Chapter 6 - Double-Stranded DNA Elasticity

Abstract

Our explicit nanohelicoidal model (EHM) is a more comprehensive one in the range of acting loads, representation of DNA molecule features, and simpler in application than many previously known mechanical models, especially for quasi-straightened DNA molecules. This model allows us to estimate the persistence length and twist-stretch coupling of a DNA molecule. It also shows with quantitative accuracy the possibility of molecule overwinding upon an initial stretching of DNA, its linear and nonlinear length thermomechanical fluctuations, and much more. Our study proves that the experimentally determined nonlinear fluctuations of the molecular length of DNA can be better understood by modeling the molecule as a helicoidal pretwisted nanostrip sensor with a nonlinear transfer function. The calculations presented here are in good agreement with the experimental data within 10% or less. Other known mechanical models do not show the possibility of nonlinearity in the variance of the thermomechanical DNA molecular length fluctuations. We have found that the nonlinear variance of the length fluctuations is an intrinsic property of the micro-nano sensors with helicoidal shape.