Cytoskeleton + Fibres

• The cytoskeleton is present throughout the cytoplasm of all eukaryotic cells. It's a network of fibres necessary for the shape and stability of a cell. It's responsible for holding organelles in place, cell movement and movement of organelles within the cell.
• Types of fibres:

  
  

  Microfilaments: Made of actin protein and contractile fibres. Responsible for movement of cell surface membrane and cytokinesis.

  
  

  Microtubules: Made of tubulin protein and polymerise (add on to end) and depolymerise (take off from end) to change length. Forms scaffold structure to determine shape of cell. Acts of tracks for movement of organelles around the cell. Spindle fibres - involved in cell division.

  
  

  Intermediate filaments: Rigid fibres, don't change length. Give mechanical strength to cells so they don't collapse, helps maintain integrity.
• Cytokinesis is the division of the cytoplasm into two daughter cells.
• Centrioles are a component of the cytoskeleton. Comprised of microtubules. Found in pairs forming a centrosome near the nucleus. Pairs are perpendicular to each other. Involved in assembly and organisation of spindle fibres during cell division.
• Other components made of cytoskeletal fibres:

  
  

  Flagella: Whip-like extension. Longer than cilia. Small number present per cell. Aids cell motility. Sensory organelle.

  
  

  Cilia: Hair-like extension. Shorter than flagella. Present in greater numbers. Stationary: Sensory organs. Mobile: Beat in rhythmic manner and cause fluids to move along surface of cell.

  
  

  Structure: 9,2 arrangement