funnels

(€)    N

Figurę 9-13 FoMfag funncl*. (o) An idcalizcd funncl landscape. As ibe chain form* increasing numbets of inu achain contacts. its internal free eneigy (its height above the native stale, N) dccrcasc* logether with its conformalional freedom (the width of the funncl). Folypeptides with differing conformations (bluck dots) fołkm different pathway* (bluck lina) in achieving the natiw fold (b) The Levinthal “golf course" landscape in whieh the cham musi seaich for the native fold (the hole)_

randomly. that is. on a lcvcl cncrgy surfaoc. (c) The classk folding landscape in which the chain musi search at random on a level cncrgy surfacc until it cncountcrs the canyon that leads it to the native siatę. (</) A rugged energy surface containing local minima in which a folding polypcptide can become transiently trap|H‘d. The folding funncls of rcal prołcins arc thought to havc such topographics [Courtesy of Ken Diii. Univcrsity of California at San Francisco.)