Microtúbulos

Microtúbulos are ubiquitous, dynamic cytoskeletal polymers found in eukaryotic cells. They are hollow cylindrical structures composed of globular protein subunits called tubulin. Tubulin exists as alpha-tubulin and beta-tubulin dimers, which assemble head-to-tail to form protofilaments. Thirteen protofilaments associate laterally to create the characteristic 25-nanometer diameter of a microtubule. Microtubules play critical roles in maintaining cell shape, intracellular transport, and cell division.

Their dynamic nature is characterized by a process called dynamic instability, where they undergo periods of growth (polymerization) and shrinkage (depolymerization). This assembly and disassembly is a tightly regulated process, often influenced by microtubule-associated proteins (MAPs). Microtubules form the structural basis of cilia and flagella, enabling cell motility. During mitosis and meiosis, they are essential components of the spindle apparatus, segregating chromosomes. Motor proteins like kinesin and dynein “walk” along microtubules, transporting vesicles, organelles, and other cellular cargo. In addition to their structural and transport functions, microtubules are involved in cell signaling pathways and can act as tracks for the movement of other cellular components.