40. Motility I

40. Motility I - Onwards and Upwards Motility I...

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4/29/11 1 207 News 1) CourseEvalUM is open for student reviews of all courses, including 207, at: http://www.CourseEvalUM.umd.edu 2) Please take 207 attitude survey (for 10 pts) at: http://perg-surveys.physics.umd.edu/MBEXpost.php (this url should be available by Monday morning) 3) Mid-term exam 3 handed back at the end of lecture 4) Mid-term exam 3 regrade requests due – next Mon 5/9 5) Final exam (130 pts) – 75 pts on electrical signaling, nervous systems, motility, muscles, and biomechanics, plus 55 pts on comprehensive Q’s. Mon 5/16 in BPS 1243/1250 at 8-10 AM!! Onwards and Upwards: Motility I - Evolutionary Survey of Molecular and Cellular Mechanisms Key concept from biomechanics: Motility depends on forces being applied against stationary “skeletons” composed of: 1) long fibers inside the cell (= cytoskeletons), 2) hard structures (= exo- and endoskeletons), 3) internal fluids (= hydroskeletons), and/or 4) external media (soil, water, air) Flagella swimming Motor protein moving Vertebrate muscle contracting against medium against cytoskeleton against endoskeleton F Fig. 7.35 Prokaryotic motility - great diversity of unrelated mechanisms Most prokaryotic mechanisms apply force outside cell membrane: 1. Swimming - prokaryotic flagella 2. Corkscrewing - endoflagella in spirochetes 3. Gliding - nonswimming movement across solid surfaces Few prokaryotic mechanisms apply force inside the cell: 1. Actin rockets - intracellular pathogens recruit host actin 2. Bacterial homologs of eukaryotic motility proteins Swimming Corkscrewing Gliding
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4/29/11 2 Prokaryotic flagella - swimming behavior Long whip-like appendages (20 μ m in length) attached to the cell at one end and free at the other Composed of >30 different proteins Different numbers and different arrangements Motile cells accomplish taxis - directional movement e.g., chemotaxis, aerotaxis, phototaxis, magnetotaxis Astonishing maximum rates (on a prokaryotic scale!) sprinting cheetah - up to 110 km/hour = 25 body lengths/sec swimming bacterium - up to 17 cm/hour = 60 cell lengths/sec www.astrographics.com Flagellum in gram-negative bacterium like E. coli Modified pilus capable of motion Extends through cell membrane Filament protein - flagellin Hollow structure - new flagellin deposition near the tip Base composed of >30 proteins Ring proteins positioned in membranes and cell wall Central shaft can rotate either clockwise or counterclockwise A true wheel - very rare in biology Madigan et al. Fig. 4.41 Proton-powered rotary motor Mot (motor) proteins convey H + down electrochemical gradient Mot proteins generate a torque that rotates the filament Fli proteins function as molecular switch to control rotation direction in response to cellular signals
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40. Motility I - Onwards and Upwards Motility I...

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