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Current time:0:00Total duration:10:11

Video transcript

all right so in a previous video I introduced the class of biological molecules called lipids so lipids lipids and I broke lipids down into two main categories we have hydrolyzable lipids hydrolyzable hydrolyzable and then not hydrolyzable and essentially what this means I mean we've kind of talked about this is these lipids can be broken down into into smaller sections and these these lipids these non-hydrolyzable or non-hydrolyzable excuse me lipids cannot be broken down into smaller sections and in this we fit probably the most abundant lipid triglycerol triglycerol and if you remember triglycerol has the main function and in our bodies at least of energy storage so we break down triglycerol because it's a hydrolyzable lipids to get energy and I want to continue talking about these hydrolyzable lipids but but the other ones that I think are are important instead of having kind of a predominant energy storage function they have a structural function in our in ourselves and kind of in the biological role so a structural function so the first one I want to talk about our phospholipids so phospho phospho lipids phospholipids and phospholipids they're hydrolyzable lipids that contain a phosphorus atom so this phosphorus atom usually comes in a form of a phosphodiester bond and i I have no expectation of you to know what a phosphodiester bond is because i don't think we talked about it so we start with phosphoric acid which is h3po4 that's phosphoric acid and it has a kind of has a structure like this we've got phosphorus double bonded to oxygen and then bonded three other times to Oh H group so we have four oxygens in total and three hydrogen's and a phosphorus atom and that might look a little bit goofy if you're paying attention because this phosphorus is bonded five times but remember that phosphorus is a third row element unlike carbon so it can bond more than more than four times it has it's capable of sharing more than eight valence electrons so we've got phosphoric acid right here and if we take these two side o H groups and replace them with Al our group so let me kind of redraw the base structure here still have it double bonded to an oxygen but if we replace those sides with O our groups say for example in a dehydration reaction this becomes a phosphodiester phosphodiester and it's an ester because this phosphorus is double bonded to an oxygen and an O R group and it's a digester because it happens twice so this is a phospho diester and this is the form that phosphorus is going to come into play for our lipid so if we start with try glycerol which is kind of that that basic hydrolyzable lipids and I guess I I better go ahead and draw out triglycerol here so this is try glycerol and if we replace this lower fatty acid chain remember all of these are fatty acids if we replace that with a phosphodiester it's going to look like this so this would be one of the of our groups this whole rest of the molecule would be the other AR group and I guess in our bodies and not to confuse you too much but but phosphodiester is at a pH in our body of around 7.4 this hydrogen right here is actually usually deprotonated so usually carries a negative charge on this oxygen so we wouldn't have an H right here instead we'd have a negative charge so this right here is a phospholipid and one of the one of the cool things about phospholipids is unlike tri glycerols now we have a specifically polar section so this right here is Pole and then we have a nonpolar section to this molecule so this is all still nonpolar and that the purple part is polar principally because of this kind of big negative charge and just this the polar nature of this phosphodiester but that allows it to play a pretty pretty cool role in cell membranes so you've probably heard of a phospholipid bilayer and what happens is you have a phosphodiester head so kind of a phosphodiester head here and then you have two kind of fatty acid tails coming off and this is polar this purple part is polar and the orange part would be nonpolar and you get a whole bunch of these and they kind of line up together the polar heads kind of line up and the nonpolar tails kind of line up and those nonpolar tails become attracted to another set of nonpolar tails so nonpolar tails and at another polar head right here and this forms a two layer membrane to ourselves so so this is kind of the thing that separates the inside contents of our cell from the outside contents and this whole middle section right here is not attracted to water because of this kind of nonpolar lipid characteristic and it keeps water over here and water over here but separates these two fluid compartments so that's a pretty neat function a structural function of the phospholipid and I don't think you can really talk about phospholipid without stopping at least briefly to mention sping go lipids there another non Hydra lot or excuse me hydrolyzable lipids so sphingolipid sphingolipid and you need to talk about sphingolipids because there are another lipid that incorporate this phosphodiester unit but instead of having it kind of on a base but try glycerol it's going to be on the base of the amino alcohol sphingosine so let me kind of draw in sphingosine and so sphingosine is an amino alcohol it's got these Oh H groups but it's also got a lot of lipid characteristics because it's really hot I'm molecular weight alcohol this is a lot of carbon here 15 carbons on this kind of tail it would it would extend out like that if I kind of drew them all out but if we replace this Oh H group with a phosphodiester just like we did with our triglycerol so can I replace it it also develops a a structural function within cell membranes but mostly within nerve cells and I'll show you why so we've got a nerve cell here with a long axon and nerves are surrounded by the insulation of myelin so we've got myelin right here and the properties of of myelin which allowed to insulate this nerve axon right here are really predominantly due to the sphingolipid concentration in myelin so sphingolipids kind of have a similar structural function within cell membranes but mostly within nerve cells and then I guess the last hydrolyzable lipids that I really want to talk about our wax is so waxes waxes and again I'll kind of do this briefly but waxes are also esters and they're made of a high molecular weight alcohol so along again a long carbon chain alcohol that might look like this with an R group but it'd be really long so it kind of look like this and then they've got a fatty acid so a fatty acid again really high molecular weight and if you form an ester out of these two molecules you end up with a product that looks a little something like this so a long-chain double bonded to an oxygen with an O R group right here this would be the ester and so you've got an ester right here but it's kind of a unique ester in the sense that it's got two really long carbon chains making it two kind of nonpolar sections here and these two nonpolar sections make the molecules very hydrophobic waxes are very hydrophobic and so we see waxes in nature often forming a real barrier against water and this happens in leaves we put waxes on our cars to protect the surface of our cars from rain and from kind of the humidity but waxes are another type of hydrolyzable lipids and their hydrolyzable again I just kind of want to beat this point home because I've got this ester group right here at carbon double bonded to oxygen with an O R group that can be hydrolyzed you can do an ester hydrolysis reaction so that's with waxes same thing with sphingolipids they've got this sorry let me make sure you know that that's an oxygen they've got this ester group right here that you can break down and you can do the same thing if I go up with phospholipids again we have this o this kind of this ester bond right here that we can hydrolyze and we could do it with with these bonds as well just like we could with try glycerol so all of these again are lipids that can be broken down into smaller units through hydrolysis reactions