1. Identifying the Substance of Genes (12.1)

2. Bacterial Transformation
Scientists wanted to understand the chemical nature of the gene--they wanted to control the way living things inherit characteristics
Griffith
He was trying to figure out what made people sick
S strain: disease-causing bacteria (smooth edges)
R strain: harmless bacteria (rough edges)
What caused the mice to get pneumonia?

3. Griffith’s Experiments
Bacterial Experiment with Mice
S strain = mice with pneumonia
R strain = mice without pneumonia
S strain heated = mice without pneumonia because the bacteria were killed with heat
S strain heated + R strain = mice with pneumonia (but how?!)

4. Griffith’s Experiments

5. Transformation
How was it that a mouse contracted bacteria when both the S strain heated and the R strain were both not lethal?
Transformation: chemical factor transferred from the heat killed strain (S strain) transferred to the R strain
a non lethal strain was transformed into a lethal form
the offspring inherited the disease and was able to pass it on = gene

6. The Cause of Transformation
What was the “gene” that allowed for transformation to happen?
Avery
First experiment: an extracted mixture from the heat killed S strain was treated with enzymes that destroyed proteins, carbohydrates, and RNA
transformation occurred = none of those were responsible
Second experiment: an extracted mixture from the heat killed S strain was treated with enzymes that destroyed DNA
transformation did NOT occur = DNA was responsible
DNA stores and transmits genetic information from one generation to the next

7. Bacterial Viruses Hershey & Chase
they studied viruses or how viruses infect living cells
Bacteriophages: a kind of virus that infects bacteria
it attaches to the bacteria and injects its genetic information into the bacteria (DNA)
the viral gene produces new bacteriophages destroying the bacteria
cell splits open = hundreds of new viruses

8. Hershey-Chase Experiment
Experiment: Which part of the virus entered the bacteria?
Bacteriophage: DNA core and a protein coat
Markers (radioactive isotopes)
32P = phosphorus-32 marks DNA
35S = sulfur-35 marks protein
Results: the radioactivity in the bacteria contained phosphorus
Hershey and Chase confirmed Avery’s results that DNA was the genetic material found in genes in all living things

9. Hershey-Chase Experiment

10. DNA
DNA makes up genes and is capable of storing, copying, and transmitting the genetic information in a cell.
Storing Information
Each cell must contain DNA to tell the cell how to develop (eye color, height, oak tree)
Copying Information
DNA needs to be copied and transmitted to other cells in order to tell the cells what to do. How can this happen if the DNA is in the nucleus?
Transmitting Information
DNA is transmitted during cell division → Chromosomes have the genes made of DNA → What happens if the information is lost?