The Discovery of DNA - a photo finish.

James Watson Francis Crick
died 7/28/2004
Maurice Wilkins
died 10/05/04
Rosalind Franklin
died in 1958
Linus Pauling
died in 1994
Erwin Chargaff
died 6/20/02

    James Watson, a biologist from Indiana University, and Francis Crick, a physicist, were working at the Cavendish Lab in Cambridge, England on the structure of DNA. Maurice Wilkins, a New Zealand physicist who had worked on the Manhattan Project, was the deputy director of the King's College biophysics lab. Linus Pauling was a Caltech chemist, who in 1951 had discovered the alpha helical nature of protein structure. Rosalind Franklin was a 30 year old English chemist who was working in an X-ray crystallography lab in Paris, France in 1951. Erwin Chargaff was a professor of biochemistry at Columbia University who discovered that the molar base ratios of A equal T and G equal C, and helped solidify our understanding of the structure of DNA.

    A primary technique for structural analysis of biological molecule is X-ray crystallography. The wavelength of X-rays is about the same as the space between the atoms in crystalline matter. Deflected X-rays can give an image pattern on a photographic plate, whose angles when analyzed mathematically can lead to the details of each atoms arrange with respect to the other atoms.

    Rosalind Elise Franklin was born in 1920 in London and attended St. Paul's Girls School where she excelled in science, mathematics, and athletics. In 1938, she was awarded a scholarship in physics and chemistry to attended Cambridge University where she undertook studies in X-ray crystallography. After earning her Ph.D. and publishing seminal papers on coal she took a job offer in one of the best labs in Paris. She was a good experimenter, perfected her X-ray techniques, and published, spoke at conferences, and was well liked by her peers. It has been reported that she was a fashion-minded lady of Paris wearing Dior and socializing as a chef for her friends. After 4 years in Paris she decided at 30 years of age to return to London. She was hired by J.T. Randall, Director of King's College  biophysics labs, to create an X-ray unit and work on DNA. She arrived at the King's College lab in 1951.

   Maurice Wilkins, the assumed overseer of the King's College lab, had in 1951 taken the first X-ray pictures of DNA that lead him to suggest the DNA structure might be a helix (similar to just announced Linus Pauling alpha helical structure of proteins). The atmosphere at King's was akin to an old boy's club (the lunch room was from men only) which lead to conflict. In addition, Randall did not clearly delineate a chain of command, and though he had hired Franklin as director of the x-RAY lab, Wilkins, who was away when Franklin was hired believed himself to be in charge. Wilkins and Franklin did not get along. Wilkins called Franklin Rosy, which she perceived as 'bad' nick name. She was never called Rosy to her face.

   Rudolf Signer, a Swiss chemist had isolated some quality calf thymus DNA, which he gave in a "jelly jar" to Maurice Wilkins at a scientific meeting sometime in 1951. At the time this was the... "best sample of DNA in the world". Franklin was given Signer's DNA by the King's College biophysics lab director, J.T. Randall.

   J.D. Watson arrived in England and having seen Wilkins pictures of DNA wanted a post-doc at King's, but instead goes to the Cavendish lab at Cambridge where he meets Francis Crick.

   Franklin discovered that Signer's DNA X-ray patterns indicated 2 forms... alpha "a wet form" and beta "a drier form". Franklin's effort often included X-ray pictures that took over 100 hours of exposure and in the November of  1951 she obtained a pattern from the wet form... a stark X-array of black stripes radiating from the centerFranklin presents the data on the "X" pattern at a colloquium, which Watson hears. She suggests that DNA is helical and Watson and Crick begin to build a model upon the "X" pattern. Franklin was asked to review the model, which she belittles and criticizes. The Director of Cavendish suggest Watson and Crick do no further model building. In May of 1952 Franklin takes the famous  photograph 51, [Anatomy of Photo 51] but sets it aside spending all her efforts on the dry form pictures that did not point as strongly toward a helix. In fact Franklin never formally published or reported on any of her X-ray photos. Conditions at King's had gotten so unsociable that Franklin decides to leave.

    Watson and Crick pursued model building, using balls and sticks. Their first model was a triple helix with the bases pointed outward. However, chemically it wouldn't hold itself together, thus they knew it was incorrect.

    In May of 1952 Linus Pauling was to go the Royal Society meetings in London, but he was denied a passport by the U.S. State Department because of McCarthyism suspicions for his anti-nuclear weapons proclamations. Some suggested he might be a communist sympathizer. Peter Pauling, Linus' son, comes to Cambridge and discusses his father's January 28, 1953 published model of DNA, not unlike the first Watson/Crick earlier incorrect version that was criticized by Franklin. It proposed a 3 stranded helix with the bases on the outside.

   Franklin became fed up with the scientific atmosphere at King's College and accepted a position at Brikbeck College, London, with crystallographer J.D. Bernal to work on the structure of viruses. In her final seminar at King's College, she never showed photo 51. Watson came to King's College to show Franklin the Pauling model, but the story goes that she confronted Watson, and so he retreated and quickly walked out of her lab.     Watson and Crick realized they had about a 2 month lead, before Pauling realized that chemically his model wouldn't hold itself together.

   The story gets mirky here. "Someone" gives photo-51 to Watson, either Franklin herself, her lab assistant, Raymond Gosling, or Wilikns showed him Franklin's photo 51 (some have called this unethical on Wilkins part). Watson immediately recognizes the significance of the "X" in photo-51; it means DNA is a helix with 10 units per turn (count the spots in the photo) with 34 Angstroms per turn. Watson sketches a copy of the photo on a newspaper and returns to Crick. Together they model the structure of DNA as a 2 chain helical, with antiparallel properties and the bases facing inward paired to hold the molecule together. Within 2 months Watson and Crick published their model. On Saturday, February 28, 1953 it is reported that Crick came into the Eagle, a Cambridge pub, and announced to everyone there that they had "found the secret of life". Franklin, in fact, came to Cambridge to see their model, and readily accepts it.

   With the discovery of the structure of DNA solved, the question of who gets the credit arises. The Director's of the Cavendish and King's College labs approach Nature and suggest that 3 papers be published in sequence: one by Watson and Crick, one by Wilkins, and a third by Franklin and Gosling. In April of 1953 the Watson and Crick paper appeared in the journal Nature 171 : 737-738  &  964-967 (1953).

    Rosalind Franklin's photo-51 was a pivotal moment in the discovery of the double helix, and maybe only Francis Crick and James Watson realized it. Franklin didn't willingly share or publish photo 51, though she did speak and presenther results including the obvious helical nature to DNA. At 38 (1958) Rosalind Franklin died of ovarian cancer, probably due to constant exposure to X-rays. In 1962 Francis Crick, James Watson, and Maurice Wilkins shared the Nobel Prize.

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