12 - Cell Motility

12 - Cell Motility - Cell Motility Bi9 05/04/2011 Overview...

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Cell Motility Bi9 05/04/2011
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Overview Cilia and Flagella Muscle contraction Actin based cell movement: crawling Regulation of motility: Rho proteins and chemotaxis
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Cilia and flagella Structurally identical often differentiated by length and number In higher eukaryotes the only only sperm use flagella for movement, ciliated cells are stationary Single-celled organisms might use both for movement
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Figure 17-8c Essential Cell Biology (© Garland Science 2010) 200 Structure of cilia 10- 200 µm
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Structure of cilia
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Figure 16-83 Molecular Biology of the Cell (© Garland Science 2008) Ciliary dynein forms bridges with tail end binding one microtubule doublet ATP-independently and head end walking towards the – end of adjacent microtubule Dynein movement along microtubules causes bending of cilia
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Regulation of ciliar assembly and length Building blocks of cilia are added at the distal end of cilia (tip) In most species bi-directional motility along the axonem called intraflagellar transport (IFT) moves building materials to the tip and disassembled material back to the cell. Equilibrium of the two transports regulates the length of cilia. (Plasmodium falciparum –malaria- cilia assemble in the cytoplasm) Transition zone: docking zone for IFT and motor proteins Basal body (microtubule organizing center) proteins regulate the assembly and stability of cilia IF T Axonem e assembl y
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Diseases associated with cilia Kartagener’s syndrome: defect of ciliary dynein Symptoms: -male sterility (immotile sperm) - susceptibility to lung infection - left-right axis determination defects (situs inversus) - congenial heart disease (due to anatomic abnormalities) Lack of functional cilia in females: ectopic pregnancy in the Fallopian tubes Smoking: leads to an overall reduction of ciliar length by 7-15% length reduction leads to ~20-40% reduction of effective cilia leading to reduced mucociliary clearance Axonemal dynein genes downregulated, the retrograde motor of cilia and basal body genes were found to be downregulated in ciliary epithelia (Leopold et al. 2009 PlosOne) http://www.ers-education.org
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Two things to sort out: Primary cilia: short and immobile cilia that lack dynein Present on almost all cells (usually one per cell) and usually fulfill sensory functions Bacterial flagella: consists of a long, rigid helical filament (made up of many units called flagellin) It rotates like a propeller driven by a rotatory motor embedded in the bacterial cell wall
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Myosins and Myosin-Powered Movements Myosins: motor proteins (similar to dyneins and kinesins) that move along actin filaments (instead of tubulin) towards + end powered by ATP (instead of GTP) For details on myosin structure and power stroke see lecture 9 processivi ty low high low
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Optical tweezers allowed the identification of step size and processivity of different myosins Experiment: optical tweezers
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Structure of skeletal muscle Muscle fiber: single cell Myofibril: contractile element made up of sarcomeres
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This note was uploaded on 01/12/2012 for the course BI 9 taught by Professor Aravin during the Spring '10 term at Caltech.

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12 - Cell Motility - Cell Motility Bi9 05/04/2011 Overview...

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