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X-Ray Studies of Nucleic Acids. 1947.

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Title:	X-Ray Studies of Nucleic Acids [4 of 13]
Creator:	Astbury, William
Contributor:	Symposia of the Society for Experimental Biology, No. 1
Publisher:
Date:	1947-00-00
Subject:	Nucleic acids -- Structure X-rays -- Diffraction
Description:	Symposia of the Society for Experimental Biology, No. 1
Type:	Text
Format:	text/plain
Language:	en
Identifier:	astbury-pg04
Source:	Master scanned with Epson GT-10000+ flatbed scanner at 600 dpi.
Rights:	http://osulibrary.orst.edu/specialcollections/coll/pauling/dna/copyright.html
Full Text:	X-RAY STUDIES OF NUCLEIC ACIDS 69 inferred from the flow properties of Na thymonucleate solutions also point in the same direction. A test that cannot long be dispensed with in any enquiry into the structure of a complex molecule is that of trying to build an accurate atomic model on the basis of known sizes and inter-bond angles. Chemical formulae are no more than a convenient shorthand, and it is always revealing, and often startling, to see what a molecule looks like in space. Dr A1. N. Davies has kindly built for me a short length of the postulated column of nucleotides, and though detailed description of this model is preferably postponed until better data are forthcoming about the dimensions of the unit cell, a few of the more interesting features should be mentioned. It is a compact edifice in which, as expected, all the ring structures are practically flat and parallel, but the pyrimidine and purine rings are not co-planar with the sugar rings (assumed to be P-d-desoxyribose throughout; see also papers by Todd and Lythgoe in this Symposium), because the glucosidic linkage joins base and sugar at an angle. There is no difficulty in bringing the bare nucleosides as close together as 3-4 A., but when they are transformed to linked nucleotides by double phosphorylation, then there arises a situation that is perhaps a little unusual. The linkage must be between C (3) and C (5) because there are no other hydroxyl groups available, and it therefore involves the 4-atom chain, -C-O-P-O-, thus: (N.B. This formula is not meant to convey any idea of the spatial arrangement in tile model. For example, the nucleotides lie transverse to the axis of the colunm, i.e. perpendicular to the plane of the paper.)