good morning welcome back we are continuing our macromolecule lectures with our next one which is lipids lipids is kind of a generic term for carbon containing compounds that are really characterized by their insolubility in water and think about what's insoluble and what's soluble you want to think about like dissolves like and if you're talking about water as your solvent then water is polar so lipids since they're nonpolar and they have a lot of carbon to carbon and carbon to hydrogen bonding this is nonpolar so they would fats are insoluble in water for that reason because they're nonpolar but lipids do dissolve in organic solvents that are nonpolar so benzene which is c6h6 that is also a solvent just like water can be a solvent but benzene is nonpolar so if you stick to that general idea for the purposes of our class that light dissolves like if you have a nonpolar solvent like benzene then it then these lipids would dissolve in that particular solvent so let's take a look at some facts about lipids they are insoluble in water so they're hydrophobic and again that's because of all of the carbon to hydrogen bonds all of these nonpolar bonds lipids are important in long-term energy storage they contain twice as much energy as a polysaccharide and they consist mainly of carbon and hydrogen atoms linked by nonpolar covalent bonds which again that's the property that makes them hydrophobic lipids differ from carbohydrates proteins and nucleic acids in that they're not quite as long or huge as those macromolecules and they're not built exactly from monomers they do have specific building blocks that we're going to put together by dehydration reactions again but slightly slightly different and lipids are also going to vary in structure and function and what i mean by that is that the structure of lipids varies widely because their hydrocarbon skeletons can be put together in several different ways for example we're going to be looking at three important types of lipids found in cells and those three types of lipids are fats phospholipids and steroids fats are nonpolar molecules composed of three fatty acids that are linked to a three carbon molecule called glycerol because of this structure fats are also called triacylglycerols or simply triglycerides in organisms energy storage is the primary role of fats and this makes sense because when you can see the large number of high energy bonds in the fatty acid chains the ratio of your carbon to carbon and the carbon to hydrogen bonds to the carbon to oxygen bonds which is low energy is much greater in fats than in energy storage carbohydrates so because of all of these bonds fats can store about twice as much chemical energy per gram as carbohydrates we can see in the images here that fats form when a dehydration reaction occurs between the hydroxyl group of glycerol and the carboxyl group of a free fatty acid the glycerol and fatty acid molecules become joined by what is called an ester linkage by a 156 class you do not need to know the name of this linkage bio 181 you do need to know so please mark that in your notebooks that the linkage between the glycerol and the fatty acids that is formed from a dehydration reaction is called an ester linkage an ester linkage occurs between two atoms one of them carrying a double bonded oxygen is linked together by an oxygen so notice that since the fatty acids are not linked into chains they're not considered monomers for that reason so fats are not polymers the structure of fats differs from the polymers that are formed when amino acids nucleotides and monosaccharides link together so that's what makes this different let's watch this recording for a few moments and we'll go through the glycerol bonding to the fatty acids but before we do that hopefully you can recognize this if you were to see this chain this is a type of oil i'm not sure which one it might be um something like coconut oil perhaps but here on the end you can see one of our functional groups highlighted in your notebooks write down which functional group this is right here that's highlighted in yellow here are the two components that we're looking at to make our lipid glycerol on the left and the fatty acid is on the right so let's go through our dehydration reaction we have the three fatty acids on the right each of those has a functional group on the end hopefully you wrote down in your notebooks that that functional group was the carboxyl group so we have fatty that's the carbon hydrogens acid is your c double bond o o h and on the left here side this is our glycerol molecule on the left our three carbon molecule with the oh groups on the right are fatty acid tails i believe this is coconut oil not positive but i think that's what that is we have our hydroxyl group on the glycerol that's going to interact with the ohs on the carboxyl group this will be our where our dehydration reaction occurs so we'll be losing removing three water molecules one for each reaction that occurs now our oxygen will be able to bond to our carbon and our end result is our triglyceride molecule in this image we can see our fatty acid it's a simple lipid consisting of a hydrocarbon chain bonded to a polar carboxyl functional group fatty acids typically contain 14 to 20 carbon atoms most found in the long non-polar hydrocarbon tails as we say fatty acids are key building blocks of important lipids found in organisms so let's take a look at the structure here just as subtle differences in the orientation of our ohs or hydroxyl groups in our sugars lead to differences are those ohs pointing up are they pointing down the bonds that they formed are different depending on the position of those hydroxyl groups so just like that the type of bond between carbons and hydrocarbon chains is a key factor in lipid structure and function