Figure 2.

As (a) unzipping or (b) shearing progresses, the free energy increases due to bond-breaking up until the reaction barrier, which is consistently the state with only one bond remaining. After this barrier is passed, the free energy steadily decreases to a relaxed minimum and only increases again when the distance between sticky ends is forced to be larger than the contour length of the main duplex. Free-energy curves are for main duplex lengths of (top to bottom) 20, 25, 30, 35, 40, 50, and 60 bp and are offset by 5 k_BT from each other at 0 bonds for clarity. Insets show characteristic configurations with either all 10 pair bonds intact, only one bond remaining, or completely unbound. Uncertainties are comparable to or smaller than the size of the symbols.