Cytoskeleton

Article By:

Lazarides, Elias Department of Biology, California Institute of Technology, Pasadena, California.

Last reviewed:April 2021

DOI:https://doi.org/10.1036/1097-8542.179500

A system of protein filaments found in the cytoplasm of cells that is responsible for cell shape, support, movement, and organization. The protein fibers that compose the structural framework of a cell are collectively known as the cytoskeleton. The filamentous cytoskeletal fibers are responsible for cell shape, cell locomotion and elasticity, interconnection of the major cytoplasmic organelles, cell division, chromosome organization and movement, and the adhesion of a cell to a surface or to other cells. Because this filamentous system is too small to be resolved by light microscopy, its several subcomponents, structural features, and cytoplasmic associations were not discovered until the electron microscope was developed. With this instrument, which can magnify a section of a cell by many thousands of times, three major classes of filaments could be resolved on the basis of their diameter and cytoplasmic distribution: actin filaments (or microfilaments) [Fig. 1], each with an average diameter of 6 nanometers (nm); microtubules (Fig. 1), with an average diameter of 25 nm; and intermediate filaments, whose diameter of 10 nm is intermediate to that of the other two classes. In muscle cells, an additional class of thick filaments, known as myosin filaments, is found whose function is to interact with actin filaments and generate the force necessary for muscle contraction. The presence of this system of filaments in all cells, as well as their diversity in structure and cytoplasmic distribution, has been recognized only in the modern period of biology. See also: Cell (biology); Cell biology; Cell organization; Cytoplasm; Electron microscope; Protein

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