Practice question

Cells rely on cytoskeletal tracks differentiated by cargo range. Short range cortical movements beneath plasma membrane up to few microns use actin filaments 7 nanometers for myosin driven transport, such as myosin Va carrying melanosomes or myosin VI endocytosis. Long range interphase transport spanning tens microns from centrosome near nucleus to periphery requires rigid persistent tracks with polarity uniform over large distances, fulfilled by microtubules 25 nanometers hollow cylinders of 13 protofilaments built from alpha beta tubulin heterodimers. Microtubules exhibit dynamic instability allowing search and capture but stabilized subsets marked by acetylation detyrosination serve as preferred highways. Kinesin motors, kinesin 1 2 3 families move toward plus end delivering mitochondria, ER to Golgi vesicles, mRNA granules, while cytoplasmic dynein with dynactin adaptor moves retrograde toward minus end returning lysosomes and signaling endosomes. Intermediate filaments lack motors and polarity, myosin filaments contractile not tracks. Therefore intracellular organelle long distance trafficking depends predominantly on microtubule network and associated motors.