this video I'm gonna tell you everything you need to know about lipid biochemistry for a biochemistry class and for the MCAT but something important to realize is these free fatty acids are at the center of lipid biochemistry and these free fatty acids can be attached to two different types of backbones we have glycerol backbone x' and we have this fing goosing backbones however in order to understand lipid biochemistry there are two organic chemistry mechanisms you should be aware of so the first mechanism involves a hydroxyl and a carboxyl and the key idea is that we nucleophilically attack forming a bond and when we form a bond we break a bond these electrons fall on this guy and we're left with this product with this ester this second mechanism involves an hydroxyl and a phospho ester where again it's the same idea we nucleophilically attack forming a bond when we form a bond we break a bond and these electrons fall on this oxygen and were left with this phosphodiester so these are the two mechanisms you may be aware of so let's quickly go over them so first let's go over this first mechanism so again in the first mechanism we have this hydroxyl in this carboxyl so the first step is we D protonate this hydrogen and then these electrons fall in the oxygen and we're left with this oxygen anion which is very nucleophilic and we also have this carbon which is very electrophilic so they can react where again we nucleophilically attack forming a bond and when we form this bond we push these pi electrons up onto this oxygen forming this tetrahedral intermediate then these electrons scoot back down forming a double bond when we do that we break this bond and these electrons fall in this oxygen and when we do that we form this product so again drawing this a little neater we're left with this product this ester so again that's the first mechanism hydroxyl with the carboxyl forming an ester so again the key idea is that we nucleophilic attack forming a bond represented by this bond so when we nucleophilic the attack forming a bond we break a bond were these green electrons fall on this guy and Reluctant this product so again we form a bond and we break a bond so that's the first mechanism this second mechanism involves a hydroxyl and a phospho ester so again this it's the same first step with D protonate this hydrogen these electrons fall on this guy and we're left with this oxygen anion which is very nucleophilic this phosphate is very electrophilic so they can react we nucleophilically attack forming a bond when we form a bond we push these PI electrons up on this oxygen when we do that we form this trigonal bi-pyramidal intermediate when we form this intermediate then these electrons couch back down form the double bond and when we do that we break this bond and these electrons following this oxygen when we do that we form this product so drawing this a little neater we're locked with our phosphodiester so again in this second mechanism we have a hydroxyl reacting with a phosphor ester forming this phosphodiester and again and it's the same idea we nucleophilically attack forming a bond represented by this bond so when we nucleophilic attack we form a bond and then we break a bond where these electrons fall in this guy and we're left with this leaving group so again these are the two mechanisms hydroxyl and carboxyl forming an ester the nitrox o non-fossil ester forming the phosphodiester so for the rest of this video we're going to refer to this mechanism as mechanism one and we're going to refer to this mechanism as mechanism two and these are the two mechanisms you need to know for lipid biochemistry so again these fatty acids are at the center of lipid biochemistry and there are two types of backbones that we can attach these fatty acids so the first type of back when I want to talk about is glycerol this glycerol backbone so what is this glycerol backbone well you've probably heard of glycolysis where we take glucose molecules and we enter them through the pathway of glycolysis however wouldn't we form this particular intermediate sometimes we can continue in finish glycolysis however other times in other circumstances we can take this compound and we can use it to form glycerol this glycerol backbone so that's how we form this glycerol backbone but why well what do we do with this glycerol backbone well we can take this glycerol backbone and add three fatty acids how do we do that well again remember we have a hydroxyl or carboxyl so remember that mechanism 1 we can use that mechanism want to attach these and again we know how we do that we nucleophilic attack forming a bond and when we form a bond we break a bond these electrons fall in this guy and when we do that we form this product this mono glyceride however we don't stop there we can also take the second hydroxyl and add a second free fatty acid there again that mechanism one the same mechanism when we do that we form this diet glyceride however we have a third hydroxyl so we can add a third free fatty acid to again that same mechanism Lynam and then we from this trial is ride this triad glyceride so this compound is called a triglyceride ER also sometimes it's called TRAI cyclists ride and this compound is the primary stored form of energy our bodies used when our body wants to store excess energy we store it in the form of this triglyceride so we can see why this guy is called a backbone it's a backbone because we attach three fatty acids to it however we can attach other compounds to this glycerol backbone for example we can take these two hydroxyl groups and add two free fatty acids through again that mechanism one however we can take this third hydroxyl group and add a phosphate through that mechanism to so again by now you're probably pretty aware of that mechanism one and that's how we had free fatty acids to these two hydroxyl groups however we can also add a phosphate to this hydroxyl group through that mechanism 2 and again remember that mechanism to we attack forming a bond then would break upon these electrons fall on this guy so if we attach a phosphate to this guy in free fatty acids to