The Discovery of The Structure of DNA

1. The Discovery of The Structure of DNA A Brief History

2. Rosalind Franklin Born: July 1920 Notting Hill, London Fields X-ray crystallography Alma Mater: Newham College, Cambridge Died: April 16, 1958 (37) Cancer of the ovary

3. What is X-ray Crystallography X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal, and diffracts into many specific directions. From the angles and intensities of these diffracted beams, a Crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their disorder and various other information.

4. Crystallography of DNA Rosalind Franklin’s photo of DNA (Photo51) Franklin was originally working on diffraction of proteins and lipids, but was redirected to work on DNA since she was the most experienced X-ray diffraction researcher at King’s College, London in 1951. She was working in the Medical Research Council’s Biophysics unit.

5. Crystallography of DNA • In 1951 Maurice Wilkins was working diffraction of DNA with Raymond Gosling a PhD student. • They had been carrying out diffraction since 1950, but Franklin was to take over the DNA work as well as guidance of Gosling’s thesis. • Franklin and Gosling discovered two types of DNA which depended on the moisture content of the structure. • There was a great deal of friction between Franklin and Wilkins so the DNA work was divided between them.

6. Maurice Wilkins Maurice Wilkins Born: December 15, 1916 Died: October 5, 2004 Was a physicist and molecular biologist. Research contributed to the scientific understanding of phosphorescence, isotope separation, optical microscopy and X-ray diffraction, and to the development of radar. He is best known for his work at King's College London on the structure of DNA.

7. The Structure of DNA incorrect models and controversy • James Watson traveled to King’s College with a preprinted manuscript of Linus Pauling’s incorrect proposal for DNA structure. • Watson confronted Franklin about collaborating, but Franklin declined. • Watson literally backs in to Wilkins • Wilkins shows Watson a diffraction photo of Franklin’s that he received from Gosling (Gosling supplied this photo to Wilkins without permission)

8. Other Important Discoveries About The Composition of DNA That Aided in The Structure of DNA • Organic Chemist Alexander Todd determined the backbone of DNA was made of repeating phosphate and deoxyribose sugar groups • Biochemist Erwin Chargaff determined DNA contained two purine bases adenine (A) and guanine (G), and two pyrimidine bases cytosine (C) and thymine (T). These bases varied widely between species but were always in a 1:1 ration of A and T as were G and C. • Linus Pauling, then the worlds leading chemist discovered the alpha helix, the structure found in many proteins. This prompted researchers of DNA to think of Helical forms. • As mentioned Rosalind Franklin and Maurice Wilkins pioneered X-ray diffraction and obtained high quality images of DNA

9. The discovery of DNA structure Francis Crick Born: June 8, 1916 Died: July 28, 2004 Francis Crick was a molecular biologist and neuroscientist, and most noted for being one of two co-discoverers of the structure of the DNA molecule 1953 James Watson Born April 6, 1928 American molecular biologist, geneticist and zoologist, best known as one of the co-discoverers of the structure of DNA with Francis Crick, in 1953

10. How Did Watson and Crick interpret the Crystallography Photo Interpretation Rosalind Franklin Photo 51

11. 1962 Nobel Prize in Physiology or Medicine James Watson September 2010 Nobel prize Watson, Crick, and Wilkins