The skeleton of the vertebrate is a familiar organ system consisting of hardened elements supporting the soft tissues of the body and play a key role in mediating bodily movements. Eukaryotic cells also posses a “skeletal system”, which is of proteinecous network and composed of three well defined filamentous structures – in the form of microtubules, microfilament and intermediate filaments.
The name cytoskeleton was coined many years ago, but it was abandoned because many of the structures observed in the cytoplasm with the light microscope were considered to be fixation artifacts.
In 1928, Koltzoff proposed the presence of an organized fibrous array in the structure of the protoplasm. He concluded that “Each cell is a system of liquid components and rigid skeletons, which generate the shape, and even though we rarely see the skeletal fibrils in living and fixed cells which only means that these fibrils are very thin or that they are not distinguished by their refractive index form the surrounding colloidal solution”.
Electron micrograph has confirmed his assumption and reveals the presence of cytoskeleton fabric formed of microtubules, microfilaments and intermediate filaments. The main protein which are present in cytoskeleton are tubulin, actin, myosin, tropomyosin, keratin, vimentin, desmin, lamin and others protein.
[...] In many they maintain cell shape, a property based on the distribution and orientation of microtubules. This is specifically found in the axon and dendrites of neurons. The role of microtubules as skeleton elements is evident in certain highly elongated processes such as the axons of nerve cell and the axopods of heliozoan protests. In mature axons, these microtubules nerve as tracks for the movement of vesicles. In developing embryo, microtubules play a key role in maintaining the extended shape of the axon as it slowly goes of the CNS into the peripheral embryonic tissues. [...]
[...] In one approach, the protein subunits of cytoskeleton structure (e.g. tubulin or keratin) are made fluorescent by covalent linkage to a small fluorescent dye. Unlike other high-resolution techniques, the cell remains alive during observation. It is also useful to reveal the location within a cell of a protein present in very low concentration. II. The use of Video Microscopy: Microscope can be greatly increased using a video camera, tape recorder and television monitor. For example, Video microscopy can be used to observe the growth or shrinkage of individual microtubules as they gain or lose subunits in vivo. [...]
[...] When cells are assembling actins filaments at a rapid rate, the end of the filament contains a cap of actins-ATP subunits, which hinders the disassembly of the filament & favors continued assembly. In vitro with high concentration of actins-ATP subunits incubated microfilaments. Both are become labeled, one end in corporate monomers at a rate of 5 to 10 times that of the other end. Decoration of S1 myosin fragment reveals Barbed (Or Plus) end of microfilament is the fast growing end while Pointed (Or Minus) end is the slow growing tip. [...]
[...] Internal cell movement The cytoskeleton acts as a "track" on which cells can move organelles, chromosomes and other things. Some examples are: 1. Vesicle movement between organelles and the cell surface, frequently studied in the squid axon Cytoplasmic streaming 3. Movement of pigment vesicles for protective coloration 4. Discharge of vesicle content for water regulation in protozoa 5. Cell division--cytokinesis Movement of chromosomes during mitosis and meiosis Cellular motors Cells have protein motors that bind two molecules, and using ATP as energy, cause one molecule to shift in relationship to the other. [...]
[...] In vitro, when microtubules are disassembled using a cold technique, a mixture in the form of rings is produced. These rings re composed of tubulin dimmers and associated protein. Presence of ring is questionable as it is observed only in vitro. The assembly disassembly process is dynamic equilibrium as can be demonstrated by the use of 3H-GTP as a marker for the addition or loss of tubulin dimer. When label is incorporated at the assembly end, migrates along the microtubule, and is lost from the disassembly end. [...]
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