Comment by dekhn
3 days ago
If I read Franklin's notes this establishes that she did in fact conceive of a double helix and base complementarity in the center (I can't see if she also recognized it was antiparallel).
That's the first actual evidence I've seen (I am a DNA nerd and have been trying to understand what her contribution to the intellectual discovery of DNA's double-helix antiparalel).
I would need to go back to Judson's book (Eighth Day of Creation) and see if he actually missed this.
I happen to be reading Judson right now. Quoting from it here:
> It is easy to feel great sympathy with Franklin. The fact remains that she never made the inductive leap... before she learned about the model proposed by Watson and Crick, she and Gosling began to draft a paper to state their conclusions so far about the B structure. That draft also survived among Franklin’s papers. It was vigorous, clear, and limited. Klug and I went over it one afternoon in his office. “You see, she was lacking one final step,” Klug said. “Well, two steps. What she missed was the presence of the dyad—the symmetry of the molecule. Which Francis had seen immediately from her information about the space group. And even though her notes earlier showed that she knew about Chargaff’s ratios, she never got to the base pairing.”
Seems like Judson accepts Klug's version of the story: she understood that the structure was helical, but not that it was doubled or base-pair. There's also a final essay at the end of the book "In defence of Rosalind Franklin" which basically reiterates this:
"She had not perceived that the backbones run in opposite directions. She had not started modelling the B form as a double helix and so had yet even to encounter the problem of fitting the bases inside."
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is all writing fiction if it wasn't written by an eyewitness?
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It's an exquisite book.
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I'm a bit confused about this discussion about whether or not she conceived of a double helix structure as this PBS Nova documentary on DNA includes a scene where they show her notes that have her muse about the possibility of a double or triple helix structure.[0]
As for base complementarity it seems likely that she would have made that leap from everything else that she knew of at the time, but I'm no expert on this subject and have not read her notes.
[0] https://youtu.be/_1FUqUSNPeI?t=2487
The paper takes things from "she could have seen it" to "she provably saw it and started acting on it".
where did she say she knew it was a double helix?
FTA:
The new paper does not challenge Watson and Crick’s achievement. Their model of DNA, rushed out in a brief article in Nature after Watson caught his glimpse of photograph 51, went well beyond Franklin’s understanding. [Watson and Crick's model's] two strands running in opposite directions and zipperlike arrangement of complementary base pairs explained how the molecule could carry genetic information and be copied each time a cell divides. “The fact that it was a helix, you know, was not the most exciting aspect of this structure,” says Soraya de Chadarevian, a science historian at the University of California, Los Angeles. Indeed, by 1952, other researchers striving to make sense of the molecule also suspected it was helical. [for example Pauling, who at one point thought DNA might be an alpha helix-like structure]
I think we already knew Franklin recognized the fibre diffraction was consistent with a helix (IIRC, Stokes had already shown that a helix would form a cross shape in a diffraction in 1950, and I believe Franklin was working with him). That wasn't the actual detail that I think is controversial.
Instead, this new paper and several previous papers based on Franklin's notes:
https://link.springer.com/article/10.1007/s10739-026-09866-7 (the paper referenced in the article) -> Franklin's notes say "“evidence for [a] 2-chain […] helix.”Footnote21" where Footnote 21 is Notebook entry for 10 February 1953 (FRKN 1/1, Franklin Papers). The images of her notes are here: https://www.jessiemillsauthor.com/journalism/photo-49-the-x-... (I can't read her handwriting, so I'm taking the 2-chain helix on faith. Also, this article https://philpapers.org/archive/NIETNC-3.pdf interprets her notes to say she recognized the complementary bases: " Franklin’s notebook entry of January 19, 1953—“diads in A. Chargaff data” (Klug index, FRKN 1/1, p. 3)—demonstrates that she had inferred complementary base pairing from the conjunction of Chargaff’s ratios and the crystallographic dyad symmetry, eleven days before Watson saw Photo 51.
So based on the above interpretation, I would probably update my understanding from:
1) Gosling collected the fibre diffraction data and Franklin recognized both that it was a helix, and that the bases were on the inside and complementary. 2) Watson and Crick deduced that DNA formed a double helix with antiparallel chains.
And now I would update it to: 1) Gosling collected the fibre diffraction data and Franklin recognized both that it was a double helix, and that the bases were on the inside and complementary. At that point I think she would have recognized the chains were antiparallel due to dyad symmetry, right?) 2) Watson and Crick deduced that DNA formed a double helix with antiparallel chains.
That's the key bit- I had not previously seen any evidence that Franklin knew it was a double helix or that she knew about the complementary bases. And since this is an area that generates a lot of strong emotions, and there's a lot of noise, I'd like to see her exact text, but I simply cannot read her handwriting.
I can read some of it. I used * for two words I couldn't read. And I'm not sure about the word "containing".
> Evidence for 2-chain (or 1-chain helix)?
> 49c - general trend is as for single containing helix
> (which differs from single * chain in integral no. residues/*
> only in contribn of high order J'n to the latter)
The crossed out bit says:
> and this is indistinguishable from double helix with residues on
> each having same ζ-value, since 2nd chain has opposite signs in
> ξ & η terms (eq 1 - 2), and eqn 2 contains only [...]
She was certainly thinking about double helixes.
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I'd like someone with more knowledge to comment on that paper - I see a lot of red flags and can't make much sense of it.
The images seem to contain commentary on Klug's commentary on Franklins work, in the same color?? The text contradicts the timelines that it cites from Klug, the paper focuses on some seemingly irrelevant details, and makes claims about the dispute I've never heard before (for example that phosphates on the outside was stolen - years after she published that finding at a conference in which Watson was in the audience). It also suggests that Klug - a fierce advocate for Franklin's legacy - was also trying to diminish her work.