 So alpha helices are fun because they're so much more diverse. We had orthogonal or aligned beta sheets but alpha helices they can be a complete mess in the structure or at least it looks like a mess right. There are no simple rules we talk that it's common that they cross each other say at 20 degrees or so but we can organize them in three dimensions so that these structures can be very complex and you can have a ton of different helices and lengths in them. Let's look a little bit at them. You see the hair that is literally three-dimensional. Each beta sheet was two-dimensional but there is no similar concept here that each helices form a two-dimensional structure of the helices. The helices pack in three dimensions which is what makes them more complicated. You could roughly start to sort this in a couple of classes or so. So maybe we have things that are more globe-infold like. Again I'll come back to what exactly what that is. You can have things that are more membrane protein like. Here we have kind of four subunits but the subunits are interacting with each other so the helices cross each other at an angle here but you will probably see that it's a bit more regularity and repeat here than in the globe in fold. You could also imagine having just four helices aligned so that they go up and down next to each other. It's a very nice ideal structure called four helical bundles or four helix bundles that we'll look at in a second. And all of these are useful in common structures that we will go through but the middle one I'm mostly going to talk about when we talk about membrane proteins in the next lecture.