Glycosaminoglycans Overview
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Glycosaminoglycans Overview

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Questions and Answers

What is the primary structural function of glycosaminoglycans (GAGs) in tissues?

  • They accelerate metabolic processes within cells.
  • They store energy as glycogen in tissues.
  • They facilitate neurotransmission between nerve cells.
  • They encapsulate and provide internal structure to organs. (correct)

    • Which of the following statements about glycosaminoglycans is true?

  • GAGs are intensely hydrophilic and act as polyanions. (correct)
  • GAGs can be classified into specialized types such as blood and adipose tissue.
  • GAGs are primarily found in the extracellular matrix of muscle tissue.
  • All GAGs are composed of the same repeating disaccharide units.

    • Which glycosaminoglycan is noted for being among the largest and most ubiquitous?

  • Keratan sulfate
  • Hyaluronic acid
  • Chondroitin sulfate
  • Heparan sulfate (correct)

    • What components make up the repeating disaccharide units in glycosaminoglycans?

    <p>Uronic acid and hexosamine</p> Signup and view all the answers

    What role do glycosaminoglycans play in response to increased tissue fluid?

    <p>They bind cations and retain water, leading to edema.</p> Signup and view all the answers

    Which property is true of fibronectin?

    <p>It plays a role in cell adhesion and migration.</p> Signup and view all the answers

    What is the primary function of laminin in epithelial tissue?

    <p>To facilitate the adhesion of epithelial cells to the basal lamina.</p> Signup and view all the answers

    Which of the following types of collagen is involved in connecting fibrillar collagens?

    <p>Collagen Type VII</p> Signup and view all the answers

    How are the subunits of fibronectin characterized?

    <p>Dimeric and aggregate to form fibrils.</p> Signup and view all the answers

    Which collagen type is most abundant and widely distributed in the body?

    <p>Type I</p> Signup and view all the answers

    Where is laminin primarily detected?

    <p>In the basal laminae of all epithelia.</p> Signup and view all the answers

    What are integrins primarily responsible for?

    <p>Acting as matrix receptors for specific sequences.</p> Signup and view all the answers

    What is the molecular weight range for fibronectin?

    <p>235 - 270 kDa</p> Signup and view all the answers

    What is the primary type of cell found in areolar tissue?

    <p>Fibroblasts</p> Signup and view all the answers

    Which characteristic distinguishes dense connective tissue from loose connective tissue?

    <p>Predominance of collagen fibers</p> Signup and view all the answers

    What is the primary function of macrophages in connective tissue?

    <p>Engulf and digest particles</p> Signup and view all the answers

    In which type of dense connective tissue are fibers arranged without a definite orientation?

    <p>Dense irregular connective tissue</p> Signup and view all the answers

    Where do macrophages primarily derive from?

    <p>Monocytes</p> Signup and view all the answers

    What component is NOT typically abundant in loose connective tissue?

    <p>Adipocytes</p> Signup and view all the answers

    What is the overall flexibility of dense connective tissue compared to loose connective tissue?

    <p>Less flexible</p> Signup and view all the answers

    Which of the following statements accurately describes the composition of areolar tissue?

    <p>An equal amount of fibers, ground substances, and cells</p> Signup and view all the answers

    What initiates the hydroxylation process in collagen synthesis?

    <p>The peptide chain reaching a certain length while still bound to ribosomes</p> Signup and view all the answers

    Which enzymes are specifically involved in the hydroxylation of collagen?

    <p>Peptidyl proline hydroxylase and peptidyl lysine hydroxylase</p> Signup and view all the answers

    What role do registration peptides play in procollagen synthesis?

    <p>They ensure proper positioning of alpha chains and prevent premature assembly</p> Signup and view all the answers

    What characterizes the diameter of collagen fibrils?

    <p>Their diameter varies between 20 to 90 nm</p> Signup and view all the answers

    What is a key feature of the striations found in collagen fibrils?

    <p>They have a periodicity of 64 nm due to overlapping subunit arrangements</p> Signup and view all the answers

    What reinforces the structure of collagen fibrils?

    <p>Covalent cross-links catalyzed by lysyl oxidase</p> Signup and view all the answers

    What is the significance of glycosylation in collagen synthesis?

