So based on the size of the protein, based on the solubility of the protein, how well dissolves in a certain type of solvent, based on the charge found on that protein, and also based on the ability of that specific protein to bind to some specific type of biological molecule. For example, certain types of proteins are able to bind to specific type of DNA sequences and DNA molecules, while other proteins cannot bind to those DNA molecules. And using that property, we can separate them because of that ability to bind. So there are eight important types of purification processes that you should be familiar with. So in this lecture, we're simply going to go through these processes quickly. But in the next several lectures, we're actually going to discuss them in much more detail.