Figure 3.

Free energy landscape for a braid formed by two DNA double helices with random, uncorrelated sequences. (A) Dependence of the free energy on the tilt angle α and braid diameter R at 70% compensation of phosphate charges by bound counterions. (B) Optimum energy at a fixed value of R, decomposed into the electrostatic (dashed) and elastic (dotted) components. (C) Dependence of the braid free energy at equilibrium (most favorable) R and α on the charge neutralization fraction θ. (Inset) Dependence of the equilibrium R on θ. The free energy was calculated from Eqs. 3–10 at a = 11.2 Å (15), λ_D = 7 Å (which corresponds to the physiological ionic strength), f₁ = 0.4, and f₂ = 0.6. F = F_DNA at optimal ${\lambda }_h^{\ast }$.