Part 1 Discovery of DNA & its structure

Learning Target 2. Know the contributions of ……make a timeline…… Griffin Avery-MacLeod-McCarty Hershey-Chase. Watson and Crick Franklin Chargaff ……make a timeline……

Griffith & Bacterial Transformation 1928- Frederick Griffith Studied 2 strains of pneumonia from mice 1 caused pneumonia 1 did not cause pneumonia Non-pneumonia kind was “transformed” into pneumonia kind

Avery-MacLeod-McCarty 1944—Oswald Avery They used process of elimination to determine which molecule gets transferred DNA was the molecule being transferred from 1 bacteria to another in Griffith’s experiment

Hershey & Chase 1952—Alfred Hershey & Martha Chase Studied bacteriophages Bacteria killing viruses Attached radioactive markers to proteins and to DNA to see which one was genetic material Determined that DNA, not protein functions as genetic material

Phage head Tail Tail fiber DNA Bacterial cell 100 nm

Other clues to DNA’s Structure: Chargaff Erwin Chargaff (American biochemist) 1950 “Chargaff’s Rules” Species have different amounts of A, T, G & C Analyzed amounts of Adenine, cytosine, guanine & thymine Amount of A = T Amount of C = G

Wilkins & Franklin Maybe a “twisted” structure Maybe a helix Early 1950’s– Maurice Wilkins & Rosalind Franklin From images captured through X-ray crystallographers Maybe a “twisted” structure Maybe a helix Maybe 2 strands Maybe nitrogen bases in middle

Rosalind Franklin and her X-ray diffraction photo of DNA (a) Rosalind Franklin Franklin’s X-ray diffraction Photograph of DNA (b)

Watson & Crick James Watson (American biologist) Francis Crick (British physicist) 1953  put all the clues together Built wire/tin model “Double Helix” Nobel Prize 1962 Watson, Crick, Wilkins