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DNA The Genetic Material: History

DNA The Genetic Material: History. 1908 | 1933. Chromosomes related to phenotype . T.H. Morgan working with Drosophila fruit flies associated phenotype with specific chromosome white-eyed male had specific X chromosome . 1908 | 1933. Genes are on chromosomes .

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DNA The Genetic Material: History

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  1. DNA The Genetic Material: History

  2. 1908 | 1933 Chromosomes related to phenotype • T.H. Morgan • working with Drosophila • fruit flies • associated phenotype with specific chromosome • white-eyed male had specific X chromosome

  3. 1908 | 1933 Genes are on chromosomes • Morgan’s conclusions • genes are on chromosomes • but is it the protein or the DNA of the chromosomes that are the genes? • initially proteins were thought to be genetic material… Why? What’s so impressiveabout proteins?!

  4. 1928 The “Transforming Principle” • Frederick Griffith • Streptococcus pneumonia bacteria • was working to find cure for pneumonia • harmless live bacteria (“rough”) mixed with heat-killed pathogenic bacteria (“smooth” has a mucus coating) causes fatal disease in mice • a substance passed from dead bacteria to live bacteria to change their phenotype • “Transforming Principle”

  5. The “Transforming Principle” mix heat-killed pathogenic & non-pathogenic bacteria live pathogenic strain of bacteria live non-pathogenic strain of bacteria heat-killed pathogenicbacteria A. B. D. C. mice die mice live mice live mice die Transformation=change in phenotype something in heat-killed bacteria could still transmit disease-causing properties

  6. What Griffith’s experiment proved • Griffith’s hypothesis: • When live, harmless bacteria and heat-killed bacteria are mixed, the heat-killed bacteria passed on disease-causing information to the live cells of the harmless bacteria, causing harmless bacteria to “transform” into bad bacteria • Transforming Factor • This factor was probably a gene because he noticed that the offspring inherited the disease as well • Suggested DNA was genetic material

  7. Transformation definition: • The process during which bacteria are changed by absorbing genetic material from an outside source

  8. Griffith’s experiment video • http://www.youtube.com/watch?v=FnXGhMbDyi4

  9. 1944 DNA is the “Transforming Principle” • Avery, McCarty & MacLeod • purified both DNA & proteins (component of chromosomes) separately from Streptococcus pneumonia bacteria • which will transform non-pathogenic bacteria? • injected protein into bacteria • no effect • injected DNA into bacteria • transformed harmless bacteria into virulent bacteria mice die What’s the conclusion?

  10. 1944 | ??!! Avery, McCarty & MacLeod • Conclusion • first experimental evidence that DNA was the genetic material-not protein Oswald Avery Maclyn McCarty Colin MacLeod

  11. Scientists were still skeptical • Protein is made of 20 amino acids. DNA is made of only 4nucleotides. Didn’t make sense • They thought, “DNA is too simple!”

  12. 1952 | 1969 Hershey Confirmation of DNA • Hershey & Chase • classic “blender” experiment • worked with bacteriophage • viruses that infect bacteria • grew phage viruses in 2 media, radioactively labeled with either • 35S in their proteins • 32P in their DNA • infected bacteria with labeled phages Why useSulfurvs.Phosphorus?

  13. Protein coat labeled with 35S DNA labeled with 32P Hershey & Chase T2 bacteriophages are labeled with radioactive isotopes S vs. P bacteriophages infect bacterial cells bacterial cells are agitated to remove viral protein coats Which radioactive marker is found inside the cell? Which molecule carries viral genetic info? 32P radioactivity foundin the bacterial cells 35S radioactivity found in the medium

  14. Phage video • http://www.youtube.com/watch?v=YG3d77SRWZI

  15. Blender experiment • Radioactive phage & bacteria in blender • 35S phage • radioactive proteins stayed in supernatant • therefore viral protein did NOT enter bacteria • 32P phage • radioactive DNA stayed in pellet • therefore viral DNA did enter bacteria • Confirmed DNA is “transforming factor” Taaa-Daaa!

  16. 1952 | 1969 Hershey Hershey & Chase Martha Chase Alfred Hershey

  17. 1947 Chargaff • DNA composition: “Chargaff’s rules” • varies from species to species • all 4 bases not in equal quantity • bases present in characteristic ratio • humans: A = 30.9% T = 29.4% G = 19.9% C = 19.8% RulesA = T C = G That’s interesting!What do you notice?

  18. 1953 | 1962 Structure of DNA • Watson & Crick • developed double helix model of DNA • other leading scientists working on question: • Rosalind Franklin • Maurice Wilkins • Linus Pauling Wilkins Pauling Franklin

  19. 1953 article in Nature Watson and Crick Watson Crick

  20. Watson and Crick speak • http://www.youtube.com/watch?v=OiiFVSvLfGE

  21. Rosalind Franklin (1920-1958)

  22. History of DNA video- summary • http://www.youtube.com/watch?v=rjW-dZBPCsQ&feature=related

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