Flashcards in Cytoskeleton Deck (62)
What is a potential side effect of MT toxins used for chemotherapy?
- MT toxins block mytosis
- BUT also affect other MT functions like axoplasmic transport
What is a pathology associated with microtubule severing proteins?
Hereditary spastic paraplesia
What is G-actin?
- filamentous polymer of actin monomer
- ~7nm in diaeter
What induces G-actin to form F-actin?
presence of divalent cations and ATP
What are 4 important roles of actin?
What are some of the actions of the accessory proteins that regulate actin?
60+ accessory proteins
- G- actin concentration (profilin)
- ADP to ATP exchange (profilin)
- sever (ADF/ Cofolin)
- cap (gelsolin)
What protein nucleates actin in a linear pattern?
What protein nucleates actin and causes it to branch?
What is Rho
monomeric GTP activated by extracellular signal which induced actin polymerization
What is the role of actin at tight junctions?
It acts as an intracellular anchor to the tight strands forming the impenetrable cell junction
- connects cytoplasm of adjacent cells
What are adherens junctions?
protein complexes that occur at cell cell junctions between epithelial and endothelial cells
- more basal than tight junctions
What is actin's role in adherens junctions?
actin links cytoplasmic face of the junctions
What are microvilli
microscopic protrusions in cell membranes that increase surface area in order to maximize functions such as absorption, secretion, adhesion and mechanical transduction
How is actin related to microvilli?
A tight MF is the core of microvilli
- Actin bundles are held together by villin and fimbrin (cross linking proteins)
- actin bundles are linked laterally to plasma membrane by myosin-I
What is microvilli inclusion disease?
loss of microvilli
Describe myosin II (involved in muscle contraction)
Head region with ATPase activity and actin binding sites & tail region
- ATPase at + end
- tail binds to other molecules
- forms hetero-oligomers ( 2 heavy chains, 2 copies each of 2 light chains)
- combine to form thick filaments in muscle
Explain the power stroke between actin and myosin during muscle contraction
ATP binds myosin head where it is hydrolyzed by ATPase -> myosin is activated and goes into extended position (high energy)
Myosin head binds to exposed actin filament
Myosin releases ADP and phosphate -> returns to low E position (bringing actin with it)
ATP binds myosin head-> actin released -> cycle restarts
Contraction = hundreds of myosin heads in same direction at the same time
What is the function of myosin V?
cargo carrier to transport vessicles
What complex regulates lamelipodia formation?
What complex regulates filopodia formation?
How does actin induce cell movement using the lamellipodium?
polymerizes at + end to protrude lamellipodium -> unpolymerized actin moves toward plus end -> Myosin II causes contraction of - end
focal contacts contain integrins
What family of extra cellular molecules act to control actin organization and cell shape? What super family are they a part of?
superfamily of Fas GTPases
When are Ras GTPases active v. inactive?
Active in GTP bound state
Inactive in GDP bound state
What is the role of Rho in relation to actin
causes formation of stress fibers & focal adhesions
What is the role of Rac activation?
formation of veils
What is the role of Cdc42?
protrusion of fillopodia
What is the role of actin in cell division?
actomyosin ring forms -> constricts -> forms clevage furrow -> separates the 2 daughter cells
highly regulated -> determine symmetry of daughter cells
What cells undergo asymmetric cell division?
erythroblast -> reticulcyte + macrophage
2n meakaryocyte -> 4n (abortive cytokenisis)-> up to 128n polyipolod megakaryocytic (abortive cytokenisis) -> platelets
spermatagonia -> sermatatid -> sperm + residual body
Give an example of cell motility in the context of development
migration of neural crest cells from extoderm adjacent to neural tube -> cover whole body as pigment cells
nerve fibers grow over long distances -> tipped by nerve growth cone (has ameboid movement)