Cytoskeleton: Difference between revisions
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==Eukaryotic cells== | ==Eukaryotic cells== | ||
[[Image:MEF_microfilaments.jpg|thumb|right|200px|Actin cytoskeleton of [[mus_musculus|mouse]] [[embryo]] [[fibroblast]]s, stained with [[phalloidin]]]] | [[Image:MEF_microfilaments.jpg|thumb|right|200px|Actin cytoskeleton of [[mus_musculus|mouse]] [[embryo]] [[fibroblast]]s, stained with [[phalloidin]]]] | ||
[[Eukaryotic]] cells contain three kinds of cytoskeletal filaments | [[Eukaryotic]] cells contain three kinds of cytoskeletal filaments: | ||
'''[[Actin]] filaments''', about 7 nm in diameter, are composed of two actin chains oriented in an helicoidal shape. They are mostly concentrated just beneath the plasma membrane, as they keep cellular shape, form cytoplasmatic protuberances (like [[pseudopod|pseudopodia]] and [[microvillus| | '''[[Actin]] filaments''', which are about 7 nm in diameter, are composed of two actin chains oriented in an helicoidal shape. They are mostly concentrated just beneath the plasma membrane, as they keep cellular shape, form cytoplasmatic protuberances (like [[pseudopod|pseudopodia]] and [[microvillus| | ||
microvilli]]), and participate in some cell-to-cell or cell-to-matrix junctions and in the [[transduction]] of signals. They are also important for [[cytokinesis]] and, along with [[myosin]], [[Skeletal muscle|muscular contraction]]. | microvilli]]), and participate in some cell-to-cell or cell-to-matrix junctions and in the [[transduction]] of signals. They are also important for [[cytokinesis]] and, along with [[myosin]], [[Skeletal muscle|muscular contraction]]. | ||
'''[[Intermediate filament]]s''', 8-11 nanometers in diameter, are the more stable (strongly bound) and heterogeneous constituents of the cytoskeleton. | '''[[Intermediate filament]]s''', 8-11 nanometers in diameter, are the more stable (strongly bound) and heterogeneous constituents of the cytoskeleton. They organize the internal structure of the cell; for example, they are structural components of the [[nuclear envelope]] and of the [[sarcomere]]s. They also participate in some cell-cell and cell-matrix junctions.Some interme diate filaments are made of [[vimentin]]s, the common structural support of many cells. Cells of the [[skin]] [[hair]] and [[nails]] have intermediate filaments made of [[keratin]]. Some filaments, made of [[lamin]], give structural support to the nuclear envelope. | ||
They organize the internal structure of the cell | |||
'''[[Microtubule]]s''' are hollow cylinders of about 25 nm in diameter, formed by 13 protofilaments which are polymers of alpha and beta [[tubulin]]. They have a very dynamic behaviour, binding [[Guanosine triphosphate|GTP]] for polymerization. They are organized by the [[centrosome]]. They play key roles in: | |||
'''[[Microtubule]]s''' are hollow cylinders of about 25 nm in diameter, formed by 13 protofilaments which are polymers of alpha and beta [[tubulin]]. They have a very dynamic behaviour, binding [[Guanosine triphosphate|GTP]] for polymerization. They are organized by the [[centrosome]]. | |||
They play key roles in: | |||
*intracellular transport (associated with [[dynein]]s and [[kinesin]]s they transport organelles like [[mitochondria]] and vesicles). | *intracellular transport (associated with [[dynein]]s and [[kinesin]]s they transport organelles like [[mitochondria]] and vesicles). | ||
*the [[axoneme]] of cilia and flagella. | *the [[axoneme]] of cilia and flagella. | ||
Revision as of 17:45, 23 January 2011
The cytoskeleton is a structural "scaffold" or "skeleton" that is present inside all eukaryotic cells. This dynamic structure maintains the shape of cells, and enables them to move, using structures such as flagella and cilia. It also has important roles in the intracellular transport of vesicles and organelles) and in cell division.
Eukaryotic cells
Eukaryotic cells contain three kinds of cytoskeletal filaments:
Actin filaments, which are about 7 nm in diameter, are composed of two actin chains oriented in an helicoidal shape. They are mostly concentrated just beneath the plasma membrane, as they keep cellular shape, form cytoplasmatic protuberances (like pseudopodia and microvilli), and participate in some cell-to-cell or cell-to-matrix junctions and in the transduction of signals. They are also important for cytokinesis and, along with myosin, muscular contraction.
Intermediate filaments, 8-11 nanometers in diameter, are the more stable (strongly bound) and heterogeneous constituents of the cytoskeleton. They organize the internal structure of the cell; for example, they are structural components of the nuclear envelope and of the sarcomeres. They also participate in some cell-cell and cell-matrix junctions.Some interme diate filaments are made of vimentins, the common structural support of many cells. Cells of the skin hair and nails have intermediate filaments made of keratin. Some filaments, made of lamin, give structural support to the nuclear envelope.
Microtubules are hollow cylinders of about 25 nm in diameter, formed by 13 protofilaments which are polymers of alpha and beta tubulin. They have a very dynamic behaviour, binding GTP for polymerization. They are organized by the centrosome. They play key roles in:
- intracellular transport (associated with dyneins and kinesins they transport organelles like mitochondria and vesicles).
- the axoneme of cilia and flagella.
- the mitotic spindle.
- synthesis of the cell wall in plants.
The cytoskeleton in prokaryote cells
The cytoskeleton was thought to be a feature only of eukaryotic cells, but homologues of the major proteins of the eukaryotic cytoskeleton have been found in prokaryotes..[1] [2]
FtsZ was the first of these to be identified. Like tubulin, FtsZ forms filaments in the presence of GTP, but these filaments do not group into tubules. During cell division, FtsZ is the first protein to move to the division site, and is essential for recruiting other proteins that produce a new cell wall between the dividing cells.
Prokaryotic actin-like proteins, such as MreB, are involved in maintaining cell shape. All non-spherical bacteria have genes that encode actin-like proteins; these proteins form a helical network beneath the cell membrane that guides the proteins involved in cell wall biosynthesis.
Some plasmids encode a partitioning system that involves an actin-like protein ParM. Filaments of ParM exhibit dynamic instability, and may partition plasmid DNA into the dividing daughter cells by a mechanism like that used by microtubules during eukaryotic mitosis.
The bacterium Caulobacter crescentus expresses a protein, crescentin, that is related to the intermediate filaments of eukaryotic cells. Crescentin is also involved in maintaining cell shape, but how it does this is unclear.
References
- ↑ Shih YL, Rothfield L (2006). "The bacterial cytoskeleton". Microbiol Mol Biol Rev 70: 729–54. PMID 16959967.
- ↑ Michie KA, Löwe J (2006). "Dynamic filaments of the bacterial cytoskeleton". Annu Rev Biochem 75: 467–92. PMID 16756499.