Entropic Barriers, Frustration, and Order: Basic Ingredients in Protein Folding.

We solve a model that takes into account entropic barriers, frustration, and the organization of a protein-like molecule. For a chain of size M , there is an effective folding transition to an ordered structure. Without frustration, this state is reached in a time that scales as M, with λ ≃ 3. This scaling is limited by the amount of frustration which leads to the dynamical selectivity of proteins: foldable proteins are limited to ∼ 300 monomers; and they are stable in one range of temperatures, independent of size and structure. These predictions explain generic properties of in vivo proteins.