 Hello, we're going to learn a little bit more about lipids or fats, right? That's how majority of the people are thinking about lipids. However, lipids are really hugely diverse group and they're really important. We wouldn't be alive without them. It's not about just about energy storage. So what they share, they share that they do not mix well with water. Just think about your dressing, salad dressing, how if you leave it alone after a while the oil will float on the top of the vinegar and so forth. So that is when you mix it up, it's emulsion. It's physical mixture, but it's not a chemical mixture. So they are not dissolved in that water. Now, they are hydrophobic. So hydrophobic, water-phobic fear of. They're afraid of water. They don't like mixing with water. Due to the non-polar hydrogen carbon bonds. You remember when you were learning about water, how hydrogen bonds are possible to make because of the polar, slightly polar covalent bond between the hydrogen and the oxygen in the molecule of water. These are non-polar. Now, we can distribute all the known lipids into three groups. Fats, which you probably know as triglycerides. Then phospholipids. I'm not sure if you've heard about them before, but they are essential part of the membranes. And steroids. I'm sure everybody heard about steroids. So when you think about steroids, com looking like honeycomb shape is what comes to mind. So the minor differences between them, remember everything is about the shape in biology is giving different influence in the different action in the biological systems. Now, phospholipids, the same as fats, have the glycerol, which is three carbon alcohol that has bonds with fatty acids. So you see they're not really polymers, but they can be really, really huge. Phospholipids are a little bit different. They have one portion that is hydrophobic and that portion is with fatty acids. But they have the tip of their molecule has a phosphate group, which is hydrophilic, and that is what is enabling the life on earth because they're making membrane, a hydrophobic part turned toward each other, a hydrophilic part toward the water. So what is how they are made, what is the structure? You can see here that there is another rule, O-L, right, alcohol. When you see in the name of the molecule O-L, you can be sure that it's alcohol. In this case, glycerol is a three carbon alcohol that has O-H group that is active group that is connecting with carboxyl group of the fatty acids and it's making the bond. Okay? How it looks like? You can see here the connection, a lot, a lot of atoms, right? So these are the chains of the fatty acids. This belongs to the fatty acid and it had O-H connected to this carbon before they made the bond. Here the H from the O-H group from the glycerol was the donor to make H2O. So even though they are not polymers, still the same procedure, dehydration reaction is the one that is happening to connect the fatty acids with the skeleton, so to speak, of the fats, which is glycerol. These fatty acids can be different, can be shorter, longer, can be saturated, can be unsaturated, have trans or cis position and so forth and usually we represent instead of repeating these carbon and hydrogen molecules, we usually represent them like this. If there is a double bond between, this is what representation usually looks like. Okay? Now, in the case of the phospholipids, we have phosphate group that is connected to the first. So phosphate group we usually write like this, but it's actually ion that has negative charge and it's PO4, not just phosphate, it's not just phosphor itself. Okay? So this phosphate group is connected to the first of the carbon molecules, carbon atoms, and the rest of them have one or two different types of fatty, long-chain fatty acids. How it looks like in our membrane? Our membrane has hydrophilic portion, which is phosphor, and then has two so-called tails of the fatty acids. Very important thing to remember when we are going to talk about the proteins, this is one of the major forces that keeps them together and again, there are other from the different molecules and so forth. So that is how the phospholipid bilayer is making our membrane. What are steroids? Very important about the shape. What do you think this is here? Usually blue and red. Testosterone. One of the astrogens, because astrogen is a group of different molecules that have similar structure. So what makes man have appearance that it has is this particular steroid female, this particular steroid. If you take a look, position of the double bond of the oxygen and one methyl group missing. Not much of the difference, but I would say it's a major difference if you think about what are the results of their actions. Functions. Fat and oils definitely energy storage and that we usually know about. However, if you're thinking about water power players, even though they're athletes and they practice really hard, they have a lot of muscles, they still have pretty significant layer of the fat under their skin. And that fat is necessary because otherwise in the water they would lose temperature and they would endanger their health. The same thing is with water mammals. Pretty significant amount of fat that is there to act as insulation to protect from the cold. Now, phospholipids and sterols, they are consisting about half of the mass of the biological membranes. Just think about if we didn't have that fatty layer, you would go to wash your hands and you would just simply dissolve. That wouldn't be quite convenient, right? So these are phospholipids are there to actually protect us, right? And to make that semi-permeable condition that enables life. Other lipids, they're often really needed in very very small quantities, but they are necessary. So completely fat-free diet is very very harmful. Many of them, as I'm called factors, think about vitamins, vitamins that are liposoluble, soluble in oils, okay? Like vitamin A, for instance, vitamin D. Then we have electron carriers that are helping through the membrane to carry the electrons. We have light absorbing pigments that are doing the photosynthesis, enabling life on earth. Hydrophobic anchors for other hydrophobic molecules. Then hormones, like I mentioned, steroids, there is a whole class of hormones that are necessary for our functioning that have cholesterol as that has very similar shape to honeycomb that we already mentioned. Those are all steroid hormones, steroid-based hormones. Then we have intercellular messengers, messengers that are triggering certain action when the signal comes. Then we have emulsifying agents and so forth. So that would be about to talk about lipids. Thank you.