"Is DNA really a double helix?"

Date:
1978
Reference:
PP/CRI/H/6/8
Catalogue details

Licence: In copyright

Credit: "Is DNA really a double helix?". Source: Wellcome Collection.

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    LE-Ifete? Í(%síhty - /v<_ 7 <tÄ*<j á'ince the double helix was first proposed ,, > the general features of the structure have stood up very well to VuiualUj experimental tests. nyst^èîïie'i DNA is^double-stranded, with the sugar-phosphate backbones running anti-parallel rather than parallel. The bases, one from each chain, are paired in the classical way; that is, adenine with thymine or guanine with cytosine. The above generalizations are supported by innumerable experiments, not least by the flood of exact sequences (of defined stretches of DNA) which are now appearing at an ever-increasing rate. The precise manner with which guanine pairs with cytosine using three hydrogen bonds is neta^rGXil'ïyL-Qpemio--doubi-v. It has not always been clear exactly how adenine pairs with thymine, but it now seems likely that, at least in most cases, this pair has a configuration not unlike that originally suggested by Watson and Crick. On the other hand, there are other features of the structure which, although highly plausible, are not supported by experiment to anything like the same extent. I will leave on one side questions involving the precise coordinates of the structure — how much the bases are tilted, how exactly the sugars are puckered, the regularity of the structure with different base sequences, for example — and mention just two general features. Is the structure really a proper double helix, with the two chains wound plec^onemically round a common axis? Is the helix predominantly right-handed (as originally claimed) or left-handed?
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