"The structure of DNA - Coldspringharbor"

Date:: [1953]

Reference:: PP/CRI/H/1/13

Catalogue details

Licence: In copyright

Credit: "The structure of DNA - Coldspringharbor". Source: Wellcome Collection.

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and so will only be given in outline. Structure B has a very strong 3*4 I reflexion on the meridian. As first pointed out by Ast bury, this can only mean that the nucleotides in it occur in groups spaced 3*4 I apart in the fibre direction. On going from Stracture B to Structure A the fibre shortens by about 30^. Thus in Structure A the groups must be about 2-§ I apart axially. The measured density of Structure A, (Franklin and Gosling 1953c) together with the cell dimensions, shows that there must be two nucleotides in each such group. 4goom*v****** ■ Thus it is very probable that the crystallographic unit consists of two distinct polynucleotide chains. Final proof of this can only come from a complete solution of the structure. Structure A has a pseudo-hexagonal lattice, in which the lattice points are 22 £ apart. This distance roughly corresponds with the diameter of fibres seen in the electron microscope, bearing in mind that the latter are quite dry. Thus it is probable that the crystallo- graphic unit and the fibre are the one and the same. Two conclusions might profitably be drawn from the above data. Firstly, the structure of DEA is regular enough to form a three dimensional crystal, This is in

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