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DNA as Molecule of Heredity: Experiments, Structure, and Replication

Learn about the experiments that identified DNA as the hereditary material, the structure of DNA and its implications, and how cells replicate DNA. Explore the groundbreaking research of Griffith, Avery, Hershey-Chase, Chargaff, Franklin, Watson, and Crick, and the Meselson-Stahl experiment. Understand the models and mechanisms of DNA replication.

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DNA as Molecule of Heredity: Experiments, Structure, and Replication

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  1. DNA as the molecule of heredity: part A • What experiments identified DNA as the hereditary material? • What is the structure of DNA, and what does the structure suggest about DNA function? • How do cells replicate DNA?

  2. Frederick Griffith 1928: bacterial transformation

  3. What is the material that transforms bacteria? DNA transformed bacteria, but not proteins. Treatment with DNase, but not RNase or proteases, eliminated transformation activity. Avery, McLeod & McCarty - 1944

  4. bacteriophage T2 http://www.youtube.com/watch?v=41aqxcxsX2w

  5. Hershey-Chase experiment - 1952

  6. Chargaff's rules

  7. Rosalind Franklin's X-ray crystallography From Campbell & Reece, Biology 7th ed., Pearson

  8. Watson-Crick model of DNA - 1953

  9. DNA as the molecule of heredity: part B • How do cells replicate DNA? • Meselson-Stahl experiment • Model of DNA replication “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” - Watson and Crick, 1953, Nature 171:737-738

  10. Possible modes of DNA replication

  11. Meselson-Stahl: density-gradient ultracentrifugation Bacteria are grown in medium with 15N (heavier isotope) or 14N to label DNA. Ultracentrifugation on CsCl gradients (20 h at 140,000 x g) separates DNA molecules by density.

  12. Meselson-Stahl experiment

  13. Meselson and Stahl’s results From Meselson & Stahl 1958 PNAS

  14. DNA polymerase adds new nucleotides to 3’-OH;DNA strands grow 5'3'

  15. DNA replication proceeds bidirectionally from an origin of replication http://www.web-books.com/MoBio/Free/Ch7A.htm

  16. Because DNA synthesis always occurs 5'3', the two strands replicate differently

  17. DNA replication complex http://www.nature.com/nature/journal/v421/n6921/box/nature01407_bx1.html

  18. More complex views of DNA replication • The trombone model • http://www.mcb.harvard.edu/Losick/images/TromboneFINALd.swf • Molecular visualization of DNA replication

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