ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The distribution of twist and writhing in a closed DNA shorter than its persistence length is examined. In this case, the only energy contribution is elastic. We have in tegrated the equations of elasticity for a homogeneous axially symmetric rod of undeformable infinitely small circular cross section with frictionless reactions, when there is no or only one self-contact. In the absence of self-contacts, the central line of the rod is drawn on a toroid. It makes ν turns around the axis of revolution of the toroid and m turns around its core. The integer, ν, is equal to one if the rod is unknotted. We prove that no infinitely thin rod with a positive Poisson ratio is stable in a toroidal conformation if there is no self-contact. However, m-leafed roses or rosettes, with but one multiple self-contact, are shown to actually be stable when their writhing is not too great. When the integer, m, is equal to two, we have figure-8 conformations. Buckling of the circle into a figure-8 conformation occurs for the constraint such that the figure-8 and the circular conformations have the same energy. This constraint is 1.845 turns for a bending-to-twisting elastic constants ratio of A/C = 1.5. For the same value of A/C, the figure-8 conformation is unstable for a constraint greater than 2.4 turns. Corrections caused by a finite value of the radius ratio, a/L, of the cross section to the length of the rod, are estimated. For instance, both the circular conformation and the infinitesimally warped circle are simultaneous solutions for particular values of the β twist. β = A/C (m2 - ν2)½ [1 + (νπa/L)2/2]. The binding of ethidium to DNAs short enough to follow first-order elasticity has been studied. Buckling occurs at an apparent average constraint of about 0.6. How the DNA molecules are distributed in figure-8 conformations and circles has been determined as the ethidium concentration is varied.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.360231004
