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MCB1 Block 3 > Cytoskeleton: Actin Filaments > Flashcards

Cytoskeleton: Actin Filaments Flashcards

1
Q

What is the protein subunit of actin?

A

Actin

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2
Q

Actin is made up of actin ____

A

monomers

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3
Q

actin monomers are also called what?

A

G-actin

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4
Q

What are the main functions of actin?

A 
maintain cell shape
changes cell shape
muscle contraction
cytoplasmic streaming
cell motility
cell division
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5
Q

G-actin polymerizes into ____

A

F-actin

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6
Q

What does F-actin stand for?

A

actin filaments

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7
Q

Explain how actin is important in maintaining cell surface shape and cell motility

A 
Cell surface shape & Cell motility
Cell division & cytokinesis
Lamellipodia, filipodia, phagocytic cups
Microvilli (intestinal epithelial cell surface) & stereocilia
Cell junctions
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8
Q

How does actin polymerize?

A

Both ends grow, the + end grows faster than the - end.

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9
Q

Are actin polar? describe

A

yes, they have - and + side

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10
Q

What shape is a F-Actin?

A

double helix

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11
Q

In order for actin monomers to attach and grow a filament, they have to be ____ bound

A

ATP

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12
Q

Why do monomers add more quickly to + end of actin filament?

A

They have higher affinity for + end

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13
Q

ATP will eventually be _____ on actin filament

A

hydrolysed to ADP

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14
Q

What prevents the actin filament from falling apart into its monomers?

A

The actin is “capped” by ATP bound actin that surround the ADP bound and prevent depolymerization

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15
Q

The rate of elongation/shortening is determined by what?

A

level of ATP-G actin

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16
Q

What happens if hydrolysis catches up with - end?

A

ADP bound monomers are exposed and actin is depolymerized - treadmilling

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17
Q

What is treadmilling?

A

length of filament remains the same b/c monomers are being added to + end and removed from - end at same rate

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18
Q

Nucleation occurs at ____ ___

A

plasma membrane

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19
Q

Where is the highest density of actin filaments?

A

cell periphery

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20
Q

What determines the changing of actin to make cell a different shape or stiffness?

A

signaling pathways, responding to their enviornemtn

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21
Q

2 or 3 actin together is called what?

A

nucleus

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22
Q

A G-actin prefers to join what?

A

It prefers to join a filament over nucleus, and that over just a few monomers that are joined

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23
Q

What is actin nucleation?

A

binding actin monomers together

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24
Q

What does Arp stand for?

A

actin-related proteins

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25
Q

What is the function of Arp2/3?

A

binds to actin monomers and stimulates the creation of a new filament

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26
Q

What is the function of prolifin?

A

exchanges ADP for ATP, readies monomer for attachment

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27
Q

Activation of 2/3 will stimulate the formation of what?

A

branching actin networks

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28
Q

What is the function of formin?

A

nucleate growth of straight, unbranched actin filaments

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29
Q

How does formin function?

A

Bound to + end and move up, help insert monomers into + end

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30
Q

What is thymosin and what is its function?

A

actin binding protein, binds G-actin and prevents F-actin assembly

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31
Q

What is prolifin and what is its function?

A

actin binding protein

binds g-actin and promotes filament assembly at + end

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32
Q

What competes with thymosin?

A

prolifin

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33
Q

What is cofilin and what is its function?

A

actin bining protein - it promotes disassembly at - end. it is severing protein

34
Q

What is gesolin and what is its function?

A

Actin binding capping protein. It caps + end and prevents further growth

35
Q

Name 4 non-muscle actin functions

A

microvilli
stress fibers
cell surface protrusions & cell migration
cytokinesis

36
Q

What kind of motor protein is on microvilli?

A

Myosin I

37
Q

What kind of motor protein is on muscle?

A

Myosin II

38
Q

What kind of motor protein is on vesicle and organelle transport for actin?

A

Myosin V

39
Q

What motor protein has contractile activity?

A

Myosin II

40
Q

Actin organization in the cell is stabilized by what?

A

cross-linking proteins

41
Q

What is filopodium?

A

tightly packed parallel bundles of actin

42
Q

What is the function of filopodium?

A

Sensors, to deform the membrane. No contractile ability

43
Q

Explain how stress fibers are packed

A

Very loosely, myosin II can enter. Contractile.

