Extracellular Matrix (ECM)
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Questions and Answers

What is the primary role of the extracellular matrix in animal tissues?

  • To produce energy for cellular activities
  • To actively regulate cell behavior and function (correct)
  • To exclusively provide physical support to tissues
  • To serve as a storage area for nutrients

    • Which of the following cells primarily secrete the macromolecules of the extracellular matrix in connective tissues?

  • Fibroblasts (correct)
  • Epithelial cells
  • Chondrocytes
  • Osteoblasts

    • How does the cytoskeleton inside a cell influence the extracellular matrix outside the cell?

  • It limits the variety of proteins produced
  • It determines the orientation of the matrix (correct)
  • It affects the secretion rate of the matrix
  • It controls the degradation of matrix components

    • Which structure is formed when the extracellular matrix becomes calcified?

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

    What are the cells called that form cartilage in specialized connective tissues?

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

    Which of the following describes a function of the extracellular matrix other than structural support?

    <p>Regulating the migration and proliferation of cells</p> Signup and view all the answers

    What is a key feature of the extracellular matrix's organization?

    <p>Its organization varies among different tissue types</p> Signup and view all the answers

    In addition to fibroblasts, which other cell type is specifically associated with bone formation?

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

    What is the primary structural characteristic of glycosaminoglycans (GAGs)?

    <p>Long, linear, highly charged polysaccharides</p> Signup and view all the answers

    Which type of collagen is primarily found in cartilage?

    <p>Type II collagen</p> Signup and view all the answers

    What role does fibronectin play in the extracellular matrix?

    <p>Guiding cell migration and adhesion</p> Signup and view all the answers

    What is the primary function of elastic fibers formed by elastin?

    <p>Granting stretchability and resilience</p> Signup and view all the answers

    Which protein comprises the major repeat domain in fibronectin?

    <p>Type III fibronectin repeat</p> Signup and view all the answers

    What is the distinguishing feature of fibrillar collagen?

    <p>Construction of long, rope-like structures</p> Signup and view all the answers

    What type of enzyme is a matrix metalloprotease?

    <p>Calcium-dependent protease</p> Signup and view all the answers

    Which of the following statements about hyaluronan is true?

    <p>Hyaluronan has a regular repeating sequence of disaccharides.</p> Signup and view all the answers

    What is the basic structure of a proteoglycan?

    <p>Core protein with multiple polysaccharide chains</p> Signup and view all the answers

    The basal lamina serves what primary purpose in tissues?

    <p>Anchoring cells to connective tissues</p> Signup and view all the answers

    What is necessary for fibronectin to assemble into fibrils?

    <p>Presence of integrins</p> Signup and view all the answers

    Which of the following statements is true about fibronectin and tension?

    <p>Tension exerts through integrins exposes cryptic binding sites in fibronectin.</p> Signup and view all the answers

    What is the thickness range of the basal lamina?

    <p>40–120 nm</p> Signup and view all the answers

    Which extracellular matrix component serves as a selective filter in the kidney glomerulus?

    <p>Basal lamina</p> Signup and view all the answers

    What role do integrins play in the assembly of fibronectin fibrils?

    <p>They link fibronectin outside the cell to the actin cytoskeleton inside.</p> Signup and view all the answers

    Which of the following components is commonly found in the basal lamina?

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

    How does the basal lamina influence cell behavior?

    <p>It promotes cell survival, proliferation, and differentiation.</p> Signup and view all the answers

    Where is fibronectin initially present during cell migration?

    <p>As small dotlike aggregates near the leading edge</p> Signup and view all the answers

    What characteristic of the basal lamina is essential for all multicellular animals?

    <p>It acts as a mechanical connection between cells and connective tissue.</p> Signup and view all the answers

    Which protein is indicated as forming the core protein of a proteoglycan found in the basal lamina?

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

    Why does fibronectin fibril formation not occur in the bloodstream?

    <p>Cells and mechanical tension are absent in blood.</p> Signup and view all the answers

    How does the basal lamina differ in its roles across various tissues?

