BIO 353 Cell Biology Study Questions for Exam #3 Fall, 2012
“The harder the conflict, the more glorious the triumph.” Thomas Paine... “Unless you really just screw up.” Bush
1. What are microfilaments?
(He said know how to identify/draw these) Note: since it is multiple choice, I doubt we will have to know how to draw them. **There are also short essay questions and, in past classes, he has asked students to draw. I thought the final was ALL MULTIPLE CHOICE???******************************** Microfilament- Analogous to actin microfilaments. Helical polymer of actin protein; two protofilaments. Smallest cytoskeleton diameter (3-6nm) structure Thinner, shorter, more flexible than microtubes. One basic 7subunit, globular actin. Structurally polar. Have fast reaction to stimuli. What super structures do they form?
1.Microvilli; structure of microfilaments lining the edge of cell 2.Stress fibers; antiparallel of actin bundles, contractile forces, wound healing ect. 3.Lamellipodia; sheet lik1.Nucleating proteins; Arp2/3 ce projections for movement, actin bundles parallel to cell surface- Same category as Filopodia 4.Filopodia; hair-like extensions or movement and sensory
5.Contractile ring; to help split cells
What other proteins do actin and microfilaments interact with? * complex help in nucleation of microfil., polymerization/ depolymerization, interaction with cell components What kinds of microfilamentous structures does each protein help form? 1. Bundling protein; F-actin is org. into diff. assemblies based on cross linking proteins 1. Contractile Bundles- Associated protein-Myosin 2 that always moves to + end of F-actin, Non-structurally polar (even tho F-actin is polar by itself), Function-contractions, motility, ect., examples- stress fibers, contractile ring 2. Non-Contractile Bundles- Arranged in tight bundles and sheets, Structurally polar. Formed at the cell’s surface. Increase surface area. Associated proteins-Arp ⅔ complex, villin; examples- complex(lamellipodia, filopodia), villin(microvilli) 1. Motor protein; Actin Molecular Motors Movement of F-actin. 1. A) Myosin 1- membrane trafficking, cell motility, cytokinesis, organelle transport 2. B) Myosin 2 - movement of opposite oriented F-actin, generates tension in stress fibers, contractile ring. ect. 1. Cross-link protein; Gel-like network of F-actin. Used for stability and support. F-actin arranged in loose 3D array with interconnections. Mixed polarity, Proteins- filamin. Example-cell cortex 2. Nucleating proteins: catalyzed by complex of proteins that include two actin-related proteins (Arps). Arps complex is analogous to the gamma-TuRC and nucleates actin filaments from their MINUS ends
2. How does myosin II form filaments? How do these filaments interact with microfilaments? What kind of cycle does the myosin head go through as it “walks” on microfilaments? * Myosin II forms filaments by the tails of 2 myosin-II wrap around one another to form a spindle in which the heads project outward from the middle in opposite directions. Clusters of myosin-II molecules then bind to each other making a bipolar myosin filament. * The head of the myosin II binds to actin
* Then through ATP hydrolysis the cell “walks” because the inorganic phosphate created by the hydrolysis displaces the myosin. The “walking” is toward the (+) end.
3. How do cells “crawl” by amoeboid movement? What are the various ways in which actin, myosin, adhesion plaques/focal contacts, and vesicle transport play a role in the process? The basic idea is Protrusion -> Adherence by integrins to ECM-> pulling itself (Retraction) by contractile bundles or possibly actin in cell cortex (still not certain how retraction force is formed) It crawls by lamellipod (crosslinked), filopodia (Parallel Bundles that depend on formin that form straight unbranched filaments that push foward) . lamellipod grow through ARPs that...
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