page_title: Cytoskeleton
section_title: Microtubules
hierarchical_section_title: Cytoskeleton / Eukaryotic cytoskeleton / Microtubules
caption_attribution_description: High magnification of "Lung cilia#80311-50" image. This image is a thin x-section cut through cilia. The inside of the cilium contain precisely arranged microtubles, the axoneme. The axoneme has a central unit containing two single microtubules and nine peripheral doublet microtubules (known as the "9+2"). Dynein sidearms project from the A tubule of each doublet. JEOL 100CX TEM
context_page_description: The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including bacteria and archaea. It extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. In eukaryotes, it is composed of three main components, microfilaments, intermediate filaments and microtubules, and these are all capable of rapid growth or disassembly dependent on the cell's requirements.
  A multitude of functions can be performed by the cytoskeleton. Its primary function is to give the cell its shape and mechanical resistance to deformation, and through association with extracellular connective tissue and other cells it stabilizes entire tissues. The cytoskeleton can also contract, thereby deforming the cell and the cell's environment and allowing cells to migrate.
context_section_description: Microtubules are hollow cylinders about 23 nm in diameter (lumen diameter of approximately 15 nm), most commonly comprising 13 protofilaments that, in turn, are polymers of alpha and beta tubulin. They have a very dynamic behavior, binding GTP for polymerization. They are commonly organized by the centrosome.
  In nine triplet sets (star-shaped), they form the centrioles, and in nine doublets oriented about two additional microtubules (wheel-shaped), they form cilia and flagella. The latter formation is commonly referred to as a "9+2" arrangement, wherein each doublet is connected to another by the protein dynein. As both flagella and cilia are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton. There are two types of cilia: motile and non-motile cilia. Cilia are short and more numerous than flagella. The motile cilia have a rhythmic waving or beating motion compared to the non-motile cilia which receive sensory information for the cell; processing signals from the other cells or the fluids surrounding it. Additionally, the microtubules control the beating (movement) of the cilia and flagella. Also, the dynein arms attached to the microtubules function as the molecular motors. The motion of the cilia and flagella is created by the microtubules sliding past one another, which requires ATP.
  They play key roles in:
  intracellular transport (associated with dyneins and kinesins, they transport organelles like mitochondria or vesicles).
  the axoneme of cilia and flagella.
  the mitotic spindle.
  synthesis of the cell wall in plants.
  In addition to the roles described above, Stuart Hameroff and Roger Penrose have proposed that microtubules function in consciousness.
caption: Cross section diagram through the cilium, showing the “9 + 2” arrangement of microtubules
exif: {}