 We already argued that as the native state forms, we're going to get more and more contacts, right, that contribute to the energy. And you could think of that moving down in an energy landscape, but we don't have to be that abstract. In particular, with simulations, we can plot this for small proteins. And what we see here in particular on the x-axis, you have the number of native contacts. And the color here then represents the free energy landscapes. And if you look at a little bit of this, you will see that these blue areas in particular are the low-lying free energy regions. And there's usually one very narrow part that typically has lots of good native contacts. What that means if we plot energy and entropy is roughly the following. Let's start with energy because that's almost easiest. So the energy during folding, well, we're going to need some sort of x-axis. I'm going to use this density again. And this just means that here I'm pretty much stretched out and here I'm pretty much folded. So let's say this one and this is zero, but it's just a sort of relative measure. And the energy starts up here. It's fairly bad. And then the closer we get, the more favorable interactions we have until I get to some point where I've squeezed out all the waters and I'm starting to push the atoms so close together that they start to repel. At some point, it's going to start going bad. But it's downhill all the way until it starts going bad. That one was easy. Entropy then. Well, that's a bit harder to understand, but it's kind of easier if we do it from the other direction. So we're going to start out here. So when I start out here, there is almost just a single state. And initially, again, my hands, they can't move, right? There is no freedom. So if I start reducing the density just a little bit, not a whole lot happens. Sure. Okay, I'll give it a little bit more freedom until I get to some point where the side chains are here, where they're free to move. And once I've started to unfold things so much that the side chains have a bit of freedom to move, the entropy will start going up quite a bit. And now I'm here and I'm free to move. Sure, there is some extra entropy to be gained just by starting to move secondary structure elements, but that's relatively smaller. So it's going to look something like that. The exact shape here is not important, but there will be a region where we have the entire transition in entropy. And you now know how to combine this. If we then have F, which is going to be the energy minus T multiplied by S, this is going to create a plot that looks roughly like the one I showed you. So we start out here with coil or fully unfolded. We have the multi-globular here. We have our folding barrier here and we have the native state here. And it's really the fact that the entropy drops over a narrow region. That's what creates this barrier. So a couple of important things. The stability here would not happen without the energy. On the other hand, I would not have the clear barrier here without the entropy part. And somewhere here you can actually start to think about the character. If you're approaching this barrier from the left, then we're folding. If you're approaching it from the right, we're unfolding. What is the nature of the free energy barrier in both cases? Is it entropy or energy? I'll come back to that to think a little bit about it for now.