生物化学试题及参考答案.docx

生物化学试题及参考答案.docx

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生物化学试题及参考答案

《〈生物化学〉Ⅰ》试题及参考答案

1.ExplanationofTerms（30）

1）EdmanDegradation

AprocedureusedtodeterminethesequenceofaminoacidresiduesfromafreeN-terminusofapolypeptidechain.TheN-terminalresidueischemicallymodified,cleavedfromthechain,andidentifiedbychromatographicprocedures,andtherestofthepolypeptideisrecovered.MultiplereactioncyclesallowidentificationofthenewN-terminalresiduegeneratedbyeachcleavagestep.

2）ProteinKinase

Anyofanumberofenzymesthatphosphorylateoneormorehydroxylorphenolicgroupsinproteins,ATPbeingthephosphoryl-groupdonor.Theattachmentofphosphorylgroupstospecificaminoacidresiduesofaproteiniscatalyzedbyproteinkinases,andremovalofphosphorylgroupsiscatalyzedbyproteinphosphatase.

3）WesternBlotting

1.Separationofproteinsbygelelectrophoresis

2.Transfertheseparatedproteinstoamembrane

3.Membraneblockingwithnonspecificprotein

4.Incubatewithprimaryandsecondaryantibody（antibody-enzymecomplex）

5.Addsubstrate

6.Formationofcolored

4）ImmunoglobulinG（IgG）

ImmunoglobulinG（IgG）isthemajorclassofantibodymoleculeandoneofthemostabundantproteinsinthebloodserum.IgGhasfourpolypeptidechains:

twolargeones,calledheavychains,andtwolightchains,linkedbynoncovalentanddisulfidebondsintoacomplexofMr150,000.

5）GProtein

Guaninenucleotidebindingprotein;anyafamilyofheterotrimericGTP-bindingandhydrolysingproteins,theyareacomponentofreceptormediatedactivationorinhibitionofadenylatecyclaseandothersecondmessengersystemssuchasphosphatidylinositolcycle.Theymediatetheintracellularactionsofmanyhormones,growthfactorsandcytokines.Thesystemiswidelydistributedbutuniquetoeukaryotes.

6）DenaturationofProteinandDNA

Proteindenaturation:

Alossofthree-dimensionalstructuresufficienttocauselossoffunctioniscalledproteindenaturation（byheat,extremesofpH,organicsolvents,urea,guanidinehydrochloride,ordetergents）.

DNAdenaturation:

ThecompleteunwindingandseparationofcomplementarystrandsofDNA.

7）GenomeandProteome

Genome:

Thewholeofthegeneticinformationofanorganism.ItiscontainedasDNAineukaryotiesandprokaryotes,andaseitherDNAorRNAinviruses.Agivenorganismhasonlyonegenomeregardlessofwhethertheorganismishaploid,diploid,orpolyploid.

Proteome:

Thecompleteexpressionprofileoftheproteinsofanorganism.

8）αHelixandβConformation

αHelix:

Conformationofapolypeptidechaininwhichsuccessiveturnsofthehelixareheldtogetherbyhydrogenbondsbetweentheamid（peptide）links.

βConformation:

Anextended,zigzagarrangementofapolypeptidechaininwhichthechainisalmostfullyextendedbutslightlypuckered.

ßsheet;Thezigzagpeptidechainscanbearrangedsidebysidetoformastructureresemblingaseriesofplates.

ßturns;Atypeofsecondarystructureinpolypeptidesconsistingoffouraminoacidresiduesarrangedinatightturn（180º）sothatthepolypeptideturnbackonitself.

9）TranscriptionandTranslation

Transcription:

ThesynthesisofeitherRNAonatemplateofDNAorDNAonatemplateofRNA.

Translation:

ThesynthesisofapolypeptidewhosesequencereflectsthenucleotidessequenceofanmRNAmolecule.

10）DNAPolymeraseandRNAPolymerase

DNAPolymerase:

TheenzymescatalysethesynthesisofDNAfromdeoxyribonucleosidetriphosphatesinthepresenceofanucleic-acidprimer.

RNAPolymerase:

Theenzymethatdirectstranscription,orsynthesisofRNA.

2.Description（30）

1）ThreemajorRNAprocessing.

Capping:

Thecapisastructuralfeaturepresentatthe5’endofmRNAmolecules.Itconsistsof7-methylguanosineandatriphasphatebridgelinkingit5’-5’totheendofpolynucleotidechain.CappingistheprocessofformingorplacingacaponanmRNAmolecule.Functions:

（a）ProtectmRNAsfromdegradation.（b）Enhancethetranslatability.（c）EnhancethetransportofmRNAsfromthenucleusintocytoplasm.（d）EnhancetheefficiencyofsplicingofmRNAs.

Polyadenylation:

Poly（A）isasequenceofadenylylresiduesatthe3’endofeukayoticmRNA.AlmostallmaturemRNAshave40-200nucleotidesofpoly（A）tail.Additionofpoly（A）tothe3’endofmRNAiscalledpolyadenylation.Functions:

（a）ProtectionofmRNA.（b）TranslatabilityofmRNA.

Splicing:

TheenzymicprocessineukaryoticcellsbywhichintronsareexcisedfromheterogeneousnuclearRNA（hnRNA）followingitstranscriptionfromDNA,andthecutendsarerejonedtoformmessengerRNA.

2）Threeclassesofgeneticrecombinationandtheirmajorfunctions.

