"The complementary structure of deoxyribonucleic acid"

Date:
1954
Reference:
PP/CRI/H/1/22
Catalogue details

Licence: In copyright

Credit: "The complementary structure of deoxyribonucleic acid". Source: Wellcome Collection.

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    Reprinted, without change of pagination from the i Proceedings of the Royal Society, A, volume 223, pp. 80-96, 1954 The complementary structure of deoxyribonucleic acid By F. H. C. Crick and J. D. Watson*! Medical Research Council Unit for the Study of the Molecular Structure of Biological Systems, Cavendish Laboratory, University of Cambridge (Communicated by Sir Lawrence Bragg, F.R.S.—Received 24 August 1953) [Plate 2] This paper describes a possible structure for the paracrystalline form of the sodium salt of deoxyribonucleic acid. The structure consists of two DNA chains wound helically round a common axis, and held together by hydrogen bonds between specific pairs of bases. The assumptions made in deriving the structure are described, and co-ordinates are given for the principal atoms. The structure of the crystalline form is discussed, briefly. Introduction The basic chemical formula of DNA is now fairly well established. It is a very long chain molecule formed by the joining together of complex monomeric units called nucleotides. Four main types of nucleotides are found in DNA, and it is probable that their sequence along a given chain is irregular. The relative amounts of the four nucleotides vary .from species to species. The linkage between successive nucleotides is regular and involves 3'-5'-phospho-di-ester bonds. Information about the three-dimensional shape is much less complete than that about its chemical formula. Physical-chemical studies, involving sedimentation, diffusion and light-scattering measurements, have suggested that the DNA chains exist in the form of thin rather rigid fibres approximately 20 Â in diameter and many thousand of angstroms in length (Jordan 1951 ; Sadron 1953). Very recently these indirect inferences have been directly confirmed by the electron micrographs of Williams (1952) and of Kahler & Lloyd (1953). Both sets of investigators have presented very good evidence for the presence in preparations of DNA of very long thin fibres with a diameter of 15 to 20 A, and so there now appears little doubt about the general asymmetrical shape of DNA. The only source of detailed information about the configuration of the atoms within the fibres is X-ray analysis (Astbury 1947; Wilkins, Stokes & Wilson 1953; Franklin & Gosling 1953a). DNA's from various sources can be extracted, purified and drawn into fibres which are highly biréfringent and give remarkably good X-ray diagrams. The same type of X-ray pattern is obtained from all soures of DNA, and the unit cell found is many times larger than that of the fundamental chemical unit, the nucleotide. It seems improbable that the structure can be solved solely by modem crystallo- graphic methods such as inequalities or vector superposition. These methods have so far been successfully used with relatively simple compounds. The DNA unit cell, however, is very large, and in fact contains a larger number of atoms than in any * Aided by a Fellowship from the National Foundation for Infantile Paralysis (U.S.A.). t Present address, Biology Division, California Institute of Technology, Pasadena 4, California.