microtubule A tubular structure, 15–25 nm in diameter, of indefinite length, and composed of subunits of the protein tubulin. It occurs in large numbers in all eukaryotic cells, either freely in the cytoplasm, or as a structural component of organelles (e.g. cilia and flagella). Microtubules appear to function in the motility of cells, the maintenance of cell shape, and the transport of materials within cells. In addition, they form part of the structure of the mitotic spindle (responsible for the movement of chromosomes during cell division), and have been implicated in sensory transduction in some receptor cells.

microtubule A microscopic tubular structure, with an external diameter of 24 nm and of variable length, found in a wide range of eukaryotic cells. Microtubules are composed of numerous subunits of the globular protein tubulin and occur singly or in pairs, triplets, or bundles. Microtubules help cells to maintain their shape (see cytoskeleton); they also occur in cilia and eukaryotic flagella (see undulipodium) and the centrioles and form the spindle during nuclear division. A further role is in the intracellular transport of materials and movement of organelles. Formation of microtubules is initiated at microtubule-organizing centres (MTOCs). Compare microfilament; intermediate filament.

microtubule A tubular structure, 15–25 nm in diameter and of indefinite length, that is composed of subunits of the protein tubulin. It occurs in large numbers in all eukaryotic cells, either freely in the cytoplasm or as a structural component of organelles (e.g. centrioles, cilia, and flagella). Microtubules appear to function in the motility of cells, the maintenance of cell shape, and the transport of materials within cells. In addition, they form part of the structure of the mitotic spindle and have been implicated in sensory transduction in some receptor cells.