CBH 17 CYTOSKELETON

• Components of the cytoplasm

  Soluble phase or hyaloplasm cytoskeleton
• Soluble phase


  Aqueous solution containing: proteins, lipids, metabolism products, mRNA, tRNA and gases
• Cytoskeleton

  Microtubules , microfilaments or actin filaments , intermediate filaments
• Microtubules


  Present in all eukaryotic cell, specially the ones with irregular shape organized in axonemes in centrioles, cilia, and flagella
• Microtubules composition

  Outer diameter of 25nm 13 protofilaments polymers: a heterodimer of alpha and beta tubulin MT associated proteins+/- ends
• Functions of microtubules

  Help to maintain cell shape , Tracks for organelle and chromosome movement , Movement of cilia and flagella
• Centrosome


  The main microtubule organizing centers in animal cells, constituted by 2 centrioles and a pericentriolar matrix

  
• Gama tubulin

  
• Microfilaments (actin filaments)


  Present in Eukaryotic cells to allow contractability and movementAbundant in muscle cells for muscle contraction
• Structure of actin filaments

  Diameter around 6-7 nmActin G (globular) Actin F (filamentous)polarity: +/- ends
• Actin binding proteins

  villin, fimbrin, myosin and spectrin
• Cilia and flagella

  Tubular expansions with the function ofmovementt
• Stable actin filaments location

  Microvilli adhesion belts muscle cell contractile ring in mitosis
• Labile location


  In many cells that have movement
• Intermediate filaments


  confer mechanical stability to cell structure

  
• Major types of intermediate filament


  Nuclear: lamins A B C Epithelial : type i keratins and type ii keratins