Microtubules mediate movement via molecular motor proteins, which include dynein and kinesin.
Microtubules can dimerize and trimerize.
The centrosome is present in eukaryotic cells and is a central site of microtubule assembly. It is especially important during cell division, when a spindle of microtubules is formed to bind chromosomes during mitosis. The centrosome consists of two centrioles arranged at 90-degree angles. Each centriole consists of 9 trimers of microtubules. New microtubules are assembled from the protein 'material' that surrounds the centrioles - the negative end is embedded in this matrix as the positive end elongates towards the cell membrane.