Discovery of DNA Fredrick Griffith – 1928 Oswald Avery – 1944 Alfred Hershey & Martha Chase

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

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

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.

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

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

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

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.

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

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.

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.

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

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