Mikrotubulens

Mikrotubulens are cylindrical polymers that form part of the cytoskeleton in eukaryotic cells. They are built from α- and β-tubulin heterodimers that assemble into protofilaments which align side by side to form a hollow tube about 25 nanometers in diameter. In cells, arrays of mikrotubulens create networks that provide structural support, determine cell shape, and serve as tracks for motor proteins such as kinesin and dynein to transport organelles and vesicles.

Functions include organization of the mitotic spindle during cell division, polarizing cells, establishing or maintaining cell polarity, and forming the axonemes of cilia and flagella. The plus end typically shows dynamic growth, while the minus end is more anchored, a property termed dynamic instability driven by GTP hydrolysis.

Regulation is complex, with microtubule-associated proteins stabilizing or destabilizing mikrotubulens, and post-translational modifications of tubulin affecting interactions with motors. Nucleation commonly begins at microtubule organizing centers such as centrosomes in animal cells, and at other sites in plants and fungi.

Pharmacological agents that stabilize mikrotubulens (taxanes) or destabilize them (vinca alkaloids) are widely used in cancer therapy, illustrating their essential role in cell division.

Although similar across eukaryotes, mikrotubulens show species- and tissue-specific variations in tubulin isoforms and regulatory proteins.