Practice question

Functional specialization within cytoskeleton explains why certain cellular processes are drug sensitive. Actin filaments 7 nanometer double helices participate in cortical tension, formation of lamellipodia filopodia, contractile ring assembly during cytokinesis powered by myosin II, and cytoplasmic streaming in plant Chara driven by myosin XI moving organelles along actin cables at up to 50 micron per second. Microtubules 25 nanometer tubes made of alpha beta tubulin heterodimers provide tracks for chromosome segregation; mitotic spindle assembled from centrosomes, kinetochores attach via Ndc80 complex to dynamic plus ends, and motors kinesin 5 Eg5 generating outward force plus dynein pull separate sister chromatids in anaphase. Vesicle transport using actin myosin occurs short range near cortex but bulk chromosome movement depends on tubulin GTP hydrolysis providing dynamic instability and error correction through Aurora B mediated detachment. Colchicine nocodazole disrupting microtubules block mitosis with metaphase arrest, while cytochalasin blocking actin spares chromosome segregation. Hence chromosome segregation not actin dependent process.