1. DNA
Ch. 10

2. The Discovery of DNA

3. Griffith’s Experiments
In 1928 Frederick Griffith studied a bacteria (S. pneumoniae) that causes pneumonia in mammals.
Griffith was working on a vaccine against a disease-causing, or virulent strain of the bacterium

4. Griffith’s Experiments
Each virulent bacterium is surrounded by a capsule
The capsule protects the bacteria from the host’s immune system

5. Griffith’s Experiments
The S. pneumoniae bacteria in the virulent strain grow in smooth-edged colonies.
Thus they are the S strain
The second strain does not cause pneumonia and lacks a capsule. These have a rough edge.
Thus they are the R strain

6. Griffith’s Experiments

7. Griffith’s Experiments

8. Griffith’s Conclusions
The heat-killed virulent bacteria cells released a hereditary factor*
This factor transfers the disease causing ability to the live harmless rough cells.
Dead S cells transferred killerness gene to R cells that were harmless

9. Transformation
This type of transfer of genetic material from one cell to another cell or from one organism to another is called transformation

10. Concluded that DNA is responsible for transformation in bacteria
Avery Experiments
Found that cells missing DNA did not transform R cells into S cells
Concluded that DNA is responsible for transformation in bacteria

11. Hershey-Chase Experiment
In Martha Chase and Alfred Hershey tested whether DNA or protein was the hereditary material viruses transfer
Basically if information is transferred via DNA or proteins

12. Hershey-Chase Experiment
After infection they found that all of the viral DNA and little of the protein had entered E. coli cells.
They concluded that DNA is the hereditary molecule in viruses

13. Hershey-Chase Experiment
Viruses that infect bacteria are called bacteriophages or just phages
Hershey-Chase used radioactive labels to mark the DNA and proteins in the bacteriophages
Then they allowed the phages to separately infect E. coli.

14. Link!

15. DNA Structure

16. Crash Course DNA