1. 12.1 Identifying the Genetic Material
What is the genetic material? DNA was isolated in 1869, but it wasn’t known to contain genetic material until these experiments…

2. Vocabulary
Vaccine- a substance that is prepared from killed or weakened microorganisms and is introduced into the body to protect the body against future infections by the microorganisms.
Virulent- able to cause disease
Bacteriophage (phage)- viruses that infect bacteria

3. Frederick Griffith’s Experiment
Year: 1928
What? Made a discovery while trying to prepare a vaccine against the pneumonia-causing bacterium, Streptococcus pneumoniae.
Discovered transformation- a change in the phenotype caused when bacterial cells take up foreign genetic material.

4. Transformation Of Bacteria Two Strains Of Streptococcus
Rough Strain
(Harmless)
Capsules
Smooth Strain
(Virulent)

5. Transformation Of Bacteria The Griffith’s 1928 Experiment
OUCH!
+ Control
- Control
- Control
Experimental

6. Griffith’s Conclusion
The harmless bacteria could turn virulent (disease-causing) when mixed with bacteria that cause disease.
TRANSFORMATION- process in which one strain of bacteria is changed by a gene of another strand of bacteria.
P. 339 in text

7. Oswald Avery’s Experiments
Year: 1944
Experimented in N.Y. City. Found that DNA was the material responsible for the transformation in Griffith’s experiments.
There was still doubt that it was DNA, most scientists believed that proteins were the genetic material.

8. The Hershey-Chase Experiment
Time: 1952
Who? Alfred Hershey and Martha Chase
Where? N.Y.
What? Proved definitely that DNA was the genetic material.
Step 1:
E. Coli virus’ were grown in radioactive sulfur (S35) in protein and phosphorus (P32) in DNA
Radioactive so scientists can easily detect them.

9. Hershey-Chase Experiment p. 341 in text
Step 2
The S phage and P phages were injected into E. Coli bacterium. They were looking at DNA and protein to see what was transferred during reproduction.
Step 3
When separated by a centrifuge, the P phage was found in the hosted bacteria (remember step 1: P is in DNA)
Step 4
Conclusion-  DNA was reproduced
The genetic material is for sure DNA

11. Using S35 Did protein enter the bacteria?
T2 grown in S35 containing media incorporate S35 into their proteins
Bacteria grown in normal non-radioactive media
T2 attach to bacteria and inject genetic material
When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet
Mix-O-Matic
The supernatant is radioactive, but the pellet is not.
Blending causes phage protein coat to fall off
Did protein enter the bacteria?
Is protein the genetic material?

12. Using P32 Did DNA enter the bacteria? Is DNA the genetic material?
T2 grown in P32 containing media incorporate P32 into their DNA
Bacteria grown in normal non-radioactive media
T2 attach to bacteria and inject genetic material
When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet
Mix-O-Matic
The pellet is radioactive, but the supernatant is not.
Blending causes phage protein coat to fall off
Did DNA enter the bacteria?
Is DNA the genetic material?