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18 Cards in this Set
- Front
- Back
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What are the three main components of the cytoskeleton, and what are their primary functions?
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Microtubules - 25nm - ciliary/flagellum, chromosomal movement, vesicle transport, secretion. Made of Alpha/Beta Tubulin.
Microfilaments (Actin!) - 7-9nm. muscle contraction, cell adhesion, motility, stabilize microvili Intermediate filaments - 10nm - between the two. Sticks around, doesn't polymerize/depolymerize. Constant. |
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What disease should we think of as soon as the word actin is mentioned? What causes it?
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Duchenne's Muscular Dystrophy - caused by defects in DYSTROPHYN (biggest gene) - dystrophyn links actin skeleton to the extracellular matrix/basal lamina. Leads to death of muscle cells.
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What are the two states actin can exist in?
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Globular actin (G-actin) monomer
filamentous actin (F-actin), made of monomers |
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What is actin treadmilling, and what proteins accelerate it?
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G-actin is bound to GTP - binds + end more readily than - end. Binding hydrolyzes GTP to GDP, makes it more likely to fall off towards - end.
Profilin/Cofilin accelerate treadmilling. |
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How do you begin to form G-actin monomers into a filament? What two protein classes can be used, and what different structures do they make?
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Need NUCLEATING PROTEINS - two classes:
Formin: makes long, unbranched, stress fibers ARP2/3 complex makes branched filaments found at LEADING EDGE of migrating cells. Highly regulated. |
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What kinds of fibers are seen at the leading edge of a cell, and which are seen at the trailing edge?
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Leading edge = active treadmilling,
trailing edge = stress fibers, cause contraction. |
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What are the 3 actin crosslinking proteins, and what do they favor the creation of?
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1. Fimbrin = make microvili
2. Alpha-Actinin = organize into stress fibers 3. Spectrin = cell cortex filaments. Strengthens cell wall/PM. |
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What's hereditary sphereocytosis?
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Mut. in spectrin, alpha actinin, ankryin. get fragile RBC's.
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During cell migration, what structure at the leading edge extends? Once it extends, what does it form?
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The lamellipodium forms new cell adhesions.
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Leading Edge - what signaling molecules/mechanisms exist to regulate the leading edge?
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Two g-proteins: CDC 42 and Rac, controlled by GDP-GTP. Timer - once GTP hydrolyzes, stops. These activate ARP2/3 to polymerize branched microfilaments at the leading edge.
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What controls actin polymerization at the trailing edge?
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G-protein at rear of cell = Rho.
Rho activates formin to make stress fibers. Also activates MYOSIN to contract and allow motion. |
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How do we ensure the cell moves only one direction?
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polarity is caused by the fact that Rho inhibits Rac = unidirectional movement.
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What proteins link cytoskeletal components to the extracellular matrix?
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Integrins
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Intermediate filaments - in epithelial cells, what are the PM regions they're attached to?
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Desmosomes/Hemidesmosomes.
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What disease is caused by a mutation in intermediate filaments?
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Muts in keratin cause epidermiosis bullosa simplex. Also may play a role in ALS.
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Intermediate fibers - what kinds are they, and where do they live?
Possible categories include: Keratins, desmins, gfap, vimentin, neurofilaments, and lamins. |
Keratins are all in the epithelial cells.
Neurofilaments in neurons Lamins in Nucleus Rest are all muscle cell associated (desmins, gfap, vimentin) |
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What two things are important for controlling the formation of actin filaments?
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ATP and Mg 2+
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What cellular components generate the signals necessary for formation of new focal adhesions during cellular migration?
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integrins - they link to the ECM and relay when it's time to make a new sticky.
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