Frederick Griffith

He studied Streptococcus pneumoniae.  The following is for what he is predominantly known.

1. grew colonies, could sitinguish the strains--Smooth (S) and Rough (R)
   Smooth synthesized polysaccharides surrounding the cell with mucous, or a capsule.
   Rough did not.
   He did not understand this phenomen:  Transformation, the change in phenotype due to incorporation of external DNA.

2. injected the strains into different mice (S-injected and R-injected mice)
   The S-injected died; the R-injected survived, but some R-injected died as well.

3. result:  mouse dies and blood sample is taken and S is found in R-injected mice.

4. used heat to deactivate S. pneumoniae; thus heating protein, not genetic material (because proteins denature more readily in the body)

Oswald Avery tried to identify the agent, only DNA worked.

Alfred Hershey / Martha Chase

The two studied T2 bacteriophages to see how they reprogrammed the host ("with protein, or DNA?").

1. Bacteria receives injection
2. Fractionate bacteria
3. centrifuge and measure radioactivity in pellet and supernatant
   • radioactive supernatant (protein-shell, capsid, of the virus)
   • radioactive pellet (DNA)
4. Thus protein did not enter the host and DNA did; thus DNA was responsible for transforming cells.

Edward Chargaff

He reported diversity in DNA compostition between different organisms and that the four bases (A,T,C,G) had corresponding frequencies in every organism
          e.g., Animal X
                    Adenine-Thymine (30% to 30%), Guanine-Cytosine (20% to 20%)

Next:  "Watson, Crick and the Double Helix."