Effect of major-minor grooves.

(a) The major-minor grooves increase ΔL_c for the entire range of AR. Shaded region represents the range of experimental values. Inset shows the ribbon configuration of the helical model without major-minor grooves (blue) and with major-minor grooves (red). Results are calculated using E_c = 668 MPa, D = 2.4 nm, and S_r = 1100 pN with the default helical parameters. (b) Feasible parameter values of D and AR necessary to reproduce the experimental mechanical properties of the B-form DNA when we use the helical model with major-minor grooves (red) and without them (blue).