Excluded Volume Effect in Unzipping DNA with a Force

TL;DR

This paper investigates how the excluded volume effect influences the unzipping transition of DNA under force, revealing that while the critical force shifts, the divergence exponent remains unchanged, and provides a universal phase diagram framework.

Contribution

It introduces a model incorporating excluded volume effects into DNA unzipping, showing the critical force's dependence on physical parameters and deriving a universal phase diagram.

Findings

The divergence exponent =2 remains unchanged with excluded volume effects.

The critical force Fc is affected by the excluded volume.

A universal, parameter-independent phase diagram is derived.

Abstract

A double stranded DNA molecule when pulled with a force acting on one end of the molecule can become either partially or completely unzipped depending on the magnitude of the force F. For a random DNA sequence, the number M of unzipped base pairs goes as M~(F-Fc)^(-2) and diverges at the critical force Fc with an exponent \chi=2. We find that when excluded volume effect is taken into account for the unzipped part of the DNA, the exponent \chi=2 is not changed but the critical force Fc is changed. The force versus temperature phase diagram depends on only two parameters in the model, the persistence length and the denaturation temperature. Furthermore a scaling form of the phase diagram can be found. This scaling form is parameter independent and depends only on the spatial dimension. It applies to all DNA molecules and should provide a useful framework for comparison with experiments.