- [Voiceover] Lipids are one of the four major macromolecules. So lipids themselves though are insoluble in water. If you mix oil and water, I don't care how much you shake it around. If you let it sit again, that oil will separate from the water. Now there are three major classes of lipids here. And all three of 'em are gonna be insoluble in water. We have the triglycerides. Now these are mostly energy based, kind of help store energy in your body. We have the phospholipids. These phopsholipids are important because they make up a majority of your cell membrane. So think of every cell in your body. Those millions and millions and millions of cells. The phospholipids are what make up the majority of the membrane that covers them, which keeps them intact. And then you have steroids. These are gonna be a lipid that is based on a ring structure. Now these aren't the steroids you think of as the illegal steroids from sports. It's just steroids that everyone has in their body. There are things like cholesterol, estrogen, testosterone. Those are steroids. So steroids, this particular type is a form of a lipid. We'll start with the triglycerides. Now more commonly, the triglycerides are known as fats, or they're known as oils. These triglycerides are made up of two main molecules, glycerol and fatty acids. But the triglycerides, tri means three. Triglycerides have three fatty acids. Now these fatty acids can either be saturated or unsaturated. In the case of saturated fatty acids, which is where the term saturated fats comes from, saturated fatty acids, a lot of times you'll see in solid form at room temperature. They're a kind of fats. Every chemical bond is filled up. But in the unsaturated fatty acids, this is where your unsaturated fats or unsaturated oils come from. The unsaturated fatty acids do not have every chemical bond filled up. They potentially could form more bonds. And these triglycerides are primarily gonna be an energy stored molecule. So if you have lipids stored in your body for long term energy use, a lot of times they're stored as triglycerides. So here's an example of how the triglycerides are formed, and then two different types. In Figure A on the left you're seeing, you have the three yellow structures. Those are your saturated fatty acids. You can see every carbon has four bonds off it. Every It's just one over another. And the top oval, the glycerol. What ends up happening here is you can see how there is an OH that is highlighted in blue. And then another H on the glycerol. Well if you take off the HOH, or H2O, by removing water, that's dehydration synthesis. You could make a new molecule. Do that three times. You bind three saturated fatty acids there, and now you have a triglyceride with your B in the middle. But if you end up having a triglyceride which is unsaturated, that's C on the right-hand side. You can notice how that as you go down those fatty acid chains, sometimes there's a carbon carbon bond. But instead of one line, meaning a single bond, there is two lines, which causes the line to kind of angle out a little bit. That means you could technically add some more bonds in there if you wanted to, some more hydrogen. So we have our triglycerides. Saturated, the middle is B. Unsaturated fatty acids is the right, letter C. The second main category of lipids is your phospholipid. Now the phospholipid still has the same glycerol. It still has fatty acids. But now there's only two fatty acids. The 3rd fatty acid has been switched as now a phosphate group. At the term phospholipid, you have a phosphate group. Two fatty acids all attaching to glycerol. Now what's unique is one end of this molecule is water soluble, hydrophillic, water-loving. But remember I said all lipids are insoluble. That's still true because the other end of the molecule is water insoluble, hydrophobic, water-fearing. So even though a portion of this phospholipid could be soluble in water, the other portion is still insoluble in water. So overall, that means the molecule cannot fully be soluble in water. So your phospholipid. Their function, cell membrane. They form the cell membrane of practically every cell in your body. Now it's not the only piece of a cell membrane but the large component of the cell membrane. So here is your phospholipid. You can see the top sphere, which is referred to as the polar head, is comprised of your glycerol molecule and the phosphate group. But coming off the other side are the two fatty acid chains. Now these two fatty acid chains, one happens to be saturated. One happens to be unsaturated. So which one's which? As you're looking at the screen, is the left-hand one the saturated or unsaturated? The one on the left, which has the term fatty acid pointing to it, that's the saturated fatty acid. The one on the right-hand side of the screen, where you have the bracket that says nonpolar, you can see there's a double-bonded carbon in the middle there. That means that's the unsaturated fatty acid. And to round off the category of lipids, we have our steroids. Now all these steroids are composed of four carbon rings. What makes these different from your carbohydrates is these rings are actually sharing a side. You can see other rings when you trace them. They both have one side that is shared between each ring. The carbohydrates do not share. There's always a bond in between each monosaccharide, or each ring. So always as four carbon rings, and always as sharing sides. The example you see here, cholesterol. Now think of it as a whole, cholesterol's bad. Not necessarily. You have to have some cholesterol in your body to function normally. Now sure, if you have too much cholesterol, it could cause a problem. We have to have some there to help with structural supports of your cell membrane and to help with other normal cell functionality. Your body naturally produces cholesterol. The question is does it produce the right amount? Or unfortunately, could it be producing too much? This producing too much of this, then we've got a problem. Estrogen, testosterone. And what's even more interesting here is the cholesterol molecule can head down and split and be converted into estrogen and testosterone. So cholesterol is actually kind of a starting material, which helps produce the male sex hormone, testosterone, and the female sex hormone, estrogen, your steroids.