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Histology > Cytoskeleton (Exam 1) > Flashcards

Cytoskeleton (Exam 1) Flashcards

1
Q

What are the 3 specific kinds of protein structures that make up the cytoskeleton

A

Microfilaments (actin) (7nm thick)
Intermediate filaments (8-10 nm thick)
Microtubules (25nm in diameter)

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2
Q

Actin filaments are highly _______ among eukaryotes

A

conserved

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3
Q

how tick are actin filaments

A

7nm thck

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4
Q

how long may actin filaments be

A

may be up to 7 micrometers long

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5
Q

actin filaments are organized into ______ and _____ networks

A

Bundles, 3-D

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6
Q

Actin filaments bind to specific transmembrane proteins either ____ or ____

A

directly, indirectly

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7
Q

Actin filaments exist in what two forms

A

Monomers (G-actin) and long chains (F-actin)

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8
Q

What are the three major varieties of actin filaments

A 
alpha actin (found in muscle tissue)
Beta actin (non-muscle actin)
Gamma actin (non-muscle actin)
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9
Q

each actin monomer (G actin) has a binding site for ____, which binds tightly to G-actin

A

ATP

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10
Q

Each actin monomer can bind tightly with two other actin monomers to form what

A

Filamentous actin (F-actin)

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11
Q

Actin monomers are oriented in the same direction and thus display

A

Polarity

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12
Q

Actin _______ is reversible

A

Polymerization

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13
Q

The rate at which actin monomers are aded to the growing filament is proportional to what

A

cytosolic concentration of actin filaments

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14
Q

what type of actin dissociates more readily from filaments than ATP-actin

A

ADP-actin

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15
Q

what is the first step in actin polymerization

A

Nucleation: a trimer is formed

additional actin monomers can be added to either end

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16
Q

ATP -actin associates with which end of actin

A

The growing (plus or barbed) ends

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17
Q

The ATP is hydrolyzed to _____ following polymerization

A

ADP

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18
Q

The barbed end grows how much faster than the pointed end

A

5-10 times faster

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19
Q

Very low concentration of G-actin favor the ____ of actin filaments

A

disassembly

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20
Q

Intermediate concentrations of G-actin favor

A

Treadmilling

  • dynamic equilibrium between the minus end and the plus end
  • results in zero net growth
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21
Q

Actin microfilaments consist of a ____ _______ chain of G-actin subunits

A

Double helical

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22
Q

name two drugs that affect actin polymerization

A

cytochalasin and Phalloidin

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23
Q

Cytochalasin role in actin polymerization

A

drug that inhibits elongation
can inhibit movements (cell division)
Binds to the barbed ends of actin

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24
Q

What is Phalloidin’s role in actin polymerization

A

Binds to actin filaments and prevents dissociation
can be labeled with fluorescent dyes to allow visualization of actin filaments
prevents depolymerization by binding to actin filaments

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25
Q

what determines the different functions of actin

A

Actin-binding proteins and not actin itself

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26
Q

Spectrin

A

is an actin binding protein
found in RBCs
binds cortical cytoskeleton to the plasma membrane

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27
Q

Dystrophin

A

Actin binding protein
binds cortical cytoskeleton to the plasma membrane
(defects can lead to muscular dystrophy)

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28
Q

Villain and Fimbrin

A

Actin binding proteins

cross-link actin filaments in microvilli

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29
Q

Calmodulin and Myosin I

A

Actin binding proteins

Cross-links actin to plasma membrane in microvilli

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30
Q

alpha actin

A

actin binding protein

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

31
Q

Filamin

A

Actin binding protein

Cross-links actin at wide angles to form screen-like gels

32
Q

Thymosin

A

Actin binding protein that controls treadmilling

captures actin monomers and prevents actin monomers from being polymerized

33
Q

Profilin

A

Actin binding protein that controls treadmilling
binds to actin monomers
facilitates exchange of bound ADP for ATP- which favors polymerization
increases actin growth

34
Q

Gelsolin

A

Actin binding protein that controls treadmilling
Destabilizes F-actin and caps actin filaments, preventing loss and addition of G-actin
in presence of calcium ion, fragments actin filaments and remains bound to plus end

