 So I want to share one example of this with you, just to show how nature has evolved to use physics to do fun things. This is a simple alpha helix that are going to occur throughout proteins. We frequently call them from blue to red, where blue is the so-called N-terminus, and red is the C-terminus. Why do we call them N and C-terminus? Well, it's actually very easy. Remember when I do some amino acids before N, C-alpha, side-chain, C, N with a hydrogen. Let's do that too. C-alpha, side-chain, C. N-terminus was the start, C-terminus was the end. N-terminus blue, C-terminus red, partly because of the oxygen. Why do I want to introduce this to you? Well, do you remember that hydrogen, sorry, that peptide bond? And that we said that it was a highly polar bond that had some resonance, so you essentially had the oxygen stealing the negative charges while the hydrogen, the positive charges. And that we could occasionally draw that as imagining having a very strong dipole here, pointing from the negative to the positive end, the so-called peptide dipole. How will these be organized in the helix? Well, it turns out they will all line up, and they will line up backwards from the C-terminus, from the end to the start. But if you know your physics, you can add dipoles. So instead of thinking of that as 20 small dipoles, you can think of one much larger dipole. Or instead of dipole, maybe we should go back to charts. So this would be equivalent to having a minus charge there and a plus charge there at the start. Minus charge at the end, plus charge at the start of the helix. In this case, nature has occasionally found advantages to pair up the plus charge with something, such as a negatively charged amino acid. And that minus charge with something, such as a positively charged amino acid. This is called helix capping, and it's a way to stabilize the secondary structure. Now you should complain because we don't want those in the insides of proteins, right? But what if this is the inside of the protein, and that is one side exposed to water, and that is another side also exposed to water, or a cavity or something. That will mean that effectively my charges are not really on the inside. They're technically in the protein, yeah, but not the inside. And here, all the peptide bonds are paired up so they don't really expose any charges. They're happy forming their hydrogen bonds. We can see this with bioinformatics. These patterns occur in alpha helices, so it's amazing, I think, how nature has found the same laws using four billion years that you found in just four lectures. You're way more efficient than natural selection thus far. But this is used for other things. What if you were nature, and you needed a protein that should bind something, such as a positive ion, maybe? Could you imagine any motif that would help you stabilize a positive ion, motif as pattern? Maybe this part of the helix, right? Because if this positive ion were now to go here, it would interact with the dipole here and be stabilized here. In practice, we'll need some water surrounded and everything, it gets more complicated. But that too happens, and it happens even inside membrane proteins, including one of the most common and important channels called the potassium channel, which is important for minor things such as every single heartbeat and nerve impulse in our bodies. We'll get back to that when I talk about membrane proteins.