Cytoskeleton

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Cytoskeleton

• Means cell skeleton
• Internal framework of cell
• Has many functions
• Anchoring cell organelles
• Provide cell shape
• Aids in cell motility
• Response to environmental signals
• Comprises
• Microtubules
• Microfilaments
• Intermediate filaments

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Microtubules

• Hollow tubes made of the protein tubulin
• Alternating dimers of a and b tubulin
• Largest of cytoskeleton filaments
• Is used for
• Maintenance of cell shape
• Motility
• Flagella or cilia
• Movement of organelles through cell
• Often involves motor molecule
• Often originate from centrosome

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Centrioles

• Located in centrosome of animal cells
• Occur in perpedicular pair
• Have 9 triplets of microtubules
• Facilitate microtubule assembly and chromosome
  separation in some cells

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Flagellum structure

• Basal body links flagellum or cilia to cell
  surface
• Basal body looks just like a centriole
• 9 2 arrangement of microtubules
• Radial spokes prevent dramatic sliding and only
  bending

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Motor molecules

• Interact with tubulin or actin
• Are fixed at one end and allowed to move freely
  at the other end
• Movement is directional
• Undulation-used for flagella and cilia movement
• Two microtubules moving relative to one another
• Organelle movement is like a ski lift tram or a
  monorail

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Cell motility

• Cell movement facilitated by flagella or cilia
• Unlike in prokaryotes, eukaryotic flagella
  undulate
• Cilia are small appendages and they move like a
  swimmers arm-active stroke and return stroke

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How cell movement works

• Dynein is motor molecule that interacts with
  tubulin
• Dynein walks along one microtubule, while bound
  to another
• This results in bending
• If no radial spokes or organelle coat, then
  microtubules would walk out of cell

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Microfilaments

• Made of two intertwined strands of actin
• Helps maintain cell shape
• Actin rearrangements allow engulfment events
• Psuedopod formation in ameoba
• Promote cytoplasmic streaming in plants
• Essential for muscle contraction
• Used by invading bacteria to move around cell
• Frequently being assembled and disassembled
  within cell

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Microfilaments 2

• Myosin interacts with actin to cause contraction
• Cytoplasmic streaming and ameoboid motion are
  similar
• Cortical cytoplasm around the perimiter of cell
  contains perpendicular actin (wind fence)
• Streaming portion has parallel actin which
  facilitates cytoplasm movement
• Plant cell wall prevents amoeboid movement of
  plant cell

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Intermediate Filaments

• Resemble cable in structure
• Are made of protein subunits
• Help maintain cell shape
• Are durable and not assembled and disassembled as
  other cytoskeleton components
• May help maintain organelle position