Chapter 12: DNA“The Blueprint of Life”

Chapter 12.1 (Pg. 338-343):Identifying the Substance of Genes

What makes up a gene?

- Scientists wanted to understand chemical nature of the gene

- Frederick Griffith- Wanted to know how bacteria cause

pneumonia in mice

- Isolated two similar types (strains) of bacteria

- S Strain: causes pneumonia- R Strain: harmless

Griffith’s Experiments

- Injected mice with different bacteria

1) S Strain: Mouse Died2) R Strain: Mouse Lives3) S Strain (Heated):

Mouse Lives4) S Strain (Heated) and

R Strain: Mouse Dies

What Happened?

Transformation

- The harmless bacteria changed into the disease causing bacteria

- Some ‘chemical factor’ transferred from the heat-killed S Strain cells into the living R Strain cells

- The ability to cause disease was inherited by the R Strain

What is the Chemical Factor?

- 1944: Oswald Avery

- Mixed heat-killed S strain and R Strain bacteria with different enzymes

Hershey-Chase Experiment

- 1952: Alfred Hershey and Martha Chase

- Used bacterial viruses to identify genetic material

- Bacteriophage: virus that infects bacteria by injecting its genetic information

- Contain DNA core and protein coat

Hershey-Chase Experiment

- Used radioactive phosphorous and sulfur

- Acted as markers

- All radioactivity in bacteria was phosphorous

- Concluded that genetic material of bacteriophage was DNA

The Role of DNA

1) Store Information

2) Copy Information

3) Transmit Information