Now, let's suppose we want to study a specific type of protein. The question is, how do we get a hold of that protein of interest? Because inside our body, any given protein always exists in a mixture of all different types of proteins and all different types of biological molecules. 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.