CEllBIO

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ascurf
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122782
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CEllBIO
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2011-12-11 21:37:42
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225 Cell Biology Extracellular matrices cell junctions
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Extracellular matrices and cell junctions intro. TOPIC 4
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  1. The two comonents of space between cells
    Glycocalyx & ECM
  2. Glycocalx Functions
    • Cell cell interactions
    • Cell-substratum interaction
    • Mechanical protection
    • Barrier
    • Receptors/signaling


    "Cell Coat"
  3. Key componants of ECM
    • Collagens
    • GAGs (glycosaminoglycans)
    • proteoglycans
    • preteoglycan aggregates
    • EC adhesions proteins ( fibronectin & laminin)
  4. Basal Lamina (4 componants)
    • ECM of animal cells
    • 50 - 200nm
  5. Type IV Collagen (don't bundle, nonfibrillar) 2D
    • Laminin (2D with IV collagen)
    • Perlecan (a preteoglycan) crosslinks ECM --> PM
    • Entactin (crosslinks with other components above)
  6. Functions of Basal Lamina
    • Mechaincal support
    • Maintance of epithilial polarity (brush tip)
    • Separtes ajacent tissue
    • Substrate for cell migration (molecular highway)
    • selectively permeable barrier
  7. Metastasis def
    • Some cancer cells show altered binding to basal lamina, premitting their passage and allowing them to migrate throughout the body
    • process = metastasis
  8. Collagens
    • Most abundant human/animal protein (>25%)
    • High tensil stregth fibrous glycopreoteins
    • Provides stregth support and protection noted in, cartilage, bone, tendon and skin
  9. Secreted by
    • fibroblasts(+other connective tissue like osteoblasts of bones)
    • Smooth mucles cells
    • epithelial cells
  10. Individual collagen is composed of ___ subunits, and each chain is called an _____
    • 3
    • a-chain(a collagen chain)
  11. The 3 a-chains form a ____ triple helix, a _______
    each ____nm in length
    • Rod like
    • coiled coil
    • 300
  12. Heterotypic a-chains def
    Collagens can be heterotypic..like alloys with different mechanical and structural properties
  13. Collagens in fibrils are covalently crossed linked to each other between?
    Lysine and hedroxylysine
  14. Organizing collagen fibers into bundles creates fibers which are ?
    Much larger, and thicker

    eg. collagen fibers of tendons results from parallel bundles of fibrils
  15. Difference of type IV collagen
    • Present in Basement Membranes (basal lamina)
    • Does not form fibrils, making making it paticularly flexible
  16. Collagen abnormalities (3)
    • Osteogensis imperfect ( Love you adam!)
    • --- Type 1 colalgen disorder
    • --- fragile bones

    • Ehlers-Danlos Syndrome (Elastic Skin)
    • --- Defect in a variety of collagen
    • --- Hyperelastic skin
    • --- Organs can somtimes rupter
    • --- Famous man = James Morris

    • Alport Syndrome
    • --Type IV collagen dissorder(not fibriler, forms webs)
    • -- Kidney dysfunction due to glomerular basment membrane
    • --->kidney failure, blood + proteins in urine
  17. LH and RH nature of Collagens
    • each of the 3 pollypeptide chains is LH (3 a.a/turn)*
    • The pollypetide chain all together is RH helix
  18. GAGs (glycosaminoglycans)
    • Long neg-charged polysaccharides composed of repeating dissacharid units.
    • 1 monosaccharide of which is always an amino surgar
    • acidic and hydrophilic (helps proteoglycans form hydrated gels *ear)
  19. GAGs and Preteoglycans are built in _____ and can be covalentlinked to a "_______" to form __________
    • Golgi
    • core protein
    • proteoglycans
  20. examples of Glycoaminoglycans (3)
    • Chrondriotin Sulfate
    • Keratan Sulfate
    • Hyaluronic acid ( only non-sulphated)
  21. Unlike other Glycoaminoglycans (GAGs) Hyaluronic acid forms _______links to a core protein to form proteoglycans
    Non-covalently
  22. Proteoglycans def
    Protein-glycoaminoglycan complexes formed by covalently linkage of GAGS to core proteins
  23. 3 types of core prteins found in proteoglycans
    • Freely soluble
    • -- eg, aggrecan
    • --- Major structural component of cartilage
    • GPI-Linked
    • --eg. Glypican--- family of heparen sulphate proteoglycans
    • Transmembrane
    • -- act as FGF corectors with CPCRs
    • eg. syndecan
  24. Syndecan
    • A core protein found in Proteoglycans
    • FCF coreceptor
    • only 3-5 GAGS (short)
  25. Proteoglycans and collagens
    • Complement each other making tissue stronger
    • Proteoglycans offer ressitance to deformation
    • Collagens offer ressitance to pulling forces

