Microtubules are microscopic hollow tubes made of the proteins alpha and beta tubulin that are part of a cell’s cytoskeleton, a network of protein filaments that extends throughout the cell, gives the cell shape, and keeps its organelles in place. Microtubules are the largest structures in the cytoskeleton at about 24 nanometers thick. They have roles in cell movement, cell division, and transporting materials within cells.