Hi. In this video, I'm going to be talking about the isolation and purification of proteins. Scientists need to study proteins for a variety of different reasons, but in order to do that, they have to obtain the protein for research. They use a variety of techniques to do this. The first is protein purification, and this allows for the isolation of a single protein out of a big protein solution. Typically, you can grow protein in bacterial cultures, or you can grow protein in cells, or you can just take cells that are growing and extract that protein. You can extract it from bacteria, cells, organisms, tissues, really anything. But then when you extract it, you just have a mixture of this protein solution with all these proteins in it. Then you run it through a specialized machine, which fractionates the protein. This means that you have this liquid, and it runs through a variety of different materials that separate it based on properties. If you run that protein solution through this machine, and it separates it by size, for instance, it aliquots these fractions, or it distributes these small amounts of liquid with only that size protein in it. So, if you have this machine, and it has the protein solution going through, and it's going to come out here, then you have all these tubes, these fractions. This one holds a 5 kilodalton, a 10 kilodalton, 15, 20, 25, 30, 35, 40 kilodalton fraction or size of a protein. When the 5 kilodalton proteins come out, they go in here. Then when the 10 kilodalton proteins come out, they go in here, and the same for the 15, 20, 25, and so on. This would be an example of separation by size. Fractionation can also separate proteins by charge or other properties, whatever property the scientist desires. In this process, you can tag your protein to give it a certain property, size, charge, or affinity for binding to something, making it easier to purify. Let's say you need to separate 5 proteins and they were all 5 kilodaltons. It would be hard this way because they would all go in one tube. What you could do is tag those proteins differently, leaving 1 as is. So then you'd have 1 five kilodalton, 1 ten kilodalton, 1 fifteen kilodalton, and so forth. This is protein purification, getting out that one single protein from a solution.
Then we have chromatography, which allows for the separation of proteins via certain properties. There are a couple of different kinds. You have column chromatography, which runs that protein solution through a porous mixture with different size pores that separate the proteins by size. You have affinity chromatography, which sorts them based on interactions with other proteins. And then you have gel filtration chromatography, which also separates them based on size. You can use different chromatography for different reasons, and they have different properties. The purpose of it is to separate out proteins. Then you have gel electrophoresis, a technique used to separate proteins based on their charge to mass ratio, so how big they are and how charged they are. Essentially, once you get that purified protein, the whole purpose of this is to obtain a protein that's purified. Once you get it, the proteins can then be studied in isolation. This is super important if you want to know the function of one protein and not the function of all of them.
This is an example of column chromatography. Here we have our column, and there's some type of liquid here, blue liquid, a protein solution. It has a ton of proteins in it, and what you see is that, over time, their proteins, a red one and a blue one, will actually migrate. Then you can collect the red protein, and then you can replace this collection device, and then collect the blue protein. Now, you have one device with the red protein in it, and one device with the blue protein in it. That way, you have those isolated proteins, and those proteins can then be used to study something else. With that, let's now move on.
