Tubulins and microtubules are demonstrated in this animation. Microtubules are conveyer belts inside the cells. They move vesicles, granules, organelles like mitochondria, and chromosomes via special attachment proteins. They also serve a cytoskeletal role. Structurally, they are linear polymers of tubulin which is a globular protein. These linear polymers are called protofilaments. The figure to the left shows a three dimensional view of a microtubule. The tubulin molecules are the bead like structures. They form heterodimers of alpha and beta tubulin. A protofilament is a linear row of tubulin dimers. Microtubules may work alone, or join with other proteins to form more complex structures called cilia, flagella or centrioles . In this unit we will cover all of these structures. Read the Chapter on Microtubules in Lodish.