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Cytoskeleton
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The cytoskeleton (also CSK) is a cellular
"scaffolding" or "skeleton" contained within
the cytoplasm that is made out of protein. The
cytoskeleton is present in all cells; it was once
thought this structure was unique to
eukaryotes, but recent research has identified
the prokaryotic cytoskeleton.
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It is a dynamic structure that maintains cell
shape, protects the cell, enables cellular motion
(using structures such as flagella, cilia and
lamellipodia), and plays important roles in
both intracellular transport (the movement of
vesicles and organelles, for example) and
cellular division.
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The concept and the term (cytosquelette, in
French) was first introduced by French
embryologist Paul Wintrebert in 1931.
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Cells contain elaborate arrays of protein fibers
that serve such functions as:
establishing cell shape
providing mechanical strength
locomotion
Cell division
intracellular transport of organelles
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The cytoskeleton is made up of three kinds of
protein filaments:
Actin filaments (also called microfilaments)
Intermediate filaments and
Microtubules
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Actin Filaments
is composed of two intertwined actin chains
most concentrated just beneath the cell membrane,
and are responsible for resisting tension and
maintaining cellular shape.
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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.
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Intermediate Filaments Intermediate
filaments are about 10 nm diameter and
provide tensile strength for the cell.
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Different intermediate filaments are:
made of vimentins, being the common
structural support of many cells.
made of keratin, found in skin cells, hair and
nails.
neurofilaments of neural cells.
made of lamin, giving structural support to the
nuclear envelope.