7.1 DNA Structure and Replication Nucleic Acids 7.1 DNA Structure and Replication

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

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

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

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…

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

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?

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?

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