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Histology -- Zach H. > Cytoskeleton (Lecture 7) > Flashcards

Cytoskeleton (Lecture 7) Flashcards

1
Q

What 2 forms are actin microfilaments found in?

A

monomers (G-actin) or long chains (F-actin)

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2
Q

True or False:

Actin microfilaments are highly conserved among eukaryotes.

A

True, actin microfilaments are hight conserved among eukaryotes.

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3
Q

What variety of actin microfilaments are found in muscle tissues?

A

alpha-actin

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4
Q

Which two varieties of microfilaments are found in non-muscle?

A

beta and gamma actin

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5
Q

What are the 2 drugs that affect actin polymerization?

A

Cytochalasin and Phalloidin

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6
Q

How does cytochalasin affect actin polymerization?

A

Blocks the growth of actin filament by binding to the barbed ends, thus blocking elongation which can inhibit movements (e.g: cell division).

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7
Q

How does phalloidin affect actin polymerization?

A

Phalloidin binds to actin filaments and prevents dissociation.

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8
Q

Which drug that affects actin polymerization of microfilaments can be used in the laboratory to allow visualization of actin filaments with fluorescent dyes?

A

Phalloidin

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9
Q

Name 3 of the 8 actin-binding proteins?

A 
Spectrin
Dystrophin 
Villin and Fimbrin 
Calmodulin and Myosin I 
alpha-Actinin 
Filamin
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10
Q

Which actin-binding protein is found in RBCs?

A

Spectrin

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11
Q

Which 2 actin-binding proteins both bond cortical cytoskeleton to the plasma membrane?

A

Spectrin and Dystrophin

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12
Q

Which 2 actin-binding proteins cross-link actin in microvilli?

A

Villin and Fimbrin

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13
Q

Which 2 actin-binding proteins cross-links actin to plasma membrane in microvilli?

A

Calmodulin and Myosin I

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14
Q

Which actin-binding protein cross-links stress fibers and connects actin to protein-plasma membrane complex complexes?

A

alpha-Actinin

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15
Q

Which actin-binding protein cross-links actin at wide angles to form screen-like gels?

A

Filamin

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16
Q

Name 4 of the 7 actin-binding proteins that control treadmilling?

A 
Thymosin 
Profilin
Gelsolin 
Cofilin 
Arp2/3 
Phalloidin 
Latrunculins
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17
Q

What does thymosin do?

A

Captures actin monomers and prevents actin monomers from being polymerized.

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18
Q

What does Profilin do?

A

Binds to actin monomers and prevents monomers from being polymerized.

Facilitates exchange of bound ADP for ATP - which favors polymerization

NOTE: that only ATP-actin monomers can be assembled into F-actin

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19
Q

What is the function of Gelsolin?

A

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 the plus end

20
Q

What does Cofilin do?

A

Triggers depolymerization of ADP-bound actin at the minus end

21
Q

What does Arp2/3 do?

A

Initiates growth of F-actin from sides of existing filament - causes branching. Thus, changes the shape of the actin.

22
Q

What does phalloidin do?

A

It prevents depolymerization by binding to actin filaments.

23
Q

What does Latrunculins do?

A

It binds to G-actin and induces F-actin depolymerization.

24
Q

In what type of cells would you expect to find an abundance of intermediate filaments?

A

Cells subject to mechanical stress.

25
Q

Are intermediate filaments found as desmosomes and hemidesmosomes.

A

YES

**Intermediate filaments strengthen epithelial cells as desmosomes and hemidesmosomes.

26
Q

What three specific types of proteins make up the cytoskeleton?

A

1) Microfilaments (actin) (7 nm thick)
2) Intermediate Filaments (8-10 nm thick)
3) Microtubules (25 nm in diameter)

27
Q

Which two domains of intermediate filaments determine its specific function?

A

The head and tail domains.

28
Q

Label, in order, the general structure/assembly of an intermediate filament, starting at the inner must layer.

A

central rod of 2 polypeptides form a coiled dimer –> dimers associate in staggered antiparallel fashion to form tetramers –> tetramers assemble end to end to form protofilaments –> 8 protofilaments are wound together to form filaments.

29
Q

Why are intermediate filaments more stable than actin?

A

Intermediate filaments are more stable than actin and do not demonstrate dynamic behaviors such as treadmilling because dimers form a staggered antiparallel structure that are polymerized and do not have distinct ends, thus treadmilling is not possible.

30
Q

What are the 2 main functions of intermediate filaments?

A

1) form a cytoplasmic network in most cells

2) associate with other cytoskeletal elements to form a scaffolding that organizes the internal structure of the cell.

31
Q

How many types of intermediate filament types are there?

A

there are 6 types

32
Q

True or False:

Protofilaments of microtubules have a fast-growing plus end and a slow-growing minus end.

A

True, thus they have polarity.

33
Q

True or False:

The plus end grows more slowly than the minus end in the presence of low calcium ion concentration.

A

False, the plus end grow more rapidly than the minus end in the presence of low calcium ion concentration.

34
Q

What happens if the concentration of tubulin-GTP drops?

A

GTP at the plus end is hydrolyzed and dimers are lost.

35
Q

What happens if there are high concentrations of tubulin-GTP?

A

The dimers are added more rapidly than GTP is hydrolyzed, and the microtubule grows.

36
Q

What are the 4 factors that inhibit microtubule polymerization?

A

Colchicines (arrest mitotic cells at meta-phase)
Colcemid
Vincristine (anti-cancer drug)
Vinblastin (anti-cancer drug – used for Hodgkins Lymphoma)

37
Q

What factor stabilizes microtubules?

A

Taxol (used to treat breast caner, thus also an anti-caner drug)

38
Q

How many heads does myosin I have?

A

1 head

39
Q

Which myosin class has 2 heads?

A

myosin II

40
Q

Kinesin and Cytoplasmic dynein both have how many heads?

A

both have 2 heads each.

41
Q

What does the tail of myosin II bind to?

A

myosin II

42
Q

What does the tail of both cytoplasmic dynein and kinesin bind to?

A

Vesicles

43
Q

What does the tail of myosin I bind to ?

A

cell membrane

44
Q

What does the head of myosin I and myosin II bind to?

A

actin

45
Q

what does the head of kinesin and cytoplasmic dynein bind to?

A

microtubules

46
Q

The direction of the head motion of myosin I and myosin II is towards what?

A

barbed (plus) end

47
Q

Does kinesin move towards the plus end or minus end of microtubules? What about cytoplasmic dynein?

A

Kinesin towards the plus end

Cytoplasmic dynein towards the minus end

Histology -- Zach H. (21 decks)

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