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. Now, remember, certain amino acids contain side chains that carry a full charge. So some amino acids contain side chains that carry a positive charge. For example, Lysine and arginine, these carry a full positive charge on their side chain.