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Molecules to Medicine III > Cytoskeleton > Flashcards

Flashcards in Cytoskeleton Deck (62)
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31

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

32

What is a pathology associated with microtubule severing proteins?

Hereditary spastic paraplesia

33

What is G-actin?

Microfilament
- filamentous polymer of actin monomer
- ~7nm in diaeter

34

What induces G-actin to form F-actin?

presence of divalent cations and ATP

35

What are 4 important roles of actin?

muscle contraction
cell mobility
epithelial polarity
cell division

36

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)

37

What protein nucleates actin in a linear pattern?

Formin

38

What protein nucleates actin and causes it to branch?

Arp2/3

39

What is Rho

monomeric GTP activated by extracellular signal which induced actin polymerization

40

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

41

What are adherens junctions?

protein complexes that occur at cell cell junctions between epithelial and endothelial cells
- more basal than tight junctions

42

What is actin's role in adherens junctions?

actin links cytoplasmic face of the junctions

43

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

44

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

45

What is microvilli inclusion disease?

loss of microvilli

46

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

47

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

48

What is the function of myosin V?

cargo carrier to transport vessicles

49

What complex regulates lamelipodia formation?

Arp2/3

50

What complex regulates filopodia formation?

formins

51

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

52

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

53

When are Ras GTPases active v. inactive?

Active in GTP bound state
Inactive in GDP bound state

54

What is the role of Rho in relation to actin

causes formation of stress fibers & focal adhesions

55

What is the role of Rac activation?

formation of veils

56

What is the role of Cdc42?

protrusion of fillopodia

57

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

58

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

59

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)

60

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