I get to do some cool things at work on a regular basis. The kind of cool things that make me an official nerd, but still . . .
One thing I get to do is extract DNA. There are a variety of tests that can be done with DNA, and the purer the DNA is, the better. Removing all the extra stuff does wonders.
The first thing I do is take a sample of cells as my source of DNA. Since I work in a hospital reference lab, these are human cells I'm working with, and usually blood cells. Now, the DNA is securely sitting inside those cells, and I'm sure you've noticed that cells don't just break open for anything. I mean, look at your arm. Think about all the things your arm goes through in the course of a day without having all its cells ruptured. Yeah, cells are pretty tough. So the cells in my centrifuge tube aren't going to just break open either, even if I vortex them really fast.
However, what I can so is break them open with a surfactant. You are familiar with surfactants in the form of soap. Soaps break open cells. Don't worry, your cells are safe for a few reasons, so don't stop using soap. But when I have cells floating in a tube and I add my strong surfactant and the cells are completely surrounded by it and get all mixed up, then the surfactant gets inside that lipid cell membrane and tears it right open. It probably even gets inside the nucleus membrane and does the same thing.
This is great, because the cell membrane and the nucleus membrane are really the only things standing between me and the DNA. However, even though the DNA is floating freely among the membrane fragments now, it's far from clean. First, there's all the membrane fragments in the way. Second, DNA does not exist by itself inside a cell. It's wrapped up around and around tons of proteins to protect it and give it stability. This is great in the cell, but I want purified DNA to run tests on. So I add a protease.
A protease is, ironically enough, another kind of protein, but it is a protein whose sole job is to go around chewing up other proteins. Once the proteins have been chewed up really small, I add another solution that will precipitate the proteins to the bottom of the tube.
Now the DNA is floating in the liquid- or supernatant- and the proteins and membranes are pelleted at the bottom. From here, it's an easy step to pour the DNA into a separate tube containing ethanol for one final wash, and to store it in a special buffer that will keep it stable until I want to use it for some interesting study.
That's one of the things I did at work today. I have a cool job.