    <p>The composition and roles vary depending on the tissue type.</p> Signup and view all the answers

    What happens to type III fibronectin repeats when tension is applied?

    <p>They unfold, exposing cryptic binding sites.</p> Signup and view all the answers

    What is the primary organizing protein of the basal lamina?

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

    Which of the following statements about laminin is correct?

    <p>Laminin can self-assemble into networks.</p> Signup and view all the answers

    What is a consequence of mice lacking the laminin γ1 chain?

    <p>They cannot make a basal lamina and die during embryogenesis.</p> Signup and view all the answers

    Which type of collagen is specifically mentioned as a crucial component of the basal lamina?

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

    Which protein is involved in anchoring the basal lamina to cells?

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

    What is the primary function of the basal lamina in tissue regeneration?

    <p>It provides a scaffold for regenerating cells.</p> Signup and view all the answers

    Which cells can pass through the basal lamina?

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

    What characteristic of type IV collagen allows it to form a flexible network in the basal lamina?

    <p>Rope-like superhelix with bends</p> Signup and view all the answers

    Which laminin isoform is predominantly found in skin?

    <p>Laminin-332</p> Signup and view all the answers

    How are laminins often categorized?

    <p>By their isoform and subunit combinations</p> Signup and view all the answers

    What disease is linked to defects in laminin-332?

    <p>Junctional epidermolysis bullosa</p> Signup and view all the answers

    What role do integrin family members play in the basal lamina?

    <p>Organizing assembly of the basal lamina</p> Signup and view all the answers

    Which of the following is NOT a function of the basal lamina?

    <p>Hosting metabolic activities</p> Signup and view all the answers

    Why is the basal lamina important for the epidermis?

    <p>It anchors the epidermis to the dermis.</p> Signup and view all the answers

    What process is used to fix and stain tissue while preventing GAG chains from collapsing?

    <p>Freeze substitution</p> Signup and view all the answers

    What are the core proteins of proteoglycans primarily stained as in electron micrographs?

    <p>Darkly stained.</p> Signup and view all the answers

    What is the main function of syndecans in fibroblasts?

    <p>Interacting with fibronectin and modulating integrin function.</p> Signup and view all the answers

    How are collagens primarily characterized?

    <p>As fibrous proteins with a triple-helical structure.</p> Signup and view all the answers

    What typically provides the structure of a collagen molecule?

    <p>Three polypeptide chains wound around each other.</p> Signup and view all the answers

    Which type of collagen is most abundant in skin and bone?

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

    What structural feature do fibril-associated collagens (types IX and XII) provide?

    <p>They link and stabilize collagen fibrils.</p> Signup and view all the answers

    What distinguishes type IV collagen from other types of collagen?

    <p>It is network-forming and primarily located in the basal lamina.</p> Signup and view all the answers

    What amino acid occupies every third position in a collagen α chain?

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

    How many distinct genes are there in the human genome that code for different collagen α chains?

    <p>42</p> Signup and view all the answers

    What is the typical diameter range of collagen fibrils?

    <p>10–300 nm</p> Signup and view all the answers

    What type of peptide influences cell growth and proliferation in relation to proteoglycans?

    <p>Soluble peptide growth factors</p> Signup and view all the answers

    How do types IX and XII collagens differ from types IV and VII collagens?

    <p>They are fibril-associated collagens.</p> Signup and view all the answers

    What role does glycosylphosphatidylinositol (GPI) play in proteoglycans?

    <p>It acts as an anchor for core proteins in plasma membranes.</p> Signup and view all the answers

    What arrangement of collagen fibrils is mainly found in tendons?

    <p>Parallel bundles</p> Signup and view all the answers

    Which property do fibril-associated collagens differ from fibrillar collagens?

    <p>They have nonhelical domains.</p> Signup and view all the answers

    How do connective-tissue cells influence the organization of collagen fibrils?

    <p>By guiding collagen fibril formation near the plasma membrane.</p> Signup and view all the answers

    What role does fibronectin play in collagen organization?

