Microtubules are rigid polymers of tubulin that give structure to cells and serve as tracks for molecular motors. Until recently, the growth and shrinkage of microtubules was thought to be confined to their ends. Over the last few years, however, evidence has emerged that exchange of tubulin in and out of microtubules can take place within the lattice and not just at the ends. I will present our recent work on the microtubule severing protein spastin on microtubule dynamics as well as measurements of the forces necessary to remove tubulin from the lattice. This seminar is sponsored by the Molecular Biophysics Training Program (MBTP), Structural and Computational Biology and Biophysics (SCBB) and the Weldon School of Biomedical Engineering.