens?

A）Theconcentrationofthemetabolicintermediatewhichisthesubstrateofthemissingenzymeislikelytoincreaseandaccumulate

B）Theconcentrationofpyruvatewillincrease

C）Thecellwillproducemoreoftheothernineenzymestomaintainsteadystate

D）Theconcentrationofthemetabolicintermediatewhichistheproductofthemissingenzymewilldecrease

E）AandD

11.Indicatewhichistrueaboutenzymes.

A）Enzymesarepermanentlychangedduringtheconversionofsubstrateintoproduct.

B）Enzymesinteractirreversiblywiththeirsubstrates.

C）Enzymeschangetheenergydifferencebetweensubstratesandproducts.

D）Enzymesreducetheenergyofactivationfortheconversionofreactantintoproduct.

E）Enzymesincreasetheenergycontentoftheproducts.

12.Considerareactionasfollows:

A+B<====>C+D,ΔG'0=+10.0Kj/mol

Howcanthisreactiongoforward?

A）Couplingofthisreactiontoahighlyexergonicreactionthroughacommonintermediate.

B）Immediateremovaloftheproducts.

C）Additionoftheappropriateenzyme.

D）AandB.

E）Alloftheabove.

13.Whichstatementisnottrueofenzymeinhibitors?

A）Acompetitiveinhibitorbindstheactivesiteoftheenzyme.

B）AllostericenzymesexhibitMichaelis-Mentonkinetics.

C）Anoncompetitiveenzymebindselsewherethantheactivesite.

D）Noncompetitiveinhibitorscannotbecompletelyovercomebyaddingmoresubstrate.

E）Competitiveinhibitioncanbecompletelyovercomebyaddingmoresubstrate.

14.YoucouldmostdramaticallydestabilizeaduplexDNAmoleculeinanaqueoussolutionby

A）Decreasingthetemperature.

B）Decreasingtheconcentrationofsalt.

C）Decreasingtheconcentrationoforganicsolvents.

D）AdjustingthepHtoavaluenear7.

E）Addingadetergent.

15.WithregardtoDNA,whichstatementisfalse?

A）Triplehelixandtetraplextendtoappearatsiteswherereplication,recombinationortranscriptionisinitiatedorregulated.

B）HydrogenbondsaretheonlyforcetostabilizeDNAstructure.

C）TheabsorbanceofDNAat260nmwillrisewhenitisdenatured.

D）Z-DNAtractsmayplayanroleintheregulationoftheexpressionofsomegenesoringeneticrecombination.

E）B-DNAisthemoststablestructureinphysiologicalcondition.

16.Withregardtobiologicalmembrane,whichstatementisfalse?

A）Theratioofproteinstolipidsisvariousindifferentmembranes.

B）Themembranewithmoreproteinshasmorecomplicatedfunctionthanthatwithfewerproteins.

C）Eachmembranehasacharacteristiccompositionoflipids.

D）Lipidssymmetricallydistributeinthetwoleafletsofamembrane.

E）Theflip-flopmovementoflipidsisdonebyakindofenzyme.

17.Whichofthefollowingstatementsaretrueabouttheinteractionsbetweensubstrateandactivesite?

Youcanassumethatthecatalysisgoestocompletion.

①CatalyticresiduescanbeaffectedbypH

②ThemajorityofbondsinE-Sinteractionsarecovalentbondssuchasdisulfideandpeptidebonds

③Thecomponentsofamixtureofthetwomirror-imageisomersofacompound,calledaracemicmixture,willbeacteduponequallybyanenzyme

④Theactivesitecanalteritselftobetterfitthesubstrate

⑤Theactivesiteispermanentlyalteredbyitsinteractionwithsubstrate

⑥Thesubstrateispermanentlyalteredbyitsinteractionwithactivesite

⑦Competitiveinhibitorshavenoaffectontheactivesite

A）①,②,③

B）②,④,⑤

C）③,④,⑤

D）②,④,⑦

E）①,④,⑥

18.Whichofthefollowingstatementsrefertoglycogen（"G"）andwhichrefertocellulose（"C"）?

①Containsbeta-1,4glycosidicbonds

②Cannotbedigestedbymammalianenzymes

③Straight-chainmoleculeofhightensilestrength

④Containsalpha1,6-glycosidicbonds

⑤Branchedmolecule

⑥Usedasastructuralcomponent

⑦Usedasanutritionalstoragemolecule

A）G=①,④,⑦;C=②,③,⑤,⑥

B）G=④,⑤,⑦;C=①,②,③,⑥

C）G=②,③,④,⑥;C=①,⑤,⑦

D）G=⑤,⑥;C=①,②,③,④,⑦

E）G=①,②,④;C=③,⑤,⑥,⑦

PartII:

Accordingtothefiguresandconditionsprovided,filltheblanks（Fewerhavetwoormoreanswers,55points）.

19.Proteinsecondarystructuresandtheirorganization（5points）.

A）Parallelβ-pleatedsheet;

B）Antiparallelβ-pleatedsheet;

C）ResiduesofProandGly;

D）ResiduesofProandVal;

E）Residuesofhydrophilicaminoacids;

F）Residuesofhydrophobicaminoacids;

G）ResidueofArg,Lys,orHis;

H）ResidueofAsp,orGlu.

a）Onedomainoftheproteiniscomposedof

b）Whataminoacidsarefrequentlyfoundin5

c）Iftheresiduesat6ispositivelycharged,thentheresidueat7isbest

d）Whatresiduesoccurmostlyat1and2?

e）Whatresiduesoccurmostlyat3and4?

20.Severaloxygendissociationcurvesareshowninthefollowingfigure.（5points）.

AssumethatcurveCcorrespondstopurifiedhemoglobinplacedinasolutioncontainingphysiologicalconcentrationsofCO2andBPGatapHof7.0.Below,indicatewhichofthecurvesreflectsthechangesnotedinphysiologicalconditionsbyplacingthecurve#onthelinesbelow（Useonlyonecurvechoice/physiologicalchange）:

a.DecreasedCO2concentration______________

b.IncreaseBPGconcentration_______________

c.Dissociationofhemoglobinintosubunits

d.AmutationthateliminatesionpairsthatstabilizetheTordeoxygenatedstate

e.Fetalhemoglobinoramutationwhichincreasebindingaffinityforoxygen

21.Supersecondarystructureofproteins（5points）.

A）--Loop;

B）GreekKey;

C）-Corner;

D）Right-handedconnectionbetweenstrands;

E）Notobserved;

F）Veryrare.

a.b.c.D

d.e.f.

22.Proteinclassification（5points）.

A）All;B）All:

C）/;D）+;E）Superfamily;F）Species

a.A

d.e.f.

23.Kineticsofenzymeinhibitionordouble-substratereaction（5points）.

a.CompetitiveinhibitionA

b.Non-competitiveinhibition

c.Uncompetitiveinhibition

d.Mixedcompetitiveinhibition

If[S2]andsubstitutefor[I]andrespectively,then:

e.Double-substrateenzymereactioninvolvingaternarycomplex

f.Double-substrateenzymereactionwithaping-pongmechanism

24.StructureaboutNucleotidesandDNA（5points）

a.Exo-2´/Endo-2´configurationofribose

b.Exo-3´/Endo-3´configurationofribose

c.HoogsteenPairs

d.Canformcruciformstructure

e.CanformH-DNA

25.Biomembranelipids（5points）

a.Sphingolipids

b.PhospholipaseA1

c.PhospholipaseA2

d.PhospholipaseC

e.Sphingosine

26.Classesofmembranetransports（5points）

a.Passive-transportersC

b.PrimaryActivetranspo