Now, if we increase the temperature of our solution or if we add some type of denaturing chemical agent, what will begin to happen is that protein will begin to unfold. It will begin to lose its tertiary structure, followed by the secondary structure, and eventually it will denature and form a non functional, biologically inactive protein. Now, at the same time, if we remove that denaturing chemical agent or if we decrease the temperature back to normal, what will happen is that denatured form of the polypeptide will basically begin to refold and eventually will fold into the fully active native state of that protein. Now, we know that this happens because it's the primary structure, it's that specific sequence of amino acids in that polypeptide that actually determines what that final three dimensional structure of that protein actually is. So the protein easily is able to go from that non functional denatural state to the fully functional native state because it's the primary structure that determines the tertiary structure of that protein. Now, the question we want to focus on in this lecture is how exactly does the folding or unfolding process actually take place?