    Helps define shape of tissue
  26. Preoteigkycans and the immune system
    Long feather GAG chains help to filther out microbes and viruses in the ECF before the reach the cell surgace
  27. Hydrated gels formed by proteoflycans aid in ____

    (hint hydration)
    Diffusion of small molecules near the surgace of the cell to help keep cells hydrated!
  28. Preoteoglycans and FGF (fibroblast growth factor)
    Preteoglycans bind to other protein sin the ECF, affecting the ability of those proteins to bind to the surface of cells

    • eg. preteoglycans can sequester(hide) growth factors like FGF
    • May also act as corectors

    (Hold then release at a later date vs formation change upon bonding with heparan sulfate (preteoglycan))
  29. Fibronectin & Laminins
    • Extra Cellular adhesions proteins (multiadhesive)
    • Bind and Crosslink -- ECM components (eg collagens)
    • Bind and Crosslink-- cell membrane proteins (eg. integrins)
    • Serves as intermediate between cells and other ECM molecules

    Help form complex molecular networks (especially laminins)
  30. Modular composition def
    Consisting of many different binding domains

    Characateristic of Fibronectin & Laminins
  31. these extra cellular adhesion proteins play an important role when tissues are involved in dynamic activities such as cell migration,growth, differentiation, and even acting like a guides in a complex lanscape
    Fibronectin & Laminin
  32. Fibronectin (structure)
    2 polypetides linked by disulphide (SS) bridges between cysteines
  33. Laminins (structure)
    • 3 different polypetides (heterotrimers) linked by SS bridges
    • Coiled structure
  34. RGD ( arginine-Glycine aspartate)
    • Tripeptide sequence motif (reaccuring sequence)
    • Present in Laminin and fibronectin
    • Common in ECM proteins
    • Recognized and bound by integrins
  35. Cell Cell/Cell ECM junctions
    • Claudins
    • tight junctions
    • Cadherins
    • adherens junctin
    • desmosomes
    • Connexins
    • gap junctions
    • Integrins
    • hemidesmosomes
    • focal adhesion

  36. Nonjunctional adhesion
    • Cadherins
    • Selectins
    • (Ig-like cell adhesions molecules)
    • Integrins
    • integral membrane proteoglycan
    • structural glycoprotein
    • proteoglycan
  37. Integrins
    • Transmembrane glycoproteins
    • Heterodimeric (composed of both a alpha & beta chain)
    • Only In animals
    • Most important class of CAM that link cells to proteins of ECM and control the cells reponse after adhesion
  38. Integrins help in the roll of cell attachment, movement, growth and survival through (3) Interactions
    • Homophilic interactoin (8 interactions Cell-cell)
    • nonjunctinal adhesive complexes between cells
    • heterophilic interactions
    • Nonjunctin adhesion to ECM
    • Junctional adhesive complexes
    • indirectly link the cytoskelton ECM
  39. Heterophilic interaction of integrins
    Heterophilic interactions are with ECM companants of other molecules then other integrins ( eg. collagen, laminin, fibronectin etc)
  40. Binding specificity of Integrins
    • Complex
    • Some bind to RGD sequence motif
    • Some recognize and bind lingands that lack RGD (non RGD recognition)
  41. Symthetic RGD peptides and nonpeptide RGD analogies have been used to inhibit the formation of fibrogen bridges between platelets, inhibiting bloof clot formation
  42. Affinity modulation & Avidity modulation def
    Affinity: modulate the strength of adhesion between integrins

