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Molecules to Medicine III > Cytoskeleton > Flashcards

Flashcards in Cytoskeleton Deck (62)
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What is a potential side effect of MT toxins used for chemotherapy?

peripheral neuropathy
- 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?

muscle contraction
cell mobility
epithelial polarity
cell division


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)
- Polymerization
- disassembly
- stabilize
- Crosslink
- 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?

Rho family
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)


Give an example of cell motility in the context of infection

polymorphonuclear leukocytes must exit blood vessels and migrate into tissues to reach infection site

As cancer cells become malignant they migrate and invade healthy tissues (metastasis) -> eventually establishing tumors in locations distant from origin