翻譯一篇生物英文論文
Molecular Structure of Deoxypentose Nucleic Acids
While the biological properties of deoxypentose nucleic acid suggest a molecular structure containing great complexity, X-ray diffraction studies described here show the basic molecular configuration has great simplicity. The purpose of this communication is to describe, in a preliminary way, some of the experimental evidence for the polynucleotide chain configuration being helical , and existing in this form when in the natural state. A fuller account of the work will be published shortly.
The structure of deoxypentose nucleic acid is the same in all species (although the nitrogen base ratios alter considerably)in nucleoprotein, extracted or in cell, and in purified nucleate. The same linear group of polynucleotide chains may pack together parallel or paracrystalline material.In all cases the x-ray diffraction photograph consists of two regions, one determined largely by the regular spacing of nucleotides along the chain, and the other by the longer spacings of the chain configuration. The sequence of different nitrogen bases along the chain is not made visible.
Oriented paracrystalline deoxypentose nucleic acid (‘structure B’ in the following communication by franklin and gosling ) gives a fibre diagram as shown in fig.1 (of.ref.4). Astbury suggested that the strong 3.4-4.reflexion corresponded to the internucleotide repeat along the fibre axis. The ~34A .layer lines, however, are not due to a repeat of a polynucleotide composition, but to the chain configuration repeat, which causes strong diffraction as the nucleotide chains have higher density than the interstitial water. The absence of reflexions on or near the meridian immediately suggests a helical structure with axis parallel to fibre length .
Fig.1.Fibre diagram of deoxypentose nucleic acid from B.coli. Fibre axis vertical