these two hydroxyls we're left with this compound which is called a phospholipid of phospho lipid and these phospholipids make up our plasma membrane our semi permeable plasma membrane which is made up of these phospholipids where this guy would represent this guy so our phospholipid is made out of many phospholipids however we don't stop at this particular compound because what we can do is we can take this phosphate group and we can add other hydroxyl groups other alcohols so again it doesn't matter what this our group is this can be any chemical structure that's not important as long as this chemical structure has a hydroxyl group we can add it to this phosphate through that mechanism to where again remember we attack forming a bond and then we break upon these electrons fall in this guy and we would form this product this phosphodiester so didn't matter what that our group was as long as we had a hydroxyl we could on it so here are different compounds you'll see in biochemistry you'll see choline ethanolamine and serine so again it doesn't matter what chemical structure we have that's not important it doesn't matter what this chemical structure is as long as it has a hydroxyl group we can add it we can add it to this phosphate group for example this serine we can add it to this phosphate group because we have a hydroxyl so as long as we have a hydroxyl we can add it again through that mechanism to where again we attack forming a bond and then we break up on these electrons falling this guy when we do that we would form this come on this phosphatidyl serine we're phosphatidyl refers to this group and then again the Sirian refers to whichever compound we added so we added a serine so therefore it's phosphatidyl serine so again this is another phospholipid that again makes up our plasma membrane however instead of adding a phosphate to this third hydroxyl group we can also add a carbohydrate to this third hydroxyl group where again we would essentially form a bond and we would break a bond and when we do that we'd form this product this glycerol glyco lipid this glycerol glycolipid however some of you I know are gonna be really curious and want to know the mechanism so quickly going over the mechanism the first step is we take this hydroxyl group and we turn it into a better leaving group so we essentially add a chemical structure to make this guy better leaving group the next step is now this guy can act as a leaving group so essentially these long electrons scootch down forming a double bond and when that happens we break this bond so when this bond is broken these electrons fall on this guy and now this guy can act as a leaving group and when we do that we formed this intermediate so this intermediate has a very electrophilic carbon so now this nucleophilic oxygen can nucleophilic attack this electrophilic carbon when we do that we form a bond when we form a bond we push these PI electrons up onto this oxygen and when we do that we form this glycosidic linkage so now we form our LeSueur glycolipid our glycerol glyco lipid however we don't always stop there we can add more carbohydrates through a very similar mechanism so we can add more carbohydrates forming these different types of glyco lipids so depending on the types of carbohydrates you add determines the type of glycolipid you form glyco lipid so now we can see there are many different types of glycerol based backbone lipids lots of different lipids that use these glycerol backbones so that concludes the lipids that use these glycerol based backbones but what about the lipids they use these finger scene based backbones well what is a finger seen backbone and how do we create this finger see where does it come from so in previous videos we've learned about glycolysis and the Krebs cycle and we refer to these two pathways a central metabolism however what's important to realize is we can take this particular intermediate of glycolysis to biosynthesize the serine amino acid and we can take this acetyl co a molecule to go through a path that we refer to as fatty acid synthesis to biosynthesize these free fatty acids now what we can do is we can react a free fatty acid with the Sirian amino acid to form this finger seam backbone so that's how we biosynthesize this finger seam backbone however why do we buy synthesize this finger same backbone what do we do with it well this finger seen can act as a backbone to add these free fatty acids and specifically what happens is we take this particular amine group to add a free fatty acid and we do that to that same mechanism one that exact same mechanism the only difference is instead of a hydroxyl group we have a naming group however this aiming group can act as a nucleophile so can nucleophilically attack this carbon forming a bond and when we form a bond we break a bond and these electrons fall on this guy and when we do that we form this product the ceramide so again the idea is we take this nitrogen and we nucleophilic attack forming a bond with this carbon that's represented by this bond and when we do that we break a bond these electrons fall on this guy but the point is we form this ceramide compound and this ceramide compound is extremely important our cells use the ceramide compound to produce a lot of very important lipids for example usually what we do is we take this head group this hydroxyl group which we refer to as the head group and we use at add a phosphate group and again we know this mechanism this through that mechanism to where again we attack forming a bond when we form a bond we break upon these electrons fall on this guy when we do that we formed this phosphorylated ceramide now once we form this phosphorylated ceramide now what we can do is we can add other hydroxyl groups so again it doesn't matter what this chemical structure is as long as it has a hydroxyl group we can add it and again we add it through that mechanism to we're getting we nucleophilic attack forming a bond and when we form a bond we break upon these electrons fall on this guy when we do that we formed this phosphodiester so doesn't matter what that our group was this could