And yet other amino acids have a full negative charge, for example, glutamate and aspartate. So we have different types of amino acids. And because proteins are composed of a variation of these different amino acids, the ones that have more side chain groups that are positively charged end up having a net positive charge. While the ones have equal amounts, they have a net neutral charge. And those that have more negatively charged side chains, those have a net negative charge. Now, because certain proteins differ from one another based on their net charge, this is another property that we can use to separate and purify proteins.