1. Frederick Griffith
• British bacteriologist
• 1928 = designed and performed experiment
on rats and bacteria that causes pneumonia.
• 2 strains of the bacteria
• Type S = causes severe pneumonia
• Type R = relatively harmless
5. • Finally he injected a mixture of living Type
R and dead Type S :
6. Results of experiments:
• Because the dead rat tissue showed living
Type S bacteria, something “brought the
Type S back to life”
• Actually one bacterial type incorporated the
DNA, or instructions, from the dead
bacteria into its own DNA
• Known as transformation. Confirmed by
Avery, MacLeod, and McCarty in 1944
8. Hershey and Chase
• 1952
• Attempted to solve the debate on whether
DNA or proteins are responsible for providing
the genetic material.
9. • They used a
bacteriophage (a
virus which
attacks bacteria)
to prove that
DNA was
definitely the
genetic material.
10.
11. Phoebus A. Levene
• Russian born; immigrated to America,
moves to Europe.
• 1920’s discovered nucleotides
(building blocks of DNA)
1. Sugar
2. Phosphate group
3. Nitrogenous base
14. Chargaff’s rules
• The relative amounts of adenine and
thymine are the same in DNA
• The relative amounts of cytosine and
guanine are the same.
• Named after Erwin Chargaff