topic 4_rivier_252 - MCB 252 Cell Biology Topic 4...

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MCB 252 Cell Biology Topic 4 Regulation of Actin Assembly
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Reading Reading: Lodish 17.2-17.3, 17.7
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MCB 252 Actin Cytoskeleton A. Properties of Actin B. Role of Actin in Cell Movement C. Regulation of Actin Assembly in Cells D. Stable Actin Structures E. Muscle Cells and Myosin Motors
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Actin Cytoskeleton Properties of Actin Actin assembly Role of ATP Treadmilling Role of actin in cell movement Actin is required for movement Actin assembly can drive movement Regulation of actin assembly in cells Proteins invovled in actin assembly/disassembly Turning the protein invovled in assembly and disassembly ON and OFF Building stable actin structures
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How Does a Cell Regulate Where Assembly Occurs?
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What are the properties of Actin polymerization in cells? 1. Nucleation is regualted so that polyer formation only occurs is specific regions of the cell. 2. Dissociation of monomers from the polymer is regulated so that dissociation primarily occurs at the minus end. 3. Association of mononers with the polymer is regulated so that growth occurs almost exclusively at the plus end. 4. Regulation is mediated by proteins that interact with G-actin or with the ends of F-actin.
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How is assembly of actin restricted to particular regions of the cell? 1. Regulation is mediated by proteins that interact with G-actin or with the ends of F-actin. 2. Signals are received by one side of a cell but not another. Signalling regulates the function of the proteins invovled in actin assembly. First we will look at the mechnaisms by which proteins modulate F- actin assembly/disassembly. Then we will look at regulation- how the proteins that modulate assembly are themselves turned ON or OFF in response to signalling.
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Proteins that Facillitate Various aspects of F-actin assembly: A Parts List STEP PROTEIN(S) Sequestering G-actin: Thymosin β 4 Nucleation: Formin, Arp2/3 complex Elongation: Formin, Profilin Disassembly: cofilin, gelsolin PREVENTING ASSEMBLY AND DISSASEMBLY (Capping Proteins) Plus end: CapZ Minus end: Tropomodulin
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polymers and move faster than they can produce actin? Answer: The concentration of G-actin in the cell is 100 x greater than the critical concentation BUT G-actin in sequestered in a pool that is not in a form that can be polymerized. Binding of Thymosin
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topic 4_rivier_252 - MCB 252 Cell Biology Topic 4...

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