1. Chapter 12: DNA and RNA

2. 12-1: Discovering DNA Frederick Griffith (1928)
tried to find better ways to fight pneumonia
isolated 2 types of bacteria that cause pneumonia
smooth: deadly form
rough: nondeadly form

3. Griffith’s Experiment
R-strain (Rough): Nonvirulent
S-strain (Smooth): Virulent
Heat Killed S-Strain: Nonvirulent
R-strain + Heat Killed S-strain: ???

4. Griffith’s Results

5. What killed the mouse?
Why did the R-strain and heat killed S-strain combination kill the mouse?

6. Transformation when one type of bacteria is changed into another
realized some molecule changed harmless rough bacteria into deadly smooth bacteria

7. Oswald Avery (1944)
wanted to find out which molecule caused transformation
found transformation was blocked when DNA was destroyed
concluded genes are made up of DNA

8. DNA is the Transforming Factor
Avery’s Experiment
Treated the R-strain and heat killed S-strain bacteria with enzymes designed to destroy proteins and DNA.
Proteins were destroyed → mouse died
DNA was destroyed → mouse lived

9. Hershey and Chase (1952) used radioactive isotopes
used bacteriophages: type of virus that infects bacteria
contains protein and DNA

10. Hershey and Chase

11. Hershey and Chase’s Results
used radioactive isotopes to label the DNA and protein in a bacteriophage
labeled DNA with phosphorus-32
labeled protein with sulfur-35
allowed bacteriophage to infect a bacterium
found bacterium was made radioactive by phosphorus-32
concluded genetic material of bacteriophage must be DNA

12. Hershey and Chase Animation