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Educator MaterialsShort Film The Double Helix

fitstheirlearningobjectivesandtheirstudents’needs.Teachersareencouragedtomodifythequiz(e.g.onlyasksomeofthequestions,explaincomplicatedvocabularyforELLstudents)asneeded.

QUIZQUESTIONSANDANSWERS1. (KeyConceptF)Inthe1950swhenWatsonandCrickwereworkingontheirmodelofDNA,manyscientists

didnotthinkthatDNAcarriedthegeneticcode.

a. Whatwastheothertypeofmoleculethatsomescientiststhoughtmightcarrygeneticinformation?Proteins

b. Whydidthisothertypeofmoleculeseemlikealikelycandidate?

Proteinswerefavoredbymanyscientistsbecausetherearemanyproteins,theycomeindifferentshapesandhavemanydifferentfunctions.Also,proteinsaremadeof20differentaminoacidcomponents,whileDNAiscomposedofonlyfourbasicsubunits.2. (KeyConceptA)WhatarethechemicalcomponentsofaDNAnucleotide?

a. aphosphate,asugar,andanitrogenousbase

b. aphosphate,anitrogenousbase,andanaminoacid

c. anitrogenousbase,asugar,andanaminoacid

d. anitrogenousbase,ATP,andasugar3. (KeyConceptB)ThetwostrandsofaDNAmoleculeareheldtogetherbyhydrogenbondsbetweenthe

a. phosphategroupsoneachstrand

b. nitrogenousbasesoneachstrand

c. basesandthephosphate-sugarbackbone

d. carbonatomsinthesugars4. (KeyConceptB)Inthediagrambelow,strandsIandIIrepresentthetwocomplementarystrandsofa

portionofaDNAdoublehelix.ThesequenceofstrandIisindicatedbelow.WhatisthesequenceofstrandII?

StrandI-----------C-T-A-C-----------

StrandII-----------?-?-?-?-------------

a. AGCA b. CTAC c. TCGT d. GATG

5. (KeyConceptC)Theinstructionsforthetraitsofanorganismaredeterminedby

a. theproportionsofA,T,C,andGinDNAmolecules

b. theorderofnucleotidesinDNAmolecules

c. thelengthofDNAmolecules

d. thewaynucleotidesarepairedinthetwostrandsofaDNAmolecule

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6. (KeyConceptsEandF)Scientistsbuildmodelsbasedonwhattheyknowfrompreviousresearchtoderivetestablehypotheses.Independently,bothWatsonandCrickandtheircompetitorLinusPaulingconstructedanincorrecttriple-helixmodelwiththenitrogenousbasesarrangedsotheywereontheexteriorofthemoleculeandthephosphategroupsontheinterior.

a. Althoughtheirmodelwaswrong,whatassumptionmadeitreasonabletobuildamodelwiththebasesprojecting totheoutside?

Thebasescontainthegeneticinformationastheyvaryinamountbetweenspeciesandintheirarrangementwithinthemolecule;basedonthisinformationitwasreasonabletoassumethatthebaseswouldbeontheoutsideoftheDNAmolecule.

b. WhatevidencecausedWatsonandCricktorevisetheirmodel?

Basedonthefilm,studentsshouldrealizethatinformationaboutthedimensionsofthedoublehelixfromFranklin’simages,aswellasChargaff’spairingrulesforthebases,ledthemtoarevisedmodel.ThefilmsaysthatWatsonhadmisrememberedsomekeymeasurementsfromFranklin’swork.HerimagesshowedtherewasmuchmorewaterinDNAthanthetriple-helixmodelallowed.Further,thetriple-helixmodelcouldnotexplainhowthethreephosphatebackbonescouldbeheldtogether.(Studentsmaynotknowtheselasttwopointsastheyarenotexplicitlystatedinthefilm.)

7. (KeyConceptC)EvenbeforethestructureofDNAwassolved,studiesindicatedthatthegeneticmaterialmusthavethefollowingproperties:

• beabletostoreinformation;

• befaithfullyreplicatedandbepassedonfromgenerationtogeneration;and

• allowforchanges,andthusevolution,tooccur.

ExplainhowthestructureofthedoublehelixshowedthatDNAhadtheseproperties.Writeoneortwosentencesperpoint.

Theorderofthebases,A,T,G,andC,containedinformation.BecauseAisalwayspairedwithTandGwithC,theorderofbasesononestranddeterminestheorderontheotherstrand.Thus,ifaDNAmoleculewereunwound,eachstrandcouldbecopiedintoacomplementarystrand,producinganexactreplicaoftheoriginalmolecule.Errorsinthecopyingmechanismcouldresultinmutations,orchangesintheDNAsequence,thatcouldbeinheritedbyfuturegenerations.

8. (KeyConceptF)In1928,FrederickGriffithconductedanexperimentinwhichheinjectedmicewithdifferentkindsofbacteria.Whenbacteriathatcausedisease(pathogenic)wereinjectedinhealthymice,thesemicegotsickanddied.Othertypesofbacteria(nonpathogenic)didnotcausethemicetodie.GriffithtooktheDNAfromdeadpathogenicbacteriaandtransferreditintolivingnonpathogenicbacteria.Thesealteredbacteriaweretheninjectedintohealthymice.Themicediedofthesamediseasecausedbythepathogenicbacteria.Basedonthisinformation,whichstatementwouldbeavalidconclusion?

a. Whenanorganismdies,theDNAchanges;itnolongerprovidesthesamegeneticinformation.

