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. We also have acidic amino acids, and these are the amino acids that carry a full negative charge on their side chain. And so, for example, if we have the amino acid Lysine, that contains a positive charge on a side chain, is in close proximity with our amino acid Aspartate, which contains a full negative charge on that particular side chain. And if these two are close enough, they can form an ionic bond.