4 ms·

Watson 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 pyr

Watson 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 ago
The 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 ago
  I 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 ago
    The 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 ago
      Good point, I updated my comment to reflect that. Here's a nice writeup: https://www.nature.com/articles/439539a https://www.nature.com/articles/439539a
      - pcrh 6y ago
        Thanks! That was interesting.
dekhn 6y ago
Nobody 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)

pcrh 6y ago

The 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 ago
I 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 ago
  The 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 ago
    Good point, I updated my comment to reflect that. Here's a nice writeup: https://www.nature.com/articles/439539a https://www.nature.com/articles/439539a
    - pcrh 6y ago
      Thanks! That was interesting.

dekhn 6y ago

Nobody 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)