Everything about The Cytoskeleton totally explained
The
cytoskeleton (also CSK) is a cellular "
scaffolding" or "
skeleton" contained within the
cytoplasm. 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. It is a dynamic structure that maintains cell shape, often 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.
The eukaryotic cytoskeleton
Eukaryotic cells contain three main kinds of cytoskeletal filaments, which are microfilaments, intermediate filaments, and microtubules. The cytoskeleton provides the cell's cytoplasm with structure and shape.
Actin filaments / Microfilaments
Around 7 nm in diameter, this filament is composed of two intertwined actin chains. Microfilaments are most concentrated just beneath the
cell membrane, and are responsible for resisting tension and maintaining cellular shape, forming cytoplasmatic protuberances (like
pseudopodia and
microvilli- although these by different mechanisms), and participation in some cell-to-cell or cell-to-matrix junctions. In association with these latter roles, microfilaments are essential to
transduction. They are also important for
cytokinesis (specifically, formation of the
cleavage furrow) and, along with
myosin,
muscular contraction.
Actin/
Myosin interactions also help produce
cytoplasmic streaming in most cells.
Intermediate filaments
microtubules, by contrast, resist compression. It may be useful to think of micro- and intermediate filaments as cables, and of microtubules as cellular support beams). Intermediate filaments organize the internal tridimensional structure of the cell, anchoring organelles and serving as structural components of the
nuclear lamina and
sarcomeres. They also participate in some cell-cell and cell-matrix junctions.
Different intermediate filaments are:
Microtubules
Microtubules are hollow cylinders about 25 nm in diameter (lumen = approximately 15nm in diameter), most commonly comprised of 13 protofilaments which, in turn, are polymers of alpha and beta
tubulin. They have a very dynamic behaviour, binding
GTP for polymerization. They are commonly organized by the
centrosome.
In nine triplet sets (star-shaped), they form the
centrioles, and in nine doublets oriented about two additional microtubules (wheel-shaped) they form cilia and flagella. The latter formation is commonly referred to as a "9+2" arrangement, wherein each doublet is connected to another by the protein
dynein. As both flagella and cilia are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton.
They play key roles in:
intracellular transport (associated with dyneins and kinesins, they transport organelles like mitochondria or vesicles).
the axoneme of cilia and flagella.
the mitotic spindle.
synthesis of the cell wall in plants.
Comparison
Further Information
Get more info on 'Cytoskeleton'.
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