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Flashcards in Cytoskeleton Deck (64):
1

What are three kinds of protein structures that make up the cytoskeleton?

> microfilaments
> intermediate filaments
> microtubules.

2

What are features of actin filaments?

highly conserved structure, filaments organize into bundles, bind to transmembrane proteins, exist as monomers (G-actin) or long chains (F-actin).

3

What does G actin have a binding site for?

> ATP (binds tightly to G-actin)

4

How many other monomers can a single actin monomer bind with?

2

5

Do actin monomers display polarity?

yes

6

What is nucleation?

> The first step of actin polymerization.
> A trimer is formed and additional actin monomers can then be added to either end.

7

ATP-actin associates which end of the actin filament?

> the plus/barbed end
> ADP is made once actin binds here.

8

What affects the rate of monomer addition to a growing filament?

the cytosolic concentration of actin monomers.

9

Which end of the actin filament grows faster?

barbed end

10

At what concentration do actin filaments disassemble?

low concentrations of G-actin

11

What is treadmilling?

> intermediate concentrations of G-actin

AND

> a dynamic equilibrium of growth and recession at the barbed and pointed ends.

12

What do high concentrations of G-actin favor?

higher concentrations of G-actin at both ends (e.g. growth)

13

What do cytochalasins do?

bind to barbed ends and prevent more actin monomers from binding. They also prevent movement/cell division.

14

What does phalloidin do?

> binds to actin filaments and prevents dissociation.
> can be labeled with fluorescent dyes to allow visualization of actin filaments

15

What determines the diversity of functions of actin?

the actin-binding proteins, not actin itself.

16

What are some actin binding proteins?

spectrin (RBC passage through capilliaries); dystrhophin (binds cytoskeleton to plasma membrane); villin/fimbrin (holds actin filaments together); calmodulin and myosin I (cross links actin to plasma membrane).

17

What actin-binding proteins control treadmilling?

thymosin and profilin. Both prevent actin from being polymerized.

18

What are intermediate filaments?

filaments that provide tensile strength in neurons and muscle, strengthen epithelial cells as desmosomes and hemidesmosomes, etc.

19

What is the structure of intermediate filaments?

> monomer consisting of a central alpha-helical rod flanked by head and tail domains.

20

How are intermediate filaments assembled?

two polypeptides form a dimer ----> dimers form tetramers ----> tetramers form protofilaments ----> 8 protofilaments form a filament.

21

What are the functions of intermediate filaments?

> form cytoplasmic networks in cells
> associate with other cytoskeletal elements to form a scaffolding that organizes the internal structure of the cell.

22

What are microtubules made of?

tubulin dimers; there is an alpha and beta subunit that make two separate helices.

23

What is dynamic instability?

alternate phases of slow growth and rapid depolymerization. GDP is quickly released from the - end.

24

What is colchine?

a drug that inhibits microtubule polymerization. It is used for cancer treatment.

25

What is taxol?

an anti-cancer drug that stabilized molecules (prevents depolymerization).

26

What are some functions of the cytoskeleton?

> cell movement
> support and strength
> phagocytosis
> mitotic spindle formation
> cytokinesis
> changes in cell shape.
> cell-to-cell and cell-to-extracellular matrix adherences

27

What molecule travels from the minus end to plus end to deposit tubulin?

kinesin

28

Which molecule carries cargo from the plus end to the minus end?

cytoplasmic dynein.

29

Which myosin molecule is the only one with two heads?

myosin I

30

What do the heads of kinesin and cytoplasmic dynein bind to?

microtubules

31

What do the heads of myosin I and II bind to?

actin

32

What do the tails of kinesin and cytoplasmic dynein bind to?

vesicles

33

What do the tails of myosin I and II bind to?

the cell membrane (I) and myosin II (II).

34

Is actin polymerization reversible?

> yes

35

_____-actin dissociates more readily from filaments than _____-actin?

> ADP
> ATP

36

**Actin fact**

> actin is a very common and very ubiquitous protein found in all cells, but in spite of the fact that it has pretty much the same structure in all cells, it is involved in a number of kinds of functions

37

This is determined by the actin-binding proteins and not by actin itself?

> the diversity of function of actin filaments

38

Spectrin (ABP)?

> found in RBCs
> binds cytoskeleton to plasma membrane

39

Dystrophin (ABP)?

> binds cortical cytoskeleton to the plasma membrane

40

Villin and Fimbrin (ABPs)?

> cross-link actin to plasma membrane in microvilli

41

alpha-actinin (ABP)?

> cross-links stress fibers and connects actin to protein plasma membrane complex complexes

42

Filamin (ABP)?

> cross-links actin at wide angles to form screen like gels

43

Thymosin (actin-binding molecule/control treadmilling)

> captures actin monomers
> prevents monomers from being polymerized

44

Profiln (actin-binding molecule/ control treadmilling)

> binds to actin monomers and prevents monomers form being polymerized

> facilitates exchange of ADP for ATP----which favors polymerization

> only ATP-actin monomers can be assembled into F-actin

45

Gelsolin (actin-binding molecule/ control treadmilling)

> destabilizes F-actin and caps actin filaments, preventing loss and addition of G-actin
> In presence of calcium ion, fragments actin filament and remains bound to plus (+) end

46

Cofilin (actin-binding molecule/ control treadmilling)

> triggers depolymerization of ADP-bound actin at minus end

47

Arp2/3 (actin-binding molecule/ control treadmilling)

> initiates growth of F-action from sides of existing filament---causes branching

48

Phalloidin (actin-binding molecule/ control treadmilling)

> prevents depolymerization by binding to actin filaments

49

Latrunculins (actin-binding molecule/ control treadmilling)

> binds to G-actin and induces F-actin depolymerization

50

These intermediate filament types are associated with keratin?

> type I
>>> acidic keratins

> type II
>>> neutral to basic keratins

51

Microtubules consist of _____ protofilaments arranged parallel to form a cylinder with a hollow core?

> 13

52

Protofilaments have a ______ growing plus (+) end and a _____ growing minus(-) end?

> fast
> slow

53

What type of tubulin dimers associate with the growing end of microtubules?

> tubulin dimers with GTP bound to the beta-tubulin

54

Low calcium ion concentration causes this end of the microtubule to grow faster than the other?

> Plus (+) end grows more rapidly than minus (-) end

55

At high concentrations of _______, the dimers are added more rapidly than GTP is hydrolyzed, and the microtubule grows?

> tubulin-GTP

56

Drugs that inhibit microtubule polymerization?

> colchicines
> colcemid
> vincristine
> vinblastine

57

This drug is used to treat Hodgkin's Lymphoma?

> vinblastine

58

Drugs that stabilize microtubules?

> taxol

59

This drug is used to treat breast cancer?

> taxol

60

How do drugs such as colchicine work to prevent polymerization of microtubules?

> by binding to the tubulin dimers and preventing their assembly into microtubules

61

How do drugs such as taxol work to stabilize microtubules?

> binds to microtubules preventing their depolymerization
> taxol disrupts mitosis by affecting the dynamic assembly of the mitotic spindle.
> antimitotic drugs bind to reverse sites on tubulin, and

62

What mediates the anterograde transport of cargos along microtubule?

> kinesin

63

What mediates the anterograde transport of cargos along microtubules?

> cytoplasmic dynein

64

This may provide a mechanism for the transport of multiple cargos along microtubules?

> raft protein complex