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22 Cards in this Set
- Front
- Back
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5-9 nm
Also called microfilaments, stress fibers, F-actin, G-actin. |
Actin Diameter
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25 nm
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Microtubule Diameter
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8-10 nm (between thin actin filaments and thicker myosin (and MT) filaments)
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Intermediate Filament Diameter
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Globular. Each monomer has 375 amino acids and each one associates with one ATP
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Actin Subunits
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Globular, alpha-tubulin subunit and beta tubulin subunit
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Microtubule Subunits
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Fibrous
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Intermediate Filament Subunit
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Requires ATP, K+ and Mg2+. Hydrolysis of ATP occurs immediately after incorporated into its filament. Two-stranded tightly wound helical polymers, somewhat flexible. Usually exist as cross-linked aggregates, linear bundles (stress fibers) and 3-dimensional gels
Slow-growing (-) end and faster-growing (+) end. |
Actin
Structure and Assembly |
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Requires GTP. Polar structure, has a (-) and (+) end. The (-) end is attached to a MTOC also called a centrosome (located next to nucleus). The (+) end extends and retracts (called dynamic instability).
GTP binds to beta-tubulin of an alpha/beta dimer, dimer binds to the (+) end of the microtubules forming a GTP cap. If rate of polymerization slows GTP is hydrolyzed it depolymerizes. 13 linear protofilaments composed of alternating alpha and beta tubulin subunits. Bundle in parallel to form a cylinder. More rigid than actin |
Microtubules
(Structure and Assembly) |
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Heterogeneous family of fibrous proteins that have a central rod-like domain composed of heptad repeats. Two proteins form a coiled-coil dimer. Two dimers form a staggered tetramer. N and C terminus give specificity to the different proteins .
4 types. Same at both ends, symmetrical (nonpolarized). Nuclear lamina controlled by de/re-phosphorylation of serine in the N-terminus. |
Intermediate Filaments
(Structure and Assembly) |
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Throughout cytoplasm, high concentration in cortex
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Actin Cellular Localization
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Throughout cytoplasm
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Microtubules
Cellular Localization |
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In nuclear lamina and throughout cytoplasm
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Intermediate Filaments
Cellular Localization |
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Myosin-I and myosin-II
alpha-actinin (links bundles together) |
Actin Accessory Proteins
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MAPs (MAP-1, MAP-2, tau) bind microtubules and stabilize them.
Motor proteins kinesin (move toward (+) end) and cytoplasmic dyneins (move toward (-) end. Require ATP hydrolysis for movement. |
Microtubule Accessory Proteins
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Forms cell cortex, cell surface movement and shape, cell migration.
Forms structures including microvilli, contractile units (muscle). Forms contractile ring in dividing cells |
Functions of Actin
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Positioning of organelles (mitochondria, pigment granules, ER).
Transport: in axons, microtubules oriented with (+) ends away from soma. In dendrites, polarity is mixed. The accessory protein MAP-2 is in the dendrites and soma, not in axon. Some tau forms (dephosphorylated) are only found in axon. |
Functions of Microtubules
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Forms nuclear lamina and provides cellular strength. Do not rupture as do MT and actin. Defect may cause Epidermolysis bullosa simplex O/H.
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Functions of Intermediate Filaments
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In ALLeucaryotic cells.
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Actin
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In MOST eucaryotic cells.
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Microtubules
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In many cell types. Prominent in epithelia, muscle cells and axons. Clinical use in typing carcinomas. Can determine tissue in which the tumor originated. Will help determine treatment.
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Intermediate Filaments
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Cytochalasins prevent actin polymerization by binding to the (+) end of the actin filament.
Phalloidins (mushroom Amanita) bind F-actin and prevent actin depolymerization. Eat meat. |
Actin Neutralizing Drugs
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Colchicine, colcemid, vinblastine, vincristine. Bind to tubulin and prevents polymerization. In contrast, taxol binds to microtubules and stabilizes them. These drugs interfere with the mitotic spindle. Clinically used to kill tumor cells.
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Microtubule Neutralizing Drugs
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