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Structure of Proteins – Protein Movement and Cell Signaling

by Kevin Ahern, PhD
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    00:01 With the exception of encoding genetic information, proteins are either involved in, or perform essentially every important function of cells. In this lecture I’ll talk about protein functions as they relate to structure, communication and signaling, and movement. With proteins, there are very important considerations that we have with respect to their overall structure.

    00:25 Proteins are very important polymers of amino acids as we know, and one of the very interesting features of them is their flexibility. Flexibility allows proteins to be able to perform things like catalysis, amazingly efficiently, and other processes that allow them to adapt as we shall see.

    00:42 The geometry of proteins is important, and this is particularly important as we consider the geometry of the individual amino acids comprising proteins. Proteins can be either polar or nonpolar for the most part, and charged. Now these different polarities or charges as are considered help to determine where a protein is placed within a cell. And last, proteins can be a of a variety of forms, they can be fibrous, meaning that they have a fairly regular repeating fiber type structure. They can be globular, which indicates a folding that happens to make a protein have its final structure, and last, proteins can be involved in membranes as either fibers or as globular proteins.

    01:29 Now I’ll start talking here about the fibrous proteins. Fibrous proteins are very important in terms of things on our body. For example, the keratin proteins are proteins that comprise our hair and our nails. These fibrous proteins that I’ll talk about are very notable for being sturdy durable, and this we know our nails and talons that are on birds for example, are very, very tough materials. Collagen is a fibrous protein that is essentially the glue that holds us together. It makes up cartilage, and connective tissues. Fibroin is the protein that makes up silk, and it too is very durable. Other fibrous proteins include elastin or fibrillin, which are involved in our connective tissues, and lamin which is involved in making structure for the nuclear envelope. Now the other proteins that make fibers actually aren't what we classify as fibrous proteins. They are in fact globular proteins that polymerize to make fibers. These include actin, which is a globular protein that is involved in making up the cytoskeleton. Another is tubulin that makes little Internet highways within our cells that proteins can travel along. These are also globular proteins, and these also go through a self-assembly process.

    02:50 Now, fibrous proteins that haven't inherent fibrous nature built into them are proteins that have mostly secondary structure, but virtually no tertiary structure. This would include the keratins; this would include things like collagen for example. If we analyze their sequence of amino acids that are there, we discover that they are very much sequence repeats. Looking at the fibrin repeat structure for example at the top right, we can see that the repeated structure contains glycine, serine, glycine, alanine, glycine, alanine, an abundance of glycine. Similarly, if we look at the partial collagen sequence below, we see again an abundance of glycine and in addition we see the abundance of proline, and a modified amino acid called hydroxyproline. So glycine is present in abundance and probably for a very good reason, because glycine is flexible. The hydroxyproline in collagen is notable because it's a modified amino acid, meaning that the amino acid proline is initially put into the protein, but then the proline has a hydroxyl group attached to it later. Now that seems to be a relatively minor consideration in terms of the overall structure of a protein, but for collagen it turns out to be very critical. The hydroxylation of proline residues inside of collagen helps them to connect with each other and when they connect with each other, it gives the resulting collagen great strength. So our collagen is able to hold things together because of that.

    04:24 Now, interestingly the reaction that puts the hydroxy group onto proline requires vitamin C. And it has been known for many years that deficiency of vitamin C results in a disease known as scurvy, and scurvy is essentially occurring because of collagen. People literally are falling apart when they are deficient in vitamin C.


    About the Lecture

    The lecture Structure of Proteins – Protein Movement and Cell Signaling by Kevin Ahern, PhD is from the course Biochemistry: Basics.


    Included Quiz Questions

    1. They commonly contain abundant glycine
    2. They derive most of their properties from their catalytic nature
    3. The have extensive tertiary structure
    4. They have almost random sequences
    1. Elastin — cell membrane
    2. Keratin — hair
    3. Collagen — tissue glue
    4. Fibroin — silk
    5. Lamin — nuclear envelope
    1. The stabilization of the structure of collagen
    2. The transportation of collagen from the nucleus to the cytoplasm
    3. The assembly of ribosomes on the mRNA
    4. The transportation of collagen from ER to Golgi bodies
    5. The catalytic reaction carried out by the collagen in the lysosomes

    Author of lecture Structure of Proteins – Protein Movement and Cell Signaling

     Kevin Ahern, PhD

    Kevin Ahern, PhD


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    Thanks
    By Gerardo C. on 30. April 2018 for Structure of Proteins – Protein Movement and Cell Signaling

    Excellent information and explanation, it's helping me a lot. Congrats, lecturio!