Cytoskeleton

Functions

  1. Mechanical support for shape of cell (esp. animal cells).
  2. Support and locators for organelles and macromolecules in cell.
  3. Movement of entire cell.
  4. Endocytosis, exocytosis, pinocytosis.
  5. Movement of organelles and vesicles along "monorails".

Three groupings of cytoskeleton components are recognized; microtubules, microfilaments, intermediate filaments.

Microtubules

  1. Structure - straight, hollow rods of globular proteins.
  2. Up to 25 µm long. 25 nm in diameter.
  3. Function - shape, support, organelle monorails.
  4. Very consistent structure across all eukaryotes.

Microfilaments

  1. Structure - solid rods of globular proteins 7nm in diameter.
  2. Function - support and muscles (1000's in parallel).

Intermediate filaments

  1. Diverse group with a variety of structures and composition.
  2. May be more permanent than the microtubules and microfilaments.
  3. Thought to anchor the nucleus.

Cilia and flagella

  1. Specialized arrangement of microtubules.
  2. Common structure - 9 pairs of microfilaments surround two pair in middle (9 + 2).
  3. Cilia structure - numerous and small (0.25 µm dia, up to 20 µm long).
  4. Cilia function - undulating waves move mucous layer of lungs.
  5. Flagella structure - one or two per cell and long (up to 200 µm).
  6. Flagella function - movement through a very viscous medium.