literally be any chemical structure you can think of as long as it has a hydroxyl group we can add it for example here are a couple common alcohols you'll see again in these how these are hydroxyl so any compound with the hydroxyl it's an alcohol so these are the common hydro alcohols you'll see in lipid biochemistry choline ethanolamine serine and other generic alcohols so again it doesn't matter what the chemical structure is as long as it has a hydroxyl you can add it for example we can add this choline how again it doesn't matter what this side of the compound is as long as the hydroxyl we can add it to that mechanism to again we attack form upon when we form a body break upon these electrons fall on this guy and if we were to do that we would form this compound so we refer to this compound as sphingomyelin so this compound is extremely important to build the myelin sheaths in our neurons so we build this Fingal myelin from this ceramide compound which is extremely important which again came from this finishing background so we refer to this as the phospho head group which we added to this hydroxyl group which again is referred to as the hydroxyl head group so we can add lots of compounds to this hydroxyl head group not just this phosphate head group but we can add lots of compounds to this hydroxyl head group for example we can also add carbohydrates to this hydroxyl head group again through that same mechanism we learned before again we know this Hydrox was a bad leaving group however we can add a chemical structure to it turning this oxygen into a better leaving group so now can act as a leaving group where these lone pairs of electrons scootch down forming a double bond and when we do that we break this bond and these electrons fall on this guy so then this guy acts as a leaving group again we break this bond so this guy acts as a leaving group and when we do that we form this compound and again we already explained how this carbon is electrophilic so this hydroxyl is nucleophilic so we can attack we can nucleophilic attack forming a bond pushing these PI electrons off onto this oxygen when we do that we form this glycosidic linkage so when we add one carbohydrate to the ceramide so when we take ceramide and we use its head group to add one carbohydrate we form a cerebroside so this is a cerebral side a surrett ceramide with one carbohydrate however we can also add more carbohydrates we can add many carbohydrates so when we had many carbohydrates we form a gangliosides and I remember this is a ganglia side because it has a gang of carbohydrates we have many carbohydrates a gang of carbohydrates and specifically you'll see with this car behind this syusai alloc acid added for it to form this ganglia side however the point is is that this is a sphingosine backbone and we can take this specific aiming group and add a free fatty acid and when we had a free fatty acid to this particular aiming group we formed this ceramide compound then again we can use the ceramide compound and add lots of different types of compounds to this hydroxyl head group for example if we had a fossil head group we formed this compound if we had one carbohydrate we form a cerebroside if we had many carbohydrates we form a ganglia side so we can see how the ceramide is used to form lots of different compounds but again they all stem from this thing they've seen backbone so that concludes the lecture on the glycerol based backbones and sphingosine backbones however there is one last category so again we know this is glycolysis and this is the Krebs cycle collectively these two pathways are for at west-central metabolism however what's important to realize is we can take these two carbons in acetyl co a two biosynthesize this is hmg-coa now once we form this hmg-coa we can use it to form this five carbon compound or we could use it to form this five carbon compound however what's important to realize is that these five carbon compounds are kind of like building blocks they're kind of like Legos like carbon Legos that ourselves used to biosynthesize larger compounds specifically larger lipids for example we can take two of these five carbon unit building blocks to build a ten carbon unit building block now that we form this 10 carbon compound we reacted with another 5 carbon compound to form a 15 carbon compound we react two of those 15 carbon compounds to form this 30 carbon scaling compound now when we form this lipid squalene realize we have free rotation among some of these bonds so we can distort and get in a very specific conformation to react with itself to form this line Estoril which can then go through more chemical modifications to form cholesterol so realize an important implication as long as we have glucose molecules we can go through glycolysis then enter to form acetyl co a to them from HMG co h2 then from these five carbon units to then from cholesterol so we can take glucose to by synthesize cholesterol which is a lipid and an extremely important lipid so once we form cholesterol we can use it to form lots of important compounds for example cholesterol can enter the lit the liver to form these bile salts which is important for fat digesting an emulsification we can also take cholesterol with some help from electromagnetic radiation the liver and kidney we can form different forms of vitamin D which is a vitamin which is a hormone also we can take cholesterol to do some chemical modifications to go through the the testes to form testosterone or can go through the ovaries to form a stir dial or it can enter two different parts of the the adrenal cortex to form different hormones like cortisol or aldosterone so we can see this cholesterol is extremely important so this cholesterol is another type of lipid because any compound that's hydrophobic is a lipid by definition so this is kind of like the third category of lipids and again so that's how you buy synthesized cholesterol and these are some of the chemical pathways that cholesterol enters into and it's it's why cholesterol so important because it's used to form vitamins and hormones and is used to emulsify and absorb fat