Difference between microtubules, microfilament
and intermediate filaments - This lecture
explains about the difference between microtubules,
micro filaments and intermediate filaments.
Microfilaments are fine, thread-like protein
fibers, 3-6 nm in diameter.
They are composed predominantly of a contractile
protein called actin, which is the most abundant
cellular protein.
Microfilaments' association with the protein
myosin is responsible for muscle contraction.
Microfilaments can also carry out cellular
movements including gliding, contraction,
and cytokinesis.
Microtubules
Microtubules are cylindrical tubes, 20-25
nm in diameter.
They are composed of subunits of the protein
tubulin--these subunits are termed alpha and
beta.
Microtubules act as a scaffold to determine
cell shape, and provide a set of "tracks"
for cell organelles and vesicles to move on.
Microtubules also form 
the spindle fibers for separating chromosomes
during mitosis.
When arranged in geometric patterns inside
flagella and cilia, they are used for locomotion.
Intermediate Filaments
Intermediate filaments 
are about 10 nm diameter 
and provide tensile strength 
for the cell.
Examples 
of the cytoskeleton in epithelial cells
In 
the epithelial (skin) cells of the intestine,
all three 
types of fibers are present.
Microfilaments project into the villi, giving
shape to the cell surface.
Microtubules grow 
out 
of the centrosome 
to 
the cell periphery.
Intermediate filaments connect adjacent cells
through desmosomes.
