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Titel: Genetical Implications of the Structure of ...
8vo (209 x 139 mm), pp , with diagrams in the text, unbound as issued (the third lead tipped onto the verso of the second), contemporary ink stamp '341' in upper blank corner, in a morocco-backed box. £18,000First edition of the second, and second-most important, paper on the discovery of the double-helix structure of DNA, published a month after Watson and Crick's first paper announcing the discovery of the structure of DNA. This is a much RARER OFFPRINT THAN THE first AND ARGUABLY AS IMPORTANT. 'Watson wrote about the structure of DNA, in his textbook, "Before the answer was known, there had always been the mild fear that it would turn out to be dull, and reveal nothing about how genes replicate and function. Fortunately, however, the answer was immensely exciting." Five weeks after Watson's and Crick's first paper in Nature, their second appeared, in which, after explaining the structure and the evidence all over again, they pursued some of the genetical implications. These flowed from the most novel, most fundamental fact of the model:'Any sequence of the pairs of the bases can fit into the structure. It follows that in a long molecule many different permutations are possible, and it therefore seems likely that the precise sequence of the bases is the code which carries the genetical information. If the actual order of the bases on one of the pair of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing.'This immediately suggested, they said, how DNA duplicated itself.'Previous discussions of self-duplication have usually involved the concept of a template, or mould. Either the template was supposed to copy itself directly or it was to produce a "negative", which in its turn was to act as a template and produce the original "positive" once again. In no case has it been explained in detail how it would do this in terms of atoms and molecules.'The elucidation of the structure of DNA called for a new kind of functional explanation.'Now our model for deoxyribonucleic acid is, in effect, a pair of templates, each of which is complementary to the other. We imagine that prior to duplication the hydrogen bonds [connecting the bases in pairs] are broken, and the two chains unwind and separate. Each chain then acts as a template for the formation on to itself of a new companion chain, so that eventually we shall have two pairs of chains, where we only had one before. Moreover, the sequence of the pairs of bases will have been duplicated exactly.'Yet perhaps not always exactly: the model, or rather the mistake whose correction by Donohue had cleared the way for the model, suggested for the first time a physical, molecular explanation for the central phenomenon of genetics, namely the occasional, random appearance of mutations. If the sequence of bases carried the information for the organism, then a mutation might be no more than a single change in that sequence. In particular, they wrote, "Spontaneous mutation may be due to a base occasionally occurring in one of its less likely tautomeric forms." For example, though adenine normally paired with thymine, in the rare event that one of its hydrogen atoms shifted to a particular different position at the moment the complementary chain was forming, then the base could bond with the other pyrimidine, cytosine. On the next cycle of replication, the adenine, taking its normal tautomeric form again, would pair as usual with thymine, but the cytosine would pair with guanine and so, on one of the two new double helices, a change in the sequence of bases would have appeared. This was plausible, immensely exciting speculation: proof that a change of a single base pair can cause a mutation was several years away' (Judson, The Eighth Day of Creation pp 184-85). Buchnummer des Verkäufers 3819
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