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Video transcript

let's talk about lipids now for those of you who are familiar with the term you might associate it with things like fat molecules and that would not be incorrect fat molecules are a very common form of lipid in fact this is an example of a fat molecule or a triglyceride right over here fat or tri glyceride triglyceride molecule right over here and this one in particular is a polyunsaturated triglyceride and we have we we have a go into in debt we go into a lot of depth on this on the video on the molecular structure of fats / triglycerides or on pot on saturated and unsaturated fats but you see the telltale signs you see a glycerol backbone right over here and three fatty acids or what were three fatty acids attached to what was a glycerol molecule we go into a lot of depth on that but fats are not the only type of a lipid and so what makes what makes all of these other things that I'm about to show you also lipids what commonality do they have with fats well lipids are just the general term the general term for a whole class of molecules that tend to not be so soluble in water that tend to kind of clump up or ball up when placed in water so not not so soluble not so soluble in water and I'm being a little bit careful with my words I didn't say outright hydrophobic there are definitely lipids that are outright hydrophobic but there are also some lipids that have some end of their molecule that's hydrophobic but then other parts of the molecule actually might be hydrophilic and there's actually words for that so you have some lipids that are just straight-out hydrophobic hydrophobic they literally try to avoid the water they're nonpolar molecule so they just clump together but then there are some that have hydrophobic parts and hydrophilic parts and these are called and I always have trouble saying this word and the amphib Pathak amphipathic molecules where some part is hydrophilic and some part is hydrophobic and we're going to see that in a few seconds when we look at phospholipids which are crucial for for the structure of cell membranes and we're going to see that a lot when you when you go into biology so what are all these other molecules and when let's think about what parts of them might be hydrophobic and what parts might be hydrophilic when you look at fats you have this long hydrocarbon chain there aren't any obvious and there aren't any obvious there aren't any obvious charges over here in fact there aren't any you know oxygen is more electronegative so you might have a little bit of a partial negative or partial positive charge a partial negative at the oxygen or maybe a partial positive end at the carbon but carbon isn't is still more electronegative than say hydrogen so you're not going to be able to form the type of polar bonds that the type of I should say hydrogen bonds you would if you had a Hydra if you had hydroxyl groups here if this was an alcohol and these hydrocarbon chains over here these these are very hydrophobic so that's what makes fat not be so soluble in water and clump up when you put it in water this molecule right over here which we would classify as an ester and that's because we have an ester group we have an ester functional group right over here where you have a carbon double bonded to an oxygen and then single bonded to another oxygen and then that oxygen is bonded to a long hydrocarbon chain and that carbon is bonded to a long hydrocarbon chain right over there this is clearly going to be hydrophobic and this this particular molecule that we're looking at right over here this is a major constituent of beeswax of bees of beeswax and if you've ever dealt with beeswax or really any type of wax and waxes in general are considered to be Alip adzuki that they don't they're not soluble in water in fact they're often used to repel water to keep water from penetrating into something so wax and in particular beeswax and beeswax isn't made up of only this molecule this is one of the main constituents it has other molecules mixed in there but this is also a lipid now what's this thing over here this this thing I have a I have one six carbon ring another six carbon whoops I have another six carbon ring another six carbon ring and then I have a five carbon ring this is the tell-tale sign and let me circle these these four rings right over here these these rings are the tell-tale signs that we are looking at a steroid at a steroid and in popular culture steroids have you know if you think of steroids is something that bodybuilders might inject illegally to to pump up their muscles but steroids are actually when you think about it in chemical terms they're actually referring to things that have this general these molecules that have this general structure where they have this six carbon ring this six carbon ring another six carbon ring in this orientation then another five carbon ring and this steroid that we're looking at this has an O H group attached to it so it's actually going to be an alcohol so a steroid that's an alcohol you would call a sterile stare all and this particular sterile is one that you've actually dealt with a lot of at least you've heard about this is cholesterol so this one in particular is cholesterol and cholesterol is often viewed as a negative thing and people want to lower their cholesterol but it's essential for life it's essential to the functioning of your cells and it is precursor molecule for your steroid hormones which make you you and this right over here is a steroid hormone it's a very well known one this is