Lecture # 13: Biological Actuators 1) Osmotic motors2) Bacterial rotors 3) Molecular rack and pinions 4) striated muscles trigger high Ca2+ H 2 0 influx high osmotic pressure 1. Osmotic Motors e.g. nematocystCnidarians: Jellyfish Corals Hydroids 2. Bacterial Rotors run & tumble behavior During run, flagella spin in same direction. During tumble, one or more flagella change direction. Howard Berg E.Coli uses a biased random walk to search for food in a complex 3D landscape. rigid rotor composed of many proteins reconstruction from Electron Micrograph artists reconstruction structure of bacterial rotor stator rigid filament rotor axis Key features of bacterial rotors: only true wheel in Nature driven by proton pump ~400 steps/rotation operates at ~ 50 Hz super efficient (90%) 40 nm 3. Molecular Rack and PinionsEukaryotic cells possess a complex cytoskeleton: actin network throughout cell microtubules associated with nucleus These two structural systems are associated with specifc motors. Structure of actin and tubulin filaments Two motors run on tubulin: kinesin and dynein -+ kinesin dynein tubulin binding site ATP binding cleft converter domain cable cargo attachment operates as hand-over-hand dimer dynein has special role as cilia/flagella motor myosin has structure similar to kinesin myosin plays important role in muscle contraction sliding filament model sarcomere electro-mechanical coupling Ca 2+ binds here Lecture # 13: Biological Actuators 1) Osmotic motors2) Bacterial rotors 3) Molecular rack and pinions 4) striated muscles