And so when the protein either folds or unfolds, it does so cooperatively. And that's why we have the Sigmoidal curve. And not only that, but it has to pass through these intermediate structures to actually get to that final structure. So when we go between these two structures, the native state, the three dimensional functional state and our denatural state, that protein must actually follow these different intermediate structures. Now, an important point must be emphasized. So let's suppose we take the protein and we denature it once.