    <p>It helps guide collagen fibril organization.</p> Signup and view all the answers

    Which statement about elastic fibers is accurate?

    <p>They are interwoven with collagen fibrils.</p> Signup and view all the answers

    What is the primary component of elastic fibers?

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

    What feature allows elastin molecules to maintain their elastic properties?

    <p>Cross-links between lysines</p> Signup and view all the answers

    What ensures the organization of collagen fibrils in the extracellular matrix?

    <p>Secretion of various macromolecules alongside collagen</p> Signup and view all the answers

    What is the primary function of the type III repeats found in fibronectin?

    <p>Binding to integrins</p> Signup and view all the answers

    Which collagen type primarily binds to type II collagen in cartilage?

    <p>Type IX collagen</p> Signup and view all the answers

    How does fibronectin form its structure?

    <p>From two subunits joined by disulfide bonds at the C-termini</p> Signup and view all the answers

    What characteristic do the segments of elastin molecules possess?

    <p>Random-coil conformation</p> Signup and view all the answers

    What is the function of tropoelastin in the formation of elastic fibers?

    <p>It is the biosynthetic precursor of elastin.</p> Signup and view all the answers

    What is the significance of the Arg-Gly-Asp (RGD) sequence in fibronectin?

    <p>It is responsible for binding to integrins</p> Signup and view all the answers

    Which of the following statements correctly describes the splicing of fibronectin mRNA?

    <p>It can generate multiple isoforms by adding or removing exons.</p> Signup and view all the answers

    What condition enhances the extensibility of elastin compared to collagen?

    <p>Hydrophobic segments</p> Signup and view all the answers

    What is a primary difference in the structure between fibril-associated collagens and fibrillar collagens?

    <p>Fibril-associated collagens do not aggregate.</p> Signup and view all the answers

    What type of structure do tenascin and thrombospondin form?

    <p>Hexamers and trimers linked at the N-termini</p> Signup and view all the answers

    What happens to mutant mice that are unable to produce fibronectin?

    <p>They develop abnormal blood vessels.</p> Signup and view all the answers

    Which feature contributes to the structural diversity of matrix proteins?

    <p>Alternative splicing of RNA transcripts</p> Signup and view all the answers

    What is the main function of fibronectin in the extracellular matrix?

    <p>Promoting cell adhesion and migration</p> Signup and view all the answers

    Which domains in fibronectin are involved in binding to fibrin or collagen?

    <p>N-terminal repeats</p> Signup and view all the answers

    Which element is critical for the structural integrity of fibronectin dimers?

    <p>Disulfide bonds</p> Signup and view all the answers

    Which of the following proteins contain the RGD sequence for mediating cell-surface binding?

    <p>Several extracellular proteins including fibronectin</p> Signup and view all the answers

    How many type III repeats are typically found in each fibronectin subunit?

    <p>15</p> Signup and view all the answers

    Which sequence motif is crucial for tight binding to integrins?

    <p>A variety of other motifs in addition to RGD</p> Signup and view all the answers

    What role do the FN repeats at the N-terminus of fibronectin serve?

    <p>Binding fibrin or collagen</p> Signup and view all the answers

    What is the primary cellular role of integrins that bind to fibronectin?

    <p>Facilitating cell adhesion and signaling</p> Signup and view all the answers

    Which type of macromolecule is primarily responsible for forming a gel-like ground substance in connective tissue?

    <p>Glycosaminoglycans (GAGs)</p> Signup and view all the answers

    What type of sugar is consistently found in the repeating disaccharide units of glycosaminoglycans?

    <p>Amino sugar</p> Signup and view all the answers

    What property of glycosaminoglycans largely contributes to their ability to occupy a large amount of space within the extracellular matrix?

    <p>Their highly charged nature</p> Signup and view all the answers

    Which of the following groups of glycosaminoglycans is characterized by having a structure that includes uronic acid?

    <p>Chondroitin sulfate and hyaluronan</p> Signup and view all the answers

    Which type of matrix protein is known for providing strength and organization to the extracellular matrix?

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

    What is the major functional role of glycoproteins in the extracellular matrix?

