 Ios isn't the only thing that we need channels for. Remember water? Water will in general not go through a membrane spontaneously. So if you want water to pass through a membrane, we're going to need a protein for that. When do we need that? Well, in a few cases in many organisms, if we have water on the inside, depending on if I'm taking up salt or so, the osmotic effect might increase the pressure. So I have too high pressure on the inside of a cell. And there are lots of other examples where we need to be able to transport water in and out, for instance, in our eyes and several other places. This is a structure called aquaporin determined by Peter H. Roughly at the same time, Rod McKinnon determined the KCSA structure. In fact, it's a large tetramir, so you see two or four subunits here. But instead of having a look at that structure, I'm going to show a simulation of this performed by Helmut Grubmiller and Berthe Schrott in Göttingen. If I were to show you this entire cell, you would not be able to see the interesting part. So we're going to zoom in on one of these subunits and then I will show you just an excerpt from the simulation. So here we go. What happens here is that I have waters and one water molecule is called yellow here. That water molecule in yellow is starting initially turning its oxygen down and hydrogen up, and then it's moving along this pore here. In the middle, it's really rotating virtually 180 degrees, and then it's turning the oxygen upwards and moving down. The reason for that is that it's a very narrow pore. If I had a gigantic pore, too much water would leak out. But this creates a beautiful way for the cells to have a regulated, reasonably large conduction of water between the inside and the outside. And what we need here in the middle is just something to stabilize that water dipole. Because even though water is not charged, that large dipole would make it very disadvantageous for the water itself to be in an ellipidic environment. So by having a few polar groups here and everything, we basically end up with a chain of water, and this literally helps the water to get through. So it's passive transport, but it's remarkably efficient and quite beautiful. And you can do that in a computer simulation in a few hundred dollar seconds. Peter Ager and Rod McKinnon, they shared the Nobel Prize in Chemistry in 2003 for their discoveries.