welcome back in this video we're going over lipids and some of which include fats and this is the third video on chapter 3 material so lipids are non-polar hydrocarbons nonpolar referring to the fact that these lipids are water-faring or hydrophobic and you'll see them in different environments such as in the fur of aquatic animals to protect them from the elements and make it easy for them to dry off after being in water lipids are also pretty diverse in their functions we can store long-term energy in the form of lipids and they can provide both physical and temperature insulation from the environment for example there are a lot of lipids in the GI tract in the gastrointestinal area of humans and animals we also have insulation provided in the form of protection from extreme temperatures lipids are important to build several types of hormones and also they're a main component of our cell membranes in the rest of this video we're going to be going over the many types of lipids we see in cells and in living things like fats oils waxes phospholipids and steroids our first type fats are comprised of two main elements fats are made of a glycerol molecule combined with Three fatty acids to form something called tri-acylglycerol so we have three fatty acids and a glycerol backbone these are connected through an ester linkage something you may have learned in chemistry and this is a dehydration synthesis reaction so three molecules of water will come out and be released as products in this reaction here's another look at that reaction I can see a three carbon compound glycerol with three hydroxyl groups here and only one fatty acid is shown here but we'll have three of them they could be the same or different fatty acids fatty acids have a long chain of hydrocarbons attached to a carboxyl group and this is actually also known as a carboxylic acid so this is why this is called a fatty so this is a fatty portion fatty acid as this can donate protons into solution the number of carbons in this fatty acid chain can be anywhere from 12 to 18. that's probably the most common but it can range from four to about 36. when you link glycerol with Three fatty acids again you get tri-acylglycerol which is also sometimes known as a triglyceride triglyceride or triglycerides plural and it's not shown here but joining these molecules The Three fatty acids and the glycerol is again a condensation reaction or dehydration synthesis so you'll also see three water molecules as products of the reaction when we look at fatty acids these can actually be saturated or unsaturated what does this mean here we're looking at the fatty acid chain portion of the fatty acid we're not looking at this polar portion if there are only single bonds between the carbons in the hydrocarbon chain the fatty acid is known as saturated saturated so this means that this is saturated with hydrogen so the maximum number of hydrogen atoms that can be attached to the carbon skeleton is maxed out stearic acid is an example of a saturated fatty acid and we find this in animal and vegetable fats it's shown linear like in a linear format here but in reality it's probably a little bit zigzagged in shape because of the tetrahedral arrangement of the surrounding carbon and hydrogen atoms around each Central carbon and these tend to be fairly linear in shape so they'll look like this overall when you have many of them and they tend to pack tightly so we see them as solids at room temperature such as butter fats and meat that are cooled down instead of being liquid they'll be solid because they pack tightly they're more rigid they tend to be associated with cardiovascular disease because they're harder to break down and they can accumulate in our blood vessels and cause problems when we see at least one or more double Bonds in the fatty acid chain of the lipid or of the fatty acid then these are known as unsaturated fatty acids here I can see just one double bond here if there's only one double bond in that carbon-carbon or the carbon backbone then that's called monounsaturated if there are more than one we call those polyunsaturated fats so here what I usually see if you sketch this and that arrangement is where you see the double bond you'll see this is the double bond you see a bending or a kink in the fatty acid tail structure because they're bent like this they can't pack tightly like the previous saturated fatty acids could this means that they tend to be liquid at room temperature so these are oils like olive oil here on the left side I can see both saturated fats that don't have any double Bonds in their fatty acid chain as well as unsaturated fats that have one or more double Bonds in the fatty acid tail region I can see two types here this one is a CIS configuration and here down here I have a trans configuration these terms come from chapter two when we were talking about geometric isomers these are molecules that have a different arrangement of atoms around the double bond CIS has the hydrogen atoms on the same side of the double bond trans the hydrogen atoms are on opposite sides of the double bond why does that matter in terms of unsaturated fats well when you have CIS fats these create a bending or a kink in the chain as you can see here that means they cannot pack tightly and they tend to be liquids at room temperature like the oil I described in the previous slide trans fats in contrast have no bending and they look and behave more like saturated fats this means they tend to be more unhealthy like the unsaturated fats and they can actually increase the amount of LDL or bad cholesterol in the body this tends to lead to fat deposits in the blood vessels and can lead to heart disease where do we get trans fats where do they come from they're not as common in nature so we can actually make these in Industry by artificially hydrogenating oils forcing the addition of more hydrogens and getting rid of the double bonds to make them more solid to make them more likely to be solid at room temperature instead of liquid this always reminds me of M M's You Know M M's the candy they melt in your mouth and not in your hands used to be one of the things they would say in commercials so if you don't want something to be liquid when you're holding your chocolate candy in your hand you can make them a little bit more solid by forcing the formation of trans fats in terms of types of fatty acids we also have a group called essential essential fatty acids whenever you see the word essential what this means is this is required for our bodies but we don't make it we can't make it ourselves so it has to come from our diet from what we eat two examples of essential fatty acids are Omega-3s and omega-6 fatty acids Omega-3s we see in fish like salmon trout tuna omega-6 you often see in nuts like walnuts or pine nuts so an example shown here is Alpha linoleic acid it's called an omega-3 fatty acid because when we number these carbons we start from the end of the hydrocarbon chain this is carbon one carbon two this is carbon number three and I see that first double bond there so this is Omega-3 and although fats often get a bad wrap they're actually important for many of our basic functions like hormone production we need them to make vitamins to store energy