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DNA Discoveries

DNA

I. Discoveries A. Friedrich Meischer (1869) 1. Isolated DNA from cells & called it "nuclein"; Properties: a. sugary b. acidic c. phosphorous

B. Robert Feulgen (1914) 1. Discovered stain for DNA, which showed it is in the nucleus of all cells

C. (1920s) 1. Discovered basic unit of DNA ­ the nucleotide: a. Sugar (Deoxyribose) b. Phosphate Group c. Nitrogenous Bases

1 DNA Discoveries

D. (1928) 1. Was working on vaccine 2. 2 types of S. pneumoniae bacterium: a. Pathogenic (disease­causing) S­type (Smooth) b. Nonpathogenic (harmless) R­type (Rough)

3. Concluded that the living R had been transformed into pathogenic S bacteria by an unknown, heritable substance (transforming factor) from the dead S cells that allowed the R cells to make capsules.

E. , Colin MacLeod, Maclyn McCarty (1944) 1. Purified substances from heat­killed S­type and exposed living R­type to them one by one 2. Identified DNA as the transforming factor

2 DNA Discoveries

F. Max Delbruck & (1940s) 1. Determined the life cycle of bacteriophages

time 0 ­ enter 10 ­ no virus visible 15 ­ pieces 20 ­ new virus 25 ­ cell bursts

G. and (1952) 1. Tagged bacteriophages with radioactive isotopes: a. Sulfur (S35) b. Phosphorus (P32)

2. Phage DNA entered bacterial cells, but not phage

3. Concluded that DNA, not , functions as genetic material

3 DNA Discoveries

H. (1950) 1. Identified ratio of nitrogenous bases (Chargaff's Rule): A=T and G=C

I. , , & (1953) 1. Franklin (& Wilkins) worked with Xray crystallography 2. Wilkins showed Watson image (), which revealed double helix structure

3. Watson & Crick built first model of DNA a. Sugar­Phosphate must be on the outside

b. To keep width consistent, base pairs must be purine with pyrimidine

4 DNA Discoveries

5 Attachments

DNA Cold Spring Harbor xray crystallography http://www.schooltube.com/video/6e2978808f6bd8a32642/ http://www.youtube.com/watch?v=2JzZSoUxLsU