Europhys. Lett.
Volume 69, Number 1, January 2005
Page(s) 142 - 148
Section Interdisciplinary physics and related areas of science and technology
Published online 10 December 2004
Europhys. Lett., 69 (1), pp. 142-148 (2005)
DOI: 10.1209/epl/i2004-10306-3

DNA loop statistics and torsional modulus

V. Rossetto

Laboratoire de Physique, École Normale Supérieure de Lyon 46 allée d'Italie, 69364 Lyon Cedex 7, France

received 23 August 2004; accepted in final form 28 October 2004
published online 10 December 2004

The modelling of DNA mechanics under external constraints is discussed. Two analytical models are widely known, but disagree, for instance, on the value of the torsional modulus. The origin of this embarassing situation is located in the concept of writhe. This letter presents a unified model for DNA establishing a relation between the different approaches. I show that the writhe created by the loops of DNA is at the origin of the discrepancy. To take this into account, I propose a new treatment of loop statistics based on numerical simulations using the most general formula for the writhe, and on analytic calculations with only one fit parameter. One can then compute the value of the torsional modulus of DNA without the need of any cut-off.

87.15.La - Biomolecules: structure and physical properties: Mechanical properties.
36.20.Ey - Conformation (statistics and dynamics).
82.35.Lr - Physical properties of polymers.

© EDP Sciences 2005