 This is a collection of videos on chapters 15 and chapter 16. Chapter 15 is on a type of molecule called a lipid. There is a lot of information in these videos, especially on chapter 16. You're going to have two weeks to ingest all of the material. The material is not terribly difficult. At least I think it is probably not terribly difficult, but the price that you have to pay is, like I said, there's a lot of material to know, even though it's not too difficult. All right, so chapter 15 is on a type of molecule called a lipid. We are not going to spend an awful lot of time on chapter 15. We're going to spend some time. There's not a lot I want you to know. We will spend an awful lot of time on chapter 16, however. All right, what's a lipid? Lipid is a type of molecule, a type of organic molecule. This is a reasonable definition for what lipids are. Lipids are a broad group of small, I put small in quotes because as far as we are concerned, all molecules are small. Lipids are small compared to other types of biological molecules. Lipids are a broad group of small, organic, relatively hydrophobic molecules. If you don't know what this word means, hydro means water, and phobic means afraid of. So lipids are molecules that have a tendency to not like water, or there you can think of them as being afraid of water. What that really means is they don't like to mix with water very easily. For the most part, there are always exceptions. When you hear the word lipid, you should think fat molecule, because that most of the time that's what people are talking about when they're talking about lipids. Just to give you an example, like I said on the previous slide, lipid molecules tend to be hydrophobic. That means they don't like to mix with water. And this is an example that is vegetable oil, and that's water underneath. And most of you probably know that if you try to mix vegetable oil and water, they separate from each other. The reason is that vegetable oil is mostly made of lipid molecules, and those lipid molecules are very hydrophobic in this case. They don't like to mix with water, and they will separate. So this is just an example of lipid molecules not liking to mix with water. We can ignore this a little bit here. There are many different kinds of lipid molecules. I'm going to break some of them into categories. We are going to briefly discuss some of the categories, and I'll tell you what I expect you to know as we go through them. There are lipid molecules called fatty acids. We will discuss these. There are lipid molecules that are waxes. We're not going to discuss those. There are lipid molecules called triacylglycerols. We will discuss those. Other lipid molecules called phospholipids. We will talk about those, and still there are others called steroids, which you may have heard of. Those are a type of lipid molecules. We will briefly discuss those as well. There are others too, but the main ones are here on the slide. All right, so I think we're going to start with fatty acids. Fatty acid is a relatively simple kind of lipid. It has a long unbranched hydrocarbon chain. That means part of the molecule is just hydrogens and carbons hold in a long line with no branches, and it ends in a carboxylic acid. So if you don't remember from the previous, I think it was two weeks ago actually, that carboxylic acid is a functional group where there's a carbon double bonded to an oxygen, and that same carbon is single bonded to an O, and the O or the oxygen is single bonded to a hydrogen. This is called a carboxylic acid, and then this carbon has to make a fourth bond, so there will always be some other stuff trailing off in the other direction. But if the other stuff here is a long unbranched hydrocarbon chain, then what you have is a fatty acid, and I will show you some examples. There is a fatty acid. This is the hydrocarbon chain. This is the carboxylic acid, and you can see there is no branch on that chain. Sometimes, and I'm going to refer to this in this way as well, sometimes people call this hydrocarbon chain a tail, and hopefully you can appreciate why it's called a tail. It's long and kind of thin or something like that, and sometimes people will call this part the head just to make it clear that it's not part of the tail. What I will tell you is that I am going to expect you to recognize different types of lipid molecules, and there are easy ways to recognize them, at least in this course. Fatty acid molecules, if I ask you to recognize them, what you're going to say is all fatty acids have one tail, and that's going to be the easiest way for you to recognize them. So if I show you a picture of a molecule and I say, hey, this is a lipid molecule, is it a fatty acid? You're going to say, does it have one tail? This is also another big tip off, but mostly you should focus on one tail. There are many different kinds of fatty acid molecules. This one on the previous page, this one here, is not the only one. The tail can be longer, the tail can be shorter. There are other little things that can be used to modify what the tail looks like, and I will show you that as well. We humans, living organisms, we need fatty acids to