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Publié dans : Technologie, Formation
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  1. 1. The Cytoskeleton <ul><li>The eukaryotic cell is a 3D structure. It has a cytoskeleton anchored to proteins in the plasma membrane </li></ul><ul><li>These proteins both maintain shape and allow movement </li></ul><ul><li>The cytoskeleton is a dynamic structure, as the microfilaments and microtubules can depolymerise and repolymerise very easily </li></ul>MICROFILAMENTS MICROTUBULES INTERMEDIATE FILAMENTS
  2. 2. The Cytoskeleton <ul><li>The cytoskeleton is made up of 3 components, in order of increasing diameter. They are … </li></ul><ul><ul><ul><ul><li>1) Actin filaments/microfilaments </li></ul></ul></ul></ul><ul><ul><ul><ul><li>2) Intermediate filaments </li></ul></ul></ul></ul><ul><ul><ul><ul><li>3) Microtubules </li></ul></ul></ul></ul>
  3. 3. 1) Microfilaments <ul><li>These are composed of actin (protein) </li></ul><ul><li>They are arranged as 2 strands of protein molecules twisted together to give a rope-like structure about 7nm in diameter </li></ul><ul><li>These are present throughout the cell but are most highly concentrated just inside the plasma membrane </li></ul><ul><li>They are important in all cell movement and contraction </li></ul>Actin fibres in a cell stained with a fluorescent strain specific for actin
  4. 4. 2) Intermediate Filaments <ul><li>These are about 10nm in diameter and are composed of tough fibrous protein strands twisted together </li></ul><ul><li>They are very stable structures in the cell and provide mechanical strength to animal cells which lack the strong cell walls of plants </li></ul><ul><li>Intermediate filaments can be anchored between the membrane to provide extra support </li></ul>The nucleus in epithelial cells is held within the cell by a basketlike network of intermediate filaments made of keratins which have been stained here using a fluorescent stain
  5. 5. 3) Microtubules <ul><li>These are hollow tubes (like straws) composed of tubulin protein (a globular protein) </li></ul><ul><li>The tubulin protein subunits of microtubules associate in a cylindrical arrangement to generate the final microtubule - a relatively rigid structure </li></ul><ul><li>Microtubules only form around a centrosome (organising centre) </li></ul><ul><li>The centrosome provides a “nucleus” from which the microtubules form. These are important in cell division as part of the spindle fibre network and can move components within the cell </li></ul>Microtubules growing in vitro from an isolated centrosome
  6. 6. Functions <ul><li>But the primary importance of the cytoskeleton is in cell motility . The cytoskeleton extends throughout the cytoplasm and determines the internal movement of cell organelles, as well as cell locomotion and muscle fibre contraction </li></ul><ul><ul><li>All of these components give mechanical support and shape to the cell </li></ul></ul>