[Background Papers]

Date:
1968-1981
Reference:
PP/CRI/H/6/12/7
Catalogue details

Licence: In copyright

Credit: [Background Papers]. Source: Wellcome Collection.

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    Although. DNA has Leen found to exist in left h.and forms Cl,2l and topological objections have been raised to th.e classical model (.3,U), arguments for the right-handedness of tie DNA double helix remain, and rest heavily on the existence and behavior of supercolled circular DNA molecules; particularly- the sequential hands these molecules produce on gel -r .elect rophoresis (5 ,6). These hands are said to reflect the integral differences in the linking numbers of DNA coils. I would like to suggest alternative explanations, and show that supercoiling need not depend on linking number. Figure 1 represents the form a rubber hand may assume after a simple manipulation. The hand is held in an open loop between the thumb and forefingers of the right and left hands and rolled between th.e right thumb and forefinger by drawing th.e thumb to the right. The rolling places turns of left-hand twist in the upper half of the hand and an equal number of turns of righ.t-h.and twist in the lower half. On moving the hands together the torsiona.1 stress is relieved s eparat ely in the: upper and lower portions of the band hy the formation of two or more right and left twisted loops. When done properly, no stress remains at th.e fingers (arrows, in figure); and the band, which, does not change its shape on being released, has the superficial appearance of supers coiled DNA, even to the presence of a relaxed central loop Carrowsl,
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