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DNAStructureandReplication

HistoricExperiments

•  Griffith‐1928•  Avery,MacLeodandMcCarty‐1944

•  Hershey,Chase‐1952•  Franklin‐1958•  MeselsonandStahl‐1958

Griffith‐1928

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Transformation

•  SomebacteriacantakeupfragmentsofDNAfromtheexternalmedium

•  DNAcanbe– Releasedfromdeadbacteria– Secretedbylivebacteria

•  Permanentlychangesthegenotypeoftherecipient

Avery,MacLeodandMcCarty

Hershey,Chase

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DNA

•  Prokaryotes‐circular•  Eukaryotes‐linear•  Doublestranded,helicalstructure

•  Composedofnucleotides

Clip

Nucleotides

•  Phosphategroup•  Deoxyribosesugar•  Nitrogenousbase–  Adenine–  Guanine–  Cytosine–  Thymine

RosalindFranklinX‐RayDiffractionAnalysis

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JamesWatsonandFrancisCrick

DeoxyribonucleicAcid

2strandsofnucleotides

Strandsheldtogetherbyhydrogenbondsbetweennitrogenousbases

Backboneisalternatingphosphateanddeoxyribosesugarunits

PhosphodiesterBond•  Chainhaspolarity•  Antiparallel

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MajorGrooveandMinorGroove

Chargaff’sRule

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3ModelsforDNAReplication