    <p>To facilitate cell migration and differentiation</p> Signup and view all the answers

    Which GAG is known for its abundance during tissue repair and morphogenesis?

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

    What causes the swelling pressure or turgor that helps the matrix resist compressive forces?

    <p>High density of negative charges on GAGs</p> Signup and view all the answers

    Which GAG is distinguished by its extensive length, up to 25,000 disaccharide units?

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

    Which matrix component primarily contributes to the resilience of connective tissues?

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

    Which of the following best describes proteoglycans in the context of the extracellular matrix?

    <p>Proteins with covalently attached GAGs</p> Signup and view all the answers

    What role do cations, such as Na+, play in the extracellular matrix containing GAGs?

    <p>They attract water, creating osmotic effects.</p> Signup and view all the answers

    Which feature makes heparin the most densely charged biological molecule?

    <p>High sulfate content in disaccharides</p> Signup and view all the answers

    How many main groups of glycosaminoglycans are classified based on their sugars and linkages?

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

    What role do microfibrils play in relation to elastin in the extracellular matrix?

    <p>They serve as scaffolding for elastin deposition.</p> Signup and view all the answers

    How do fibroblasts interact with collagen in the extracellular matrix?

    <p>They pull on collagen to orient and compact it.</p> Signup and view all the answers

    What is the consequence of mutations in the elastin gene?

    <p>Narrowing of the aorta and excessive smooth muscle proliferation.</p> Signup and view all the answers

    Which protein is essential for the integrity of elastic fibers and binds to elastin?

    <p>Fibrillin.</p> Signup and view all the answers

    What effects can be caused by abnormal matrix density?

    <p>Certain fibrotic diseases and a risk factor for cancer.</p> Signup and view all the answers

    How does the behavior of fibroblasts relate to the extracellular matrix they produce?

    <p>They create a matrix that determines their own migration and proliferation.</p> Signup and view all the answers

    What is one of the primary functions of glycoproteins in the extracellular matrix?

    <p>Organizing the matrix and helping cells attach to it.</p> Signup and view all the answers

    What happens when fibroblasts tug on a collagen gel?

    <p>The gel contracts to a smaller volume.</p> Signup and view all the answers

    In which condition is the aorta prone to rupture due to structural weakness?

    <p>Marfan syndrome.</p> Signup and view all the answers

    What is a primary difference between the extracellular matrix in tendons and brain tissue?

    <p>Tendons have a dense and rigid matrix while brain tissue has a softer matrix.</p> Signup and view all the answers

    Which of the following statements is true regarding the production of collagen by fibroblasts?

    <p>Fibroblasts determine the orientation of the collagen fibrils they produce.</p> Signup and view all the answers

    What type of interaction do cells have with the extracellular matrix?

    <p>Both mechanical and chemical interactions.</p> Signup and view all the answers

    What role do proteoglycans play in the extracellular matrix?

    <p>They concentrate signal proteins and regulate their activity.</p> Signup and view all the answers

    How do fibroblast growth factors (FGFs) interact with proteoglycans?

    <p>Proteoglycans enhance FGF activity and facilitate receptor activation.</p> Signup and view all the answers

    Which glycoprotein contributes to cell movement and organization in developing tissues?

    <p>Fibronectin.</p> Signup and view all the answers

    What is the significance of the negative charges present in the extracellular matrix?

    <p>They facilitate the binding and function of signal molecules.</p> Signup and view all the answers

    What is a characteristic feature of the elastic fibers in the extracellular matrix?

    <p>They can extend and contract like a rubber band.</p> Signup and view all the answers

    What effect does the alignment of collagen fibers have on fibroblast behavior?

    <p>It facilitates the movement and orientation of fibroblasts.</p> Signup and view all the answers

    What function does type IV collagen serve in the basal lamina?

    <p>It assembles into a sheet-like mesh vital for the basal lamina structure.</p> Signup and view all the answers

    What is one of the primary roles of fibronectin in the extracellular matrix?

