Microtubules ( + + ) are a component of the cytoskeleton, found throughout the cytoplasm. These tubular polymers of tubulin can grow as long as 50 micrometres and are highly dynamic. The outer diameter of a microtubule is about 24 nm while the inner diameter is about 12 nm. They are found in eukaryotic cells, as well as some Bacteria, and are formed by the polymerization of a dimer of two globular proteins, alpha and beta tubulin.