Practice question

Generation of ciliary and flagellar bending explained by sliding filament model originally proposed by Afzelius and refined by Satir Summers Gibbons and later cryo EM studies visualizing dynein power stroke in situ. Axonemal dynein heavy chains anchored on A tubule of doublet hydrolyze ATP in AAA ring inducing 8 nm movement bending of linker domain that swings stalk toward microtubule plus tip causing interdoublet sliding up to several hundred nanometers in disintegrated axonemes. Because doublets anchored at basal body microtubule organizing center and interconnected by elastic nexin links length 40 nm sliding cannot produce free translation but converts into local curvature generating bending moment. Successive coordinated activation on opposite sides of axoneme propagates bend wave from base to tip at 10 to 20 Hz frequency for cilia 50 Hz for flagella. ATP binding to AAA1 causes detachment low affinity state hydrolysis priming stroke Pi release power stroke inducing sliding between doublets. Thus dynein induces sliding between microtubule doublets by hydrolyzing ATP not depolymerizing tubulin at plus ends which would shorten axoneme contrary to constant length observation during beat cycle.