Unzipping DNA from the condensed globule state--Effects of unraveling

TL;DR

This paper provides a theoretical analysis of DNA unzipping from a condensed globule state under external force, revealing distinct scaling behaviors and transition characteristics compared to unzipping from an extended coil state.

Contribution

It introduces a theoretical model for DNA unzipping from a condensed globule, highlighting different critical behaviors and transition properties.

Findings

Unzipping occurs at a critical force Fc with M~(Fc-F)^{-3}

Force remains nearly constant during extension before a sudden drop at unraveling

Remaining globule size scales as N^{3/4} at transition

Abstract

We study theoretically the unzipping of a double stranded DNA from a condensed globule state by an external force. At constant force, we find that the double stranded DNA unzips an at critical force Fc and the number of unzipped monomers M goes as M~(Fc-F)^{-3}, for both the homogeneous and heterogeneous double stranded DNA sequence. This is different from the case of unzipping from an extended coil state in which the number of unzipped monomers M goes as M~(Fc-F)^{-chi}, where the exponent chi is either 1 or 2 depending on whether the double stranded DNA sequence is homogeneous or heterogeneous respectively. In the case of unzipping at constant extension, we find that for a double stranded DNA with a very large number N of base pairs, the force remains almost constant as a function of the extension, before the unraveling transition, at which the force drops abruptly to zero. Right at the unraveling transition, the number of base pairs remaining in the condensed globule state is still very large and goes as N^{3/4}, in agreement with theoretical predictions of the unraveling transition of polymers stretched by an external force.