Practice question

Dynein heavy chains are among the largest AAA+ machines, containing six concatenated AAA modules forming an asymmetric ring. AAA1 is primary catalytic site where ATP binding closes interface with AAA2, straightening linker and detaching stalk from microtubule. Hydrolysis and phosphate release trigger linker swing from pre to post power stroke, pulling tail forward while microtubule-binding domain reattaches downstream. This cycle strictly depends on ATP concentration and hydrolysis; nonhydrolyzable analogs such as AMP-PNP arrest motility in strong binding state, vanadate traps ADP-Pi intermediate. Dynein moves toward minus ends, positioning Golgi ribbon adjacent to centrosome and driving retrograde transport of autophagosomes, endosomes and interphase nuclei. Disruption fragments Golgi into scattered ministacks. Claiming independence from ATP contradicts enzymology and single molecule assays showing velocity dependence on Mg-ATP with Michaelis-Menten kinetics, while other statements regarding Golgi positioning, organelle transport and directionality align with extensive siRNA, dominant negative p150 and knockout studies in mammalian culture and in vivo models.