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."
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.
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.
Clickbait headline which misframes the controversy, to nobody's benefit.
Helical DNA was the strongest candidate by 51, in part because earlier and cruder X-ray diffraction images had existed for some time (10+ years) and were suggestive of this structure. All of the scientists in question, and many others, collaborated on that possibility at that time, and long before 'Photo 51'. It was not a surprise, but rather the focus of their work.
Franklin was making the famous improved images with the explicit intent of revealing or disproving the helical structure. She and her lab produced the most definitive evidence for helical B-DNA (Photo 51) in early 52, but during 52 the conclusion was still a matter of debate (and humor) amongst them - in particular Franklin was not convinced that A-DNA was helical. From Wiki:
> In July 1952, as a practical joke on Wilkins (who frequently expressed his view that both forms of DNA were helical), Franklin and Gosling produced a funeral notice regretting the 'death' of helical A-DNA
This left the molecular structure and number of strands as open questions. Triple helix models had been attempted by Pauling, Watson and Crick at that time. Watson and Crick though were first to develop the successful double helix model with antiparallel base pairs in early 1953. It is likely that Franklin had also come to the conclusion that DNA was a double helix by this time (based on her draft notes + circumstantial evidence) but she did not do so in total isolation, nor did she complete the final molecular part of the puzzle (though she had worked on it).
TL;DR DNA structure was not a eureka moment spurred by a single breakthrough thought or piece of evidence; many scientists collaborated on eliminating various likely possibilities for years until the correct model was found.
This is not a case where she was running to the scientific society saying “double helix!” and they told her to get lost. She was sitting on evidence. We’ll never know how long it would have taken her to figure out its meaning, but we know Watson was first to recognize it out loud.
If any of you have time, I’ll tell you how I invented Twitter, Reddit, and AI assistants.
what? she was doing a form of crystallography that ONLY makes sense if it's a helix? Like, any time you are doing fiber diffraction it's pretty much "a helix". Who claimed she didn't realize it was a helix? I thought the claim was that she didn't recognize the significance of the helical parameters, which of course she couldn't, she wasn't a chemist and didn't have a model in mind with knowable parameters.
She might have measured those parameters, but she still didn't know what she had (as evidenced by how she subsequently spent a ton of time on Z-dna)
I beleive fibre diffraction also works on parallel fibres (non-helical). For example, long chains of beta-sheet (look at beta keratin, which is one of the early non-helical structures analyzed by Astbury).
> Science historian Alistair Sponsel of the Science History Institute and crystallographer Brian Sutton of KCL argue Franklin knew the earlier photo had revealed a helix—the epiphany Watson claimed for himself—and that is precisely why she made a second, more refined version, photograph 51.
It was Watson and Crick who discovered the double helix, even if Franklin did write something down about a single helix from a previous photo that they didn't read.
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."
Why would someone care about this rando's fictional (because he wasn't there) version of the story?
It's an exquisite book.
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
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.
Clickbait headline which misframes the controversy, to nobody's benefit.
Helical DNA was the strongest candidate by 51, in part because earlier and cruder X-ray diffraction images had existed for some time (10+ years) and were suggestive of this structure. All of the scientists in question, and many others, collaborated on that possibility at that time, and long before 'Photo 51'. It was not a surprise, but rather the focus of their work.
Franklin was making the famous improved images with the explicit intent of revealing or disproving the helical structure. She and her lab produced the most definitive evidence for helical B-DNA (Photo 51) in early 52, but during 52 the conclusion was still a matter of debate (and humor) amongst them - in particular Franklin was not convinced that A-DNA was helical. From Wiki:
> In July 1952, as a practical joke on Wilkins (who frequently expressed his view that both forms of DNA were helical), Franklin and Gosling produced a funeral notice regretting the 'death' of helical A-DNA
This left the molecular structure and number of strands as open questions. Triple helix models had been attempted by Pauling, Watson and Crick at that time. Watson and Crick though were first to develop the successful double helix model with antiparallel base pairs in early 1953. It is likely that Franklin had also come to the conclusion that DNA was a double helix by this time (based on her draft notes + circumstantial evidence) but she did not do so in total isolation, nor did she complete the final molecular part of the puzzle (though she had worked on it).
TL;DR DNA structure was not a eureka moment spurred by a single breakthrough thought or piece of evidence; many scientists collaborated on eliminating various likely possibilities for years until the correct model was found.
This is not a case where she was running to the scientific society saying “double helix!” and they told her to get lost. She was sitting on evidence. We’ll never know how long it would have taken her to figure out its meaning, but we know Watson was first to recognize it out loud.
If any of you have time, I’ll tell you how I invented Twitter, Reddit, and AI assistants.
what? she was doing a form of crystallography that ONLY makes sense if it's a helix? Like, any time you are doing fiber diffraction it's pretty much "a helix". Who claimed she didn't realize it was a helix? I thought the claim was that she didn't recognize the significance of the helical parameters, which of course she couldn't, she wasn't a chemist and didn't have a model in mind with knowable parameters.
She might have measured those parameters, but she still didn't know what she had (as evidenced by how she subsequently spent a ton of time on Z-dna)
I beleive fibre diffraction also works on parallel fibres (non-helical). For example, long chains of beta-sheet (look at beta keratin, which is one of the early non-helical structures analyzed by Astbury).
Beta keratin fibers are helical. (The pitch is much longer, but still helical, not alpha helices obvs).
> Science historian Alistair Sponsel of the Science History Institute and crystallographer Brian Sutton of KCL argue Franklin knew the earlier photo had revealed a helix—the epiphany Watson claimed for himself—and that is precisely why she made a second, more refined version, photograph 51.
It was Watson and Crick who discovered the double helix, even if Franklin did write something down about a single helix from a previous photo that they didn't read.
dupe, see older post here: https://news.ycombinator.com/item?id=49998006
Related: https://www.nature.com/articles/d41586-023-01313-5
Link added to toptext. Thank you!@