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mcb 3010 > Cytoskeleton Regulation > Flashcards

Cytoskeleton Regulation Flashcards

1
Q

MTs nucleate at the

A

Microtubule-organizing centre (MTOC)

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2
Q

Microtubules are nucleated from their _________ ends with the ______ end growing outward from the MTOC

A

minus, plus

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3
Q

_______ makes up the first part of the 13 part ring structure

A

MTOC

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4
Q

True of false: MTOC allows for skipping of the lag step

A

True (allows for first tubulin dimers to be added)

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5
Q

What happens if we mutate or remove the gamma tubulin from a cell

A

MTOC formation is extremely slow and less organized

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6
Q

What direction does MT grow in

A

in most cases, minus end is stabilized and plus end is growing or shrinking, UNLESS minus end is not bound by MTOC

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7
Q

Alpha is always toward the _____ _____ and beta toward the _______/_______ end

A

gamma tubulin, plus/growing end

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8
Q

Most animal cells have a single well-defined MTOC called the _________ located near the _______

A

centrosome, nucleus

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9
Q

_________ emanate from the centrosome in animal cells

A

microtubules

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10
Q

The cytoplasmic microtubules emanate in what kind of formation

A

Star-like

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11
Q

A centrosome is composed of a fibrous matrix that contains _____copies of γ-tubulin.

A

50

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12
Q

What end is anchored and stabilized at the MTOC

A

minus end

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13
Q

What cells and MTs do not always need to start at an MTOC

A

highly polarized cells, more stable MT’s

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14
Q

Embedded in the centrosome is a pair of structures called ________ arranged at right angles to each other.

A

centrioles

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15
Q

When do centrioles duplicate and when do they move to opposite poles of nucleus

A

Duplicate during cell division, move to opposite poles when mitosis begins

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16
Q

“Highway of the cell”

A

Microtubules

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17
Q

Nucleating sites

A

gamma-tubulin ring complexes

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18
Q

Centrioles are surrounded by a

A

centrosome matrix

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19
Q

Tubulin rings are capable of

A

polymerizing MTs

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20
Q

MT aster

A

MTOC with plus end growing outwards from centrosome and minus end anchored and stabalized

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21
Q

In animal cells, the astral configuration, with plus ends pointing out, acts as a device to

A

survey the outlying regions of the cell to position the centrosome at its center

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22
Q

Where is the cis-golgi network found

A

right near nucleus

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23
Q

Are MTOC found in differentiated cells (ex. epithelial cells that from cell-cell junctions, become highly polarized)

A

no

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24
Q

Actin filaments are often nucleated at the

A

plasma membrane

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25
Q

In contrast to microtubule nucleation, actin nucleation occurs most frequently at or near the _______ _______

A

plasma membrane

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25
Q

Actin nucleation can be catalyzed by 2 different regulated factors

A

-ARP complex
-Formins

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26
Q

What gives proper shape to nucleate actin monomers (branched)

A

Orientation of ARP2 and 3 proteins, (fit into ARP complex and starts to grow)

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27
Q

Filament nucleation by ARP occurs at __________ angles

A

70 degree angles

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28
Q

Where does ARP complex bind on polymer of straight actin

A

Middle

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29
Q

What type of actin is present at the growing tip of actin polymer

A

ATP

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30
Q

Does ARP complex have greater affinity for ADP or ATP bound actin

A

ADP, (binds to middle where ADP is found)

31
Q

many large-scale actin structures are made up of parallel bundles of unbranched actin filaments nucleated by the

A

formins

32
Q

A family of dimeric proteins that have a binding site for monomeric actin

A

Formin

33
Q

As the nucleated filament grows, formin remains associated with the rapidly growing _____ end

A

plus

34
Q

Difference between formin and ARP

A

Formin associated with the plus end or nucleated filament, ARP is bound ro the minus end

35
Q

Lampelopodia made up of

A

Branched actin

36
Q

Filopodia made up of

A

Fillamentous actin

37
Q

In most vertebrate cells, approximately ____ of actin is in filaments and _____ is soluble.

A

50%, 50%

38
Q

Specialized proteins such as ________ prevent actin nucleation by binding to monomeric actin

A

thymosin

39
Q

How is “locked“ actin recruited for polymerization? - what does it depend on

A

Another monomeric binding protein called profilin

40
Q

What does profilin do

A

binds to actin at the face that normally binds the minus end, promoting the attachment of the monomer to a free growing plus end.