survive. Our bodies can make some fatty acids, other fatty acid molecules we have to get from our diet. If there's a fatty acid that you need to get from your diet, it's called an essential fatty acid. I don't care that you know that, but I'm throwing in a little bit of human biology there. Okay, there are some fatty acid molecules that are saturated. If you remember from the previous week, what saturated meant in this case is that a collection of carbon atoms has all single bonds, and as a consequence of having all single bonds, the collection of carbon atoms has the maximum number of hydrogen atoms stuffed onto those carbon atoms as you could possibly get. Well, this is a saturated fatty acid. The reason is because the tail here has carbons that are all single bonded, which means that tail has the maximum number of hydrogens stuck onto those carbons as you can possibly get without breaking the bonding rules. So this is an example of a saturated fatty acid. There are other ones that are unsaturated. What that means is they have a collection of carbons, and we're going to talk about the tail again, but this time the carbons don't have the maximum number of hydrogen stuffed onto them because there will be a double, at least one double, or at least one triple bond between some of the carbon atoms in the tail. So here are two examples of unsaturated fatty acids. There's this one over here, there's this one in the lower left. You can probably see the double bond, right? That double bond there means that you can't put as many hydrogens onto the tail, onto the carbons in the tail without breaking the bonding rules. So these are examples of unsaturated fatty acids. Now I want you to pause and think about this. I want you to look at these bottom two molecules. There's something obviously different about them, but we've talked about this last week as well. If you look carefully, the the number of carbon atoms is the same. In fact, the the formula for this molecule down here and the chemical formula for that molecule right there, they're identical to each other. Same number of carbons, same number of hydrogen, same number of oxygens as well. What's the difference between the two of them? Well again, you can pause the video and think about this. This one obviously has a bend, right? It looks bent and it is in real life. I drew the hydrogens coming off of the double bonds in both molecules and if you notice in this molecule here, the hydrogens come off of the double bonds pointing in opposite directions. Down here in this molecule, the hydrogens come off of the double bond, there's the double bond pointing in the same direction. So these, we talked about this last week, these are cis slash trans isomers of each other. Isomer, if you remember, means two isomers are molecules that have the same formula, but the atoms are attached in different ways. Cis trans isomers are molecules that have the same formula. They have a double bond usually between carbon atoms and then the atoms coming off of the double bond either point in the same direction. If they point in the same direction, it's called the cis isomer. If they point in opposite directions, it's called the trans isomer. So this molecule up here with the hydrogens pointing in opposite directions, it's called a trans fatty acid. And you can probably guess this one down here is called a cis fatty acid. And if you have heard of things like saturated fats, what that means is your fat molecule has these hydrocarbon tails, but it has all single bonds between the carbons, which means it has the maximum number of hydrogen atoms attached to those carbons. Unsaturated fats are fat molecules that have hydrocarbon tails where there's at least a double or a triple bond between some carbons, so the maximum number of hydrogens are not there. You may have also heard of trans fats. I don't remember if those are good for you or bad for you, but you can have a pretty good guess as to what makes trans fats trans fats. They have a hydrocarbon tail, those kinds of fat molecules. The hydrocarbon tail has a double bond and in the trans fats the hydrogens come off of the double bonds pointing in opposite directions. Again, I don't remember if that's good for you or bad for you to eat, but at least now you know a little bit of the chemistry for why that people say trans fats. So we are done talking about fatty acids. You should know that they come in saturated and unsaturated types. You should know that they can have cis and trans isomers if they are unsaturated with double bonds. You should know that they have one tail and that they end and they have a carboxylic acid at one end of the tail. So that's the end of fatty acids. The next type of lipid molecule that I want to talk about is called a triacylglycerol. Usually people don't say this word. Usually people call them triglycerides. So if you've ever had a blood test or maybe not all blood tests do this, but the blood tests that I get test my triglycerides levels in my blood. They're testing the levels of this kind of fat molecule in my blood and probably in a lot of people's blood. Triacylglycerols are made of a molecule. This little bit here is part of a molecule