Practice question

Mitotic spindle bipolarity depends on antagonistic motor force balance between outward pushing and inward pulling motors establishing steady state length and facilitating chromosome bi orientation. Kinesin-5 family member Eg5 KSP is homotetrameric motor formed by antiparallel dimerization of dimers through centrally located tetramerization domain placing two motor heads at each end of dumbbell shape about 80 nm long. This geometry enables simultaneous crosslinking of antiparallel interpolar microtubules emerging from opposite poles and walking toward plus ends of each at about 20 nm per second sliding microtubules apart. Resulting force pushes poles outward during prometaphase and maintains spindle length at metaphase opposing minus directed kinesin-14 NCD HSET and dynein that pull poles together. Inhibitors like monastrol STLC block ATPase trapping Eg5 in ADP state causing monopolar spindles mitotic arrest apoptosis used therapeutically. Function not organelle transport but bipolar sliding essential for chromosome segregation fidelity checkpoint satisfaction and anaphase spindle elongation. Additional regulatory inputs including phosphorylation, small GTPases, and cargo adaptors fine tune filament assembly stability and motor activity matching cellular demands during division, migration, and mechanical stress responses efficiently.