Glycerolipids and Glycerophospholipids – Lipids

by Kevin Ahern, PhD

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    00:02 Now fats of course, are fatty acids that are linked via ester bonds to a glycerol backbone.

    00:09 We describe these molecules as triacylglycerols. 'Tri' meaning three, 'acyl' meaning fatty acid, and glycerol being that the molecules that they are linked to. Now there are two different classes of compounds but they have the same basic structure. Fats are triacylglycerols that are solid at room temperature. Oils by contrast, are triacylglycerols that are liquid at room temperature. Now the glycerol backbone is shown here in red and that is the only portion of the fat molecule that has any polarity associated with that at all. Fats are overall very, very nonpolar and this has some very important implications when fats have to move in the body. The three fatty acids linked to glycerol are joined by ester bonds and these ester bonds help to hold the molecule together and must be cleaved in order to release the fatty acids so that it can be metabolized by cells.

    01:09 This shows in another way the same structure that you saw in the last screen but now using the stick configuration. You can see here that this fat contains at what we call position one, that is the top position on the glycerol molecule, a saturated fatty acid called palmitic acid. Palmitic acid is one of the most common saturated fatty acids and when we examine fats we typically see that position one has a saturated fatty acid contained on it.

    01:37 Position two here has oleic acid and you can notice that it's an unsaturated fatty acid and that's also a very common finding at position number two. In this case position number three has linolenic acid associated with it and position three varies a little bit more in terms of the composition of the fatty acids that are contained within it. This could be described as a polyunsaturated fat because it contains a polyunsaturated fatty acid. The more unsaturated fatty acids are contained in a fat, the more likely it will be liquid at room temperature and will no longer be described as a fat, but rather would be described as an oil.

    02:14 Now I'd like to turn our attention to a group of molecules that are related to the fats that we've seen before. These are the glycerolphospholipids or the phosphoglycerides. At first glance they may look quite different from the fats but in fact the related. We can see for example in the middle of this molecule, the glycerol backbone that comprises the glycerolphospholipids, the same glycerol backbone that we saw in the fats. On the top two carbons of the glycerol backbone, we can see attached to it, fatty acids, just like we saw in the fat. The difference on this figure is in the in the very bottom, in the bottom of this we can see in carbon number three, that there's a phosphate. That phosphate was not present in the fats that we saw before. This gives rise to we call the phosphatidyl backbone of the glycerolphospholipids.

    03:00 The phosphatidyl backbone is a molecule that is attached to another molecule, the other molecule there is labelled on the lower right as R. Now that R can be occupied by a variety of other compounds. These other compounds include for example, ethanolamine, serine, glycerol, choline or inositol. These are all small molecules and these are all molecules that are either charged or polar and glycerolphospholipids are notable for being very, very polar at one end as we shall see. Now this shows for example a molecule we call phosphatidylcholine.

    03:37 In this case we've linked choline to the phosphate of the earlier phosphatidyl compound. This is phosphatidylethanolamine. You can see the hydrophilic head that's here. Now hydrophilic of course referring to this portion of the molecule likes to interact with water and in this case it happens because, first of all, the phosphate is negatively charged and also the NH3 is positively charged. The other portion of the molecule has a long hydrophobic tail of the fatty acids, so this is a very amphiphilic compound. Again amphiphilic meaning it has character of both being polar and nonpolar.

    04:16 Now glycerolphospholipids are notable and important because they're one of the major components making up the lipid bilayer that you can see here. The lipid bilayer is arranged such that it has on either the portion facing out of the cell or the portion facing in the cell, a polar component of the glycerolphospholipid that we can see. So you can see from the enlargement for example, that the very top of this top layer of the bilayer has a hydrophilic head, something like what we saw in the phosphatidyl compound. That could be duplicated on the bottom blue balls seen in the lipid bilayer there. Within the middle of the lipid bilayer, that's where all the fatty acids are residing and that's where it will be very, very nonpolar.

    About the Lecture

    The lecture Glycerolipids and Glycerophospholipids – Lipids by Kevin Ahern, PhD is from the course Biochemistry: Basics.

    Included Quiz Questions

    1. They are liquid at room temperature
    2. They are sphingolipids that are liquid at room temperature
    3. They have fewer unsaturated fatty acids than fats
    4. They are the same as fats except they contain sphingosine
    1. It contains glycerol and a phosphate
    2. It contains three fatty acids and glycerol
    3. It is a sphingolipid
    4. It does not contain fatty acids
    1. It is a component of the lipid bilayer
    2. It has a polar component that is negatively charged
    3. It is a sphingolipid
    4. It contains at least one sugar molecule

    Author of lecture Glycerolipids and Glycerophospholipids – Lipids

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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    Once again, simple and perfect explanation of Lipids.
    By Suhas M. on 16. August 2018 for Glycerolipids and Glycerophospholipids – Lipids

    I have followed Dr Ahern through all the basics of biochem lectures and he has never failed to deliver.