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Lipid Links – Complex Carbohydrates

by Kevin Ahern, PhD
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    00:00 In addition to bonds between individual carbohydrates, carbohydrates can also form bonds to other biomolecules. On the screen you see a glycolipid, meaning a sugar that has been attached to a lipid and you can see the lipid designated beneath the sugar as shown here. Now, one example of a glycolipid would be a molecule that looks like this; on the top we have glucose, drawn in the axial equatorial form as you can see and that glucose is linked in the alpha position to a molecule that is a diacylglycerol. Diacylglycerol is related to fat. Normally if this were fat, this would have a glycerol backbone which would be the three carbons that you see in the green and each carbon would be attached to a fatty acid. In this case we have instead of a triacylglycerol which would be a fat, we have diacylglycerol linked to a glucose.

    00:57 Such a molecule could exist for example, in the membrane of a cell. Glycoglycerol lipids are exist, but they are not very common. A much more common glycolipid is that of the sphingolipid as can be seen on this slide here. Now sphingolipids are related in structure to glycoglycerol lipids but they are not the same, the glycoglycerol lipid had a glycerol backbone which consisted of three carbons. The sphingolipids have a backbone that's a little bit different.

    01:27 You can see on the right side of the molecule, part of this backbone, that includes the N, the carbon that's bonded above it and then the CH2 which is bonded to the glucose at the very top. This backbone is common to sphingolipids. In contrast to the glycero lipid that we saw before, the diacylglycerol, these sphingolipids have only one fatty acid and they have another molecule attached to that that looks like a fatty acid known as sphingosine. Now, in the third position at the very top is glucose, when we combine a glucose to a sphingolipid, we create something called a cerebroside. Cerebrosides are very common components of nerve tissue, they were discovered for example in the brain. Whenever a simple sugar like glucose in this case, is attached, a cerebroside is formed. However, if we attach a more complex sugar to the very top, what we discover is we make a ganglioside. This figure shows a sphingolipid that is a ganglioside. The complex carbohydrate that's linked to the top is pretty hairy to be sure, but the important thing is that gangliosides, like cerebrosides, very, very important components of brain tissue and nerve tissue.


    About the Lecture

    The lecture Lipid Links – Complex Carbohydrates by Kevin Ahern, PhD is from the course Biochemistry: Basics.


    Included Quiz Questions

    1. It is a sphingolipid containing a single sugar
    2. It contains glycerol
    3. It is a glycerolphospholipid containing a complex sugar
    4. It is a sphingolipid containing a complex sugar
    1. In the lipid bilayers of nerve cells
    2. In the cytoplasm of cells
    3. In the membranes of liver cells
    4. In LDLs

    Author of lecture Lipid Links – Complex Carbohydrates

     Kevin Ahern, PhD

    Kevin Ahern, PhD


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