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Phospholipid structure

Video transcript

in this video we're going to actually explore in detail the structure of phospholipids in our cell membrane now just to briefly remind us our phospholipid is often drawn like this it has that polar phosphate head group and it has two fatty acid chains and all of this is held together by glycerol backbone but what does that really mean what does this picture actually look like down to a molecule well let's talk about the first one the fatty acid and just to remind us are actually two fatty acids times two you can see that there are two tails hanging down here so if fatty acid is basically a carboxylic acid attached to a very long carbon chain and so our carboxylic acid is like this as a double bonded oh and an hydroxyl group and it has that really long carbon chain which we're just going to call an R group the next one is our glycerol backbone and glycerol is a pretty basic structure it looks like this it has three carbons attached to three hydroxyl groups three alcohol groups and there's only one glycerol in each phospholipid the last one is our phosphate group that big polar head group that we talked about and just like you would think there's a phosphorus in a phosphate group and there are four oxygens attached to it now what does this actually look like all put together just for the sake of time I pre drawn a picture of all of this put together and it looks like this so you can see that we have our two fatty acid chains attached through an ester bond with our glycerol attached through another ester bond with our phosphate group now you'll notice that one of the negative oxygens is missing and it's been replaced with a hydroxyl group an alcohol group and that's what this is in the orange well that's because in our cell a phospholipid actually looks like this the negative oxygen actually picks up a hydrogen and becomes an alcohol group now a phospholipid molecule that looks like this is actually pretty rare in our cell membrane and the reason why is because phospholipids can occur and the reason why is because this molecule could actually bond with several different molecules giving a really diverse set of phospholipids and again for the sake of time I pre drawn these molecules and unless you're a researcher who really really loves the cell membrane you probably won't need to know this by heart because these structures get a little complicated but it's still a good idea to get acquainted to what they kind of look like so there's serine choline ethanolamine inositol and glycerol and you notice that I've also drawn these particular special hydroxyl groups in orange and the reason why is because these hydroxyl groups in orange from serine choline and so on can actually bond to our phosphate group through what we call a phospho ester bond now what will this actually look like in a real molecule what would it look like if serine actually bonded with this phospholipid well we're going to transition briefly into another slide just because I'm running out of space and I notice that there are five different phospholipids that I can actually occur there's phosphatidyl serine phosphatidylcholine so title at Faneuil mean phosphatidyl ethanolamine phosphatidyl in phosphatidyl inositol and dai phosphatidyl glyceryl also known as cardiolipin and you'll notice that in this last one there are actually two phosphatidyl groups that actually bond to a middle glyceryl and again unless you're someone who really researches is cell membrane you probably don't need to know these structures by heart but what we do need to know is that the phospholipids in our cell membrane are actually very very diverse and there are several different forms that it can take so if we were to take a look in detail at the phospholipids that make up our cell membrane we would actually find all of these scattered throughout the membrane now we're just going to go back to our original picture just remind us this is again our non-polar side and this side in the yellow is polar and so if we were to match up our general picture of a phospholipid to the picture that we've drawn here it would actually look like this this is our polar head group and we have two fatty acids here and again you'll notice that the glycerol group isn't really drawn in because that's what holds everything together then just to wrap up we need to talk about one brief thing so we have our phospholipids like this now this ro so-called R group is made up of a really long chain of carbons now in many cases these carbons can actually form double bonds with each other like a lot of different carbons do and remember that double bonds occur in the form of cysts and occur in the form of trans so a cyst bond in chemistry is when we have a double bonded carbon and we have the carbons on each side being on the same side while in a trans bond our carbons are on opposite sides and again these are hydrogen's and if we were to zoom out of this detailed molecule in the case of hands our fatty acid would just be pretty straight like that but in the case of sis we can actually create a kink because this Bend from our sis but actually gives it a king and this actually has a lot of significance when we talk about the fluidity of a cell membrane so in summary our phospholipids are made up of three major things fatty acids glycerol and phosphate and these three things actually look like this if we were to draw out a detailed molecule and not only so but there's an O H group on this polar phosphate group that actually can bond with several different types of molecules producing a really really diverse set of phospholipids that make up our cell membrane