Review for Midterm复习.docx

Review for Midterm复习.docx

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ReviewforMidterm复习

ReviewforMidterm

Chapters2-7,21,and8-9

NucleicAcidsConveyGeneticInformation

Chapter2

Whatarethe4basepairsfoundinDNA?

adenine（A）

guanine（G）

thymine（T）

cytosine（C）

Thereare2methodsscientistsusetostudybiology.

Whatarethey?

1.Discoveryscience

2.Hypothesis-drivenscience

DiscoveryScience

Whatisdiscoveryscience?

Discoveryscienceisrecordingobservationsandmeasurements.

Howishypothesis-drivensciencedifferentfromdiscoveryscience?

Itbeginswithaquestion.

Hypothesis-drivenscience

Whatisahypothesis?

Thehypothesisisaproposedanswertothisquestion.Itisaneducatedguess.

Thestepsinhypothesis-drivenscienceare:

1.observationsofphenomena

2.formationofaquestionabouttheobservations

3.formationofahypothesistoanswerthequestion

4.Makingapredictionthatallowsthehypothesistobetested

5.Testingthehypothesis

Basedontheresultsofthetestingthehypothesiswillbeacceptedorrejected.

SummaryofGriffithexperiment

Smoothbacteriaescapetheimmunesystemandkillmice.

Roughbacteriaaredestroyedbytheimmunesystem.

Treatingsmoothbacteriawithheatkillsthemandtheyarenolongerinfectious.

Addingheatkilledsmoothbacteriatoroughbacteriatransformssomeofthemintosmoothbacteria.

Thesubstanceiscalledthetransformingprinciple.

ToshowtherewerenoproteinsintheirpurifiedDNA,Avery,MacLeodandMcCartytreatedthesampleswithproteasesandshowedthatthisdidnotaffecttransformation.Proteaseswoulddegradetheproteins.

TheyalsotreatedthesampleswithRNases（ribonucleases）.RNaseswoulddegradeanycontaminatingRNA.Againthisdidnotstoptransformation.

ThentheytreatedtheirsampleswithDNases.DNaseswoulddegradetheDNAintheirsamples.TreatmentofsamplesofthetransformingprinciplewithDNaseseliminateditsabilitytotransformbacteria.

SummaryofHershey-Chaseexperiment

BacteriophageT2DNAwaslabeledwith32PandseparatelyT2proteinwaslabeledwith35S.

E.coliwereinfectedwiththeT2samplesandthentheT2wereremovedfromthesurfaceofthebacteriabyagitationinablender.

Thesampleswerecentrifugedandtheamountsofradioactivityinthepelletandsupernatantsweremeasured.

The35SproteindidnotentertheE.coli,butthe32PDNAdidentertheE.coli.

HersheyandChaseconcluded:

DNAisthetransformingprincipleandthehereditaryorgeneticmaterial.

WhydidmostscientistsnotbelievethisaftertheexperimentsbyGriffithandothers?

Sometimesitisdifficultforscientiststochangetheirmindsaboutwhattheythink.

Whatisitcalledwhenscientistschangethewaytheythinkaboutanimportantaspectofscience?

DNAisadoublehelix

WatsonandCrickstudiedthex-raydiffractionpatternsandmadeseveralpotentialmodelsofDNA.Eventuallytheyproposedthedouble-strandedhelixstructureofDNA.

AalwaysbindstoTandGalwaysbindstoC.ThetwostrandsofDNAarecomplementary.BecauseofthisthetwostrandsofDNAcaneasilybecopied.

E.RNAdiffersfromDNAin3ways:

HowisRNAdifferentfromDNA?

RNAdiffersfromDNAin3ways:

1.itissinglestranded

2.ithasthesugarribose

3.ithasuracilinsteadofthymine

F.TranscriptionandTranslation

DNARNAprotein

ThehereditaryinformationinDNAistranscribedintoRNA.

TheRNAdirectsthesynthesisofproteinsintranslation.

1.Thereare3differentkindsofRNA.

Whatarethey?

a.mRNA（messenger）

b.tRNA（transfer）

c.rRNA（ribosomal）

AlloftheDNApresentinaspeciesiscalledthegenome.

ThestudyofalltheDNAinaspeciesiscalledgenomics.

TheImportanceofWeakChemicalInteractions

Chapter3

Someofthemoleculesinacellareverylargewithmolecularweightsof104to1012.

Whatarethesecalled?

Thesearecalledmacromolecules（macro=big）.

A.CharacteristicsofChemicalBonds

Achemicalbondisanattractiveforcethatholdsatomstogether.

Thestrengthofachemicalbondiscorrelatedwiththedistancebetweenthetwoatoms.

1.Covalentbonds

When2atomsshareanelectronintheoutershell,abondisformed.Whatisthenameforthisbond?

covalent

Chemicalbondsdifferintheirfreedomofrotation.Singlecovalentbondscanfreelyrotate.Doubleandtriplecovalentbondsdonotrotate,whichholdstheatomsinthesameplane.

Noncovalentbondsaregenerallymuchweakerthancovalentbonds.

Whatarethe4kindsofnoncovalentbonds?

1.Hydrogenbonds

2.hydrophobicbonds

3.ionicbonds

4.VanderWaalsbonds

b.FreeEnergy

Whatisthenamefortheenergythatisavailablefordoingwork?

Inspontaneousreactions,thereisadecreaseinfreeenergy（∆Gisanegativenumber）.

Atequilibrium,thereisnofreeenergy

（∆G=0）

Thisgivestheformula:

∆G=-RTlnKeqorKeq=e-∆G/RT

Thereisarelationshipbetweenth