Figure 2.
Simple models of random coil proteins. A) The freely-jointed chain is a 3D random walk of rigid monomers of length L, and B) the wormlike chain model represents a continuous, homogenous polymer. Both chains can occupy numerous conformations at low fractional extensions (end-to-end distance z ≪ molecular contour length) but only one conformation when z = Lc. C) External force is required to extend a flexible polymer. The molecular restoring force than opposes the external force is the entropic force generated by the polymer. This entropic force is powered by diffusion and is the apparent force that recoils the protein when external force is removed.