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. nematocyst Cnidarians: 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 artist’s 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 Pinions’ Eukaryotic 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