Role Of Cytoskeleton In Cell Motility

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🌟Role Of Cytoskeleton in Motility Of Amoeba and Macrophages.
✔️Cytoskeleton in Eukaryotic Cells is a dynamic network of interlinking protein filaments present in the cytoplasm of all cells, excluding bacteria and archaea.
✔️It extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms.
✔️The cytoskeleton is responsible for contraction, cell motility, movement of organelles and vesicles through the cytoplasm, cytokinesis, Modulating Shape of the Cell( forming pseudopods or false feet in case of amoeba) & Even in Cell division by forming Furrow.
✔️The Cytoskeleton is made up of 3 types of Protein Filaments:
1.) Microtubules
2.)Microfilaments/Actin Filaments
3.)Intermediate Filaments

✔️Actin Filaments (F-actin) grow from the polymerization of G-actin monomers.

✔️Actin is a highly abundant structural protein found in all eukaryotic cells (except for nematode sperm).

✔️The monomeric, globular form of actin, known as G-actin, forms the basic unit for actin filaments. In many cases actin filaments may bundle together with other actin filaments, or, together with their associated motor proteins (e.g. myosin superfamily) form an elaborate network known as the actin cytoskeleton.
✔️This occurs primarily at or near the plasma membrane. Consequently a region of high actin filament density is commonly found at the cell periphery and is known as the cell cortex.

✔️Actin filaments in the cell cortex determine the shape, stiffness and movement of the cell surface. The actin cytoskeleton can also generate the intracellular forces that are required for many cellular functions including cell motility, muscle contraction, cell division, cytokinesis, vesicle and organelle movement and cell signaling.
✔️How do actin monomers polymerize to form an actin filament?
✨Actin filaments are highly dynamic and their polymerization is usually correlated to their disassembly. Generally, actin filament polymerization occurs over three phases:
1)Nucleation phase
2)Elongation phase
3)Steady state phase.

✔️1)Nucleation~ During the nucleation phase the formation of a stable ‘actin nucleus’ occurs. This is usually comprised of three actin monomers in complex.
2) Elongation~ In the elongation phase,G-actin monomers are rapidly added to the filament at the (+ve) or barbed end and this is often facilitated by additional elongation factors such as FORMIN. For this process to occur, the (+) end of the filament must be exposed, and this means removal of *capping protein.
NOTE:- FORMINS are a group of proteins that are involved in the polymerization of actin and associate with the fast-growing end (barbed end) of actin filaments.
3)Steady State Phase~ In the steady state phase, the filament dynamics enter a state of equilibrium where monomer disassembly from the (-) end and polymerization at the (+) end is balanced and maintained by a critical concentration of G-actin monomers in the cytosol.
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