Practice question

Motile cilia and flagella beating powered exclusively by axonemal dynein distinct isoforms from cytoplasmic dynein-1 adapted for high duty cycle sliding. Outer and inner dynein arms attached every 24 and 96 nm along A tubule heavy chains contain AAA ring and microtubule binding stalk pointing toward adjacent B tubule executing ATP hydrolysis cycle. Cycle drives linker bending delivering power stroke causing interdoublet sliding about 5 microns per second in disintegrated axoneme. In intact cilia doublets anchored at basal body and crosslinked by nexin dynein regulatory complex forces converted into bending propagating wave. Kinases phosphatases regulate dynein via central pair radial spoke signaling pathway orchestrating oscillatory activity switching sides. Kinesin-1 drives anterograde intraflagellar transport constructing flagellum not beating myosin systems unrelated operating on actin stathmin sequesters tubulin dimer. Therefore dynein provides motive force for ciliary clearance mucus propulsion and sperm propulsion defects cause Kartagener syndrome primary ciliary dyskinesia with situs inversus. 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.