DNA Ch. 10
The Discovery of DNA
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
Griffith’s Experiments Each virulent bacterium is surrounded by a capsule The capsule protects the bacteria from the host’s immune system
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
Griffith’s Experiments
Griffith’s Experiments
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
Transformation This type of transfer of genetic material from one cell to another cell or from one organism to another is called transformation
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
Hershey-Chase Experiment In 1952 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
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
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.
Link! https://www.youtube.com/watch?v=X1cd68YkVdM
DNA Structure
Crash Course DNA https://www.youtube.com/watch?v=8kK2zwjRV0M