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12 Cards in this Set
- Front
- Back
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Actin Microfilaments characteristics
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1. Helical polymers of actin proteins; two protofilaments
2. seven nanometers in diameter 3. structurally polar; plus and minus end 4. thinner, shorter and more flexible than microtubules; in total length of all actin filaments in most cells is ~30 X's that of microtubules 4. Globular actin is basic subunit, highly conserved 5. in most cases fast reactions to stimuli 6. located throughout cell many arrangements, that are most highly concentrated in the cell's cortex 7. actin filaments found primarily in linear bundles, 2-d (sheets bundles) and 3-d (gels) networks; rarely occur in isolation |
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Mechanisms of polymerization and depolymerization
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1. similar strategy as microtubules
2. nucleotide (ATP) exchange/hydrolysis cycle 3. ATP cap 4. microfilament organizing centers small, distributed, modular |
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Actin binding proteins modify behavior
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Actin monomers can become
1. nucleating proteins or monomer sequestering proteins or actin filaments. 2. Actin filaments can become: severing protein, cross linking protein (in cell cortex), capping protein, side binding proteins, motor protein, and bundling protein (in filopodia) |
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Actin binding proteins modify behavior 2
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There are 100s of proteins that bind actin and affect its nucleation, polymerization, and interactions with cellular components (including itself)
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Influencing nucleation
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nucleation can be catalyzed by a complex of proteins that includes tow actin related proteins (Arps). theses arps form a complex like gamma TuRC that nucleates actin filament growth from the minus end
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Influence bundling
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F-actin is organized into different assemblies based on type of cross linking proteins
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Contractile bundles
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Description: F actin arranged in tight bundles of opposite polarities
Function: contractions, motility, adhesion to surfaces, cytokinesis Example: stress fiber, contractile ring Associated protein: Myosin II (many others) |
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Non-contractile bundles and sheets
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Description: F actin arranged in tight bundles and thin sheets, bundles and are structurally polar
Function: formation of non-contractile outgrowths at cell surface. Dynamic and ephemeral in mobile cells (wound healing, probing environment (growth cones), stable in cells requiring increased surface area Examples: Filopodia - tight stiff, thin, ephemeral; Microvilli - tight, stiff, thing stable' Lamellipodia = thin sheet like, ephemeral Associated proteins : ARP 2/3 complex (lamellipodia); villin (microvilli) |
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Gel-like network
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Description: F actin arranged in a loose yet highly viscous 3d open array with many interconnections; mixed polarity
Function: forming dense bed of f actin in cell cortex; support of plasma membrane and cytoplasm Example: cell cortex |
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Actin Molecular Motors
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Myosin responsible for a variety of cellular movement; large family of proteins; nonprocessive (kinesin, dynein, are processive)
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Myosin 1
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member of the myosin superfamily involved in a number of cellular functions including membrane trafficking, cell motility, cyotkinesis, organelle transport
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Myosin 2
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1. conventional myosin
2. skeletal muscle, smooth muscle and nonmuscle 3. crucial for the movement of opposite oriented f actin: generates tension in stress fibers, contractile ring, adhesion belts, and muscle contraction. |