long-term and several of these or many of these fats can also be beneficial they can reduce the risk for heart attack lower the amount of triglycerides in the blood lower blood pressure and even perhaps reduce inflammation our next type of lipid are waxes so waxes are made of long fatty acid chains that bond to long chain alcohols through Ester linkages so here's an example down here I have a fatty acid chain over here and I see the carboxylic acid portion the long chain alcohol and we form an ester Bond so this is a dehydration synthesis reaction water comes out waxes like the other lipids are water Fury and they're good at making something waterproof they prevent water from sticking to the surface we find them on feathers of some birds the surface of leaves from certain plants we'll see them even over the surface of some bacteria to make them really sticky and hard to break down hard for the immune system to get rid of our next type of lipid are phospholipids and these are critical to our cell membranes if I look at the structure over here on the right I can see that phospholipids are composed of two fatty acid tails and that makes up the water fearing portion of the phospholipid these are attached to the glycerol backbone which itself is attached to some kind of phosphate group and this phosphate group is often modified the modifiers can be charged or polar some kind of water loving molecule will be attached there so I can see that the general structure of this fossil lipid looks like a polar head water loving head that's spherical attached to two water-faring tails because this molecule has both a hydrophilic portion and a hydrophobic portion we call that an amphipathic molecule amphipathic meaning hydrophobic and hydrophilic shown in this figure are three ways to represent phospholipids we see a structural model over here a space filling model over here with the atoms depicted and then something that looks like the picture I'd sketched on the previous slide a symbol if I look at these fatty acid Tails they can be saturated or unsaturated and that will determine if they're more fluid or they tend to be more solid if you ever take a shower and use soap or shampoo soap or shampoo or composed of phospholipids so how does it work so imagine you had a long day you feel kind of greasy and dirty and you get in the shower and you rub some soap on your arm what happens is the phospholipids come off the soap and the tail portion the water fairing portion will trap the oil and dirt in the center of a structure we call the micelle so the micelle is a bunch of phospholipids that break down and reform trapping the oil and dirt in the center where the water fearing portion is found and they arrange themselves into these spherical shapes this is just a cross section of that sphere where the water loving portion the hydrophilic portion will face the water and Milli oh I don't know of millions but depending on how much you're using many many myself will wash away the oil and dirt using the water from your shower head for example if you ever use missile or water to remove your makeup it's the same idea you'll see it looks like water with little bubbles inside the liquid and that those bubbles are these micelles earlier I mentioned that phospholipids are really important to the cell membrane also known as the plasma membrane so let's say we have a cell here the cell is usually some kind of spherical or close to spherical structure where we have the cell embedded in some kind of body of water so the outside is mostly water and the inside of the cell is also mostly water and if I were to cut out a piece right here and blow it up you can see a magnified picture of that over here I can see that the cell membrane is made of a phospholipid bilayer two layers of phospholipids so the water loving portion is facing the outside of the cell and also facing the inside of the cell both of which are mostly made of water and the water fearing portion the Tails of the bilayer face each other because they don't like water they want to get away from the water because of the arrangement of phospholipids in this bilayer where the polar or hydrophilic heads are facing outside and inside most things cannot cross into or out of the cells this makes it a nice a barrier where most things can't pass and harm the cell or things can't be lost from the cell very easily but it also means that phospholipids themselves cannot flip very frequently it's very unlikely that this phospholipid will transfer will flip and move to the other side of the bilayer it's not impossible it does happen but very uh very infrequently not very common instead what happens more frequently is that these phospholipids move laterally to the right or to the left and that contributes to the dynamic nature of the plasma membrane it's fluid things are moving around our last type of lipid are steroids steroids look very different from the other lipids we've seen so far because they have a fused ring structure I can see three six-sided rings and one five-sided ring the structure looks very different but we still classify them as lipids because steroids are hydrophobic also known as nonpolar so they're not soluble in water and some of them have a short tail like the one shown here some of them also might have a hydroxyl group that functional group we saw earlier and that puts them in the alcohol classification as well we call those steroles stir rolls cholesterol is the most common steroid and it gets a bad rap but it's actually pretty important our liver produces cholesterol and we need cholesterol in order to make hormones such as testosterone and estrogen also we need it to make vitamin D and bile salts which are important in lipid breakdown so when we're eating fats we need to break them down we use bile salts to do so not shown here but in the future we're going to learn how steroids are also important in in something called membrane fluidity we need to make sure our cell membranes are not too fluid or they break apart but also that they don't freeze and crack in the winter time interestingly there's actually no association between the amount of cholesterol you eat and blood cholesterol or heart disease I should say so no matter how much cholesterol you eat it's not really associated with heart disease it's really saturated fats that appear to have a greater role in heart disease if I look at the combination of what we saw earlier that phospholipid bilayer that makes up cell membranes as well as steroids earlier I mentioned that most things cannot pass into or out of the cell because of this water fearing or hydrophobic region things like glucose would not be able to pass for instance because glucose is water loving it does not mix well with a water-faring portion however steroids like our hormones estrogen and testosterone can pass because they are lipophilic so they're fat loving or water fairing you can say either these can pass through our cell membranes pretty easily and that's one of the reasons we can take hormones orally or we can take them even through a patch on the skin surface they can diffuse across and into our cells that takes us to the end of the third part of chapter three in the next video we're going to start proteins our third macromolecule type