Cell Envelope & Biological Membranes

in this video, we're going to begin our lesson on the cell envelope and biological membranes. And so the term cell envelope is a term that refers to all of the surface layers surrounding the cell, which includes structures such as the cell membranes and cell walls, and some other possible structures as well. That we'll get to talk more about later in our course. Now the specific structures that compose the cell envelope may actually vary and different types of cells. And so depending on the cell type, the cell envelope may also change. However, cell membranes are always included in the cell envelope and that is because all cells have a cell membrane, regardless if they are pro carry, attic or eukaryotic cells, all cells have cell membrane that's part of the cell envelope. And so if we take a look at our image down below, we can get a better understanding of this term cell envelope. So notice on the far left hand side, we're showing you a representation of a bacterial cell and we're zooming into the perimeter or the surface of this bacterial cell here, uh to get this image and notice that on the perimeter of the cell there is the cell membrane, which we're showing you right here. But then there can also be what's known as a cell wall. And so here we can label the cell wall now, collectively the cell membrane, and the cell wall can be referred to as the cell envelope. And so the envelope again is just referring to all of the surface layers surrounding the cell on the perimeter of the cell. And so this year concludes our brief introduction to the cell envelope. And we'll be able to talk more about the cell envelope and biological membranes as we move forward. So I'll see you all in our next video.

in this video, we're going to begin our intro to biological membranes. And so first recall from our previous lesson videos that foss photo lipids, our am fee empathic molecules. And recall that this term Amphipolis thick, just means that the molecule has both hydra filic or water loving and hydrophobic or water fearing groups. And so these antipathy CFA. So lipids are the major component of biological membranes. And so biological membranes can be defined as foss follow lipid bi layers where there are two layers of phosphor oh lipids and embedded within the fossil lipid bi layer. Our other embedded molecules such as for example proteins and cholesterol and these biological membranes. They're also called cell membranes or just plasma membranes. And so it's good to know that these terms are referring to the same thing. And so if we take a look at our image down below, notice uh on the left hand side over here we're showing you an ECM of a membrane or a scanning electron micrografx of a membrane. That's this image that you see here. And the membrane here is represented by this border and notice that we're zooming into this particular section of the membrane right here. And that's what you see in this image over here. And so notice that this biological membrane, the major component, are these fossil lipids, which are these structures like what you see right here is a fossil lipid. And these fossil lipids are creating a bi layer, two layers of fossil lipids but embedded within this fossil lipid bi layer are also many other types of molecules, such as for example, proteins like what you see here. Um and there are also uh cholesterol molecules like what you see here in these positions. And so you can see that these biological membrane consists of an assortment of many different types of molecules where fossil lipids are the major component. But there are also many other molecules like proteins and cholesterol as well. Now, scientists use what's known as the fluid mosaic model to describe the nature of biological membranes. And that's because biological membranes are somewhat fluid. They are a semi fluid because they are not super super rigid. They can actually have some flexibility in the membrane and molecules are able to shift past one another almost like a fossil lipid ocean where one of these proteins may not necessarily be stuck in this position. It can move throughout the membrane in either direction and so that makes the membrane have a fluid type of nature. But the membrane is also a mosaic. And mosaics are these art pieces that are made up of a bunch of smaller individual pieces. And really that's what this membrane is. It is a single structure that is made up of a whole bunch of smaller individual pieces that are brought together such as these proteins and the fossil lipids and the cholesterol and things of that nature. Um Now what's also interesting to note is that proteins can actually make up a big portion of these biological membranes. uh some biological membranes are comprised of anywhere between 20 to 80% protein by mass. And so this goes to show how these proteins can make up a pretty large percentage of the membrane and these proteins, they are not stuck in their position. Uh These proteins have the ability to move laterally within the cell membrane. And so once again, any of these individual proteins that you see are is not going to be stuck in this one position. They have the ability to defuse laterally or horizontally throughout the membrane in either direction. Okay. And so this year concludes our brief introduction to biological membranes, and we'll be able to talk a lot more about them as we move forward in our course. But for now I'll see you all in our next video.

All right. So here we have an example. Problem that's asking Membranes are a fluid mosaic of what major components. And we've got these four potential answer options down below. And so, of course, we know from our last lesson video that Foss follow lipids make up the major component of biological membranes. And so we would expect that one of the major components listed for the answer should be phosphor lipids. But when we take a look at answer option a notice that it has a lot of molecules listed, but no fossil lipids, which is the major component. And so option A is not gonna be the best answer option here and noticed that all of the other answer options do mention fossil lipids. So very nice. Now we have the major component considered in those three answer options. Now what we need to realize next is that new Clague acids are not going to be a major component of biological membranes. In fact, they're not really component biological membranes at all. And so for that reason, we could go ahead and eliminate answer option to see now when we take a look at option, be an option D, which will notice is the real difference between them is cholesterol or glucose. Now. Glucose, we did not mention, is going to be a major component of biological membranes. And in fact, it turns out that glucose is not a major component of biological membranes. But we did mention in our last lesson video that cholesterol is a major component of animal cell membranes or biological membranes, and so be here is going to be the correct answer. Fossil lipids, proteins and cholesterol are major components of cell membranes, and so we could go ahead and indicate that be Here is the correct answer for this example. And if we go back up to our image from our previous lesson video, you can see that proteins are certainly a major component of the membrane. Cholesterol is also a major component of the membrane, and once again, these little structures that we see here with the two tails. These are all fossil lipids, and so they're the major component of biological membranes. So once again, be here is the correct answer to this example, and that concludes this example. So I'll see you all in our next video