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Subject - Biochemistry, Cell Biology

Microtubules (from Greek mikros "small" and Latin tubulus "tubes") are protein filaments that occur in all eukaryotes and are involved in the cytoskeleton, flagella, and cilia, as well as in the spindle apparatus that forms during cell division. Within cells, they act as a guiderail along which vesicles and organelles are transported.

These tubular structures have an outer diameter of 25 nm and an inner diameter of 15 nm. A single microtubule is made of 13 protofilaments that make up the tubular structure. The protofilaments in turn are made of dimers composed of α- and β-tubulin. Microtubules have a plus end and a minus end, which exhibit structural and kinetic polarity. Polymerization of the dimeric building blocks dominates at the plus end, while dimers are primarily released at the minus end. Many proteins have been found that are associated with microtubules and perform a stabilizing function; these are known as MAPs (microtubule associated proteins). Microtubule organizing centers, to which the microtubules are primarily anchored by their minus end, are also important.

Microtubules are very dynamic structures that are constantly undergoing construction and deconstruction. Some substances, like the alkaloid colchicine, can bind to tubulin components, disrupting their aggregation and the formation of the microtubules. If the spindle apparatus is affected in this way, cell division is disrupted. These spindle or mitotic toxins include substances used in the treatment of cancer Vinblastin und Paclitaxel (German learning unit).

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