testosterone testosterone testosterone testosterone and you see the tell-tale you have a six carbon ring right over here another six carbon ring right over here the double bond is in a different place and cholesterol here that you have a double bond right over there then you have another six carbon ring and then you have the five carbon ring instead of an O H group here you have a double bond you have a carbonyl group you have a carbon double bonded to an oxygen but it actually does still have an O h group up here but this is a derivative of cholesterol this is a testosterone it is a steroid hormone this is another steroid hormone this is cortisol cortisol also can be derived from cholesterol and you see the tell-tale signs you see the six carbon ring this has a double bond right over there you see another you see another six carbon ring six carbon like this it's actually hard to see the double bond so I just won't even refer to them I'll just refer to the the general shape so you have a six carbon ring there six carbon ring there six carbon ring there and then five carbon whoops and then a five carbon ring just like that so once again they all have this steroid base structure but then they all they also have other parts that make them different for example that is different than that is different than that and just so you can visualize these things in three dimensions in an actual molecule they're not going to look exactly like this and even talk about what's something an atomic scale looks like it's kind of strange because the light behaves in weird ways but you can imagine the molecule would look like this if you if you if you actually if this is kind of a ball and stick model well here you're thinking about it what it actually might look like in space where the white balls or hydrogen the gray ones are carbon and the red ones are oxygen so this is also this right over here is what a car a cortisol molecule would look like if you think into kind of a space-filling visualization now I talked about amphipathic molecules and phospholipids are probably the most well known example of it and phospholipids they have a lot in common with triglycerides and that you have this three carbon backbone right over here three carbon three carbon backbone let me do that in a different color so you have a three carbon backbone right over here so this is a carbon that's a carbon that's a carbon there each of them are attached to oxygen so you could imagine that this could have been derived from glycerol and then two of the carbons like in a triglyceride are bound to a fatty acid like this but then one of the one of the carbons the third carbon instead of being bond to a fatty acid like you have in a triglyceride is bounded to a phosphate group so this right over here this right over here is a phosphate group and this R could just be another another chain another another chain of another organic chain so to speak but when we talked about amphipathic molecules I always have to say it slowly so it's a bit of a tongue twister for me we're talking about having a a phobic and a hydrophilic end well what's the hydrophobic end here well this these this change from the fatty acids especially the hydrocarbon chains right over here these are going to be hydrophobic hydro hydrophobic while the phosphate end right over here it has charged charged molecules dissolve in water very very well and so this one over here is going to be hydrophilic it's going to be it's going to be I guess you can say it's going to be attracted to water and that's why phospholipids and this is just one type of phospholipids these chains could be different we have a we have a unsaturated chain here and then a fatty acid chain then we have a saturated fatty acid chain on the left this is just a I actually just made up this molecule but and it could be different depending on the phospholipid you're talking about but this general property of having a hydrophilic head and hydrophobic tails make them very well suited for cellular membranes because you can imagine so hydro that end is hydro hydrophilic and then you have these hydrophobic hydrophobic tails and actually let me see if I can copy and paste this really fast you actually just draw it really fast so let me just draw a bunch of them whoops nope I'm having trouble all right let me just switch back to my drawing tool so let me just draw a bunch of the hydrophilic heads and then a bunch of the hydrophobic whoops actually I'll draw a few more hydrophilic heads out here and then I'll draw all the hydrophobic tails hydrophobic hydrophobic tails let me draw them draw them really fast I'm almost almost done right over here I had republic' tails right over here and this configuration that I've just drawn where you have a bilayer of phospholipids phospholipids a phospholipid bilayer this is how cellular membranes are constructed because this you have you have water or things that are very water based inside the cell this could be inside inside the cell and this could be outside this is outside the cell and so the phosphate ends is attracted to the water and then but the the hydrophobic the the hydrocarbon tails those are going to they're going to orient themselves in this way to get away to get away for the water really don't just let the phosphate the phosphate ends interact with the water and so this forms a nice boundary for the cell and we're going to study that thoroughly as we go more in to biology so hopefully this gives you more appreciation of what a lip it is and the different types of lipids
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