that used to be called glycerol before it got attached to all of this other stuff over here. So triacylglycerol, the reason it has glycerol in the name is that this little bit of the molecule used to be a molecule called glycerol. If you notice the triacylglycerols have three tails. Number one, two, three. And that's why the tri is there because there are three of them. And if you notice this little bit here, those three little bits there used to be carboxylic acids. They are not anymore because you need a hydrogen connected to this oxygen here, but they used to be. So the way that you make a triacylglycerol or the way that you make a triglyceride molecule is you take three fatty acids and you connect them to a glycerol molecule. If you don't need to know this, I'm just trying to explain where these molecules come from and where the names come from. The thing that I want you to know is that triglycerides, three tails. And that's going to be the easiest way for you to look at a lipid molecule and say oh what kind is it? Is it fatty acid? Fatty acids have one tail. Is it a triglyceride? Well triglycerides have three tails. So that's about it for triglycerides. Triglycerides a lot of times are found in vegetable oils so fried foods have a lot of triglycerides because you're going to fry the stuff in oil. These are used for energy storage in our bodies so they have a lot of energy stored up in them. And that is about it as far as triglycerides are concerned. The primary thing that I want you to know is that triglyceride molecules have three hydrocarbon tails. The next kind of lipid molecule is called a glycerophospholipid. Again usually people don't say this mouth full of a word. They usually cut out the glyceropart and they just call them phospholipids. Phospholipids are similar to triglycerides but guess what? They only have two tails instead of three. So with phospholipids it's two fatty acids attached to a glycerol molecule and then in place of the third tail there's something else called a phosphate group. There are many different kinds of phospholipid molecules again. This is just an example. This is a little bit of a cartoony picture but this is usually what you see in biology textbooks. There's my two tails. This part here well you can see it says glycerol. That's the part that used to be the glycerol and with a triglyceride there would have been a third tail stuck here but there isn't right? You can only see you can see two tails and in the place of that third tail there's something else. This thing here is called a phosphate group. I don't care that you know that and usually there's some other collection of atoms decorating the molecule as well that does some fancy stuff that we're not going to ever talk about but what I want you to know is that phospholipids have two tails. That's the easiest way to look at a lipid molecule and kind of put it into a category. Another thing that I want to point out and we've already used this word a little while ago the tails are hydrophobic. What that means is this part of the molecule over here doesn't like to mix with water. The weird thing is that the other part of the molecule here does like to mix with water and when you have molecules that like to mix with water you use this word spell it so that maybe you can see it hydrophilic again hydro means water philic means love or likes or something like that. Phospholipid molecules are a little bit weird part of the molecule does not like to mix with water the other part really does sometimes oh they even do it in this picture sometimes they call this part here they call it the head and again I already mentioned this these parts here down here a lot of times are referred to as the tails and they say tails right there this is a cartoon drawing of a phospholipid where they're just showing you the head they're not showing you any of the individual atoms those are the tails a lot of times phospholipid molecules are drawn like this in biology textbooks so just trying to show you what is actually going on these are the hydrocarbon tails that's the phosphate group and the glycerol and the other stuff. Phospholipids are a little bit weird and they are very important in biology they're very important in all living things. The weird thing about phospholipids is that if you throw them into a bunch of water if I throw a bunch of phospholipid molecules into water they will basically arrange themselves into this kind of pattern this pattern is called a bilayer bi means two layer just means layer so this thing has two layers and you can probably see that this is layer number one this down here is layer number two so that's where the word bilayer comes from the reason that the phospholipid molecules assemble in this way when you throw them into water is probably clear but maybe not and that is the yellow parts here the tails they don't like to mix with water so they will bury themselves away from the water molecules but the head parts these gray things up here and the gray things down there they do like to mix with water so they will point themselves toward the water and the easiest way to make all parts of those molecules happy is to have all the