when two carbon atoms form a double bond the attached atoms are found in a plane and the carbon atoms involved in a double bond are locked into place so these hydrogens you can kind of twist and spin um this carboxyl group on the end you can rotate these things like a mobile but when you have a double bond like this they're locked in so the rotation right here is tight and that's just chemistry um don't have to really think about this too much just kind of giving you some background information so these cannot rotate freely like the other carbons in the chain and as a result certain double bonds between carbon atoms produce like a kink in an otherwise straight chain so you can see up here where they're all single bonded this double bond kind of makes this molecule bend down a little bit so it kind of bends it kinks hydrocarbon chains that consists of only single bonds between the carbons are called saturated if one or more double bonds exist in your hydrocarbon chain then they're called unsaturated fats the choice of term is logical if your hydrocarbon chain does not contain a double bond it's saturated with the maximum number of hydrogen atoms that can attach to the skeleton so at every point along the carbon you have two hydrogens two hydrogens two hydrogens on the end here three hydrogens where you have this double bond right there's no hydrogens here carbon can only make four bonds and so the four bonds there are two between the carbons meaning that there's no hydrogens here so these are saturated with hydrogens this is not saturated with hydrogens it's missing the two that you would see up here because of the double bond foods that contain lipids with many double bonds are said to be poly unsaturated and are advertised as healthier foods than saturated lipid foods and some recent research does suggest that the polyunsaturated lipids may help protect the heart from disease so how exactly this occurs where they're taking a look at something else that occurs that we can kind of count on from the besides the structure here is that the saturation or unsaturation actually changes the physical state so if the lipids are composed of straight chains many of these interactions will form along the chain and the lipids pack tighter together right if you can just stack these on top of each other because it's a nice chain so you can just stack on one on top the other on top of the other and you can pack them in tight so saturated fats are for they usually form solids if the hydrocarbons are bent like down here then the unsaturated fatty acids they have fewer interactions you can't stack them on top of each other the same and so they are liquids this just gives you a visual of our saturated fats such as butter and meats animal fats and unsaturated fats which you would find more in fish or salmon and then your liquid oils your olive oils and sunflower oils or saff flower oils grape seed oils these are all unsaturated the fluidity of lipids depends on the length and saturation of their hydrocarbon tails or the chains butter is consists primarily of saturated lipids waxes are also saturated lipids and they have extremely long hydrocarbon tails an example of this would be beeswax and it's particularly stiff at room temperature oils like we just talked about they're dominated by polyunsaturated fats and their hydrocarbon tails have multiple carbon to carbon double bonds in them typically highly saturated lipids such as butter have high melting points and are solid at room temperature the as we said the saturated lipids with really long tails like waxes they're super stiff at room temperature and the highly unsaturated lipids are liquid at room temperature unsaturated lipids may be converted to saturated lipids by breaking double bonds and adding hydrogen atoms by a process known as hydrogenation we see this in products like crisco and yummy foods the more hydrogens the yummier and tastier uh the product tends to be when you go through that process of forcing those hydrogens on breaking those double bonds adding hydrogens this actually creates a different structure the hydrogenation creates what are called trans fats and in this slide you can see the difference between our stat saturated unsaturated and our trans fat so here's our saturated example and you can see it's got a lot of carbons hydrogens and it's a straight chain it's going to be able to pack tight next to each other because it's in a straight change straight chain picture like a ream of paper they're all nice and flat all the paper stacks on top of each other and that's pretty dense if you took and made pleats if you open the pack of paper took out each sheet and made pleats of the paper then they're not going to stack as well that'll be a little bit lighter and fluffier now the unsaturated such as a type of vegetable oil you can see two double bonds here and the h's are on the same side where the double bond occurs they're both on this side of the carbon in this double bond again your hydrogens are on the same side this tends to be this is called a cis double bond it means cis means same side or same when you look at when the hydrogenation process occurs what ends up happening is the hydrogens end up on opposite sides so trans is going to be this configuration with one hydrogen on this side of the chain and the other hydrogen on this side because this is a double bond remember this doesn't rotate and spin around these are more locked in place and for some reason this configuration is what causes the health issues so i don't know the details beyond that maybe it's something that you will be interested in going into health or maybe somebody's going to be a dietitian and they find out more about this but from a chemistry standpoint this is what these look like and this is the culprit of the problem with