 Let's try to understand the beta sheet the same way we already went through the components of the beta sheet and how this looked This is going to be more complex for a number of reasons It's a two-dimensional structure and in contrast to that simple alpha helix It's going to turn out that this is a proper phase transition. It can't really coexist I'm also going to need to choose to study a particular case So for now I'm going to stick to this structure that we went through this so-called anti-parallel helix But you need to remember that there are more helix than anti-parallel ones We can either organize in this way anti-parallel or we have the other alternative when they are parallel But when they are parallel with typically when we get to the end of this helix I need to have some other secondary structure element to get back to the start of the second not helix to get back to this part of the second strand here and Those extra elements such as helix is complicated things by an order of magnitude So let's keep things reasonably simple at least and stick to this case In particular when I'm at the end of one strand here, and then I need to quickly turn around and move to the other strand It's going to be very useful to have those small glycine turns that I mentioned. So at the end of a Beta strand it's not just some sort of random quick turn But usually a very well-defined structure with glycines and a hydrogel bond in the middle that really Terminates the end of helix, but still Why do I keep calling it helix if you're determined at the end of the beta strand? But it's still going to be Unfavorable in terms of entropy so we will be paying for that the nice properties of beta sheets is that what we pair them up This way they will frequently have well They will have all the amino acid sites is pointing out and if I look at this from the side instead Do you see here that I have amino acids here, and then I have amino acids here If you now pick amino acids with one property here and another property here I have as effectively created a divider here a divider that will have property a here and property B here and A very common such property is hydrophobicity So if I take the sheets and make every single residue hydrophobic and every sorry every other Residue hydrophobic and every other residue hydrophilic I will effectively end up with a sheet that has one hydrophobic side and one hydrophilic side If I then pick two sheets like this, I will end up with something like this So this is something called the fatty acid binding protein that I will tell you more about later but this is a small pocket again an NMR structure and Here we've turned the two hydrophobic faces to the inside while the hydrophilic ones are exposed on the outside and That what that gives is a small bag essentially in your cells where the outer sole side here is soluble in water While the inner side, what do you think it binds? It's a fatty acid binding Protein so it binds hydrophobic fatty acids here So that way we can transport fatty acids and later use them inside to build up the lipids and our cell membranes I'll talk about that when it comes to membrane proteins. So just by using these simple building blocks and pairing up specific amino acids I can create a specific property of a small protein and make it perform a function But we'll talk more about that when I talk about proteins for now And we're going to try to determine how quickly the beta sheet folds