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55 Cards in this Set
- Front
- Back
How does globular actin polymerize into F-actin?
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By binding ATP
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Is F-actin polarized?
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YES
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What is necessary for globular actin to be competent for assembly?
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ATP must be bound and have induced a conformational change.
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What confers filament stability?
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an ATP cap
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Are subunit binding and ATP hydrolysis coupled?
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No
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From what end does Actin polymerize?
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the plus end
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What does the fact that the plus end is fast growing and minus end is slow growing allow?
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Treadmilling
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What does Actin use treadmilling for?
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Locomotion of migrating cells
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Define Critical concentration of actin:
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The free subunit conc at which on and off rates of assembly are equal
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At which end is the concentration of free Actin higher?
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Minus end - that's where it falls off
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What is the critical conc?
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.5 uM
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What are the concentrations at:
-minus end -plus end What state is achieved by this? |
Minus = .8 uM
Plus = .1 uM Steady state where plus end is always making, minus is always disintegrating |
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What state is favored in cells; polymerization, depolymerization, or equilibrium?
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Polymerization - the conc of free globular actin is 1000x higher than the crit conc of 0.1
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What disrupts F actin?
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Cytochalasin
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What stabilizes F actin?
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Phalloidin
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What is the big difference between Actin and IFs again?
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No binding proteins for IFs; there are for Actins.
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4 classes of Actin binding proteins:
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1. Regulation
2. Severing 3. Cross-linking 4. Motor |
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What are the regulation ABPs?
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-Thymosin B4
-Profilin -Tropomodulin -Capping protein |
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What are the Severing ABPs?
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-ADF
-Cofilin -Gelsolin |
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What are the crosslinking ABPs?
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-Spectrin
-Dystrophin -Fimbrin -Filamin -a-actinin |
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What is the motor ABP?
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Myosin
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Which end of f-actin does tropomodulin bind to regulate?
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Minus end
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Which end of f-actin does capping protein bind to regulate?
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Plus end
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What does Thymosin B4 bind?
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Free g-Actin to prevent polymerization
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What does profilin do?
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Activates
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How do bacteria and viruses take advantage of actin?
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By inducing its polymerization and then using it for motility.
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Phalloidins
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Stabilize Factin by locking subunits together
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Cytochalasins
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depolymerize F-actin by binding to plus ends
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What is the name of capping protein?
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capZ
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What is ARP2/3 complex?
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Actin-related protein - another regulatory protein
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How many actin binding sites do Crosslinking ABPs have?
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Two - "bivalent"
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What inhibits crosslinking with Actin?
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Calcium
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What determines how closely packed actin filaments will be when they bind an ABP?
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The distance of protein between Actin binding sites
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What would exhibit tight packing?
What would exhibit loose packing? |
Tight = structural, microvilli
Loose = muscle (myosin xlink) |
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What stabilizes microvilli?
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Core actin filaments crosslinked by Fimbrin and Villin, rooted in spectrin, keratin, and more actin.
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Which ABP causes orthagonal crosslinking of Actin filaments?
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FILAMIN
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What is the product of actin orthagonal crosslinking?
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A GEL that can dissolve into SOL
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Why is Filamin important?
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Because it anchors the actin crosslinked network to a glycoprotein that is attached to a platelet clot on the other side.
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Does actin only play a role in stabilizing clots to the cytoskeleton?
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No; it also links the skeletal muscle membrane to the cortical F-actin cytoskeleton.
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What actin filament stabilizes the muscle myocyte's cytoskeleton to the basal lamina?
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Dystrophin
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What is the order of connecting molecules between Actin/myosin in the sarcomere and the Basal lamina?
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Actin-Desmin-Actin cytoskeleton - Dystrophin - integral glycoproteins - laminin
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What results when Dystrophin is defective?
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The membrane tears during contraction
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What is the name of the disease of membrane tearing during contractions?
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Duchenne muscular dystrophy
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Does actin always just link extracellular stuff to the intra cytoskeleton?
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No; also links the cytoskeleton to the extracellular matrix.
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What are myosin ATPase motors used for?
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Moving actin microfilaments for moving vesicles, or protrusion of the cell surface.
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What type of movement can be achieved via Actin microfilaments?
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Amoeboid
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What is the name of the model of amoeboid movement?
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DENDRITIC NUCLEATION MODEL
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Which form of myosin binds membranes for vesicle translocation?
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Myosin I
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Which form of myosin is involved in actin filament sliding?
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Myosin II
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What cell function is dependent on actin-based lamellipodia formation?
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Macrophage phagocytosis
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What disease results from defective phagocytosis?
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Wiskott-Aldrich
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What provides the push for membrane extrusion during phagoyctosis?
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Actin polymerization
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What activates Actin polymerization for phagocytosis?
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Arp2/3 - activated by W (wiskott aldrich syndrome protein); Active ARP nucleates F-actin growth.
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What stops the polymerization during phagocytosis?
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Capping protein
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How do pathogens (bacteria and viruses) harness Actin's movement?
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By binding ARP2/3 at their tails
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