In this video, we're going to introduce our 2nd class of isoprenoid lipids, which are the steroids. Now before we get started, let's first revisit our lipid map to make sure we're all on the same page. And of course, we know that we've already explored our fatty acid based lipids in our previous lesson videos, and so in this flowchart, we're just abbreviating it like this. And so currently, we're starting to explore our isoprenes and isoprenoids, and we've already talked about our terpenes and terpenoids. And so in this video, we're going to introduce the steroids. And so steroids, again, are isoprenoid lipids themselves. And what makes them so unique is that they have a core 17 carbon tetracyclic ring structure called Gonane. And so if we take a look at our image down below over here on the left, what you'll notice is that we're starting here with these isoprene units and by combining these isoprene units, we're able to build this molecule here called Gonane. And so this molecule that you see right here exactly as it is, is called Gonane. And this Gonane molecule is actually found at the core of our steroids. And so this steroid gonane core, as you can see down below in our image, again has 4 rings that are fused together which is why we call it a tetracyclic ring. Tetra meaning 4 and then of course, cyclic ring, referring to the cyclic ring structures. And so, these four rings that are fused together, you can see that there are 36 membered rings that you can see, we can call A, B, and C. These are all 6 membered rings here, here, and here. And then we also have one 5 membered ring as well and we can call this 1 ring D. And so, what's important to note is that although it might not be obvious that the gonane structure is actually derived from isoprene units, it's important to remember that gonane and all of our steroids are biosynthetically derived from Isoprene units and that is what makes these steroids Isoprenoids because they're derived from Isoprenes, so that's always important to keep in mind. Now, it's also important to note that sterols are very specific types of steroids that have at least 1 hydroxyl group. And so, of course, hydroxyl groups are just OH groups and if you take a look down below at our image over here, notice that simply by adding a hydroxyl group to the gonane core, we're able to get our sterol. So this is our sterol if you will because of the, hydroxyl group. Now, in our next lesson video, we're going to talk about a very specific type of sterile called cholesterol. But for now, this here concludes our introduction to the steroids and again, we're going to continue to talk more about, some specific steroids as we move forward in our course. So I'll see you guys in that video.
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concept
Steroids
Video duration:
3m
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Video transcript
In this video, we're going to talk about our most abundant steroid, which is cholesterol. And so cholesterol, as we just mentioned, is a lipid steroid. But more specifically, cholesterol is actually a lipid sterol. And, of course, this o at the end of the word indicates that there's a hydroxyl group that's present. And so cholesterol has a c 3 hydroxyl group and a c 17 hydrocarbon side chain. Now as we mentioned, cholesterol is the most abundant steroid, but specifically in animals, such as our cells, and they're commonly found in animal cell membranes. Now cholesterol is also derived from cyclization of the terpene lipid molecule called squalene. And so if we take a look at our image down below right here, which you'll note is that we've got these isoprene units over here. Notice we have a total of 6, 6 different isoprene units here. And these 6 isoprene units can, be combined to create this squalene molecule. And so squalene, as we mentioned up above, is this terpene lipid that we see here, and it can actually syclize itself to generate cholesterol, whose structure we're showing you right here. And so notice that cholesterol has a hydroxyl group at this position, which would be the c 3 position, And then it also has this hydrocarbon chain that we see up here, which is showing up at the c 17 position here. Now again, in most cases, it's not going to be important for you guys to know how to number all of the carbon atoms in cholesterol. However, in many cases, it will be helpful to know that position 1 has the hydroxyl group, and position 17 has the hydrocarbon chain. And so, generally, what we'll see moving forward is that cholesterol is going to be found membrane of animal cells. So you can see here that we've got these cholesterol molecules embedded in this membrane. Now another important thing to note is that cholesterol is actually a precursor molecule for a lot of other molecules, including molecules known as bile acids, such as cholic acid, which really are important for digestion of fats. And so we'll be able to talk more about this idea of bile lipids and the digestion of fats later in our course when we're talking about lipid metabolism. But for now, what I want you guys to know is that cholesterol is a precursor molecule for a lot of molecules including bile acids like cholic acid. And so what you'll notice is we can take this cholesterol molecule right here, and we can convert it into a bile acid like what we have down below. And so this is a bile acid, specifically cholic acid, and, cholic acid is one of the most prevalent bile acids. And so again, the main takeaway here is that cholesterol is a precursor molecule for bile acids. And so this here concludes our introduction to cholesterol, and as we move forward, we'll be able to talk more about cholesterol's function. So I'll see you guys in our next video.
