Elasticity of a DNA chain dotted with bubbles under force

TL;DR

This paper investigates how the elasticity and extension of a DNA chain with bubbles respond to different applied forces, revealing phase transition behaviors and the influence of external forces on bubble states.

Contribution

It introduces a detailed analysis of DNA elasticity under force, identifying a tricritical point and contrasting behaviors under stretching and unzipping forces.

Findings

Existence of a tricritical point in the force-temperature phase diagram.

Force-induced transition changes from first-order to continuous at the TCP.

Elasticity is affected only when external force penetrates the bound phase.

Abstract

The flexibility and the extension along the direction of the force are shown to be related to the bubble number fluctuation and the average number of bubbles respectively, when the strands of the DNA are subjected to a force along the same direction, here we call a stretching force. The force-temperature phase diagram shows the existence of a tricritical point (TCP), where the first-order force induced zipping transition becomes continuous. On the other hand, when the forces are being applied in opposite directions, here we call an unzipping force, the transition remains first-order,with the possibility of vanishing of the low-temperature re-entrant phase for a semiflexible DNA. Moreover, we found that the bulk elasticity changes only if an external force penetrates the bound phase and affect the bubble states