heads point toward the water and have all the tails basically move themselves away from the water and when you do this you make this thing which kind of looks like a sand which would no meat or something like that it's just two pieces of bread or two layers this kind of thing is very important in in all living organisms if you've ever studied biology and they say oh this is a cell a little bit of biology and then there's a border between the inside of the cell and the rest of the world which i'm just going to call the outside of the cell and this is the border right this thing right here that is usually called something like a cell membrane the cell membrane is largely made of phospholipid molecules the reason that the cell membrane is largely made of those kinds of molecules is because the inside of your cell is mostly water molecules the outside of your cell is usually also mostly water molecules so what this thing does what this bilayer does when it's part of this membrane is it acts like a border and it controls what things can get into the cell and what things can get out of the cell because there are a lot of things outside of the cell that are dissolved in water that may want to go into the cell some of them may need to go into the cell some of them may be bad if they go into the cell and this little thing here this membrane here this bilayer is like a border because if their molecules dissolved in the water they're going to have a really hard time passing through this yellow layer because the yellow layer does not like to mix with water and it does not like to mix with things that like to mix with water so if you have this surrounding the inside of your cell you can control what kind of molecules get in and what kind of molecules get out and that is mostly done by phospholipids and other molecules that are associated with phospholipids but we just care about phospholipids so what do you want to know phospholipids two tails triglycerides three tails fatty acids one tail the last kind of lipid molecule that i'm going to talk about is a steroid you have probably heard of steroids before this is a different kind of lipid they don't necessarily have to have tails there are many different kinds of steroid molecules they can be hormones like testosterone estrogen things like that they can be part of cell membranes cholesterol which you may have heard of as well cholesterol is a steroid molecule that is part of cell membranes and i just talked about cell membranes on the previous slide they tend to be essential what that means is if you don't make them you ain't going to live this guy took an awful lot of steroids and i am not his biggest fan this is an example of a steroid molecule the way that you can tell that a steroid molecule is a steroid molecule is that it will have four rings and you can see the rings here's ring number one number two number three and number four and with steroid molecules they are always arranged in this way i don't expect you to look at that and know how they're going to be arranged and things like that if i show you a molecule and i say it's a lipid molecule and i say hey is this a steroid you're going to look at it and you're going to say does it have four rings if it does i'm going to say that it's a steroid the thing that makes different steroid molecules different from each other is all of the other crap that decorates those four rings you can remember you probably know at least some of these this is an alcohol functional group this is a methyl that's a methyl side chain this is some craziness over here but if you tack those things on in those spots to the four rings then you make the steroid molecule called cholesterol so here's the summary of chapter 15 we are already at the end i know this is a long video but we covered the entire chapter lipid molecules are at least partly hydrophobic that means they don't like to mix with water there are many different kinds are triglycerides three tails there are fatty acids one tail there are phospholipids two tails there are steroids four rings there are other there are other ones too right i mentioned waxes and there are other things but those are the ones that i want you to know and those are the ones i want you to be able to recognize they are important if you don't make lipids you ain't gonna live they're used for a lot of different jobs in living organisms they're used to store energy sometimes they're used to control how flexible the cell membrane is that's usually what cholesterol does and they can be hormones as well and they can do many other things what do i want you to know i want you to know the difference between fatty acid triglyceride phospholipid and steroids i want you to know that lipids usually cannot dissolve in water or they don't do so easily you should know what lipids are used for you should know that steroids are kind of lipid because a lot of times people don't know that and steroids are obviously important in human biology you should also know that cholesterol is a type of steroid and that is the end of the discussion on chapter 15 so there are going to be eight more videos i believe on chapter 16 see you in the next video