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Discovery of DNA

Discovery of DNA. Fredrick Griffith – 1928 Oswald Avery – 1944 Alfred Hershey & Martha Chase - 1952. Griffith. S – Strain virulent (contains capsule – causes the disease) R – Strain non-virulent (no capsule – does not cause disease. Griffith – Background Information.

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Discovery of DNA

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  1. Discovery of DNA Fredrick Griffith – 1928 Oswald Avery – 1944 Alfred Hershey & Martha Chase - 1952

  2. Griffith • S – Strain virulent (contains capsule – causes the disease) • R – Strain non-virulent (no capsule – does not cause disease

  3. Griffith – Background Information • Studied Streptococcus pneumoniae • Attempted to make vaccine for pneumonia • 2 strains R cells (rough) S cells (smooth)

  4. Griffith – Experiment / Results • E 1: Inject mice w/ live R cells  mice LIVE • E 2: Inject mice w/ live S cells  mice DIE • E 3: Inject mice w/ heat killed S cells  mice  LIVE • E 4: Inject mice w/ heat killed S cells and live R cells  mice DIE • Heredity material from S cells transform R cells into S cells.

  5. Griffith Conclusion • Transformation – transfer of genetic material from 1 cell to another or 1 organism to another.

  6. Avery Background Information • Tested to see if the transforming agent in Griffith’s experiment was Protein, DNA, or RNA

  7. Avery’s Experiment • E 1 – used protease to destroy proteins in heat killed S cells • E 2 – used RNA ase to destroy RNA in heat killed S cells • E 3 – used DNA ase to destroy DNA in heat killed S cells Separately mixed 3 batches of heat killed S cells with live R cells and injected the mice

  8. Avery’s Results • Cells missing proteins and RNA were able to transform R cells into S cells and kill the mice • Cells missing DNA did NOT transform R cells into S cells and mice lived.

  9. Avery’s Conclusion • DNA is the transforming agent in BACTERIA. DNA is responsible for transformation in bacteria

  10. Hershey / Chase Background Info • Tested whether DNA or proteins were heredity material viruses transfer when viruses enter a bacterial cell • Bacteriophage (phage) – virus that infects bacterial cells.

  11. Hershey/Chase Experiment • Used radioactive isotopes to label proteins and DNA in “phage”. • Radio Sulfur to label proteins • Radio Phosphorus to label DNA • Allowed protein labeled and DNA labeled phages to infect E-coli (bacteria) and tested E-coli for the radioisotopes.

  12. Hershey/Chase Results • They found ALL viral DNA and little of the protein had entered E-coli cells

  13. Hershey/Chase Conclusion • That DNA is the heredity material in viruses.

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