 So based on that you hopefully agree with me that it appears that protein folds evolve too, or at least the structures. Previously we talked about evolution in terms of sequences, right, that swapping out one amino acid for another, but while we are another the folds themselves evolve. It's interesting to compare how nature is doing this in different type of organisms. We have bacteria, we have humus and everything, and in fact we already looked at a few examples like that. Remember when I showed you a bacterial ion channel, KCSA, and then we compared that to a human or at least eukaryotic ion channel that was much more complex. Now this is a bit unfair because these don't have the same function, but that's kind of the point. In a bacterium we have a very simple genome and it's a killer machine optimized for efficiency. We have something that's entirely optimized for just being regulated against pH. In humans for a couple of pretty nice reasons we have a nervous system, but a nervous system is an exceptionally wasteful thing. Think of all that ATP and the NKA pump. To be able to handle and steer the nervous system within this needs this voltage controlling, and what nature is pretty much done there, it has stolen this idea, again evolved, and then attached an entire extra domain here with four helices to each of the subunits. It's going to turn out that's mostly how evolution works. It's very rare that you're growing something entirely new by adding or changing one amino acid at the time, but evolution tends to happen in domains, as we will see in the bioinformatics lecture. Based on this you might start to think that in general eukaryotic or vertebrates have more advanced, larger proteins. That's kind of true and kind of not. I'm not sure whether I agree entirely with Finkelstein there. The point is that each of these units, a domain, the domains per se are not necessarily more complicated, because again this domain is pretty much the same as the central domain here, but eukaryotes tend to assemble many more domains and they do them in more complicated manners. Eukaryotic membrane proteins, for instance, they have more advanced functionality, they are usually floppier and everything. We're not exactly sure why, but possibly because they need to interact with the membranes and lots of different tissue and everything. So in general we simply still know much more about prokaryotic proteins than eukaryotic ones. The prokaryotes are easier to study.