Professor Irwin Tobias
Department of Chemistry
Rutgers University
Piscataway, New Jersey

Monday, April 24, 2000
3:00 pm (CT)
3269 Beckman Institute

Abstract

In theoretical work on the molecule, DNA is, at times, treated as a naturally straight, inextensible, isotropic elastic rod of circular cross section. It is shown that, consistent with this level of approximation, there exists a general connection between the dependence of the free energy of supercoiling of DNA plasmids on their linking number difference, DLk, and the writhe distribution in plasmids all of a given value of DLk. The general results are illustrated for two cases: (i) large plasmids, for which the free energy of supercoiling, observed to vary as the square of DLk, is shown to imply a normal writhe distribution, and (ii) miniplasmids, for which a theoretical expression for the free energy of supercoiling involving the frequencies of the normal modes of vibration of a circular elastic ring is available. In this latter case, the writhe distribution, it turns out, is not normal.

Tea and coffee will be served in R3151 Beckman Institute at 2:15pm.