    <p>It promotes the activity of specific growth factors.</p> Signup and view all the answers

    How do glycoproteins contribute to cell signaling?

    <p>By binding directly to secreted signal proteins and receptors.</p> Signup and view all the answers

    In Drosophila, what is the consequence of a mutation in the Dally gene?

    <p>It greatly reduces Dpp activity and affects oocyte development.</p> Signup and view all the answers

    What defines the structure of glycosaminoglycan (GAG) chains?

    <p>They are covalently linked to protein to form proteoglycans.</p> Signup and view all the answers

    Which matrix components contribute to the tensile strength of the extracellular matrix?

    <p>Fibrillar collagens</p> Signup and view all the answers

    What role does the basal lamina serve in tissues?

    <p>It provides cellular support and influences migration and differentiation.</p> Signup and view all the answers

    Which of the following does NOT describe the function of the extracellular matrix?

    <p>It prevents all forms of cell interaction.</p> Signup and view all the answers

    What is a key characteristic of the elastin molecules in the extracellular matrix?

    <p>They allow stretching and recoiling of matrix fibers.</p> Signup and view all the answers

    What crucial role does the interaction of matrix components with cell-surface receptors play?

    <p>It generates signals that influence cell behavior.</p> Signup and view all the answers

    What is the primary effect of heparan sulfate chains in proteoglycans?

    <p>They bind and affect the activity of growth factors.</p> Signup and view all the answers

    What role does the basal lamina play in neuromuscular junction regeneration?

    <p>It facilitates the reconstruction of the synapse at the correct location.</p> Signup and view all the answers

    What is agrin's role in the junctional basal lamina?

    <p>It regulates the assembly of acetylcholine receptors and other proteins.</p> Signup and view all the answers

    What happens when a cell lacks the necessary enzymes to degrade the surrounding matrix?

    <p>The cell is inhibited from dividing and migrating.</p> Signup and view all the answers

    Why is matrix degradation important during tissue repair?

    <p>It allows for the rapid assembly of new tissue components.</p> Signup and view all the answers

    What are matrix metalloproteases primarily responsible for?

    <p>Degrading matrix proteins like collagen and laminin.</p> Signup and view all the answers

    How do proteases ensure that matrix degradation occurs at the correct location?

    <p>They are anchored to the cell surface and activated in situ.</p> Signup and view all the answers

    What can occur as a result of the proteolytic cleavage of type IV collagen?

    <p>Release of fragments that inhibit blood vessel formation.</p> Signup and view all the answers

    What happens to the basal lamina at the neuromuscular junction when a muscle cell is injured but not the nerve?

    <p>It directs the regenerating nerve to the original synaptic site.</p> Signup and view all the answers

    What is the primary function of serine proteases in matrix degradation?

    <p>They degrade matrix proteins, often alongside matrix metalloproteases.</p> Signup and view all the answers

    How do cell behaviors such as migration relate to matrix degradation?

    <p>Matrix degradation facilitates movements through the extracellular matrix.</p> Signup and view all the answers

    Why is localized matrix degradation significant during white blood cell migration?

    <p>It enables white blood cells to escape confinement by a basal lamina.</p> Signup and view all the answers

    What happens to muscle cells in some forms of muscular dystrophy?

    <p>They degenerate after a period of normal development.</p> Signup and view all the answers

    What is a consequence of the lack of protease regulation in the extracellular matrix?

    <p>Random degradation of the matrix.</p> Signup and view all the answers

    What unique characteristic does the synaptic region of the basal lamina possess?

    <p>It includes distinct isoforms of collagen and laminin.</p> Signup and view all the answers

    What is the primary role of the propeptides present in pro-α chains during collagen assembly?

    <p>To guide the intracellular formation of triple-stranded collagen molecules</p> Signup and view all the answers

    Which type of collagen is most abundant in the human body, accounting for 90% of body collagen?

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

    What deficiency causes defective pro-α chains and results in scurvy?

    <p>Vitamin C</p> Signup and view all the answers

    Which of the following collagens is associated with myopia and blindness?

