Discovery of the DNA Structure
The people responsible for the discovery of the double-helical structure of DNA were Francis Crick, Rosalind Franklin, Linus Pauling, James Watson and Maurice Wilkins. The story starts in 1951 when several things happened.
Rosalind Franklin (1920-1958), a graduate in physical chemistry, had been working since 1947 on x-ray crystallographic methods at the Central State Chemistry Labs. in Paris. She helped found the science of high strength carbon fibers that found application as graphite rods in nuclear power plants. As an expert on x-ray crystallography she was head hunted in 1951 by John Randall, of the Medical Research Council Biophysics Research Unit at King’s college, London, to work on an x-ray picture of DNA taken by a graduate student Raymond Gosling. The working relationship at King’s college did not get off to a good start because of a misunderstanding. New Zealander Maurice Wilkins (1916-2004), a physics graduate and member of the Medical Research Council Biophysics Research Unit, who had been working on nucleic acids and x-ray diffraction of DNA, was away on holiday when Franklin arrived. Gosling, his second in command, stood in for him at the first office meeting and, since no work had been done on DNA for several months, it was all given to Franklin. Franklin was the kind of person that once they are given something to solve they keep it to themselves until it is complete; not the way that Wilkins liked to run the lab at King’s college. When Wilkins returned he thought that Franklin was a high class technical assistant who was to supply the team with experimental data for it to analyze. This was not to be. Relationships were strained between Wilkins and Franklin, whereas Gosling got on with them both. Thus the seeds were sown for a rough ride for all concerned.
To solve the structure of DNA four ideas had to come together. That the phosphate backbone was on the outside, bases on the inside. That the molecule was a double helix. That the strands were antiparallel. That it had a specific base pairing.
Franklin soon found out that by bundling super thin strands of DNA and zapping them with a super fine x-ray beam there were two forms of hydration — the A form (easy to photograph) that is dry and the B form (hard to photograph) that is wet. Her B form photographs showed a fuzzy cross which meant a helix. Since the water would be attracted to the phosphates in the backbone, and the DNA was easily hydrated and dehydrated, she guessed that the backbone was on the outside and the bases were on the inside. The first part of the problem was solved.
In the November of 1951 Franklin gave a departmental seminar to bring the unit up to date on what she had achieved so far. In it she presented the A and B form data. In the audience was an American James Watson (1928- ), a zoology graduate, who had become interested in molecular biology, with particular emphasis on DNA. He was on a National Foundation of Infantile Paralysis Fellowship at the University of Cambridge, England, and was working under Laurence Bragg and his x-ray team. After the seminar Watson caught the train back to Cambridge and, based on what he had heard and seen, he and Francis Crick (1916-2004) built their first model of DNA. This was slightly unethical as Bragg’s Cambridge team had a gentleman’s agreement that they would work on x-ray crystallography of protein and Randall’s team in London would work on DNA. Watson had not taken notes, knew nothing about crystallography, and had only remembered bits of Franklin’s talk. So, when Watson and Crick invited Franklin and Wilkins to view the model, Franklin tore its construction to shreds. The model was a triple helix with bases on the outside. Egos wounded, Bragg banned Crick and Watson from working on DNA.
In May, 1952 Franklin got the first good photograph of the B form of DNA. The photograph showed a double helix, which was the second part of the problem that had to be proved. Franklin, though, was a perfectionist when it came to research and would not release any data until she had more information on the A form which was giving the most data.
Meanwhile, in America, Linus Pauling (1901-1994), was working on the structure of DNA and was very close to solving the puzzle. He was a physical chemist with an interest in biological chemistry, who in 1950 constructed the first satisfactory model of a protein molecule and was twice winner of the Nobel prize (1954 chemistry and 1962 Peace). In May, 1952 he applied for a passport to visit England for a conference, but it was refused because of accusations of him being a communist. Had he attended the conference he would almost certainly have met Franklin. Had they collaborated, with her data and his knowledge, they would almost certainly have solved the structure of DNA.