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Problem
Problem
Which of the following structures is a sterol?
A) A.
B) B.
C) C.
D) D.
A
B
C
D
4
concept
Steroids
Video duration:
4m
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Video transcript
So in our previous videos, we talked about how cholesterol is commonly found in animal cell membranes. And so in this video, we're going to talk about cholesterol specific membrane functions. And so cholesterol will actually regulate an animal cell membrane's fluidity, but it actually turns out that cholesterol will have multiple regulation effects that depend on the temperature. And so cholesterol's regulation effect on animal cell membranes fluidity is dictated by the temperature. And so by changing the temperature, we can change cholesterol's regulation effect. And really there are 2 different regulation effects that you guys should know. But the good thing is is that they're complete opposites of each other. And so just by knowing one of these regulation effects, you'll automatically be able to know the other one. And so the first one here is under conditions of really really high temperatures. And so when the temperatures are really really high, membranes actually risk being way too fluid. And too fluid is not always a good thing for cells. And so cholesterol's job under these specific conditions is to help reduce the membrane fluidity to make sure that they're not too fluid and to help increase the the membrane's rigidness and viscosity. And so if we take a look at our image down below over here, notice we're showing you a membrane here under high temperatures with no cholesterol. And under these high temperatures without any cholesterol, notice that the membrane is simply way too fluid. Notice that these phospholipid molecules are really spaced apart because they're moving really, really fast at these high temperatures. And so, when the membrane is too fluid like this, it actually means that it's also going to be relatively more permeable. And so things that normally cannot cross the membrane are able to win the membranes to fluid. And again, that's not always a good thing for the cell. And so cholesterol, like this sloth right here, what it's able to do is to slow down these fast moving phospholipid molecules so that the membrane becomes less fluid, as we mentioned up above, and more rigid and more viscous. So, when it's more less fluid like this, those molecules that were penetrating might not be able to penetrate any longer. Thanks to cholesterol's regulation effect. And so, the second effect here again is the complete opposite of this first effect. And so at really, really low temperatures, the membranes are going to risk being too rigid this time instead of being too fluid. And so under these conditions, cholesterol is actually going to help increase the membrane fluidity to make sure that they're not, too rigid, and they're also going to help decrease the rigidness and viscosity. And so over here on the far left, notice that we're showing you a membrane here at low temperatures with no cholesterol, and notice that all of these phospholipid molecules here are really tightly packed together, and so this membrane is too rigid. And when it's too rigid, molecules that used to be able to penetrate might not be able to penetrate anymore, because the membrane is too rigid. And so cholesterol's job is to get in between these phospholipid molecules to make sure that they're not too rigid and forming 2 ordered structures. And so here what we have is an image of Jack Nicholson from the movie The Shining where he's saying, here's cholesterol, and he's getting in between these cholesterol these phospholipid molecules to make sure that they're not too rigid. And so really, this is, what you guys need to know about cholesterol's membrane functions, and we'll be able to get some practice in our next few videos. So I'll see you guys there.
5
Problem
Problem
What is the effect of cholesterol in a membrane?
A) Increases membrane fluidity by preventing acyl chain packing.
B) Reduces membrane fluidity acyl chain movement.
D) Both a & b.
E) Neither a or b.
A
Increases membrane fluidity by preventing acyl chain packing.