Proteoglycans – Complex Carbohydrates

by Kevin Ahern, PhD

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    00:01 to die.

    00:02 Now another related set of molecules are the proteoglycans. The proteoglycans sound very much like the peptidoglycans, but in this case we have not short peptides that are attached to the glycan units, but now longer proteins. The glycans they are linked to are the glycosaminoglycans that we had to start. Now these glycosaminoglycans bind cations and water. Cations of course being positively charged molecules. Glycosaminoglycans are long polymers of negatively charged residues and so it's not surprising that they will interact as we've seen before. These proteoglycans place an important function for cells, including regulating the movement of molecules through the extracellular matrix. These proteoglycans can project into that extracellular matrix and affect things going through them. These proteoglycans may also have an impact on protein stability and molecules that are involved in signaling and as we've seen before with the synovial fluid and hyaluronic acid, they can form lubricants because of the nature of the chemistry that the effect of the water that they are in.

    01:11 Now in this slide I've drawn the structure of an interesting proteoglycan to show you a little bit about the arrangement of it. In the center part of the slide, you see hyaluronic acid, the polymer I described just just a minute ago. Attached to the hyaluronic acid are orange colored proteins that are linked to the hyaluronic acid and that project outwards.

    01:33 The proteins themselves are linked to individual glycans as you can see, some being chondroitin sulfate, some being keratan sulfate. Now as I've mentioned, the chemistry of these is interesting, and each of the individual black fibers that you see on the screen is polyanionic, meaning it has hundreds or thousands of negative charges. These polyanionic components alter the chemistry of the molecule as I have described, but one of the interesting things about these is the fact that all of the individual units are being held fairly close together by that protein. That protein is forcing those negative charges to stay in close proximity. The negative charges don't want to stay in close proximity and so they stretch and move as far away as they can. When you examine the structure of these molecules under a microscope, what you discover is a very feathery structure arising from the fact that each fiber is trying to get as far away from each of the other fibers as it can.

    02:34 In this lecture, I hope I have communicated to you the importance and the complexity of carbohydrates. We have seen that carbohydrates vary from the very simple sugar to the most complex of the proteoglycans as we can see here, giving cells everything that they need, from energy, to structure to altered chemistry.

    About the Lecture

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

    Included Quiz Questions

    1. They provide immunity since they act as immunoglobins.
    2. They bind to cations and water molecules.
    3. They affect protein stability.
    4. They regulate the movement of molecules through the extracellular matrix.
    5. They play an important role in the body as joint lubricants.

    Author of lecture Proteoglycans – Complex Carbohydrates

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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