41
Q

GO REVIEW FORMIN

A

oh ya

42
Q

Profilin is localized where and binds to what

A

localized at the cytosolic face of PM and binds to phospholipids awaiting activation by extracellular signals

43
Q

intracellular mechanisms that regulate profilin activity

A

profilin phosphorylation and profilin binding to inositol phospholipids

44
Q

How does extraceullular signal (RTK activation) affect profilin

A

Profilin is released (it is bound to PM) and oes to “unlock” actin making it available for polymerization

45
Q

What acts as staging areas for addition of actin to the growing plus end of the actin filament (where formin is bound)

A

formin whiskers

46
Q

the cell sequesters unpolymerized tubulin subunits through the

A

stathmins

47
Q

What do stathmins do

A

-bind to two tubulin heterodimers preventing their addition onto growing filaments
-phosphorylation to release tubulin and enhance polymerization

48
Q

Cancer cells frequently overexpress ______ resulting in an increased rate of microtubules turnover

A

Stathmins

49
Q

Severing proteins regulate the _______ and ________ behaviour of actin filaments

A

length, kinetic

50
Q

How does severing existing long filaments into smaller filaments affect the assembly of new filaments

A

Severing existing long filaments into smaller filaments accelerates the assembly of new filaments by exposing more plus ends

51
Q

What happens if you sever a filament in the center

A

you do not have the ATP (or GTP) cap anymore and you will have catastrophe right away

52
Q

What does katanin do (general)

A

Breaks 13 longitudinal bonds to sever a microtubule

53
Q

How does katanin break bonds

A

Katanin hydrolyzes ATP to perform this task and is directed to the centrosome where it releases microtubules directly from the centrosome

54
Q

Proteins that bind along the sides of filaments can either _______ or ________ them

A

stabalize, destabalize

55
Q

_________ are prominant in neurons and stabalize microtubules

A

MAPs (such as MAP2 and tau)

56
Q

Tau proteins with alzheimer’s disease

A

hyperphosphorylation of Tau proteins, cannot stabalize MTs (neurofibrillary tangles)

57
Q

Dementia associated with Alzheimer’s tau proteins

A

Impaired communication between neurons because the MT is not able to maintain a stable connection, cannot maintain the synapses needed for communication

58
Q

Where is Tau found

A

In the axon

59
Q

The MTs in the dendrites have a larger space between them when compared to the MTs in the axon.

A

Tau has both N an C terminals bound to one MT, stabalizes and creates a short tail (short space)-DENDRITE
MAP2 binds two diferent MTs, creates a long tail (larger space) -AXON

60
Q

Actin filaments are stabilized by the binding of __________

A

tropomyosin

61
Q

what does cofilin do and how

A

destabalizes actin filaments by binding and forcing filaments to twist more tightly.

62
Q

What does cofilin bind to

A

preferentially binds to old ADP-containing filaments

63
Q

What does tropomyosin do in terms of cofilin

A

protects actin filaments from cofilin

64
Q

concentrations of proteins when binding along side a filament vs to a filament

A

along side- high concentrations
to-low concentrations

65
Q

Filaggrin

A

bundles keratin filaments in the outer layer of the skin to give them toughness

66
Q

Plectin

A

cross-links intermediate filaments to microtubules and actin filament bundles

67
Q

Mutations in gene for plectin

A

cause a disease in humans that combines epidermis bullosa, muscular dystrophy, and neurodegeneration. called Epidermolysis bullosa simplex with muscular dystrophy (EBS-MD)

68
Q

________ and _______ cross-link actin into parallel bundles

A

Villin, fimbrin

69
Q

What forms the core of a microvillus

A

A bundle of parallel actin filaments cross-linked by the actin-bundling proteins villin and fimbrin

70
Q

web-forming/stabalizing proteins

A

filamins and spectrins

71
Q

What protein is lacking with some types of cancer cells

A

filamin

72
Q

Spectrins

A

-allow red blood cells to spring back to original shape after squeezing through a blood vessel
-Provide flexible stiffness to most other types of vertebrate cell

73
Q

How are the gamma-tubulin ring complex and the ARP complex similar

A

Similarities:
-both bind to and stabalize the minus end of a cytoskeleton element and promote nucleation

74
Q

How are the gamma-tubulin ring complex and the ARP complex different

A

Diferences:
-ARP is associated with branched actin given it interacts with ‘older’ actin filaments at a 70 degree angle, gamma tubulin builds microtubules which are not branched

mcb 3010 (20 decks)

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