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CH369_lecture5_2-3-2009

CH369_lecture5_2-3-2009 - Motor proteins Lessons from...

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Motor proteins
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Lessons from biological system Spider silk, made of a protein called fibroin, consists of Ala- and Gly-rich β sheets interspersed with more amorphous segments of polypeptide.
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Cell migration and metastasis Normal functions Wound healing Fighting infection Pathological -metastasis Crawling
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What happens during muscle contraction? Do muscle cells become shorter? What is the energy source?
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Cytoskeleton Cytoskeleton –Molecules serve the functions to a cell much like skeletal systems to the body The cytoskeleton accounts for the majority of a cell’s mass provides the cell with rigidity and shape , much like the skeletal system of the body. Unlike the animal skeletal system, the components of the cytoskeleton are ever- changing.
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Globular proteins. They are responsible for carrying out the bulk of the metabolic reactions of cells: harvesting and storing free energy, transforming biological compounds into others, decoding genetic information. Fibrous proteins They are elongated and often insoluble, abundant. These proteins determine the shape and other physical attributes of cells and organisms.
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Microfilament A major portion of the eukaryotic cytoskeleton consists of microfilaments, or polymers of actin. In many cells, a network of microfilaments supports the plasma membrane and therefore determines cell shape
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Structure of actin Electron X-ray Modeled micrograph crystal based on structure x-ray crystal structure
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Actin F-actin (for filamentous actin) - Polymerized actin G-actin, the globular monomeric form
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Actin assembly - Most of the actin subunits in a microfilament contain bound ADP - The presence of ATP to actin is not essential for polymerization
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Actin Hydrolyzes ATP and binds to both ATP and ADP
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Microfilaments are dynamic structures Dissociation polymerization Treadmilling: rate of dissociation = polymerization
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Capping stops polymerization In vivo, the rate of polymerization > dissociation
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Cell migration Crawling Extracellular signals, regulate the assembly and disassembly of Microfilaments.
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Myosin : A motor protein associated with actin A skeleton muscle fiber
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Myosin is composed of a homodimer Coiled-coil
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Crystal structure of the myosin head
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Hydrolysis of ATP
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Motor proteins Molecules can convert the chemical reaction energy into mechanical forces/movement No external forces required http://wileyplus.com
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