ch 33.txt

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ch 33.txt
2013-07-17 00:25:37


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  1. What is the primary mechanism by which the actin cytoskeleton generates cell motility?
    • Polymerization/Depolymerization driven: Filament assembly or disassembly can create the motility w help from Profilin and Arp2/3. The process of ATP hydrolysis occurs and treadmilling to give the motility ??
    • Myosin motors: also act to generate motility through a process of binding, the POWER STROKE and unbinding, generating the contractile force for movement.
  2. ****What effect does ATP hydrolysis have on actin and actin filaments?
    • Irreversible step for actin subunits, result is ADP-actin with Pi. seen in cytoskeleton and mechanisms of movement
    • Treadmilling results: Giving the effect of a monomer moving on a treatmill. the ADP bound actin at pointed end dissociate, at a faster rate than the ATP-bound actin can associate. ATP-bound must associate faster to catch up
  3. What are the different types of microfilament arrays seen in different cell types and what are their functions? Please see the textbook for a more complete discussion of these arrays than what I covered in class.
    • Near actin periphery:
    • In Brush Border Epithelial Tissue: aid in SURFACE EXPANSION
    • In Plant epidermis: aid in CYTOPLAMIC FLOWING
    • In RBCs: act as STRUCTURAL MATRIX for membrane STABILITY
    • Microfilament functions: Absorption, secretion and Cell motility role
    • In Amoeboid: actin role in CELL CRAWLING
    • Intracellular motility
    • Contractile rings in Rat Kidney and Fission Yeast
    • Muscle fibers in vertebrae
    • Stress fibers in Amoeboid cells
  4. What is the relationship between actin and the Arp proteins?
    • Arp: Actin related proteins that are 60% identical to actin But do NOT form FILAMENTS. Have same contacts with ATP but different surfaces
    • Related in that Arp2/3: involved in NUCLEATING Branched ACTIN FILAMENTS
    • Arps are involved in vesicle formation and microtubule based transport