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Nucleic Acids 7.1 DNA Structure and Replication. Data-based question  Analysis of the Hershey-Chase experiment provided evidence that DNA is the genetic.

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Presentation on theme: "Nucleic Acids 7.1 DNA Structure and Replication. Data-based question  Analysis of the Hershey-Chase experiment provided evidence that DNA is the genetic."— Presentation transcript:

1 Nucleic Acids 7.1 DNA Structure and Replication

2 Data-based question  Analysis of the Hershey-Chase experiment provided evidence that DNA is the genetic material  p344

3 The Hershey-Chase experiment  Analysis of the Hershey-Chase experiment provided evidence that DNA is the genetic material

4 Watson, Crick, and Franklin  Making careful observations: Rosalind Franklin’s X-ray diffraction provided crucial evidence that DNA was a helix  Read pages 345-347

5 Watson and Crick’s Model  Several lines of experimental evidence came together to lead to the knowledge of the structure of DNA  Molecular modelling of Linus Pauling  X-ray diffraction by Rosaling Franklin  Base composition studies of Erwin Chagall  Insight and imagination were also important…

6 Watson 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

7 Watson and Crick’s Model  Franklin’s x-ray diffractions showed that the DNA was tightly packed  Bases must fit closely together  Would work if a pyramidine and purine were paired and upside down relative to each other  But what pairs?

8 Watson and Crick’s Model  Adenine has a surplus negative charge and Thyamine has a surplus positive charge  Cytosine and Guanine have the ability to form 3 hydrogen bonds  SO?

9 Watson and Crick’s Model  The idea of complementary base pairing immediately suggested a mechanism for DNA replication  Semi-conservative replication


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