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

    How are collagen fibrils structurally strengthened after their formation?

    <p>By covalent cross-links between lysine residues</p> Signup and view all the answers

    What is the function of lysyl oxidase in collagen structure?

    <p>To deaminate lysines and hydroxylysines</p> Signup and view all the answers

    Which type of collagen forms a sheet-like network in the basal lamina?

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

    What consequence does impaired cross-linking of collagen have on tissues?

    <p>Fragility of collagenous structures</p> Signup and view all the answers

    What type of collagen is primarily associated with fragile skin and blood vessels prone to rupture?

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

    What is the main type of collagen associated with anchoring fibrils beneath stratified squamous epithelia?

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

    Which one of the following statements about collagen types is true?

    <p>Type IV collagen forms a network in the basal lamina.</p> Signup and view all the answers

    What happens to collagen turnover in individuals with scurvy?

    <p>It stops completely.</p> Signup and view all the answers

    Which type of collagen has lateral associations with type I fibrils and is involved in skeletal and muscle abnormalities?

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

    What condition arises from a deficiency of vitamin C affecting collagen synthesis?

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

    What distinguishes hyaluronan from typical glycosaminoglycans (GAGs)?

    <p>All its disaccharide units are identical.</p> Signup and view all the answers

    How is hyaluronan synthesized and released by cells?

    <p>It is directly spun out from the cell surface by an enzyme complex.</p> Signup and view all the answers

    What role does hyaluronan play during embryonic development?

    <p>It serves as a space filler to influence structural changes.</p> Signup and view all the answers

    What happens to excess hyaluronan after cell migration has concluded?

    <p>It is degraded by hyaluronidase.</p> Signup and view all the answers

    What is a key characteristic that differentiates proteoglycans from glycoproteins?

    <p>Proteoglycans consist mostly of long, unbranched GAG chains.</p> Signup and view all the answers

    What is the main function of decorin within the extracellular matrix?

    <p>To regulate fibril assembly and diameter.</p> Signup and view all the answers

    Which of the following describes the properties of aggrecan?

    <p>It can have a mass of about 3 × 10^6 daltons with more than 100 GAG chains.</p> Signup and view all the answers

    How does the structural makeup of proteoglycans contribute to their function in the extracellular matrix?

    <p>Due to their potential for limitless heterogeneity.</p> Signup and view all the answers

    What role does hyaluronan play in wound healing?

    <p>It serves as a lubricant in joint fluid.</p> Signup and view all the answers

    Which statement about the modification of GAGs in proteoglycans is accurate?

    <p>GAGs undergo a series of coordinated modifications while in the Golgi apparatus.</p> Signup and view all the answers

    Which of the following is NOT a feature of glycosaminoglycans (GAGs)?

    <p>They are generally found in the nucleus.</p> Signup and view all the answers

    What enzymatic activity is responsible for linking GAG chains to their core proteins?

    <p>Glycosyl transferases.</p> Signup and view all the answers

    Which aspect of proteoglycans facilitates their interaction with other matrix components?

    <p>Presence of variable GAG chains.</p> Signup and view all the answers

    What function does the linkage tetrasaccharide serve in the synthesis of proteoglycans?

    <p>It serves as a primer for polysaccharide growth.</p> Signup and view all the answers

    Study Notes

    Extracellular Matrix of Animals

    • Tissues are composed of cells and a complex extracellular matrix (ECM)
    • ECM is a network of macromolecules secreted by cells, organized in a meshwork
    • ECM composition varies, allowing for diverse tissue properties (e.g., bone, teeth, cornea, tendons, jellyfish jelly, beetle/lobster carapace)
    • ECM is active in regulating cell behaviors (survival, development, migration, proliferation, shape, function)

    Major ECM Macromolecules

    • ECM is made of three main classes of macromolecules:
      • Glycosaminoglycans (GAGs): Large, highly charged polysaccharides (often covalently linked to protein as proteoglycans)
      • Fibrous proteins: Primarily collagens
      • Non-collagen glycoproteins: With asparagine-linked oligosaccharides
    • Each tissue has a unique ECM blend for its specific needs

