Unzipping DNA from the condensed globule state—Effects of unraveling

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 , where the exponent χ 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.

Manipulating a single adsorbed DNA for a critical endpoint

“…The recognition of force as a thermodynamic variable for this process has helped in completing the phase transition picture of dsDNA [5]. Even though the nature of the thermal denaturation of DNA remains a puzzle, the force induced unzipping transition is theoretically well-settled [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In addition, the force-induced unzipping transition has emerged as a possible scenario for opening of DNA [19] with the replication Y-fork as the junction of two-phase coexistence, the zipped and the unzipped DNA.…”