So if we have a sample, if we have a solution of proteins, how do we know the protein that we want to study is in that mixture in the first place? And if that protein is in that mixture, how do we purify that sample and isolate that protein among all different types of proteins found in that mixture? Well, to answer question number one, to basically determine whether or not our protein is present in that sample, we have to conduct a protein assay. Now, what is a protein assay? Well, a protein assay is some type of test. It's some type of procedure that allows us to identify the presence of that specific protein of interest based on some type of specific property or some type of specific functionality of that protein.