now let's look at some lipids and one of the examples I've drawn here is of a fatty acid and this is the first type of lipid that we're going to look at and you will see immediately that it's mostly carbons and hydrogen's so typically we have a ratio of carbons to hydrogen's that is very close to 1 to 2 so for every carbon we have approximately two hydrogen's give or take and so what characterizes this fatty acid is we have this long carbon tail and the carbons all have hydrogen's attached and when we have single covalent bonds between all the carbons we call this saturated because it has every single hydrogen on there that we could possibly get on there so this presence of all the hydrogen's that we could possibly get on there means that saturated or saturated with hydrogen's now as we've seen before carbon makes four covalent bonds it could make a double covalent bond with itself so just imagine that we had a double covalent bond with carbon two carbon here so that leaves only one extra bond before the hydrogen here so we have a double covalent bond between these two carbons single covalent bonds on the adjacent carbons and then a single covalent bond with a hydrogen this is now a double covalent bond and that makes this an unsaturated molecule because we now have introduced a double covalent bond if we had more than one double covalent bond this would be what we call poly unsaturated so right now this is mono unsaturated because we have one double bond now the interesting thing about this double bond is that if we go back to a saturated molecule here for a little bit and we look at these single covalent bonds around the carbons the single covalent bonds have some degrees of freedom so they're like little axles the hydrogen's can actually just kind of spin around so there's nothing to prevent these hydrogen's from spinning kind of like if you've ever seen some of these sci-fi movies with the Space Station's with a outer part that rotate around the inner arm that's very similar to what we would have here those hydrogen's can rotate freely around that carbon and this single covalent bond act kind of as an axial now when we replace the single covalent bond there with a double covalent bond this makes the molecule rigid and usually will introduce a kink in the molecule so if we look at this this long carbon tail typically the way carbons will bond would look more like this so we have our hydrogen's coming off this way and so forth and I'll just draw lines that denote that this molecule continues on but in any case sorry about that in any case we have a configuration that really looks more like this and so oftentimes when we abbreviate a fatty acid which is what this is we will abbreviate the carbon tail just simply as a zigzag line and it's understood that there are two hydrogen's coming off each carbon like so now another thing about this though is when we introduce the double bond that will introduce a kink in the molecule so that our fatty acid then will not be this kind of nice zigzag and more or less of linear shape but will have a kink in it like so so it will Bend this molecule and this will become important later on when we study a different kind of lipid that is built from these fatty acids so far we have looked at the fatty acid tail which is consisting of carbon and hydrogen regardless of where whether it's single bonded or double bonded we still see that all of these are non polar covalent bonds so they don't like water they don't interact well with water at all and anytime you put something like this into water these hydrocarbon tails will sequester themselves away from water as much as I can and this is why if you put cooking oil on top of water it'll form a slick and they'll form two different layers because those things will not interact with one another however when we look at the head of this thing we have something called a voxel grip and that's this part right here and you'll notice it has oxygens and these oxygens are polar and so water will interact with the head of this thing but will not interact with the tail now another thing we will notice is this is called a fatty acid and you're wondering well why is it called a fatty acid well remember our hydroxyl group and we've seen what it can do in water we've seen what it does in carbonic acid well here we have a hydroxyl group at the head of this thing we're sorry a carboxyl group at the head of this thing that has a hydroxyl on it and so what can happen well this hydrogen can leave and it can leave its electron behind and this is therefore a carboxylic acid because it can put proton into solution and it can give up a hydrogen ion so this is a fatty acid because it can give up a proton now the next type of lipid that we're going to talk about is a triglyceride and the triglycerides will be made up of three fatty acids plus another molecule so fatty acids and lipids don't polymerize the way sugars do but they do linked on to other molecules and the molecule of interest that we're going to be looking at now is called a glycerol molecule and it's got three carbons and then we have got some hydroxyl groups coming off of these three carbons like so and then we'll just draw them like this and then the rest we have hydrogen's so this molecule