So remember that proteins are polypeptides, consist of 20 different types of amino acids. And these amino acids differ from one another based on their side chain group. So we have different types of side chains. We have non polar side chains, which are hydrophobic, and we also have polar side chains, which are hydrophilic. So it turns out if we take our polymer of amino acids, if we take the polypeptide and place it into an aqueous solution, the hydrophobic effect and hydrophobic interactions will take into effect. And what that means is all those amino acids that contain the nonpolar hydrophobic groups, for example, Valine, Alanine, Leucine, isolucine, methionine, Tryptophan, phenylalanine, and so forth, all these different non polar side chains will end up aggregating together in the core at the center of that protein.