In this video, we're gonna do a quick refresher on lipids. So recall that lipids are a major class of macro molecule that all living cells contain and lipids are incredibly diverse in both their structures as well as their functions. And that makes them a little bit challenging to group together and to talk about. But one thing that all lipids have in common is that all lipids are hydrophobic. And so recall from your previous biology courses that the root hydro means water and that phobic or phobia means fears. And so hydrophobic means water fearing and, of course, this means that they don't dissolve very well with water or mix well with water. Now, examples of lipids include phospholipids, fats, oils, waxes and steroids. And in our example below, what we're gonna do is match each of these lipids with their corresponding description and function in the blocks below. So the first block says major component of cell or plasma membrane. And recall from your previous bio courses that this is the phospholipid. Now the next block says, long term energy storage, but specifically in plants. And so these are our oils. And like in the images below, vegetable oils and olive oils are extracted and produced by plants and they tend to be liquids at room temperature. Now, if we compare that directly to the next block, which is long term energy storage, but in animals, these are going to be our fats. And so fats are instance for instance, for this example. Now in our previous videos, we talked about how carbohydrates are used as short term energy sources. And so all that's saying is that, cells typically use their short term energy sources first, so they'll use their carbohydrate energy sources. And then once those are depleted, they'll turn to use their long term energy sources such as fats and oils. Now, in the next block, it says sex hormones, and this includes estrogen and testosterone. And it also includes components of plasma membrane such as cholesterol. And from this image, you can get a quick glimpse at how these are structurally diverse group of lipids. And these are, of course, the steroids. Now the last block is, says protection and prevention of water loss, and this includes beeswax and earwax. And, of course, this has got to be the waxes. And so in our next video, what we're gonna do is talk about a very biologically important lipid, and this is the phospholipid. So I'll see you guys in that video.
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concept
Phospholipids
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2m
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Video transcript
So phospholipids are biologically relevant lipids that are amphipathic. And so recall from your previous biology courses, all this means is that they contain both a hydrophilic and a hydrophobic part. And we covered hydrophobic in our previous videos, which again means water fearing. So hydrophilic means the complete opposite, water loving. And so phospholipids contain a polar hydrophilic head and non polar hydrophobic tails, where the tails are hydrocarbon chains because they're long chains of just hydrogen and carbon atoms. And the amphipathic nature of a phospholipid allows them to form membranes and that allows them to compartmentalize the cell. And we'll talk about the hydrophobic effect later on in our course. However, what I want you guys to know in this video is that the hydrophobic effect explains how phospholipids form membranes when they're in aqueous solutions. And so, down here in our example, we have 2 different representations of head, which is polar, hydrophilic. And a head, which is polar, hydroph and hydrophilic. And so that head consists of a phosphate group, as well as a glycerol molecule. And, down below, what you'll see is that there are these tails that are non polar hydrophobic tails, which are hydrocarbons. And so over here, what you'll see is that we have a phospholipid and they are able to form membranes when they're in aqueous solutions. So they will continuously clump together, and they can form specific membranes as you can see in this diagram. And so that transitions us perfectly into our next video where we're gonna talk about cell membranes. So I'll see you guys in that video.
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concept
Cell Membranes
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2m
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Video transcript
So we already know that all cells contain a cell or a plasma membrane that separates the inside of a cell from the outside or the exterior. And we'll be talking about membranes at different points throughout our entire biochemistry course. But in this video, we're just gonna do a quick review. So recall from your previous biology courses that the fluid mosaic model describes a membrane's fluidity as well as the assortment of components that are embedded inside which means that they are partially penetratable. Which means that they are partially penetratable. Some things can cross the membrane whereas other things cannot, and that contributes to its functions such as the transport of materials or biosignalling. And typically, only small nonpolar molecules, such as for instance, carbon dioxide or oxygen gas, are capable of freely crossing the membrane from one side to the other without requiring an input of energy. And so down below what we have is the typical structure of a a cell membrane, and I don't want you guys to memorize all of these components. It's more so a review and a refresher. And so notice that the major component of the plasma membrane is the phospholipid which is represented by all of these yellow balls and the brown tails, and they create the phospholipid bilayer which again is very fluid like. So these phospholipids can shift past one another and they can move from one side of the membrane to the other side of the membrane. And the proteins that are embedded inside of it, again, create a mosaic like look. And so all of these proteins can also shift in the membrane, so they're not stationary or stuck. They can move around and squeeze between the phospholipids. And so we have a bunch of different types of proteins. We have channel proteins that allow membrane. We've got, cholesterol inside the whole membrane. We've got, cholesterol inside of the membrane that helps to create, make it more rigid. And we've talked about how carbohydrates can be attached to different, molecules to create glycoproteins and glycolipids, and all of these components come together to to create the cell membrane as we know it. And so this concludes our refresher on the cell membrane and I'll see you guys in the practice videos.
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Problem
Problem
Which of the following is incorrectly matched?
A
Oils; short-term energy storage in plants
B
Fats; long-term energy storage in animals
C
Phospholipids; major component of cell membranes
D
Steroids; include sex hormones & cholesterol
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Problem
Problem
What characteristic do all lipids have in common?
A
Polymers of glycerols & hydrocarbon chains
B
Hydrophilic
C
Hydrophobic
D
Polar
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Problem
Problem
What types of molecules are able to freely cross a semi-permeable membrane without an energy input?