 There are more fibrous proteins. The next one I'm going to show you is elastin. So elastin reminds, it reminds us a little bit of collagen, but where collagen is very strong elastin you can probably almost guess from the name what it contains. So elastin has a property of forming the actual, the amino acids backbones are relatively short or yes, compared to collagen and you would have lots of chains and then these chains are, they form crosslinks because they contain, these chains contain lysines, well whatever something like this. So they're normally curled up and then you have lots of small crosslinks between them. Lysine itself that's a charged amino acid typically and lysine would not crosslink but lysine there's called lysyl oxidase and then you have an extra molecule between the two chains that helps create this link. It's beyond the protein part of the course, but the whole idea is that you have something that's almost spring-like here and quite flexible and then we have small, think of them as more rigid rods between them. Now what happens if I take this entire structure and pull it? If you pull it the whole idea is that I'm not going to change the crosslinks but these structures that were previously curled up they can now take almost this form right? So they're going to be stretched out and in principle it can be significantly longer than it was before. So this creates an elastic structure that there is also the built-in tension here, I can stretch it and when I let go of it it's going to go back to its previous form. So with tension I'm going to extend it and when I let go of the tension it will relax back to its previous form. That creates a number of structures such as blood vessels in your body because our blood vessels in particular when you, well you are young, I'm not anymore, when you're young these are very elastic structures and they have to be elastic just because with every single heartbeat we're changing the pressure quite a lot in the blood vessels but then we gradually get older. Well in principle what mostly happens is not so much the blood vessel changing but what happens is that we're depositing calcium and fat and other things on the inside that gradually harden up the vessels. It's not the blood vessels per se that become stiff but all the deposits on the inside which eventually lead to coronary heart disease then later. But there are other things not necessarily related to age. What if the agent that created these cross-links, two license will not spontaneously cross-links, you needed those enzymes right? So what if you develop a deficiency in those enzymes for whatever reason? Well if you have a deficiency in those enzymes we're not really going to create as many bonds between these walls anymore and then you might have blood vessels that rupture and that can in worst case lead to an aorta rupture which is something that is probably way about 50% lethality if it happens outside a hospital at least. So this is potentially dangerous, it's potentially very severe diseases and it's something we would like to get better at treating. The other aspect is that all these blood vessels of middle age to elderly people like me what if we could somehow treat this? What if you need a bypass surgery in a few decades? What we try to do today is we try to take blood vessels from your thigh or something but those blood vessels are not necessarily in a whole lot better shape it's just we take them because they're compatible with your body. What if we could make an artificial blood vessels because again that these are just amino acids in theory we should be able to express these in bacteria. That's actually what the part on the right here is that is an artificial elastin like molecule where you create a something that's based on amino acids so again it's biocompatible but it's engineered it's man-made. There are there are other challenges with this they will they might wear out eventually you would ideally like the body to somehow start filling this in with its own cells. That starts to come with bioregeneration and everything and there have been a number of scandals in this area. Polo Macharini was one of them but the promises for this field are great. I think we will become better and better doing this with technology but make no mistake it's not easy and think of this as research hopes we're still not doing this regularly yet but in contrast to say material science or something the advantage of doing this with proteins is that we will always have materials that are inherently biocompatible. They should not set off your immune defense which is a huge advantage so that's elastin. I'm going to move over to the last fibrous protein we're going to be looking at which is keratin.