Cell biologists have found an elaborate meshwork of actin filaments that form part of the cell's skeleton, or cytoskeleton. Actually, there are three different networks of filaments that are called cytoskeleton. One is the network of microtubules such as those that serve as tracks for kinesin motors. A second is the less well-understood network made up of what are called intermediate filaments, of which more later. The third is the actin meshwork that defines a cell's shape and enables it to move. Unlike a bony skeleton, the actin cytoskeleton can change shape continually, which it must do if a mere blob of a cell is to change its shape continually, extending and retracting such special structures as pseudo pods and ruffles. It is as if the cell could construct bones (actin) and muscles (myosin) on the spot, exactly when and where they are needed.
Cytoskeleton in a living cell is basically defined as a matrix of protein filaments and tubules that occurs within the cytosol (the liquid part of the cytoplasm). It gives the cell a definite shape, transports vital substances around the cell, and may also be involved in cell movement (The Hutchinson Encyclopedia, 2003).
The cytoskeleton is responsible for the mechanical integration of cellular space; unpacked, this phrase covers a host of actions and interactions, mediated by a large and growing ensemble of proteins. Some of the cytoskeleton's functions would be performed on a building site by scaffolding, girders and struts, tracks, cables and pulleys. It supplies mechanical support as well as motive power: “cytobones” and “cytomuscles,” The traffic in vesicles outlined above is spatially organized by a spiderweb of rails, along which vesicles travel with the aid of motor proteins powered by ATP. Organelles, including the endomembrane system, keep their place because they are pegged out on the tracery of cytoskeletal filaments...................
