 Today, we're going to talk about the drug discovery or even the drug design process. This is a gigantic topic and I will only have a chance to scratch a little bit on the surface. But we're going to try to approach this from biophysics, see how we use our fundamental understanding of physics first, proteins, things like homology modeling that you picked up in lecture 11, but also a bit of molecular dynamics simulation and other tools that we can use, including enthalpy and entropy. So what do we need to design drugs? Well, you might think that that's a very clinical endeavor, but that's not really the case. This is mostly chemistry, although a particular branch called medicinal chemistry. And in principle, the steps we're going to go through are roughly these. First we need to be biologists rather than chemists, actually. So we need to find some sort of target. That can be harder than you might think. What does the target say for blood pressure? We might not know, in that case we do. Then we need to understand the process of that target that could, for instance, be solving the structure of the protein we're interested in. Then we need a strategy for change, I would say. And again, that could be how should we activate that protein more or how should we activate it less? Or do we want to steer the processes in some completely different direction? If we want to do drug design, at some point it's a good idea to design maybe not a drug, but design what I call a small compound, something we can eat, and that might be a drug or a small molecule. And then we have the trial and error stage or optimization. We're going to need to make this molecule better. It's the chance that you get something that works when you start is virtually zero. Then you need to be lucky or have a strategy to avoid side effects. So minor side effects might be okay, but if you have severe side effects, there is no way this is going to pass all the tests. Then we need to do lots of clinical testing. And if all this works, you're either going to have something that can cure a disease or potentially even make your company a lot of money. I will go through almost all of these stages. I might not go into details about clinical testing, but I will tell you a little bit about the stages one has to go through there too and how it works. But the first thing we're going to need to do here is to think about targets and biology. And I'm going to do that in particular in the context of COVID-19 that is very much on the table right now.