Cytoskeleton

    The cytoskeleton is a series of intercellular proteins that help a cell with shape, support, and movement.  Cytoskeleton has three main structural components:  microfilaments, intermediate filaments, and microtubules.  The cytoskeleton mediates movement by helping the cell move in its environment and mediating the movement of the cell's components.   

Microfilaments are the smallest component of the cytoskeleton at about 7 nanometers in diameter.
  They are composed of G-actin protein and are wound in a helical shape.

Intermediate filaments are 8-12 nanometers in diameter and are twisted together in a cord shape. 
They are composed of keratin and keratin-like proteins.  These filaments are tough and resist tension. 

Microtubules are composed of alpha and beta tubulin that form long, hollow cylinders.  
These are fairly strong proteins and are the largest component of cytoskeleton at 25 nanometers. 
Tubular monomers can be lengthened or shortened from the positive end.  

Microtubules have three different functions. 
They make up the centrioles in a cell, the flagella and cilia of a cell, and they serve as "tracks" for transport vesicles to move along. 

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