44
Q

Name actin cross linking proteins that help form parallel cables/bundles

A

alpha-actinin, fimbrin, villin

45
Q

Name actin cross linking proteins that help form webs/gels

A

spectrin, filamin

46
Q

Describe the characteristics of alpha actinin

A

cross linking protein
loosely packed bundles
found in stress fibers and during cytokinesis
contractile

47
Q

Describe the characteristics of fimbrin

A

cross linking protein
tight packed bundles
found in microvilli
non-contractile

48
Q

What are stress fibers made out of?

A

contractile bundles of actin filaments

49
Q

How is actin connected to the ECM?

A

focal adhesions - they are like footholds for actin to attach to the ECM

50
Q

What is the function of focal adhesions and cell movement

A

they act like a foothold and are a place for actin to push off from to help move cell forward

51
Q

What is the function of dystrophin?

A

anchors actin cytoskeleton to the sarcolemma (muscle cell membrane) in skeletal muscles

52
Q

What is the function of vinculin & talin?

A

attach actin cytoskeleton to membranes in focal adhesions

53
Q

What spans near the apical surface of every cell?

A

loosely packed parallel bundles of actin filaments.

54
Q

What is a cadherin?

A

attachment of actin bundles

55
Q

What type of crosslinking proteins are in microvilli?

A

fimbrin & villin

56
Q

Do actin in microvilli contract?

A

No

57
Q

Where are steroecilia located?

A

epididymis for reabsorption

hair cells of inner ear - mechanosensory

58
Q

Describe stereocilia

A

non-contractile, non motile

made of f-actin

59
Q

What kind of cross links does filamin make?

A

3D crosslinks - web like structure

60
Q

What kind of crosslinks does spectrin make?

A

2D web

61
Q

Describe spectrin and its function

A

protein - links to adaptor proteins that bind to transmembrane proteins to short filaments in actin
allows for structural support needed in RBC

62
Q

What is the name of the family of proteins that control the actin cytoskeleton?

A

Rho GTPases

63
Q

Where are Rho GTPases located and what is their function?

A

located @ cell surface, they activate nucleating proteins

64
Q

When will lamellipodia, filipodia, and stress fibers be activated?

A

when cell is triggered to migrate

65
Q

rac, cdc42, rho are all examples of

A

Rho GTPases

66
Q

What is lamellipodia?

A

Leading edge - the thing that points out and forms when cell needs to migrate

67
Q

What do Rho GTPases activate in first step for cell migration?

A

Arp2/3 complex → actin polymerization @ leading edge

68
Q

What is a protein besides Arp2/3 that needs to be activated for cell migration?

A

Cofilin → depolymerisation @ trailing edge

69
Q

If the cell forms a lamellipodia, will it move forward?

A

No - it also needs to attach to ECM so it can be pushed

70
Q

Describe steps in cell movement if a cell needs to migrate

A
  1. Rho GTPases activate Arp2/3
  2. Arp 2/3 causes polymerization and lamellipodia @ leading end
  3. myosin motor protein causes contraction at rear of cell → pushes cell forward
  4. New contacts to ECM are made at front, contacts at back are diassembled
71
Q

Key words: WASP mutation, haematopoietic cells are what disease?

A

Wiskott-Aldrich Syndrome

72
Q

What is the defect in Wiskott-Aldrich Syndrome ?

A

Mutation of WASP

73
Q

What is WASP?

A

Wiskott-Aldrich syndrome protein

74
Q

What is the function of WASP?

A

WASP activates Arp2/3 in WBC.

75
Q

A loss of function of WASP results in what?

A

inability of WBC to move - severe immunedefeciency

76
Q

Characteristics: Thrombocytopenia, eczema, recurrent infections; death before adulthood without bone marrow transplant are what disease?

A

Wiskott-Aldrich Syndrome

77
Q

What is the mode of inheritance for Wiskott-Aldrich Syndrome?

A

x-linked

78
Q

What is the mechanism for Wiskott-Aldrich Syndrome?

A

Mutation causes failure of actin nucleation (Arp 2/3) and disruption of signaling pathways ! prevents WBC from migrating to site of infection

79
Q

Describe how actin is important in cytokinesis?

A

actin & myosin II form a contractile ring under plasma membrane and pinch the cell, dividing it into two

80
Q

Cytochalasins, Phalloidin, & Latrunculin are all drugs that do what?

A

drugs that inhibit actin-based function. they are used in research, not for treatments.

MCB1 Block 3 (15 decks)

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