    Glycosaminoglycans (GAGs)

    • Structure: Unbranched polysaccharide chains of repeating disaccharide units (amino sugar + uronic acid, usually sulfated)
    • Charge: Highly negatively charged due to sulfate and carboxyl groups
    • Volume: Occupy large extracellular space due to extended conformations, forming hydrated gels
    • Functions: Resist compressive forces, allow rapid diffusion of nutrients, etc.
    • Types: Hyaluronan, Chondroitin sulfate, Dermatan sulfate, Heparin, Heparan sulfate, Keratan sulfate
    • Defects: Can lead to genetic diseases with short stature, premature aging, and generalized defects in tissues.

    Hyaluronan (Hyaluronic Acid)

    • Structure: Simplest GAG, long unbranched chain, no sulfated sugars
    • Synthesis: Secreted directly from cell surface by enzyme complex
    • Functions: Resist compressive forces, important in tissue morphogenesis and repair. Act as a space filler for cell movements. Found in large amounts during embryonic development and wound healing.

    Proteoglycans

    • Structure: GAG chains covalently linked to a core protein (except hyaluronan)
    • Synthesis: Core protein made by ribosomes, GAG chains assembled in Golgi
    • Modifications: Sulfation and epimerization in Golgi, increase negative charge
    • Diversity: Highly variable; can be large (e.g., aggrecan in cartilage) or smaller (e.g., decorin)
    • Functions: Form hydrated gel, collagen embedding, cell migration/differentiation guidance, and large polymeric complexes for specific tissue properties

    Collagens

    • Structure: Triple-stranded helical structures of α-chains (rope-like)
    • Abundance: Most abundant proteins in mammals (e.g., type I in skin, bone)
    • Diversity: Over 40 types depending on combination of α-chains
    • Polymerization: Form fibrils (10–300 nm diameter), bundles (collagen fibers)
    • Types: Fibril-forming (type I, II, III, V), Fibril-associated (IX, XII), Network-forming (IV, VII)
    • Post-translational Modifications: Hydroxylation of proline and lysine, Glycosylation, formation of triple-stranded pro-collagen (procollagen is processed), covalent cross-links, require vitamin C
    • Diseases: Defects in collagen synthesis lead to conditions like osteogenesis imperfecta, vascular Ehlers-Danlos syndrome, and others.

    Elastin

    • Structure: Highly hydrophobic, rich in proline and glycine, not glycosylated
    • Solubility/Polymerization: Soluble tropoelastin secreted extracellularly, assembled into a highly cross-linked network
    • Functions: Provides elasticity to tissues (skin, blood vessels, lungs), cross-links for stiffness
    • Association with Microfibrils Elastin protein is sheathed with microfibrils (e.g., fibrillin) that provide scaffolding
    • Diseases: Defects lead to conditions like Marfan syndrome

    Basal Lamina

    • Structure: Thin, specialized ECM beneath epithelia and certain other cells
    • Composition: Laminin, type IV collagen, Nidogen, Perlecan
    • Functions: Mechanical support, cell adhesion, and selective barrier between cell types (like in kidneys), directs cell polarity, organization of adjacent plasma membranes, cell proliferation/differentiation, cell migration

    ECM Degradation

    • Degraded by proteolytic enzymes (metalloproteases, serine proteases, collagenases; need tight control)
    • Crucial for tissue repair, cell division, and migration
    • Important in cell movement through the ECM, and for some diseases, especially cancer

    Interactions with Signal Molecules

    • ECM regulates cell signaling:
      • GAGs/Proteoglycans bind secreted proteins, like growth factors (fibroblast growth factors, VEGF, others), concentrate signal molecules
      • Influence signaling by acting as co-receptors
      • Defects in proteoglycans can alter tissue development and signaling.

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    Description

    This quiz explores the role and components of the extracellular matrix in animal tissues. It covers topics such as cell types associated with the extracellular matrix and its functions beyond structural support. Test your knowledge of the intricate relationships between cells and the extracellular matrix.

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