FIG. 1.

Transition paths from force spectroscopy experiments. (a) Representation of an optical tweezer experiment at constant force when the populations of the folded and unfolded states are equal. A molecular construct is attached via a typically long and soft polymeric linker to a mesoscopic pulling device. x is the end-to-end distance of the molecule, and q is the total measured extension. The fluctuations of the folded or unfolded molecule can be faster than those of the bead. (b) Measured extension q as a function of time t for the constant force experiments. The extension fluctuates about values characteristic of the folded and unfolded states with fast transitions between these conformational states. The transition paths (purple solid lines) pass directly between pre-defined limits (red lines). (c) Zoom-in on the transition paths aligned to start at the same time.