 So the last big hydrophobic residue would be Tyre, the tryptophan. Tryptophan has two rings. You have a five-membered rings here with an NH group. That is actually slightly polar, which can be important in some cases. And then you have a large six-membered ring here, which is quite hydrophobic. This is going to be a large, big, bulky, planar structure. It's really difficult to put this on the inside of a protein. It has a few other properties that are interesting too, that this part will actually mean that it's fluorescent. So if we shine light on it, depending on its environment, whether it's insolvent or on the inside of the protein, I will actually see emission of light that's a slightly different wavelength. And that is cool because then I can study the interior of a protein without really adding any particular spectroscopic probe. The protein itself might have built-in probes if I have tryptophan. And in this case, it's actually useful that if you look at that abundance column, it has low abundance. It's just one codon producing. And that means there are going to be very few of these amino acids, hydrogen, and a typical protein, maybe just two or three, which of course makes it even more advantageous if I use them with spectroscopy to study how a particular part of the protein behaves. The other interesting thing is that this, some 15 years ago, this was turned out into the poster child of the smallest proteins we can imagine. So I haven't really defined what a protein is for, right? Well, for a physicist, we might just start to think of proteins once we have 10 amino acids or something, so that it starts to be interesting in how we can fold the chain. To a typical chemist, that would just be a polypeptide. So polypeptide is everything that has more than one amino acid. While a real chemist or life scientist, they would likely say, you know, around 100 residues or so, things start to become interesting and then they might actually have some sort of role functionally. But what Anderson and coworkers did around the turn of the millennium was that they rather went after a definition. You said that, but if we had this inside versus outside that I mentioned in terms of the hydrophobic effect, a proper definition of a protein should be once we get to the point, I have some residues that are fully buried on the inside of something, and then I have other amino acids residues on the surface. And when they designed this, they signed a sequel called TRP-KH. It's the world's smallest proteins, a ballpark of 20 residues. So what you have here in the middle is exactly the side chain of the tryptophan is buried, and then you have a few other residues around it, then we're not showing all of them here, but so there is a small hydrophobic core here, and then we have water soluble residues around it. Why am I showing you that? Well, that is one of the first proteins that people have been able to fold purely in a computer. And by being able to fold this in a computer, we're essentially proving that Christian Altersen was right, right? Let me show that to you. It's somewhat fast, so I'll get started right away. So I'm starting the clock now. So you do see that the whole thing collapsed fairly quickly, and now I had this tryptophan side chain somewhat in the middle. All these white residues are the hydrophobic ones. This is not quite the right structure. It's unfolding again. It's refolding again. It's trying to find its shape, and somewhere here it's going to make a jump and find something that is really happy, and then I think we have both a small helix and some things around it. So somewhere there, this is the happy final end state where we have hydrophobic things on the outside and hydrophilic things on the inside. There are a couple of things to learn from this. First, you see that it took time. Even if this was just a few seconds for us for the computer, this was an infinity. So the Leventhal paradox is kind of related to the entropy and searching. We need to go through many things. On the other hand, we would be paying too much if we instantly had to jump to one fixed state. So protein folding is going to be about this balance. On the one hand, the hydrophobic effect and forming stable interactions, but gradually gaining more and more energy, enthalpy, before we're starting to pay too much entropy. This will be more complicated for larger proteins, but the solution to Leventhal's paradox is really going to lie in how we balance these things as we go downhill and find these states. And as this simple computer simulation showed us, this does work. There is no magic life elixir to forming at least small proteins.