Figure 2.

(a) An example of a free energy diagram often used to describe protein folding and unfolding. The free energy, G, is plotted as a function of a generalized folding coordinate, x. The symbols U, ‡, and F represent the unfolded ensemble, the transition state ensemble, and the folded ensemble, respectively. (b) An example of how an imperfect compensation of entropy (TS) and enthalpy (H) leads to a (in this case, entropic) barrier on the folding coordinate. (c) A two-dimensional free energy diagram allowing for multiple unfolding pathways. x₁ and x₂ represent generalized unfolding reaction coordinates.