Plus end tends to be near the outside of the cell. Provide intracellular support and spatial organization within the cell. Non-motor: control microtubule organization in the cytosol (tau in neurons) Motor: move along the microtubules and associate with transport vesicles (kinesin and dynein) Provide structural support and mechanical strength to the cell. Contribute to cell mobility and motility by pushing out the leading edge of the cell (lamellipodium) and pulling in the trailing edge. Myosins are the motor proteins associated with microfilaments. Unconventional contribute to cell mobility and motility in non-muscle cells. Branched nucleation occurs at branching points: axonemal: highly organized and stable; part of structures (axonemes) involved in cell movement (flagella, cilia, cytoplasmic: loosely organized, dynamic, located in the cytosol. Heterodimers assemble, maintaining their orientation, to form protofilaments. Minus ends are clustered and anchored by a centrosome in the mtoc. Classes i v: differ depending on cell type. -helical domains wrap around each other to form rope- like dimers.