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