HomologousrecombinationinvolvesgeneticexchangesbetweenanytwoDNAmoleculesthatshareanextendedregionofnearlyidenticalsequence.Functions:

（a）ContributestotherepairofseveraltypesofDNAdamage.（b）Ineukaryoticcells,itprovidesatransientphysicallinkbetweenchromatidesthatpromotestheorderlysegregationofchromosomesatthefirstmeioticcelldivision.（c）Itenhancesthegeneticdiversityinapopulation.

Site-specificrecombinationdiffersfromhomologousrecombinationinthattheexchangesoccuronlyataparticularDNAsequence.Functions:

（a）Regulatingtheexpressionofcertaingenes.（b）PromotingprogrammedDNArearrangementsduringembryonicdevelopment.（c）Completechromosomereplication

DNAtranspositionisdistinctfrombothotherclassesinthatitusuallyinvolvesashortsegmentofDNAwiththeremarkablecapacitytomovefromonelocationinachromosometoanother.Functions:

（a）Completechromosomereplication.（b）Moveonegeneticelementsfromonelocationtoanotherandmaintenanceofgeneticdiversity.

3）Fourtypesofweakinteractions（noncovalentbonds）withinandbetweenbiomolecules.

4）Eightmajorproteinfunctions.

1.Catalysis

2.Structure

3.Movement

4.Defense

5.Regulation

6.Transport

7.Storage

8.StressResponse

5）Thebiologicalfunctionsofthelipids.

1.Energystorage（fatsandoils）.

2.Majorstructuralelementsofbiologicalmembrane（phospholipidsandsterols）.

3.Others（enzymecofactors,light-absorbingpigments,hormone,electroncarrier）.

6）DNArepairsystems.

Mismatchrepair:

AsystemforthecorrectionoferrorsintroducedduringDNAreplicationwhenanincorrectbase,whichcannotformhydrogenbondswiththecorrespondingbaseintheparentstrand,isincorporatedintothedaughterstrand.

Base-excisionrepair:

AdamagebaseisrecognizedbyanenzymecalledDNAglycosylase,whichbreakstheglycosidicbondbetweenthedamagedbaseanditssugar.Thisleavesanapurinicorapyrimidinicsite（APsite）,whichisasugarwithoutitspurineorpyrimidinebase.OncetheAPsiteiscreated,itisrecognizedbyanAPendonucleasethatcutsornikestheDNAstrandonthe5’sideoftheAPsite.

Nucleotide-excisionrepair:

Bulkybasedamagecanberemoveddirectly,withouthelpfromaDNAglycosylase.Inthispathway,theincisingenzyme（excinuclease）systemrecognizesthestrandwiththebulkydamageandmakescutsoneithersideofthedamage,removinganoligonucleotidewiththedamage.

Directrepair:

OnetypeofDNAdamagerepairsystemwithoutremovingabaseornucleotide.

DNArecombination

3.Enzymesareextraordinarycatalysts.Therateenhancementsbroughtaboutbyenzymeareintherangeof5to17ordersofmagnitudeenzymesarealsoveryspecific,readilydiscriminatingbetweensubstrateswithquitesimilarstructures.Howcantheseenormousandhighlyselectiverateenhancementsbeexplained?

Wheredotheenergiescomefromforthedramaticlowingoftheactivationenergiesforspecificreactions?

Bindingenergyisamajorsourceoffreeenergyusedbyenzymestolowertheactivationenergiesofreactions.

1.Muchofthecatalyticpowerofenzymesisultimatelyderivedfromthefreeenergyreleasedinformingmultipleweakbondsandinteractionsbetweenanenzymeanditssubstrate.Thisbindingenergycontributestospecificityaswellascatalysis.

2.Weakinteractionsareoptimizedinthereactiontransitionstate;enzymeactivesitesarecomplementarynottothesubstratesperse,buttothetransitionstatesthroughwhichsubstratespassastheyareconvertedintoproductsduringthecourseofanenzymaticreaction.

4.DNAsequencingisreadilyautomatedusingavariationofSanger’ssequencingmethodinwhichthedideoxynucleotidesusedforeachreactionarelabeledwithadifferentlycoloredfluorescenttag.DescribethestrategyofautomatingDNAsequencingreactions.

5.Describetheseparationprinciplesofproteinsonthebasisofsize（size-exclusionchromatography）,charge（ion-exchangechromatography）,andbindingspecificity（affinitychromatography）.

size-exclusionchromatography

ion-exchangechromatography

affinitychromatography

6.Writethree-letterandone-letterabbreviationsforthe20standardaminoacids.ThetopiccanbesimplifiedbygroupingtheaminoacidsintofivemainclassesbasedonthepropertiesoftheirRgroups.Describethefivegroupsandtheirproperties.

AminoacidscanbeclassifiedbyRgroup:

Nonpolar,aliphaticgroups:

Gly（G）Ala（A）Pro（P）Val（V）Leu（L）Ile（I）Met（M）

AromaticRgroups:

Phe（F）Tyr（Y）Trp（W）

Polar,unchargedRgroups:

Ser（S）Thr（T）Cys（C）Asp（D）Glu（E）

NegativelychargedRgroups:

Asn（N）Gln（Q）

PositivelychargedRgroups:

Lys（K）Arg（R）His（H）

《〈生物化学〉Ⅱ》试题及参考答案

1.ExplanationofTerms

（1）Apolipoproteins:

Apolipoproteinsarelipid-bindingproteinsintheblood,responsibleforthetransportoftriacylglycerols,phospholipids,cholesterol,andcholesterylestersbetweenorgans.

（2）Photorespiration:

Alight-dependentcatabolicprocessoccurringconcomitantlywithphotosynthesisinplants（especiallyC3plants）whereby