And then that hydrophobic core is held together by Van der Valle's interaction. And we can also have a special type of covalent bond known as the disulfide bridge that also holds our structure together. So here we have one disulfide bond, a second disulfide bond, and a third disulfide bond between these 15 amino acids. Now, we can also have hydrogen bonds, and we can have ionic interactions. Now, if we examine those polar molecules on the surface, the side chains of those polar amino acids can basically interact and form hydrogen bonds with the water molecules that are found in close proximity, and that can stabilize the structure, the tertiary structure of our polypeptide. And finally, we can also have ionic interactions.