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  • Title: DNA kinks and bubbles: temperature dependence of the elastic energy of sharply bent 10-nm-size DNA molecules.
    Author: Sanchez DS, Qu H, Bulla D, Zocchi G.
    Journal: Phys Rev E Stat Nonlin Soft Matter Phys; 2013 Feb; 87(2):022710. PubMed ID: 23496551.
    Abstract:
    A 10-nm-long DNA molecule can bend through large angles reversibly. Past the linear regime, its equilibrium nonlinear bending elasticity is governed by a critical bending torque τ(c)≈30pN×nm at which the molecule develops a kink. This nonlinearity has long been attributed to the nucleation of a bubble or melted region in the molecule. Here we measure the temperature dependence of the critical bending torque for nicked DNA, and determine that the entropy associated with the kink in the nonlinear regime is negligible. Thus in the case of nicked DNA the kink is not a bubble, but a compact region deformed beyond a yield strain. We further argue that, with our boundary conditions, the same is likely true for intact DNA. The present measurements confirm that the critical bending torque τ(c) is a materials parameter of DNA mechanics analogous to the bending modulus B≈200pN×nm.
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