35
Q

Cofilin

A

Actin binding protein that controls treadmilling

Triggers depolymerization of ADP- bound Actin at the minus end

36
Q

Arp 2/3

A

Actin binding protein that controls treadmilling

initiates growth of F-actin from sides of existing filament- causes branching

37
Q

Latrunculins

A

Actin binding protein that controls treadmilling

binds to G-Actin and induces F-actin depolymerization

38
Q

how thick are intermediate filaments

A

8-10nm

39
Q

where are intermediate filaments most abundant

A

in cells that are subject to mechanical stress

40
Q

What is the function of intermediate filaments

A

Provide tensile strength in cells such as neurons and muscle
strengthen epithelial cells as desmosomes and hemidesmosomes
form a cytoplasmic network in most cells
associate with other cytoskeletal elements to form a scaffolding that organizes the internal structure of the cell

41
Q

What structural component do all intermediate filaments have

A

A common monomer consisting of a central alpha-helical rod flanked by head and tail domains

42
Q

what determines the specific functions of intermediate filaments

A

Head and tail domains

43
Q

Describe intermediate filament structure

A

Central rod of two polypeptides form a cold dimer
- Rods are aligned tail-to-tail and head-to-head
-dimers associated in a staggered antiparallel fashion to form tetramers
tetramers assemble end to end to form protofilaments
pairs of protofilaments associate laterally to form a protofibril
4 protofibrils are wound together to form filaments (8 protofilaments)

44
Q

Which are more stable actin filaments or intermediate filaments

A

intermediate filaments

because dimers align in antiparallel fashion, polymerized filaments do not have distinct ends (no treadmilling)

45
Q

Type I Intermediate filaments

A

Acidic Keratins

46
Q

Type II intermediate filaments

A

Neutral to basic keratins

47
Q

Type III intermediate filaments

A

Vimentin
Desmin
Glial fibrillary acidic protein
Peripherin

48
Q

Type IV Intermediate filaments

A

Neurofilaments

49
Q

Type V intermediate filaments

A

Nuclear lamins (associated with nuclear membrane and assembly of nuclear membrane)

50
Q

Type VI intermediate filaments

A

Nestin

51
Q

How large is the diameter of microtubules

A

25 micrometers

52
Q

What is a structural characteristic across microtubules

A

alpha and beta tubulin

53
Q

Microtubules consist of how many protofilaments

A

13

54
Q

how are the 13 protofilaments arranged

A

parallel to form a cylinder with a hollow core

55
Q

How are microtubules similar to actin

A

they have a + and - end (display polarity)

56
Q

What tubule dimers with GTP bound associate with the growing end of a microtubule

A

Beta tubulin

57
Q

The plus end of a microtubule grows more rapidly in the presence of what

A

low calcium ion concentration

58
Q

what destabilizes a microtubule

A

hydrolysis of GTP to GDP

59
Q

which Tubulin subunit faces the plus end

A

The beta tubulin

60
Q

Factors that inhibit microtubule polymerization

A

Colchicines (originally used to arrest mitotic cells, would arrest in metaphase)
Colcemid
Vincristine (anticancer drug)
Vinblastin (anticancer drug used to treat Hodgkin’s lymphoma)
Nocodazole

61
Q

Factors that stabilize microtubules

A

Taxol (anticancer drug- used to treat ovarian cancer)

blocks mitotic division by not allowing formation of mitotic spindle

62
Q

Functions of the cytoskeleton

A 
cell movement
support and strength for the cell
phagocytosis 
Mitotic spindle formation
Cytokinesis 
Cell-to-Cell and cell-to-extracellular matrix adherence
changes in cell shape
63
Q

Anterograde

A

Transports cargo along microtubule

mediated by Kinesin (toward the plus end)

64
Q

Retrograde transport

A

Dynein

runs toward minus end or back to axon hillock

65
Q

what does myosin I bind to

A

Actin and cell membrane

66
Q

how many heads does myosin I have

A

one

67
Q

What does the tail of myosin I bind to

A

Vesicles

68
Q

How many heads does Myosin V have

A

Two heads

69
Q

What does the heads of myosin V bind to

A

Actin

70
Q

What do the tails of myosin V bind to

A

Vesicles

71
Q

How many heads does myosin II have

A

Two heads

72
Q

what does the tails of myosin II bind to

A

Myosin

73
Q

What do the heads of myosin II bind to

A

Actin

Histology (10 decks)

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