right here is a glycerol molecule and a glycerol is a type of sugar alcohol so what will happen is we can link a fatty acid onto a glycerol molecule and in this reaction we will get water as a by-product so we can actually take the hydrogen off of here and the hydrogen off of here and a hydroxyl group off of one of these so we can take the hydroxyl group off of here and link it with a hydrogen off of here to get water so we link one of these things on here and we get water as a by-product and if I redraw this on here we basically have something that looks like this so this will be attached to a carbon obviously when a when the oxygen here and then remember I said that the fatty acid can just be abbreviated as a jagged or a zigzag line so our fatty acid could link onto here like this and produce a water as a byproduct of this linking now once we have done this we have something called a mono glyceride because we have linked one fatty acid to the glycerol molecule now if we were to do this one more time and link another fatty acid to the glycerol molecule and once again in this case you know I'll denote the head group here where the other oxygen there but typically we could link a second fatty acid on here and now we have a dye glyceride we could do this one more time and we could have a triglyceride and I'll make this one with a double bond so that it's kind of kinked do it this way so we could link three fatty acids onto one glycerol molecule but you'll notice we don't have any more room for any more fatty acids so we can get three up to three fatty acids on this blister or molecule to create a triglyceride and we can't add any more because there's no more room so one thing we know about triglycerides as you need one glycerol molecule which kind of acts as a key chain to link these fatty acids on like keys but the key chain can only hold up to three keys now I have another kind of molecule very similar to a triglyceride that is called a phospholipid so what it would look like is we would have atoms that will be attached to what is called a phosphate group and the phosphate group I'm gonna draw a little bit differently it is going to look like this so there's going to be a phosphorus in the middle of it it all looks something like this so this would be a phosphate group and a lot of times because we're not really interested in what's on the other end of this thing we just abbreviate this with a letter R and the letter R simply means for our purposes the rest of the molecule so the letter R can stand in for the rest of the molecule now another thing you'll remember that I said a few moments ago is that a single covalent bond between a carbon can rotate so we have this diglyceride here we can just as easily find the hydroxyl group on the other side of this thing because remember so this is oxygen here that this bond here is free to rotate so a lot of times what we will find is that the phosphate group will be on this side so if I were to erase this thing will really draw it again and draw it the core of this molecule we have our glycerol molecule and we're going to have a fatty acid attached and I'll just draw it like this and I'll draw another fatty acid here and remember there are hydrogen's on the other carbons here I'll put the hydrogen on this one over here and we'll put the oxygen here and what we'll find is we get something that looks a lot like this and here again our is just the rest of the molecule so we get something that looks like this and once again we have this molecule that is centered around a core of glycerol so here is our glycerol molecule with the center of everything and of course I'm going to go back and denote the oxygens in red because air every time you see one of these oxygens we have a polar covalent bond and therefore we have an affinity for water so the typical thing that we will say is that the head of the phospholipid molecule tends to like water whereas the tails do not and this will become very important especially when we get into membrane structure of cells in the next chapter so this is a very important property of phospholipids and we will find that phospholipids are an extremely important structural component of cells the next lipid that we're going to talk about is based on this four ring structure well we have four rings and our carbon they have other components on them and this is the basis for a molecule called cholesterol which is not only an important component in cell membranes that gives it stiffness but it also is the basis for all of our steroid hormones so cholesterol is a steroid and it is the basis for all the hormones like cortisol estrogen progesterone testosterone and so forth so without cholesterol we would not be able to produce a very important bunch of hormones that governs how our body functions and also governs a lot of the processes within our body not only that but cholesterol is produced in the liver so the body can manufacture its own cholesterol and in some individuals they manufacture more cholesterol than they need and this can become a problem because if you have too much cholesterol aspect especially if your serum levels in blood of cholesterol are too high then you are at risk for things like core Denari artery disease and other problems