This video shows how the constant addition of tubulin bound to GTP provides a cap that prevents the microtubule from falling apart. UC Berkeley scientists found that the hydrolyzation of GTP to GDP (change of red to violet) compacts the tubulin into a strained configuration that rapidly peels the microtubule apart if the cap disappears.
(Photo Credit: Eva Nogales lab, UC Berkeley)
This video shows how the microtubule rapidly peels apart once the growing tubulin cap disappears. This peeling or depolymerization does work inside the cell. A chromosome attached by its kinetochore to a microtubule will be pulled because the kinetochore remains attached to the shortening microtubule as it peels apart.
(Photo Credit: Eva Nogales lab, UC Berkeley)