13 Pages

Human Biology
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Malcolm Mac Kinnon

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NROB60 Study Package: Week 4 Homira Osman Week 4: Lecture May 27, 2008 Lecture Topics Lecture IV Readings: The Cytoskeleton (Pages 35 38, 40 41) Lecture Summaries [L4] - Different Child Brain (Part 1) o - Child Brain (Part 2) o - The Cytoskeleton o Scaffolding A flexible, changeable scaffold It gives the neuron its characteristic shape o Extends throughout the cytoplasm o Some fibers are permanent o Most fibers are synthesized or disassembled according to the cells needs o The bones of the cytoskeleton are the microtubules, microfilaments, and neurofilaments o Elements of the cytoskeleton are dynamically regulated and are very likely in continual motion NROB60 Study Package: Week 4 Homira Osman The Cytoskeleton - 5 important functions: o (I) Cell shape Provides mechanical strength Helps determine the shape of the cell o (II) Internal organization Stabilize the positions of organelles Dynamic, changing from moment to moment in response to cells needs o (III) Intracellular transport Transport materials into the cell Transport materials within the cytoplasm railroad track o (IV) Assembly of cells into tissues Connect to fibres in extracellular space Link cells together and to supporting material outside of cells Mechanical strength and allow transfer of information o (V) Movement Migration of white blood cells; extension of nerve cells, allow movement of cilia an flagella Microtubules - 20 nm in diameter - Big - Run longitudinally down neurites - Appears as a straight, thick-walled, hollow pipe - Composed of smaller strands of tubulin braided together (pearls on a string) - Formed through polymerization - Regulated by various signals o E.g.: microtubule-associated proteins (MAPs) (neuron specific type TAU) - Anchor the microtubules to one another and to other parts of the neuron Microfilaments - 5 nm in diameter (small) (same thickness as plasma membrane) - Throughout neuron but more numerous in neurites - Two thin strands of ACTIN protein braided together - Formed through polymerization - Constantly undergoing assembly and disassembly - Regulated by signals in the neuron - Running longitudinally down the core - Anchored to the membrane by attachments with a meshwork of fibrous proteins that line the inside of the membrane (like a spider web) Neurofilaments (Intermediate) - 10 nm in diameter - Exist in all cells as intermediate filaments (only called neurofilaments in neurons) - Composed of multiple sub-units linked together - Appears as a straight, thick-walled, hollow pipe - Composed of three protein strands woven together NROB60 Study Package: Week 4 Homira Osman - Each protein is an individual, long protein molecule - Each protein molecule is tightly coiled in a tight, spring-like configuration - Mechanically very strong - Cross link within the neuron Axons Carrying Outgoing Signals To The Target - Axonal Transport: slow axoplasmic flow; fast anterograde vs retrograde Axoplasmic Transport - Proteins of the axon must be synthesized in the soma and then shipped down the axon - Slow Axoplasmic Transport: 1-10 mm per day - Fast Axoplasmic Transport: Up to 1000 mm per day A mechanism for the movement of material on the microtubules of the axon - Trapped in membrane enclosed vesicles, material is transported from the soma to the axon terminal by the action of the protein kinesin, which walks along mictotubules at the expense of ATP
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