History of DNA How it Was Discovered

Friedrich Miescher 1869 (Germany) Isolated deoxyribonucleic acid from nucleus of cells Called this white, slightly acidic chemical “nuclein” Didn’t know it was genetic material

Frederick Griffith 1928 (England) Working on vaccine for pneumonia bacteria Discovered that by killing inside of bacteria, it wouldn’t give disease to mice

Many Scientists 1940 By this time, many scientists isolated all of the chemicals found in DNA Phosphate (PO4) Sugar (deoxyribose) Four nitrogen bases (adenine, thymine, cytosine, guanine) Now called “deoxyribose nucleic acid” or DNA

Oswald Avery 1944 (USA) Worked with bacteria that causes pneumonia Used DNA-destroying enzyme to destroy DNA inside bacteria before inserting it into animal Animal didn’t get pneumonia DNA is genetic material

A = 30% G = 20% T = 30% C = 20% Erwin Chargaff 1950 (USA) Biochemist who discovered that ratio of adenine to thymine was always 1:1 and the ratio of cytosine to guanine was always 1:1 in ALL living organisms In human DNA, for example, the four bases are present in these percentages: A=30.9% and T=29.4%; G=19.9% and C=19.8% Termed “Chargaff’s Rules” A = 30% G = 20% T = 30% C = 20%

Rosalind Franklin 1951 (England) Worked on x-ray crystal diffraction photographs (how xrays bounced off crystals) of DNA structure Worked in same area as Maurice Wilkins who tended to treat her as his assistant Wilkins was working on separate DNA projects

Structure … was still unknown How did the phosphate, deoxyribose, and 4 nitrogenous bases fit together?

James Watson and Francis Crick, 1953 (England) Wilkins showed Watson Dr. Franklin’s x-ray photograph Watson said "The instant I saw the picture, my mouth fell open and my pulse began to race.” Showed photo to Crick who instantly began work with Watson on DNA model using balls and sticks 1953 scientific paper published called “A Structure for Deoxyribose Nucleic Acid”

Nobel Prize 1962 Maurice Wilkins, Francis Crick, and James Watson received Nobel Prizes for Physiology or Medicine for work on DNA structure Rosalind Franklin died 4 yrs earlier in 1958 at age 37 of ovarian cancer Nobel prizes are only given to living persons so she will never be honored