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"...nor for identifying it as a double helix..." I think you're wrong about this part. Maybe someone else had speculated that it might be a double helix (I do
by radford-neal 6y ago
"...nor for identifying it as a double helix..."
I think you're wrong about this part. Maybe someone else had speculated that it might be a double helix (I don't know), but to take such a speculation seriously one has to work out the details, and see that they are compatible with the X-ray crystallography data.
- pcrh 6y agoRosalind Franklin and Ray Gosling figured out it was a double helix. Pauling was speculating it was a triple helix. They published their finding in the same edition of Nature as Watson and Crick published their model.
- radford-neal 6y agoWatson and Crick's paper contains the sentence "The novel feature of the structure is the manner in which the two chains are held together by the purine and pyrimidine bases." Perhaps this claim to novelty is incorrect - I certainly don't know enough about the history to have an independent opinion - but I think one must take the conventional view to be that Watson and Crick did indeed discover the structure of DNA.
- pcrh 6y agoThe conventional view is unfortunately incorrect. They proposed an (almost) correct view of how the nucleotides were arranged into a helix. Their proposal included the feature that each strand of the double helix was in fact a "mirror image" of the other, thus could be divided and copied to yield two identical copies for inheritance by two cells. The actual atomic structure of DNA was not experimentally determined until much later.
- dekhn 6y agoI don't think they ever said that it was a true mirror image, just that it was two antiparallel strands. The original Watson and Crick model was almost perfecftly correct even without the need for explicit 3D crystal structure, the major problem being that the water content of the fiber used in the study was wrong, so they made a model of A-DNA structure, rather than B-DNA structure. If you look down the axis of the double helix in the W&C structure, there is significant free space in the interior because of the way the bases have moved, where in B-DNA, the itnerior is packed with tightly stacked bases. [edit: I had forgotten that the original W&C paper says there are only two H-bonds between G and C rather than 3, which is another detail of the structure which was not completely correct.]
- pcrh 6y agoThe original W&C model did not postulate three H-bonds between G and C, but two, which is one of the reasons why it is only "almost" correct.
- dekhn 6y agoNobody proposed or suggested the idea underlying that sentence other than W&C; it was their illumination. They did stumble for a while until external folks corrected some of their misunderstandings (specifically, which of the keto-enol forms of the bases were expected at physiological condition)
- dekhn 6y agoI believe Franklin only identified the structure as being helical (if you look at the fiber diffraction images, that "X" shape is indicative of helicity) and that the phosphates were on the outside, but not that it was a double helix, nor that the strands were antiparallel, or the specific structure of the base pairs (all of which were the key insights made by W&C).
- pcrh 6y agoI think you are correct. The observation that was apparently key to W&C modelling the structure correctly was that the phosphates were on the outside of the helix. In my view of the history of this discovery, this would possibly be the only thing "stolen" from Rosalind Franklin by W&C. Nevertheless, despite the rhetoric that often surrounds this issue, it is worth noting 0) that Franklin was dead at the time the relevant Nobels were awarded, and they are not awarded posthumously; 1) the Nobel W&C received was actually awarded to three people, the third being Wilkins, who was a co-investigator with Franklin.
- dekhn 6y agoActually, phosphates on the outside were actually part of Furberg's model from '52 - see Model I in http://actachemscand.org/pdf/acta_vol_06_p0634-0640.pdf http://actachemscand.org/pdf/acta_vol_06_p0634-0640.pdf which W&C specifically mention in their paper. I personally agree about Franklin and the Nobel- I think most people just read Dark Lady and believe its conclusion. I always recommend that people read Eighth Day of Creation, which presents a very compelling alternate view based on primary data.
- pcrh 6y agoSorry for the potato quality, but here are the reports by both Watson and Crick as well as Rosalind Franklin. One directly follows the other. https://i.imgur.com/f423vS5.jpg https://i.imgur.com/f423vS5.jpg https://i.imgur.com/84fdLlp.jpg https://i.imgur.com/84fdLlp.jpg