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The History of DNA
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Early Work
FriedrichMiescher,1869,firstisolatesasubstancefromthenucleusofcellsthathecalls“nuclein.” later“nucleicacid.”
Biochemistsidentifytwotypesofnucleicacids,RNAandDNA.
In1929,PhoebusLevineattheRockefellercenteridentifiesthefourbasesofDNA.
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What Does DNA Do?ResearchersknewthatDNAwasfoundinchromosomes,theydoubtedthatitwasthehereditarymaterial.
Onlyfourbases.Howcouldforbasescodeforallsortsofproteins?
Researchersthoughtthattheproteinalsofoundinchromosomeswasprobablythehereditaryfactor.
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Frederick Griffith
In1928,FrederickGriffithcarriedoutexperimentsonpneumoniabacteriainmice.
Discovery:somethinginheat-killedvirulentbacteriacouldbetransferredtolive,harmlessbacteriaandmakethemvirulent.
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Griffith’s Experiment
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Oswald Avery
Isolatedproteins,carbohydrates,nucleicacidsandappliedthemtonon-virulentbacteria.Onlynucleicacids(DNA)causedachange.
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Avery’s Work
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Erwin Chargaff
ChargaffstudiedDNAitself,providingsomecluesaboutitsstructure.
DiscoveredthattherearealwaysequalamountsofthebasesAdenineandThymine,andequalamountsofCytosineandGuanine.
Chargaffproposedthatthesebasespairwithoneanother.
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Wilkins and Franklin
RosalindFranklinandMauriceWilkinsworkedwithX-raycrystalographytofindmorecluesaboutthestructureofDNA.
Franklin’sX-rayimagessuggestedahelicalstructure.
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Franklin and Wilkins
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Watson and Crick
JamesWatsonandFrancisCrickwerealsoworkingondiscoveringthestructureofDNA.
AppliedChargaff’srule,assumedthatAalwayspairswithT,CwithG.
WatsonwasnotentirelyconvincedofthehelicalstructurethatFranklinhadsuggested,andhiscritiqueofherworkledhertodoubtherself.
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Watson and CrickWilkinsconsultedwithWatsonandCrick.WithoutFranklin’sknowledge,hehandedthemthedatathatheandFranklinhadworkedon.
Watsonimmediatelyrecognizedthesignificance.HeandCrickwenttoworkonamodelofDNA.
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The First DNA Model