Chiral elasticity of DNA

DNA has been described as a semiflexible polymer. But DNA is chiral, so its bending Hamiltonian contains nonlinear terms coupling the curvature κ to the torsion τ , leading to an average 〈τ〉 independent of κ, and variance 〈∆τ〉 scaling as 1/κ. We perform atomistic MD simulations of 31 base-pair DNA sequences with explicit solvent, in which “restraints” are imposed to “encourage” the DNA to bend. We extract bending moduli by fitting to bending and torsional angle distributions. We find that chiral elasticity matters whenever DNA bends on a radius less than about 5 nm.