Cytoskeleton, a system of filaments or fibres that is present in the cytoplasm
of eukaryotic cells (cells containing a nucleus). The cytoskeleton organizes
other constituents of the cell, maintains the cell’s shape, and is responsible for
the locomotion of the cell itself and the movement of the various organelles
within it. The filaments that comprise the cytoskeleton are so small that their
existence was only discovered because of the greater resolving power of the
electron microscope.
Three major types of filaments make up the cytoskeleton: actin filaments,
microtubules, and intermediate filaments. Actin filaments occur in a cell in the
form of meshworks or bundles of parallel fibres; they help determine the
shape of the cell and also help it adhere to the substrate. The constantly
changing arrays of actin filaments help move the cell and mediate specific
activities within it, such as cell cleavage during mitosis. Microtubules are
longer filaments that are constantly assembling and disassembling; they play
a crucial role in moving the daughter chromosomes to the newly forming
daughter cells during mitosis, and bundles of microtubules form the cilia
and flagellafound in protozoans and in the cells of some multicellular animals.
Intermediate filaments, in contrast to actin filaments and microtubules, are
very stable structures that form the true skeleton of the cell. They anchor the
nucleus and position it within the cell, and they give the cell its elastic
properties and its ability to withstand tension.
