So let's suppose we have a beaker. In that beaker we have a sample a mixture of different types of proteins as shown in the following diagram. Now, what we want to do is we want to use several of the different types of procedures that we spoke of earlier and basically purify our sample, purify and isolate some specific type of protein found inside that mixture. And the way that this is usually done is we choose some specific type of procedure. We carry that procedure out and then we extract that sample and we place that sample into an SDS page setup. So we expose our sample to SDS polyacrylamide gel electrophoresis to basically separate our proteins based on size.