the history of dna - mr. bauman scienceon discovering the structure of dna. applied chargaff ’s...

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