tubular formations in animals and plant cells. The diameter of microtubules, or threads, is 150–290 angstroms (Å), rarely up to 400 Å; the inner diameter is 100–200 Å. The wall of aomicrotubule consists of 7–15, more often 12–13, threads 30–40 Å in diameter, constructed of globular protein subparticles approximately 35 Å in size.

There are two basic kinds of microtubules: cytoplasmic microtubules and those of the spindle of cell division. Cytoplasmic microtubules support the cell and ensure intracellular transport, cell movement, and contraction of the cell and its components. According to some data, cytoplasmic microtubules are active in the construction of microtubules of the spindle of cell division.