mikrotubulis

Mikrotubulis, known in English as the microtubule, is a hollow, cylindrical polymer about 25 nanometers in diameter and is built from α-tubulin and β-tubulin dimers arranged into protofilaments that assemble into a tube. The structure is polar, possessing a plus end that preferentially grows and a minus end.

Microtubule nucleation typically occurs at microtubule-organizing centers, such as the centrosome in animal cells, where γ-tubulin ring complexes template new filaments. Rapid polymerization and catastrophe at the plus end lead to dynamic instability, allowing the network to adapt rapidly to cellular needs. Accessory proteins regulate stability and turnover.

Functions span intracellular transport, where motor proteins kinesin and dynein move cargo along microtubules; to cell division, where microtubules form the mitotic spindle that segregates chromosomes; and to cilia and flagella, whose axonemes rely on stable microtubule bundles for motility and structure. It also helps position organelles and shape the cytoplasm.

Microtubule dynamics are tightly controlled by microtubule-associated proteins and post-translational modifications of tubulin. Drugs targeting microtubules affect cell division and are used in cancer therapy. Taxanes stabilize microtubules, while vinca alkaloids destabilize them, disrupting mitosis.

Microtubules are found in all eukaryotes and exist in two main forms: cytoplasmic microtubules and axonemal microtubules in cilia and flagella. Their proper function is essential for cell viability, development, and neuronal transport; defects can contribute to neurodegenerative diseases and developmental disorders.