in this video, we're going to introduce our second class of ice opera noid 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 flow chart, we're just abbreviating it like this. And so currently we're starting to explore our ISA preens and ice opera noise. And we've already talked about our Turpin's interpret noise. And so in this video we're going to introduce the steroids. And so steroids again, our ice opera annoyed lipids themselves. And what makes them so unique is that they have a core carbon tetra cyclic ring structure called go nine. And so, if we take a look at our image down below, over here on the left, which will notice, is that we're starting here with ease is a prion units. And by combining these I supreme units were able to build this molecule here called go nine. And so this molecule that you see right here exactly as it is is called groaning and this Gonen molecule is actually found at the core of our steroids. And so this steroid Gonen core, as you can see down below in our image again has four rings that air fused together. Which is why we call it a tetra cyclic ring tetra, meaning for and then, of course, cyclic ring referring to the cyclic ring structures. And so these four rings that refused together you can see that there are 36 member ID rings that you can see. We can call a B and C uh, these are all six member ID rings here, here and here. And then we also have one five member ID ring as well, and we can call this one ring D. And so what's important to note is that although it might not be obvious that the Gonen structure is actually derived from ice supreme units, it's important to remember that Go nine and all of our steroids are bio synthetically derived from isil preen units. And that is what makes these steroids ice opera noise because they're derived from ice supreme. So that's always important to keep in mind. Now it's also important to note that stare Rawls are very specific types of steroids that have at least one hydroxy al group. And so, of course, hydroxyl groups are just o h groups. And if you take a look down below at our image over here, noticed that simply by adding ah, hydroxyl group to the Gonen corps were able to get our sterile. So this is our stare all, 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 Maura about some specific steroids as we move forward in our course. So I'll see you guys in that video.

in this video we're going to talk about are 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 stare, Raul. And of course, this all at the end of the word indicates that there is ah, hydroxyl group that's present, and so cholesterol has a C three hydroxyl group and a C hydrocarbon side chain. Now, as we mentioned, cholesterol is the most abundant steroid, but specifically in animals such as ourselves, and they're commonly found in animal cell membranes. Now, cholesterol is also derived from civilization of the Turpin lipid molecule called squalene. Okay. And so if we take a look at our image down below right here, which you'll note is that we've got these is a pre Munitz over here. Notice we have a total 66 Different is a pre Munitz here, and these six I supreme units can be combined to create this squalling molecule. And so squalling as we mentioned up above is this Turpin lipid that we see here and it can actually sick lies itself to generate cholesterol whose structure we're showing you right here and so notice that cholesterol has ah hydroxyl group at this position, which would be the C three 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 and cholesterol. However, in many cases it will be helpful to know that Position one 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 embedded in the plasma membranes 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 colic acid, which really are important for digestion of fats. And so we'll be able to talk more about this idea of bio 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 ah lot of molecules, including bile acids like cola kassid. 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 Kulick acid and Kulik Acid is one of the most prevalent bile acids. And so again, the main take away here is that cholesterol's a precursor molecule for bile passes. And so this year concludes our introduction to cholesterol and as we move forward, will be able to talk Maura about cholesterols functions, so I'll see you guys in our next video.

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 membranes fluidity. But it actually turns out that cholesterol will have multiple regulation effects that depend on the temperature and so cholesterols regulation effect on animal cell membranes. Fluidity is dictated by the temperature, and so by changing the temperature, we can change cholesterols regulation effect. And really there are two 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 will 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 two fluid is not always a good thing for cells. And so cholesterols 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 membranes, 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 fossil lipid 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 fossil lipid molecules so that the membrane becomes less fluid, as we mentioned up above and mawr rigid and more viscous. So when it's less fluid like this, those molecules that we're penetrating might not be able to penetrate any longer, thanks to cholesterols 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 air 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, uh, too rigid. And they're also going to help decrease the rigidness and viscosity. And so over here on the far left noticed that we're showing you a membrane here at low temperatures with no cholesterol and noticed that all of these fossil lipid 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 cholesterols job is to get in between these fossil lipid molecules to make sure that they're not too rigid and forming two ordered structures. And so here. What we have is an image of Jack Nicholson from the movie The Shining, where you're saying here's cholesterol and he's getting in between these cholesterol, these fossil lipid molecules to make sure that they're not too rigid. And so really, this is what you guys need to know about cholesterols membrane functions, and we'll be able to get some practice and our next few videos, so I'll see you guys there.