So we have a sharp transition from the folded to the unfolded. And we can also look at the graph going the other way. So as we decrease the temperature, as we return it back to normal, or we remove those chemical agents, we see a sharp transition from the denatured to that fully folded active state of that protein. The question is, why exactly does this actually happen? Well, it happens because of the cooperative nature of protein folding and unfolding. So what do we mean by protein folding?