    Avidity: modulate number of integrin molecules involved
  43. Inside-out Signaling
    • Begins in cell, causes effects outside cell
    • can modulate affinity and avidity of integrins
  44. Activation of collagen affinity in an integrin by talin
    (inside out signalling)
    7 steps
    • 1) inactive bent
    • 2) Talin binds (beta)
    • 3) Active (straight)
    • 4) Affinity modulation (change in shape)
    • 5) Avidity modulation ( Increase in # of molecules)
    • 6) Complmentary
    • 7) Both increase strength of adhesion
  45. inside-out signalling which can often result in clustering of activated integrins by lateral diffusion in the membrane is an example of____
    Avidity modulation
  46. Outside in Singnalling
    • The binfing of EC ligands which alter the cytosolic interaction of integrins with cytoskeleton components
    • --> Alter the activity kinases
    • --> leads to changes in extant protein activity or even gene expression
  47. All classical cadherins have (3)
    • Single transmembrane spanning domain
    • Conserved cytosolic C-terminus (involved in binding B-catenin)
    • 5 extracellular domains
    • Often found as cluster of dimers

    Dimers engage in variable interdigitation with similar cadherins on neighbouring cells
  48. Caderins homophilic interactions are ____ dependent
    Ca++
  49. Metastasis sequence
    • 1) downregualtion of cadherins
    • 2) down strength of adhesions
    • 3) allows cancer cells to invade tissue
  50. Major Roles of Cadherins
    • Embryonic tissue formations (compact tissue)
    • Metastasis
    • Adhesion of epithelial cells (adherens junctions, desmosomes)
    • Adhesions of other cell types (adhesive complezes that hold neurons to each other)
  51. Focal Adhesions Def
    Clusters of intergins that link ECM to actin microfilaments of the cytoskeleton
  52. Focal adhesion are seen in vivo in _________
    • Muscles and tendon
    • as well as commonly in vitro
  53. Discrete attachment points imply
    • Focal adhesion
    • ex. fibroblasts attached to teh surfface of a coated culture dish are not uniformly attached
  54. Focal Adhesions can _______/______ quickly, and are thought to develope from a much smaller less complex, ____________
    • Assemble / Disassemble
    • Focal Complexes
  55. Typsin
    Used to realease cell from the coated dishes when subculturing
  56. Focal Adhesion Kinases (FAKs)
    • interact directly with intergrins
    • indirectly eith Talin and Paxillin
  57. Changes in the activity FAKs lead to
    • Changes in extant protein activity
    • Changes in gene expression
  58. Hemidesmosomes def
    • Clusters of interins that link basement membrane to intermidiate filaments of cytoskeleton.
    • eg. keratins of epithlial tissue
    • Vimentins of connective tissue

    Tightest Attachment of Cell & ECM
  59. Hemidesmosomes associated Disorders
    • Autoimmune blistering disorders
    • eg.bullous pemphigoid
    • skin detaches allowing space to fill with ECM aka blister)

    • eg. epidermolysis bullosa
    • inside & outside blisters
    • results in extreamly fragile skin
  60. Tight Junctions Def
    Gate and fence function

    • Form a gasket like seal around adjacent animals cells @ apical aspect of adjacent epithial cells
    • Mediated by transmembrane proteins claudins
  61. physological use of tight junctions
    • blood brain barrier between endothelial cells of capillaries
    • Prevent water loss by skin to environment
  62. Furuse et al 2002
    Dirst to demonstrate that skin epithelial cells have tight junctions

