"The configuration of the nucleic acids"

Date:
1955
Reference:
PP/CRI/H/1/39
Catalogue details

Licence: In copyright

Credit: "The configuration of the nucleic acids". Source: Wellcome Collection.

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    helical phosphate-sugar chains winding round the same axis, The sequence of the atoms in the two chains is in opposite directions, since 4he chains are related by diad axes perpendicular to the fibre axis. The chains are linked together by hydrogen bonds between their bases, a base from one chain being paired off with the opposite base on the other chain. In structure B the planes of the bases are roughly perpendicular to the fibre axis, as shomi in fig, 2. .In structure A they are tilted some 25° away from this position, , The phosphate-sugar chains are on the outside of the structure, being some 9 ^ from the axis, where w as the bases are much nearer in. Not all pair|s of bases are possible. If it is assumed that the bases only occur in their most likely tautomeric forms the only pairs that will fit in are ^ ; adenine with thymine or guanine with cytosine (or its derivatives). The model places no restriction on the sequence of bases along a single chain. However if the sequence of bases along one chain were known, the sequence along the other could be written down because of the specific pairing. Thus each chain, with its bases, can be regarded as the complement of the other. A precise description of the original model has been given by us elsewher Ç41 , but this has been shown by the King's College group to Cx] yiv'iOX be incorrect in detail. In particular the radius of model is a little smaller than originally suggested, the phophates probably being at about 9 A from the fibre axis rather than 1GA, The main features of the model, then, are as follows: 1. It contains two chains coiled round the same axis, but running in opposite directions and related by perpendicular diads. 2, The chains are helical.
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