us hydrogenating our food creating these trans fats this is a table demonstrating the differences when you're talking about heart disease with how each of these types of fats come into play with increasing your risk in heart disease and you can see clearly here the trans fat increasing your risk for heart disease now we will end our talk on our fatty acids here our fats are true fats with this yummy picture of this donut and the process of hydrogenation adding those hydrogens is what makes this donut taste so good so let's talk about our phospholipids this is our next group and they are very important because they're the major component of all cell membranes they are structurally similar to fats they consist of a glycerol that's linked to a phosphate group and two hydrocarbon chains the phosphate group is also bonded to a small organic molecule that is charged or polar this is our structure of our phospholipid with fatty acid tails and these types of phospholipids are found in the domains bacteria and eukarya the domain archaea the phospholipid doesn't have fatty acid tails but instead have what's called an isoprenoid tail and this gives the archaea [Music] additional structural components and it helps them to live in those in extreme environments better so that's one of the difference that's why they can survive or one of the reasons that they can survive in those harsh environments but nonetheless in all three domains the phospholipids are crucial components of the plasma membrane most phospholipids they have the glycerol linked to two fatty acids this is different than your true fat fat which had the third hydroxyl attached to another fatty acid but in our phospholipid instead of that third fatty acid tail the height the carbon is attached to a phosphate group so right here you see the phosphate group again this is another one of our functional groups and then the phosphate group is attached to um this small charged organic molecule and this is called choline this uh molecule up top here and even the choline just like the phosphate has a charge as well so the glycerol phosphate choline section is usually what we refer to as the head of our phospholipid and then we have these are hydrophilic right because they have that charge this is a polar head so light dissolves like that means it's hydrophilic because it likes water because of this polar charge and then the hydrophobic tails are water fearing because they are not like water there is no polarity here this is all nonpolar covalent bonding because this molecule has both a hydrophilic and hydrophobic region this is called amphipathic phospholipids are amphipathic the amphipathic nature of many lipids is by far their most important biological feature it's responsible for life's defining barrier that plasma membrane if mixed with an aqueous solution amphipathic lipids will spontaneously form hollow bubbles that resemble small cells these are called b cells missiles tend to form from free fatty acids or other simple amphipathic lipids with single hydrocarbon chains phospholipids which have bulkier nonpolar regions consisting of two hydrocarbon tails tend to form a bilayer lipid bilayers consisting of phospholipids are often called phospholipid bilayers so when there's the one tail and not two tails they instantly form this kind of ball shape orientation that's because the hydrophilic head in an aqueous solution here is hydrophilic so it doesn't mind being in contact with the water where the tails are hydrophobic so they orient themselves inward amongst each other if the structure has two tails then it forms a bilayer and the tails from the two bilayers are oriented towards one another and the hydrophilic heads on this outer part of the bilayer is in water but since it's forming it's got this hollow area there's going to be aqueous solution in here too let's imagine if you're talking about a cell right the outside of this cell is bathed in fluid and the inside of a cell is also composed of water and so the hydrophilic heads will orient towards the outside of the cell which is bathed in fluid and the heads will be towards the inside of a cell which is also bathed in fluid that's what makes this a great membrane forming this barrier between the outside of the cell and the inside of the cell this is just another image showing you close up if this was the outside of our cell right our body is composed of all that water so the outer membrane the outer portion of the phospholipid bilayer will be oriented towards the outside of the cell where this perhaps is oriented towards the inside of the cell which is also composed of a lot of water in there we're going to finish up our fats with these steroids there are two types of steroids there are fat steroids and there are protein steroids all steroids are synthesized from cholesterol so our fat steroids my question to you for your notebook are fat steroids soluble in water are fat steroids soluble in water think about that for a moment an example of a protein steroid would be insulin so insulin is a protein steroid so all are steroids are lipids in which the carbon skeleton contains four fused drinks this is because the cholesterol is our base molecule for making steroids it's the cholesterol that's the four-ring structure and here is our image of our four-ringed cholesterol right here and you know keep in mind that in order to make steroids that you need for your body you have to have cholesterol so you just want to keep that in mind sometimes people think of cholesterol as not good but we all have cholesterol it's actually an important component in our cell membrane it has to do with its fluidity and permeability and we'll talk about that more when we talk about cell membranes i'm going to leave this lecture here and in the next one we will pick up with proteins