    • Devloped mice lacking Claudin1
    • Lead to dehydration and death shortly after birth
  63. Leakiness of tight junctions regulated allowing __
    ____ rather then transcellular pathways
    • Paracellular (inbetween cells)
    • Gate function
  64. Adherens Junctions Def
    • Clusters of cadherins
    • indirectly link bundles of cytoskeletal actin microfilaments between adjacent epithelial cells and cardiac muscles

    Enable mechanical, chemical and electrical connectivity between cells.
  65. The intercalated discs of cardiac muscles are junctional complexes made up of.....
    • Adherens junctions
    • desdomones
    • gap junctions

    All which indirectly link sarcomere (contratile unit) microfilaments of adhacent cardiac muscles
  66. Catenins def (use)
    adpater protein catenins mediate indirect linkage of cadherins and microfilaments.
  67. a-catenin vs B-catenins
    B are linked to cytosolic C-termini of cadherins
  68. a links to B-caternin microfilaments
  69. Roles of adherens junctions
    • Cell adhesions,
    • shape change
    • Singalling
    • link the intergrins of focal adhesion
    • Cadherins of an adheren junction provide for "outside in" signalling

    (form adhesion belts around cells"
  70. Desmosomes def
    • Spot welds between cells ( great strength)
    • clusters of cadherins that indirectly link bundles of intermediate filament etween adjacent cells
  71. Types of intermidate fillament involved in desmosomes are.............. Indirectly linakge mediated by............
    • Keratins (between ajacent epithlial cells)
    • Vimentin (connective tissue and muslcle tissue)

    Plakoglobins and desmoplakins
  72. Desmosomes are most numerous in cells that...
    • Are subject to mechanical stress
    • eg, Gingina, cardiac muscles
  73. Autoimmune dissorder assocaited with Desmosomes
    • Pemphigus vulgaris
    • Autoimmune blistering disorder
  74. Gap Junctions Def
    • Clusters of channels
    • allow commuication between adjacent animal cells
  75. Gap junctions allow communication through (3)
    • Share electrical signals (between cardiac muscle cells)
    • ion flow at electrical synapses
    • Metabolic cooperation (sharing important metabolites)
  76. each gap junction channel is formed by
    Connexons composed of 6 connexins
  77. Gap junctions allow for nonspecific passage of sulutes up to ______DA and complete exclude >_____Da
    • 1200
    • 2000
  78. Examples of Gap Junctions
    • -well coordinated responses
    • -Synchronous contraction of carfiac myocytes
    • -Coordinated unidirection beating of cilia along tracheal epithelial cells
    • -Uterine smooth muscle contractions during birth
    • -Rapid reflex reactions
  79. Gap junctin gating is regulated by...
    • pH
    • PKC (phosphorylation by protein kinase C)
    • Chages ins cytosolic [Ca++]

    (closed when high cytosolic Ca concentration, protective)
  80. Plasmodesmata Def
    • Communication junctions between PLANTS
    • transport proteins
    • 30-60 nm traffic
    • full dialated 50kDa proteins

    opening lined with plama membrane
  81. Plants cells Lack_______ and instead have _____
    • Adhesion molecules
    • Cell walls
  82. Function of plant cell walls
    • Maintance of wall pressure
    • Mechanical support
    • Protection from abrasion, pathogens, osmotic influx
    • Mediate cell interactions
    • Barrier to large molecules
  83. Structure of a plant cell wall
    • Like reinforced gel
    • Cellulose (fibrous element)
    • Pectin, hemicelluloses ( gel-like matrix)
  84. Cellulose
    • glc-B(1-4)Glc
    • organized in microfibrils
    • rigidity
    • resists tensile forces
  85. hemicellulose
    • Branced polysaccharides
    • Form crosslinks to cellulose microfibrils
  86. Pectin
    • Heterogenous class of negativelely charge polyssacharides
    • Form hydraded gels like GAGs
    • Act like molecular sieve
    • role in defence

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