 Today we're gonna talk about membrane proteins, but before doing that we're gonna need to have a closer look at the membranes Which is not a protein component of life, but still an exceptionally important player in molecular biophysics So this is a somewhat long story already in the late 19th century Overtoned made the observation that fat soluble compounds have it much easier time entering the roots of plants and Somehow that means that there must be walls or something in these cells that are full of fat or oil and a few decades later Gordon and the Grendel proposed that this was in fact small lipid bilayers. I'll show you some examples here This is from the late 1930s Which is probably the real physical hard evidence that cells human cells consist of this lipoid face and this was Schmidt beer Ponder who in 1938 made experiments with polarized lights on the red blood cells and Based on the scattering they proposed that this was this lipid bilayer in human cells too. So the idea here said you would have water out here Oil face here and then water on that side, which would effectively create a very permeable wall for some molecules Such as oxygen important for red blood cells while for instance water can't go through this so that the cell would actually have an interior This was confirmed in the early 1950s with electron microscopy and electron microscopy actually gives us a chance to look at the structure of these memories So let's do that Here is an example of an isolated cell and I think it is in fact a red blood cells from David Roberts of work in 1981 do you see these two layers here? So you might think that that's the upper and lower layer of the lipid leaflets and that's wrong So this in fact turns out to be two full layers of lipids So this is one bilayer and that is one bilayer It's very common in cells that they have an outer layer and an inner layer But that's possibly beyond the concept of this class bacteria for instance They might have a small cytoskeleton here with sugars and everything creating a somewhat rigid surface Do you see here? This might be an easier time here We have one cell on the left and one cell on the right and this is also an electron micrograph And then we have magnified the part in the middle here, too You see two bilayers and each bilayer so you have one bilayer in the left cell and one bilayer in the right cell And we can't quite see the atomic detail yet, but you see a very clear pattern of the bands here, right? The reason why we get those bands is that if we look at a lipid some parts of the lipids are going to interact much stronger with electrons than others I'll show you which ones in a second So let's see if we could take this image and magnify just this part. What molecule would we eventually find inside it? This one