 The way they did that was that they started from plain simple alpha helices because they're easy to insert in membranes and then we systematically changed the composition here. W, tryptophan, A, alanine, L, leucine and there's something else I'm not showing here simply because it's not really part of the helix but the black part up here is a proline. Do you remember prolines? Prolines are strong helix breakers so when I put the proline here that's going to mean the end of the alpha helix and then there will be some small coil but still that's important if the helix has a clear beginning and a clear end that's going to mean that it will not for as if the helix is too short one way to adapt that would be for the helix to become slightly longer right but by putting a proline at the start and a proline at the end I ensure that the length I gave this helix is going to stay that way it's not going to be able to extend the helix to fit better. W, tryptophan, that was that particular residue that I mentioned that really will anchor things to the head groups so by putting a tryptophan there I can almost force that part to stay in the head groups I can't pull it down and I can't push it up. A and L, alanine is a small residue formally it's a hydrophobic side chain but it's so small that it can really go either in water or oil. L, leucine is a longer hydrophobic side chain but plain simple nothing special with it if I introduce more leucines more of the red parts here I'm going to make the helix more hydrophobic if I introduce more alanine I will make it more hydrophilic so by changing the A and L composition here and also the length I can choose A how hydrophobic my helix is will I have the hydrophobic part mixed or will it be hydrophobic on one side hydrophilic on the other and then I can also adjust the length while ensuring things stay in the head group region and this is roughly what I'm doing a bit they looked at the length distributions of helices and that's how they saw these parts that in particular with the anchors the tryptophan here right with the anchors you can actually get helices that are surprisingly short maybe just 12 residuals longer so to still go straight through the membrane normally I would need say 20 residues or so for it to be stable but this one works it's just that it's going to distort the lipids heavily but NMR tells us it does go straight through the membrane at some point when the helix starts to becoming maybe 2021-22 residues it's starting to be a stretch and when you go all the way out to 24 we can see in the NMR experiment because we're starting ordering that this lipid is now no longer straight but it has tilted relative to the membrane that's not good per se we will distort the here the lipids more but again that is the only way to keep the helix stable so be it and most of the simple understanding of the parts I showed you where things go we're determined this way so what if we now take that helix but instead of drawing it the way we have it here let's assume that I take a helix that's roughly 50 percent alanine and 50 percent lucine but I put all the alanines on that side and all the lucines on that side well to first approximation I would have the same average composition as this helix but my helix up here would be had roughly hydrophilic here and hydrophobic there so that particular helix would actually prefer to sit this way in the bilayer with the lucines the hydrophobic side facing down and the alanines the hydrophilic side facing up