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b. WhenDNAfromoneorganismistransferredtoanotherorganism,theDNAnolongerfunctions.

c. DNAindifferenttypesofbacteriacarriesexactlythesametypeofinformation.

d. WhenDNAfromoneorganismistransferredtoanotherorganism,itcangivenewtraitstothesecondorganism.

9. (KeyConceptF)ThefollowingtableisasampleofthedataErwinChargaffpublishedin1952.

Proportions*ofNitrogenousBasesintheDNAofDifferentOrganismsOrganism Tissue %Adenine %Guanine %Cytosine %ThymineYeast 31.3 18.7 17.1 32.9Seaurchin Sperm 32.8 17.7 18.4 32.1Rat Bone

marrow28.6 21.4 21.5 28.4

Human Thymus 30.9 19.9 19.8 29.4Human Sperm 30.3 19.5 19.9 30.3*Definedasmolesofnitrogenousconstituentsper100gofatomsofphosphate.Source:E.ChargaffandJ.Davidson,Eds.TheNucleicAcids.AcademicPress,1955.

a. Whichofthefollowingobservationscanbesupportedbythedatainthetable?(Placeacheckmarkintheboxnexttothecorrectstatements.)

√Ineachanimal,thepercentageofadenineisthesameasthepercentageofthymineintheDNA.

☐Theproportionsofadenine+thymineandguanine+cytosinearethesameinallorganisms.

☐Largerorganismshavegreateramountsofeachnitrogenousbasethansmallerorganismshave.

☐ThetotallengthofDNAmoleculesinallorganismsisaboutthesame.

b. Inoneortwosentences,explainhowtheseobservationshelpedWatsonandCrickdeveloptheirmodelofDNA.

Itsuggeststhatinthedoublehelix,adeninealwayspairswiththymineandguaninealwayspairswithcytosine.

c. Inoneortwosentences,explainwhytheproportionsofnitrogenousbasesintheDNAoftwodifferenthumantissues(thymusandsperm)areaboutthesame.

AllbodycellsandtissuesinaparticularorganismcontainthesameDNA.

10. TheimageontherightshowsthefamousphotoB51takeninMay1952byRosalindFranklinandherstudentRaymondGosling.Thisx-raydiffractionpatternprovidedinformationaboutthepositionsofatomsinaDNAmolecule.

a. (KeyConceptG)IdentifytheclueinthisphotothatrevealedthatDNAisahelix.

TheclueistheXshapeintheimage.

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b. (KeyConceptD)Measurementsrevealedthatthedistancebetweenthetwostrandswasalwaysequal.ExplainhowthisinformationhelpedWatsonandCrickbuildasuccessfulmodelofDNA.

WatsonandCrickconcludedthatalargepurinemolecule(adenineorguanine)alwaysbondswithasmallerpyrimidinemolecule(cytosineorthymine)—thatway,thedistancebetweenthetwostrandsofDNAisalwaysthesame.

c. (KeyConceptE)WasthisinformationconsistentwiththedataobtainedbyChargaff(question9)?Explainyouranswer.

Yes.ChargaffdiscoveredthatintheDNAofanorganism,theproportionofadenine(apurine)isthesameastheproportionofthymine(apyrimidine).Thesameistrueforguanine(apurine)andcytosine(apyrimidine).Thesedataareconsistentwithamodelinwhichapurineononestrandalwaysbondswithapyrimidineontheotherstrand.

KEYREFERENCESWatson,J.D.,andCrick,F.H.C.1953.Astructurefordeoxyribosenucleicacid.Nature171:737-738.Wilkins,M.H.F.,Stokes,A.R.,andWilson,H.R.1953.Molecularstructureofdeoxypentosenucleicacids.Nature171:738-740.Franklin,R.,andGosling,R.G.1953.Molecularconfigurationinsodiumthymonucleate.Nature171:740-741.Griffith,F.1928.Thesignificanceofpneumococcaltypes.JournalofHygiene27:113-159.Avery,O.T.,MacLeod,C.M.,andMcCarty,M.1944.Studiesonthechemicalnatureofthesubstanceinducingtransformationofpneumococcaltypes.TheJournalofExperimentalMedicine79:137-158.Hershey,A.D.,andChase,M.1952.Independentfunctionsofviralproteinandnucleicacidingrowthofabacteriophage.JournalofGeneralPhysiology36:39-56.Chargaff,E.1950.Chemicalspecificityofnucleicacidsandmechanismoftheirenzymaticdegradation.Experientia6(6):201-209.Judson,H.F.TheEighthDayofCreation:MakersoftheRevolutioninBiology.(1979)Watson,J.TheDoubleHelix:APersonalAccountoftheDiscoveryoftheStructureofDNA.(1968)Olby,R.ThePathtotheDoubleHelix:TheDiscoveryofDNA(UniversityofWashingtonPress,Seattle:1974&revised1994).Olby,R.FrancisCrick:HunterofLife'sSecrets(ColdSpringHarborLaboratoryPress:August25,2009)

AUTHORSWrittenbyCindyGay,SteamboatSpringsHighSchool,CO,LauraBonetta,PhD,HHMI,andMaryColvard,Cobleskill-RichmondvilleHighSchool(retired),Deposit,NewYorkEditedbyLauraBonetta,PhD,DennisLiu,PhD,ErikoClements,PhD,HHMIandSusanDodge,consultant;copyeditedbyLindaFelaco;illustrationsbyHeatherMcDonald,PhDReviewedbyKarolinLuger,PhD,ColoradoStateUniversity.

FIELDTESTERSAyseAydemir,LindaCiota,DonnaBalado,JenniferKaltenbach,LauraJulien,LilleenFerraro,EllenPerry,StaceyStrandberg