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Learn the toughest concepts covered in Biochemistry with step-by-step video tutorials and practice problems by world-class tutors

10. Lipids

Biological Membranes


Biological Membranes

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in this video, we're going to begin our introduction to biological membranes. Now. It's important to recall from way back In our previous lesson videos, we said that in aqueous solutions, antipathy, lipids can spontaneously aggregate or clump together via the hydro phobic effect. And so, if you don't remember anything about the hydrophobic effect and the ability for antipathy lipids to spontaneously aggregate via the hydrophobic effect, then make sure to go back and check out those older lesson videos before you continue here. Now the ability for antipathy lipids to spontaneously aggregate via the hydrophobic effect will actually lead to the formation of three different types of membranes. The first are the myself. The second are the liposomes or the vesicles, and the third are the lipid bi layers. And so notice down below in our image. Over here on the far left, we're showing you the missile here in the middle was showing you the liposome or the vesicles. And then over here on the far right, we're showing you the lipid bi layer. And so starting over here on the far left with the myself, which will notice, is that it is a mono layer of lipids, and this is what allows it to have a hydrophobic core at its center. And so, if you were to zoom in on one of these lipid molecules in the myself, you would see that it's likely going to be a free fatty acid. And that's because free fatty acids have this triangular shaped geometry, if you will, that makes them so suitable for the formation of myself upon their aggregation via the hydrophobic effect. Now liposomes or vesicles, as you can see over here, they actually have a bi layer of lipids, so you can see that there's a layer of lipids here on the outside, but also here on the inside there is a second layer, and so this is what allows liposomes or vesicles toe have an acquis core at its center instead of having a hydrophobic core at its center. Like my cells do now, liposomes air vesicles. They're generally very small, and Onley contain a handful of dissolved molecules in the acquis court. And if we were to zoom in on one of these lipid molecules in the liposome, you would see that it's likely going to be a free fossil lipid like this one, which, upon aggregation with other ones, allowed them to form a vesicles or by layer because of their proper square shaped geometry that's suitable for the formation of vesicles and by layers and then last but not least over here on the far right we have the lipid bi layer, which will notice also has a bi layer of lipids here. And the real difference between the lipid, bi layer and liposome or the vesicles is again that the light was omar. Vesicles are generally much smaller, with only a handful of molecules and the acquis core, whereas lipid bi layers are going to be much, much, much larger. And they can encapsulate an entire cell and create entire organelles. Now notice that this lipid bi layer here has two different sheets or leaflets. There's this sheet or this leaflet right here that we can call the extra cellular leaflet or sheet, and that's because it's on the outside of the cell and notice that this other leaflet over here we can call the intra cellular leaflet or sheet again because it's on the inside here of our self, and so it's important to be able to distinguish between these two different leaflets. Now, one thing that I wanna let you guys know here is that both glycerol Oh, and stuffing Go finger Oh, fossil lipids have optimal shapes or geometries that allow them to form lipid bi layers and liposomes or vesicles. And so, as we already mentioned, uh, the my cell here is generally formed from free fatty acids, which have this triangular shaped geometry and free fossil lipids. Uh, they have a square shape geometry and so down below. Here, what we're showing you is that the free fatty acids with their triangular is shaped geometry. They are not suitable for forming vesicles or by layers because they are not able to close these gaps that form here and here. And that makes them unstable as of vesicles. Laura lipid bi layer and the same goes for free. Try as a legless roles. They tend to have a trapezoid shaped geometry like what you see here and again. That geometry or shape will create these gaps that make it make them very unstable as they try to form vesicles or by layers. And so really, the Onley lipids that are capable of forming these liposomes or lipid bi layers are the free fossil lipids. Either the glycerol Oh, fossil lipids or this finger. Oh, fossil lipids. And so this year really concludes our introduction to biological membranes. And as we move forward through our course, we're going to learn Mawr and Mawr about thes biological membranes. So I'll see you guys in our next video.

Biological Membranes

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So in our last lesson video, we introduced three different membrane structures, which were the mice, elves, the lipo zones or the vesicles and the lipid bi layers. And so, in this video we're going to introduce the biological membranes. So biological membranes are lipid bi layers themselves. However, they're more than just a lipid. Bi layer. Biological membranes are lipid bi layers with other membrane embedded molecules as well, such as proteins, for instance, and so recall from your previous biology courses that the fluid mosaic model applies to biological membranes. And so recall that the fluid mosaic model was basically saying that biological membranes are both fluid and a mosaic of membrane embedded proteins. And so, if we take a look at our image down below notice over here on the far left, we're showing you a scanning electron micrografx or an ECM of a biological membrane right here, and notice that we're zooming into this specific region of the biological membrane, and we're getting this image right here, and so notice that most of the membrane molecules are indeed these Foss follow lipids but also embedded within the biological membrane. Notice that there's a good portion of these purple structures, which are proteins, and so recall that the fluid mosaic model applies to membranes like this one, where the fossil lipids themselves that we see here, and the proteins and really all of the membrane embedded molecules are really fluid because they're capable of shifting around and moving to different areas within the membrane. And the membrane is also a mosaic because all of these different membrane components specifically these proteins, can really make the biological membrane look like a mosaic. Now, to put things in perspective, a little bit, biological membranes can actually be comprised of anywhere between 20 toe 80% proteins by Mass, and that is quite a lot of proteins. And so again, we already knew that biological membranes were going to be composed of mostly lipid structures because they are lipid bi layers. But maybe he didn't really realize how much protein could actually be embedded within the bi layer. And so this here goes to show that when we're talking about biological membranes, we cannot forget about the protein aspect of it, because there can be quite a lot of proteins embedded within a biological membrane. Now, another important thing to note is that membrane lipid composition can actually very quite a lot from cell to cell, from sheet to sheet and between different organelles. And so clearly different cells can have different fossil lipid composition and different proteins embedded and the sheets. A sheet can also differ, too, so this extra cellular sheet could have a different membrane composition than the interest cellular sheet. And then also the membrane composition can also vary between different organelles, and so the mitochondria can have a different membrane composition, then the nuclear membrane or then the end of Plasvic particular membrane. And so this is just a general idea that's important to keep in mind. And so this year concludes our review and introduction to biological membranes, and we'll be able to apply the concept that we've learned and reviewed a zoo. We move forward in our practice problems, so I'll see you guys there

Membranes are a fluid mosaic of what components?

a) Proteins, cholesterol, and triacyglycerols. 

b) Phospholipids, proteins, and cholesterol. 

c) Phospholipids, nucleic acids, and cholesterol. 

d) Eicosanoids, proteins, and phospholipids.


Which of the following lipids would likely not be involved in a lipid bilayer structure? 

a) Phospholipid.

b) Cholesterol.

c) Glycolipid.

d) Sphingolipid. 

e) Triacylglyceride. 

f) Glycerophospholipid.


Membrane components within a lipid bilayer are held together primarily by: 

a) Hydrogen bonds. 

b) Covalent bonds. 

c) Disulfide bonds. 

d) Hydrophobic interactions. 

e) Electrostatic interactions. 

f) All of the above.