Quaternary Structure 1. If in its unfolded state the protein sampled all possible conformations on its way to its folded state protein folding would never occur. I 1 -I n until it finally reaches the folded F or native N state. In order to convert from one intermediate state to the next the polypeptide chain must overcome a kinetic barrier. This is the origin of the folding funnel figure shown in your text.
Proteins occasionally take detours to off pathway species.
These motifs do not typically fold independently. They often serve important functions. A single polypeptide chain can fold into multiple domains. Often each domain possesses its own function. Many proteins possess more than one polypeptide chain.