8/30/10 1 DNA Structure and Replication Historic Experiments • Griffith ‐ 1928 • Avery, MacLeod and McCarty ‐ 1944 • Hershey, Chase ‐ 1952 • Franklin‐1958 • Meselson and Stahl ‐ 1958 Griffith‐1928
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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