Switching gears a little, let's look at some questions related to lipids. If you haven't answered question 16 yet, pause the video here. So, which of the following is true about sterols? The answer is that all sterols share a fused ring structure which actually includes 4 rings. I'll draw it out for you right now. It is made up of 3 6 membered rings and one 5 membered ring. And that is a sterile or I should say the backbone of a sterile molecule. Now the other, question or the other statements here are obviously false. So, sterols sterols are not only found in the membranes of living cells. They can be found in the membranes of dead cells. Just kidding. They can be, found many many other places. They're used as hormones. So they're I have a wide variety of uses in the body. They're found all over the place. They're not soluble in water. I mean look at that structure. That is screaming hydrophobic. It does have this Oh, so it can form H bonds and actually when it it is embedded in the membrane, you know, you'll have sort of the surface of the membrane there. This being the inside and this the outside. So this this can interact with water. This obviously can't. Cholesterol is actually the main sterile in humans whereas ergosterol is the main, sterile in fungi. So this is completely backwards basically. Yeah. Ergosterol in fungi and cholesterol in humans. Now, the fluidity of the membrane is generally increased by increasing the number of double bonds in fatty acids. And if you remember, increasing the number of double bonds in the fatty acid actually lower its melting point significantly. And additionally, all of these other statements are false. So let's go through them. Increasing temperature will increase the fluidity. Decreasing temperature, decreases fluidity. And that's why, the composition of fatty acids in the membrane of an organism really depends on where it lives. If it lives in colder climates, it's going to want, more unsaturated fatty acids because they'll stay more fluid at the lower temperatures. If it lives in a a warmer climate, it's going to want more unsaturated fatty acids because those will, remain more rigid at higher temperatures. It wouldn't, you know, if there were more unsaturated fatty acids at high temperatures, they would become too fluid and the membrane would fall apart more or less. Binding of water to fatty acyl side chains, good luck with that. Water and those fatty acyl side chains want nothing to do with each other. And an increase in the percentage of, phosphatidylethanolamine is actually the opposite of the case. If you, phosphatidylethanolamine actually decreases fluidity. Not, you know, by a huge amount but it does a little bit And actually phosphatidylcholine increases fluidity. Alright. Looking at question 18, sphingazine is not a component of cardiolipin. Sphingazine is an essential component of sphingolipids. It's pretty much where they get their name from And it's more or less what they're using in place of glycerol, and also, fatty acid. If you think of phospholipids as having glycerol and 2 fatty acids, sphingolipids, will sometimes have that fatty acid, but they or rather they they don't they won't have 2 fatty acids that is to say. They'll only possibly have 1. The sphingosine molecule sort of replaces the glycerol and fatty acid or one of the fatty acid side chains. Cardiolipin is actually a really kinda strange molecule and it's found in, in, muscles and sorry, mitochondrial, membranes and in, bacterial membranes. So mitochondrial and bacterial membranes. It's kinda strange looking molecule if you wanna look it up. The rest of these are sphingolipids. So they will have sphingosine. Let's take a look at question 19 now. Fatty acids are components of cerebrocytes which again are sphingolipids. So they're going to have a sphingosine molecule attached to a fatty acid and also some sort of head group. And, carotenes, these are isoprenes. And these guys, all sterols. Alright. Moving on. Which of the following statements concerning fatty acids is correct? And the answer is that a fatty acid is the precursor of prostaglandins and that fatty acid is arachidonic acid. And this is what's known as an cosinoid. And, just looking at the wrong answer choices, phosphatidic acid is a common fatty acid. No. It's not a fatty acid. Fatty acids all contain 1 or more double bonds? No. Some are unsaturated or some are saturated, right? So this is wrong because there are some saturated fatty acids. Fatty acids are constituent of sterols. No, they're not. Sterols are those 4 few those 4 fused rings. Fatty acids are strongly hydrophilic. No way. Super hydrophobic. Right? Alright. So let's finish it up here. And diagram this molecule. I'm just going to do it in a skeletal structure to keep it nice and simple. So I'm actually gonna start by drawing my esters just to kind of give shape to the rest of my molecule. Alright. So there are my esters. This is my glycerol. And here is my phosphate group. And, again, I apologize that this is not the prettiest picture in the world. World. So here we have choline. This is, of course, our phosphate right here. Glycerol is our backbone right there. Let's do our fatty acids now. So, we know that it has this fatty acid which we can see contains 1 double bond at carbon 9 and it has this fatty acid which is completely saturated. It doesn't tell us which one goes where but we should know that if there is only 1 unsaturated fatty acid, that's going to appear at position 2 on the glycerol. So here's position 1, 2, and this is, we have 3 there. It's I know my drawing is like super, super horrible. Acid naming convention here. So let's start with Dodeca and acid naming convention here. So let's start with dodecanoic acid. It's going to have 12 carbons and again, 0 double bonds. That's what those numbers mean. So 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. There, we're done. And now, palmitoleic acid. This is going to have 16 carbons, 1 double bond, and that double bond is going to be between carbon 9 and 10. So 1, 2, 3, 4, 5, 6, 7, 8, 9. Double bond 10, 11, 12, 13, 14, 15, 16. And there we go. That is our molecular structure. I'm sorry it's such a hideous picture. Let's try to forget about it as we turn the page.