Presentation on theme: "7.1 DNA Structure and Replication"— Presentation transcript:
17.1 DNA Structure and Replication Nucleic Acids7.1 DNA Structure and Replication
2Data-based questionAnalysis of the Hershey-Chase experiment provided evidence that DNA is the genetic materialp344
3The Hershey-Chase experiment Analysis of the Hershey-Chase experiment provided evidence that DNA is the genetic material
4Watson, Crick, and Franklin Making careful observations: Rosalind Franklin’s X-ray diffraction provided crucial evidence that DNA was a helixRead pages
5Watson and Crick’s Model Several lines of experimental evidence came together to lead to the knowledge of the structure of DNAMolecular modelling of Linus PaulingX-ray diffraction by Rosaling FranklinBase composition studies of Erwin ChagallInsight and imagination were also important…
6Watson and Crick’s Model First suggestion:Sugar phosphate strands wrapped around one another and nitrogen bases pointed out.PROBLEM?Nitrogen bases are relatively hydrophobic compared to the sugar-phosphate backbone
7Watson and Crick’s Model Franklin’s x-ray diffractions showed that the DNA was tightly packedBases must fit closely togetherWould work if a pyramidine and purine were paired and upside down relative to each otherBut what pairs?
8Watson and Crick’s Model Adenine has a surplus negative charge and Thyamine has a surplus positive chargeCytosine and Guanine have the ability to form 3 hydrogen bondsSO?
9Watson and Crick’s Model The idea of complementary base pairing immediately suggested a mechanism for DNA replicationSemi-conservative replication