Not releasing the information on the B form proved to be Franklin’s downfall, for she got bogged down with calculations and obsessed in trying to determine whether the A form was helical. Gosling got so frustrated trying to visualize the geometry of the arcs that oranges were used to simulate the spatial relations of the several curves. Finally on Friday the 18th July, 1952 Rosalind took up her fountain pen and, in capital letters, wrote, on a 3 x 6 inch card with a hand inked black border, a death notice for the DNA helix (Crystalline) which she and Gosling signed; referring only to the A form “crystalline” DNA. Franklin continued to waste most of the winter of 1952 with work on the A form. She did meet with Crick who tried to offer advice, but, since his character was typically patronizing, she rejected an opportunity to collaborate. An opportunity missed, for they would most certainly have solved the puzzle in months.
Meanwhile, because of lack of communication at the King’s College lab, Wilkins was trying to reproduce Franklin’s results, but he failed to get the same quality. Back in Cambridge Watson and Crick were working with a lot of volatile enthusiasm, but no data.
In January 1953 Linus Pauling sent his son Peter, who was studying at Cambridge, a draft copy of his paper on DNA for comment. Watson knew Peter and somehow got a sight of the DNA paper. The outcome was that Watson took the paper to Franklin for comment, but she dismissed it as rubbish, being further annoyed as she had written to Pauling for information, but none had been sent. Upset at his reception Watson went to talk to Wilkins who he met in the main passageway to the lab. Wilkins who had been given a clear copy of Franklin’s B form photograph by Raymond Gosling in a corridor a few days early, showed it to Watson without Franklin’s consent or knowledge. Then, in February, Max Perutz, head of the Medical Research Council Unit housed at the Cavendish Laboratory in Cambridge, where Crick was a research student, received a government report that contained the data presented by Franklin at her departmental seminar. The report was not confidential, but it was private. Perutz passed the report on to Crick without asking Randall or Franklin’s permission.
Watson and Crick now had all Franklin’s data which showed that DNA was a multiple helix. Crick, who had worked on proteins, soon realized that Franklin’s data implied an antiparallel double helix. On the 10th of February Franklin began working on the B form again. According to Franklin’s note book she had had the antiparallel idea for the A form, but had not applied it to the B form, had she done so she would have solved part three of the puzzle earlier.
The last part of the puzzle focused on the base pairing and required a thorough knowledge of Chargaff’s rules. Watson and Crick had come to an elementary understanding of Chargaff’s rules the year before, with Crick even arranging a meeting with Chargaff, where he had to admit that he did not even understand the basics, let alone the rules. Franklin was conversant with Chargaff’s rules and so, with all the facts at her fingertips and her superior knowledge of chemistry, it was only a matter of time before she used logic to figure out the last part of the puzzle. In fact she had produced a draft paper, with Gosling, dated the 17th of March, 1953, which outlined that the molecule was a double helix, had specific base pairing and the antiparallel A form, which had not been applied to the B form. Franklin did not realize that Watson and Crick were racing to publish first, which they did on the 18th of March, 1953, so beating her because she had not published.
The Watson and Crick paper entitled “A Structure for Deoxyribose Nucleic Acid” written on the 2nd of April, 1953 and published in “Nature” on the 25th April, 1953 cites no authorities or historical record. It opens with the sentence “We wish to suggest a structure for the salt of deoxyribose nucleic acid (DNA). This structure has novel features which are of considerable biological interest.”. It contains no experimental proofs. It contains only hypotheses. No acknowledgement is made to Franklin and Wilkins at King’s College, London beyond the following statement. “We have also been stimulated by a knowledge of the general nature of the unpublished results and ideas of Dr. M.H.F. Wilkins, Dr. R.E. Franklin, and their co-workers at King’s College London.”.
In 1962 Watson, Crick and Wilkins received the Nobel Prize in Physiology or Medicine. They proposed that the DNA molecule takes the shape of a double helix, an elegantly simple structure that resembles a gently twisted ladder. The rails of the ladder are made of alternating units of phosphate and the sugar deoxyribose; the rungs are each composed of a pair of nitrogen-containing nucleotides. In their Nobel lectures they cite 98 references, none are Franklin’s. Only Wilkins included her in his acknowledgements. Franklin died in 1958. The Nobel Prize is only awarded to living persons.
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