Oral bio cytoskeleton

• Cytoskeleton


  Internal structural and functional supportive components present in a cell

  
• Cytoskeleton


  • Structural framework for the cell
  • Intracellular transport
  • Cell junctions support
  • Signals transmission
  • Motility

  
• Structural elements of cytoskeleton

  • Microfilaments
  • Intermediate filaments
  • Microtubules

  
• Microfilaments


  • Diameter: 6-8 nm
  • Composition: Globular Actin protein, polymerized into long filaments

  
• Microfilament function

  1. Form track for movement of 'myosin' & serve as 'intracellular muscles' for maintenance cell shape, movement and contractility of a cell

  2. Act as "web" beneath the apical membrane of the cell in adhesive type of cell junctions

  3. Structural "core" of microvilli and filopodia

  
• Intermediate filaments


  • Diameter: 10nm approx.
  • Diverse composition
  • Mesenchymal cells: polymers of 'vimentin'
  • Epithelial cells: polymers of 'cytokeratin'

  
• Intermediate Filament Assemblys


  Functions
• Microtubules


  • Size: 25nm in diameter
  • Composition: 'tubulin' protein, rings stacked end to end form tubules

  
• Microtubule Assembly


  Functions
• Comparison of cytoskeletal elements

  • Microfilaments
  • Intermediate Filaments
  • Microtubules

  
• Intercellular junctions


  • Occluding/tight junctions (Zonula Occludens)
  • Adhesive junctions
  • Communicating/ Gap junctions
• Zonula


  Junction that completely encircles the cell
• Macula


  More circumscribed/ patch like junction
• Components of cellular junctions

  • Transmembrane Adhesive Protein
  • Cytoplasmic Adapter Proteins
  • Cytoskeletal Component

  
• Tight/ Occluding junctions


  • Opposing cell membranes → close contact
  • Total space obliterated between cells
  • Functions: Control passage of material through intercellular space (Water and ions e.g. salivary glands)
  • Act as a 'fence' to maintain apical and basal domain
• Tight junctions


  • Transmembrane Adhesive Protein: Occludins
  • Cytoplasmic Adapter Proteins: Cell polarity related proteins, vesicular transport related proteins, kinases, transcription factors and tumour suppressor proteins
  • Cytoskeletal Component: Actin filaments

  
• Adhesive junctions


  • Intercellular space maintained→ 20nm Approx.
  • Functions: Hold the cells together
  • Cellular signaling
  • Interact with cytoskeleton→ change cell shape and motility

  
• Cell-cell junctions


  • Zonula Adherens
  • Desmosomes
• Zonula Adherens


  • Transmembrane Adhesive Protein: E-Cadherin
  • Cytoplasmic Adapter Proteins: α and β Catenin
  • Cytoskeletal Component: Actin filaments

  
• Desmosomes


  • Transmembrane Adhesive Protein: Desmoglein and Desmocollin
  • Cytoplasmic Adapter Proteins: Desmoplakin, plakoglobin and plakophilin
  • Cytoskeletal Component: Intermediate filaments

  
• Cell-matrix junctions


  Focal Adhesion and Hemidesmosomes

  
• Hemidesmosomes


  • Transmembrane Adhesive Protein: Integrin α6β4
  • Cytoplasmic Adapter Proteins: Bullous pemphigoid antigen 230 (BP 230) and plectin
  • Cytoskeletal Component: Intermediate filaments

  
• Gap/ Communicating junctions


  • Plaque like regions on the cell membrane
  • Intercellular space narrows-→ 2-3 nm
  • Aqueous channels are formed between adjacent cells
  • Six connexin proteins → connexon
  • Connexon has central channel of → 2nm Approx.

  
• Gap junctions


  • Transmembrane Adhesive Protein: Connexins
• Gap junctions


  • Transport of small molecules and ions from one cell to other
  • Electrically couple the cells for coordinated response to a stimulus
• Components of intercellular junctions

  • Tight/ Occluding junctions
  • Zonula adherins
  • Macula adherins/ desmosomes
  • Focal Adhesions
  • Hemidesmosomes
  • Gap/ Communicating junctions
• Basal lamina


  Layer of extracellular matrix, organized as thin sheet between epithelium and underlying connective tissue

  
• Functions of basal lamina


  • Along with hemidesmosome attaches epithelium- connective tissue
  • Filter to control passage of molecules between epithelium-connective tissue
  • Important signaling functions for epithelial differentiation and maintenance of cell polarity

  
• Structure of basal lamina

  • Lamina lucida
  • Lamina densa
  • Lamina fibroreticularis
• Basal lamina components


  • Type IV Collagen
  • Laminin
  • Heparan sulphate
  • Fibronectin
  • Type III Collagen
  • Type VII Collagen

  
• Fibroblasts


  • Predominant cells of connective tissue
  • Form and maintain the fibrous components and ground substance of connective tissues
  • Always found associated with collagen fiber bundles

  
• Cellular organization of fibroblasts

  • Resting Stage
  • Active Stage
• Other characteristics of fibroblasts

  • Contraction and motility
  • Junctions between fibroblasts
  • Heterogenicity
  • Aging
• Fibronexus


  A specialized focal contact with extracellular matrix components, where a dense plaque is present in cytoplasmic side of cell membrane, the cytoskeletal component of cell, actin is linked by transmembrane αβ integrin complex to extracellular fibrils of a glycoprotein called fibronectin

  
• Secretory products of fibroblasts

  • Collagen
  • Elastin
  • Proteoglycans
  • Glycoproteins
  • Growth Factors And Cytokines

  
• Collagen


  • Most abundant protein in the body
  • At least 27 types of collagen discovered
  • Major producers of collagen: mesenchymal cells e.g. fibroblasts, chondroblasts, osteoblasts, odontoblasts and cememtoblasts
  • Structure: Three polypeptide α chains coiled around each other in triple helix configuration
  • Common features: Presence of amino acid glycine in every third position (Gly-X-Y repeating sequence)
  • Presence of hydroxyproline and hydroxylysine

  
• Collagen subfamilies and types

  • Fibril forming collagens
  • Network forming collagens
  • Anchoring fibrils
  • Transmembrane collagens
  • Multiplexins

  
• Results of aging


  • Decrease in the production of extracellular matrix
  • Increase in the production of degradative enzymes
  • Altogether leads to loss of elasticity, skin fragility, and poor wound healing with age
• Secretory products of fibroblasts

  • Collagen
  • Elastin
  • Proteoglycans
  • Glycoproteins
  • Growth Factors And Cytokines

  
• Collagen


  Most abundant protein in the body, at least 27 types discovered, major producers are mesenchymal cells