in this video, we're going to begin our lesson on bacterial and eukaryotic cell membranes. And so one thing to note is that in this video we're not really going to talk about our kale cell membranes because the membranes of Arcadia are a little bit different. And so we'll talk about those separately in a different video. And once again for now we're focusing mainly on bacterial and you carry attic cell membranes. And so recall from our previous lesson videos that the major component of cell membranes are phosphor, the lipids and so both bacterial and eukaryotic fossil lipids have what's known as a glitz Arrgh phosphate head. And they also have these fatty acid tails. And so sometimes the glycerol phosphate head is just called the head. And the fatty acid tails are sometimes just referred to as the tails. Now recall also from our previous lesson videos that fossil lipids are antipathy like molecules and the term antipathy, it just means that they have both hydro filic as well as hydrophobic groups. And so hydra filic recall means water loving and that is going to be the hydra filic head. More specifically, the hydra filic glycerol phosphate head. And then the hydrophobic part is going to be the fatty acid tails or the hydrophobic tails for short. And so if we take a look at our image down below, notice on the left hand side, we're showing you a lipid bi layer, a phosphor lipid bi layer. And we're zooming into just one specific fossil lipid here to look at the fossil lipid structure. And so notice that the fossil olympic structure, which is just represented as this circle with two tails coming off um is uh can also be represented with its complex chemical structure, which you see over here and notice that the circular part, which is represented right here in this box, is referring to the glycerol phosphate head or the head of the fossil lipid. And notice that this green box down here, along with these green tails coming off. These are referring to the fatty acid tales. Now, one thing that's also really important to note here is that the fatty acid tales, what you see down below is connected to the glycerol phosphate head. By these linkages known as ester linkages. And so what you see here highlighted in yellow are the ester linkages. And so that's something important to note that bacterial and eukaryotic fossil lipids use an ester linkage in order to connect their glycerol phosphate head group to the fatty acid tales. And so this is important because these ester linkages are unique to only bacterial and eukaryotic fossil lipids because our kale fossil lipids tend to use ether linkages, which is a different type of linkage than an ester linkage. And so we'll talk more about the ether linkage and the r. K. L. Cell membranes later in a different video. But for now, this year concludes our brief introduction to bacterial and eukaryotic cell membranes and as we move forward, will continue to learn more and more about these membranes. So I'll see while in our next video.

in this video, we're going to focus on cholesterol and animal membranes. And so really only animal membranes have a molecule known as cholesterol, which is a molecule that is going to help make the membranes a lot more rigid than bacterial membranes. And there are these specific regions within membranes that are known as lipid rafts. And these lipid rafts are really just dense regions of cholesterol that can move laterally together through the fluid membrane. And so you can imagine them as little dense regions that are going to be uh somewhat acting like a raft in an ocean of fossil lipids. And so if we take a look at our image down below, we can get a better understanding of this. And so notice on the left and we're focusing in on bacterial cell membranes which noticed they are made up mainly of fossil lipids with proteins embedded in them, but notice that there is the absence of cholesterol. So cholesterol is absent and so we're representing cholesterol as this uh molecule that you see right here. And so bacterial cell membranes do not have cholesterol. However, eukaryotic cell membranes, mainly animal cell membranes do have cholesterol. And so cholesterol is present an animal cell membranes. And so notice that you can see cholesterol embedded throughout the membrane along with the fastball lipids and other proteins as well. And dense regions that have lots of cholesterol can create these lipid rafts. And so this lipid raft region right here would stay somewhat together and could move laterally within the membrane within this ocean of fossil lipids. And so lipid rafts can have a lot of uh important implications and bio signaling and in other processes as well. But here we're focusing mainly on is that animal cell membranes have cholesterol. Whereas bacterial cell membranes do not have cholesterol. Now, our kale cell membranes are going to have a unique type of lipid composition, and so they're going to be different than the membranes of bacteria or you carry a and so we'll talk more about the r k. L cell membranes later in a different video.