    <p>It affects the amount of carbohydrate linked to hydroxylysine</p> Signup and view all the answers

    What is the primary structural unit from which collagen fibrils are formed?

    <p>Tropocollagen</p> Signup and view all the answers

    What is the main function of procollagen peptidases in collagen synthesis?

    <p>To remove registration peptides from procollagen</p> Signup and view all the answers

    Which types of collagen are classified as interstitial collagens?

    <p>I, II, and III</p> Signup and view all the answers

    Which type of collagen does not form fibrils or fibers?

    <p>Type IV</p> Signup and view all the answers

    What distinguishes type I collagen fibers from type II collagen fibrils?

    <p>Type I fibers form as bundles, while type II do not assemble into fibers</p> Signup and view all the answers

    What is the role of lysyl oxidases in collagen synthesis?

    <p>To catalyze the formation of covalent crosslinks in fibrillar structures</p> Signup and view all the answers

    Which statement correctly describes reticular fibers?

    <p>Stain black with silver salts and are not visible in standard preparations</p> Signup and view all the answers

    What is a distinguishing feature of type III collagen compared to type I collagen?

    <p>Type III collagen contains a higher percentage of hexoses than type I</p> Signup and view all the answers

    Why do light bands in collagen structure stain less than dark bands?

    <p>Light bands contain fewer chemical groups that react to stains</p> Signup and view all the answers

    Study Notes

    Glycosaminoglycans (GAGs) Overview

    • Also known as mucopolysaccharides, GAGs are linear polysaccharides made of repeating disaccharide units.
    • Composed of uronic acid (glucuronic or iduronic acid) and hexosamine (glucosamine or galactosamine).
    • Heparan sulfate is the largest and most ubiquitous GAG, with molecular weights of hundreds to thousands of kDa.
    • GAGs are intensely hydrophilic, leading to significant hydration and binding of cations like sodium.

    Functions of GAGs

    • Structural Role:
      • Provide internal structure to organs, enclosing and supporting tissues such as tendons, ligaments, and specialized types like bone and cartilage.
    • Defense Role:
      • Play a critical role in the body's defense mechanisms, contributing to tissue fluid dynamics and edema.

    Fibronectin and Collagen Types

    • Fibronectin:
      • Dimeric glycoprotein (molecular weight 235-270 kDa) synthesized by fibroblasts and epithelial cells.
      • Contains binding sites for cells, collagen, and GAGs, assisting in cell adhesion and migration.
    • Collagen Types:
      • Type I: Most abundant collagen, forming large eosinophilic bundles.
      • Type IV: Major structural protein of the basal lamina in all epithelia.
      • Type VII: Short collagens linking fibrillar collagens to one another, forming anchoring fibrils in basement membranes.

    Collagen Synthesis

    • Commences with alpha chain assembly on polyribosomes in the rough endoplasmic reticulum (RER).
    • Registration peptides ensure proper assembly and solubility of procollagen.
    • Enzymes such as peptidyl proline hydroxylase and peptidyl lysine hydroxylase catalyze hydroxylation, while glycosylation of hydroxylysine varies across collagen types.
    • Procollagen is converted to tropocollagen by removing registration peptides, followed by spontaneous fibril aggregation and reinforcement through lysyl oxidase-catalyzed crosslinks.

    Reticular Fibers

    • Extremely thin fibers (0.5 to 2 µm) forming extensive networks in specific organs.
    • Invisible in H&E preparations; require silver salts for visualization due to their high glycoprotein content.
    • Main composition consists of type III collagen.

    Connective Tissue Types

    • Loose Connective Tissue:
      • Abundant areolar tissue supporting epithelial tissues with a mix of fibers, ground substances, and predominant cells like fibroblasts and macrophages.
    • Dense Connective Tissue:
      • Characterized by stronger collagen fibers; may be dense irregular (no definite orientation) or dense regular (organized orientation).
      • Contains fewer cells compared to loose connective tissue, though fibroblasts remain the most common.

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    Description

    Explore the structure and function of glycosaminoglycans (GAGs), also known as mucopolysaccharides. This quiz covers their similarities to blood plasma, composition in tissue fluid, and importance in biology. Test your knowledge on these linear polysaccharides and their repeating disaccharide units.

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