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MOLECULAR STRUCTURE OF NUCLEIC ACIDS A Structure for Deoxyribose Nucleic Acid We wish to suggest a structure for the salt of deoxyribose nucleic acidDNA This structure has novel features which are of considerable biologicalinterest A structure for nucleic acid has already been proposed by Paulingand Corey 1 They kindly made their manuscript available to us in advanceof publication Their model consists of three intertwined chains with thephosphates near the fibre axis and the bases on the outside In our opinionthis structure is unsatisfactory for two reasons 1 We believe that thematerial which gives the X-ray diagrams is the salt not the free acidWithout the acidic hydrogen atoms it is not clear what forces would holdthe structure together especially as the negatively charged phosphatesnear the axis will repel each other 2 Some of the van der Waals distancesappear to be too small Another three-chain structure has also been suggested by Fraser in thepress In his model the phosphates are on the outside and the bases onthe inside linked together by hydrogen bonds This structure as describedis rather ill-defined and for this reason we shall not comment on it We wish to put forward a radically different structure for the salt ofdeoxyribose nucleic acid This structure has two helical chains each coiledround the same axis see diagram We have made the usual chemical assumptionsnamely that each chain consists of phosphate diester groups joining -D-deoxyribofuranoseresidues with 35 linkages The two chains but not their bases are relatedby a dyad perpendicular to the fibre axis Both chains follow right- handedhelices but owing to the dyad the sequences of the atoms in the two chainsrun in opposite directions Each chain loosely resembles Furbergs2 modelNo 1 that is the bases are on the inside of the helix and the phosphateson the outside The configuration of the sugar and the atoms near it isclose to Furbergs standard configuration the sugar being roughly perpendicularto the attached base There is a residue on
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