Molecular Structure of Nucleic Acids
A Structure for Deoxyribose Nucleic Acid
Watson and Crick
Structures for nucleic acid proposed formerly are unsatisfied. We suggest a structure of two helical chains each coiled round the same axis. We assumed that both chains are right hand helices and antiparallel. Each of these chains consists of phosphate diester group joining beta-D-deoxyribofuranose residues with 3’, 5’ linkages. This structure repeats after 10 residues or 34A. The phosphates are on the outside of the helix. Each of these phosphorus atoms stands 10A off fibre chain. The two chains are held together by paired purine and pyrimidine bases inside of the helix. The planes of the bases are perpendicular to the fibre axis. The ratio of the amounts of adenine to thymine and the ratio of guanine to cytosine are always very close to unity for deoxyribose nucleic acid. It suggests that they exclusively pair together. The specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. The sequence of bases on a single chain does not appear to be restricted in any way. If the sequence on one chain is given, then the sequence on the other chain is determined. And the sugars are perpendicular to the attached bases. It suggests that it is impossible to build this structure with a ribose sugar in place of the deoxyribose. The structure’s water content is rather high and the structure could be more compact at lower water content.
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