Microtubules: Definition, Structure, & Function

Microtubules Definition

  • All eukaryotic cells have microtubules in their cytoplasm, with the uncommon exception of human erythrocytes.
  • They are small, bead-like, hollow tubular structures that support cell shape maintenance.
  • They are tiny tubes that serve as the cell’s motors and may be found inside cells.

Structure of Microtubules

  • They are lengthy fibers (of undetermined length) with a diameter of around 24 nm.
  • Each microtubule looks to have a light or hollow core and a dense wall that is 6 nm thick. A microtubule’s wall is composed of 13 protofilaments, which have a diameter of 4 to 5 nm and are globular in shape.
  • Chemically, they are composed of the protein components -tubulin (tubulin A) and -tubulin, which are two separate forms of protein (tubulin B), each of which has a mass of M.W. 55,000 daltons.
Image Credit: ScienceFacts.net
  • A repeating array of tubulin subunits makes up a microtubule’s wall.
  • According to assembly studies, the structural unit is an 8 nm long dimer.
  • As a result, there are 13 protofilaments in each microtubule, each made up of dimers that run perpendicular to the tubule’s long axis. The repeating unit is a heterodimer that is positioned “head to tail” (i.e., “head to tail”) within the microtubule.
  • As a result, every microtubule has a distinct polarity since its two ends are not physically identical.

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Microtubules Assembly

  • Microtubules go through reversible assembly and disassembly based on the needs of the cell or organelles (i.e., polymerization-depolymerization).
  • Certain proteins linked to microtubules control their polymerization (MAPs).
  • One end of the tubule called the A end (or net assembly end), and the other end, called the D end, are used to preferentially add dimers to form microtubules (or net disassembly end). GTP hydrolyzes to GDP in such an assemblage. Consequently, assembling tubulin in the formation of microtubules is a well-planned and regulated procedure.
  • These assemblies are oriented at the centromeres, basal bodies, and centrioles of the chromosomes. Other controlling variables in the in vivo polymerization of tubulin include calcium and calmodulin (an acidic protein with four Ca2+ binding sites).
  • Microtubules can cooperate with other proteins or function independently to create more complicated structures. Organelles found in cells that are created from unique microtubule assemblies include:
  1. Cilia and flagella
  2. Basal bodies and centrioles

Functions of Microtubules

  • Through specialized attachment proteins, they transport chromosomes, and organelles like mitochondria, vesicles, and granules.
  • They contribute to a number of the cell’s motor activities and, along with microfilaments and intermediate filaments, compose the cytoskeleton of the cell.
  • Microtubules, which are a component of the cell’s cytoskeleton, support
  • Giving cellular membranes and cells their form
  • Cell movement, which also includes muscle cell contraction,
  • Particular organelles are moved about the cell by microtubule “conveyor belts” or “roadways.”
  • Chromosome movement during cell division and mitotic spindle formation occurs during mitosis and meiosis.


  1. Microtubules: the basics
  2. Cytoskeleton Tutorial
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