 So today we're going to go over electrophoresis. There's going to be two parts to this module. The first part deals with DNA, and the second part deals with proteins. So with DNA, the electrophoresis is going to be separating the DNA fragments based on size. When you look at DNA, it's made out of nucleic acid, which have a negative charge. And that negative charge is going to be drawn toward the positive charge. What I'm talking about is that when you use electrophoresis, you're taking a sample and applying an external stimulus to it. That external stimulus is going to be an electric field. So the negatively charged particles are going to be attracted and migrate toward the positively charged electrode, which is going to be the anode. When we do electrophoresis, there's several things that we need to consider. The first thing is what kind of medium are we going to use? There's a lot of different types of medium that you can use. And today, we're going to use agarose gel. There's two main reasons for using agarose. The first one is that the agarose gel is a porous gel, and it acts just like a sieve. When you go home and watch your vegetables, you put them in a sieve, and it helps drain the water through while keeping the bigger particles inside the sieve. And that's exactly what agarose does. It lets the smaller DNA fragments travel for a longer distance and keeps the larger DNA fragments closer to the starting line, which is going to be your line of wells. So that porous gel is going to be useful for separating our DNA fragments. Also, it's a lot hardier and sturdier, so it's a lot harder to mess up. And for that reason, we're going to use agarose today. In beginning to run your sample, you need to draw your gel map. The gel map is going to tell you which samples are in which order in the wells, because once things start to run, you're going to see some separation of the DNA, and you're going to have to remember the order. So that way, you're not getting sample one mixed up with sample three or four, et cetera. So I always start from right to left. That's the same way that I load my gels. And when I do, I write my sample map down, so I know exactly which samples are going in which wells. I always suggest you have this. I've been in way too many places around other students, or they have forgotten to do this, and then you're left sitting going, what sample is which sample. And you don't want to have to run the whole procedure over again, so this is really time and energy saving. If things go wrong, there are several things that you can consider. So the first thing that you can consider is the strength of the field that you're using. Did you use enough voltage? Do you need to increase your voltage? Do you need to decrease the voltage? Something to consider. The next one is going to be the net charge. Are you sure that you have assumed the correct charge? DNA is negative, but protein is one of those things that can change charge, depending on the pH of its surrounding buffer. Lastly, dealing with the medium, is it thick enough? Did you add enough agarose? Is it dense enough? And does it have the right ionic strength? All of these, if you address 1 through 5, will help you troubleshoot if something ever was to go wrong in your experiment.