Chapter 13.1

1. Chapter 13.1 The Hunt for Fame Fortune and DNA AP Biology Fall 2010

2. Early and Puzzling Clues • Johann Miescher is credited with the discovery of DNA in the late 1800’s

3. Early and Puzzling Clues • In 1928, Fred Griffith was working with S (pathogenic) and R (nonpathogenic) strains of a pneumonia-causing bacterium • Injected mice with R cells; mice lived • Injected mice with S cells; mice died • Blood samples contained many live S cells • S cells were heat-killed, then injected into mice; mice lived • Live R cells plus heat killed S cells were injected into mice; mice died • Live S cells were found in blood

4. Griffith Experiments

5. Early and Puzzling Clues • Some substance from the S cells had transformed the R cells • Both proteins and nucleic acids were candidates • In 1944, Oswald Avery showed the substance was DNA

6. Avery Experiments

7. Confirmation of DNA Function • Viruses called bacteriophages use bacterial cells for reproduction • Because they consist of only a protein coat and a nucleic acid core, these viruses were used in experiments by Hershey and Chase to prove which of these was the heredity material • It was the nucleic acid

9. Confirmation of DNA Function • 35S labeled proteins in the bacteriophage coat did not enter the bacteria and thus were not participating in providing directions for new virus assembly • 32P labeled DNA in the viral core did not enter the bacteria and directed new virus assembly

10. Confirmation of DNA Function • Linus Pauling deduced the structure and secrets of the protein collagen, bringing the biology community one step closer to DNA structural details

11. Enter Watson and Crick • Watson and Crick used numerous sources of data to build various models of DNA • In 1953, they discovered and published the structure of DNA