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Histology > Cytoskeleton > Flashcards

Cytoskeleton Flashcards

1
Q

Describe microfilaments (actin)

A

They are highly conserved in eukaryotes.

They bind to specific transmembrane proteins directly or indirectly.

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2
Q

What are G-actin and F-actin?

A

G-actin is actin as a monomer and F-actin is actin polymerized.

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3
Q

What is the first step of actin polymerization?

A

Nucleation- ATP binds tightly to G-actin, G-actin binds tightly with 2 other G-actin to form a trimer.

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4
Q

Do all actin filaments display polarity and why or why not?

A

Yes they do because all actin monomers are oriented in the same direction.

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5
Q

Which end of the chain can actin monomers be added?

A

Either side, but the barbed side is 5-10x faster than the pointed side.

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6
Q

Once the G-actin + it’s bound ATP is added to the chain what happens to the ATP?

A

It is hydrolyzed to ADP

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7
Q

What determines the rate of actin polymerization?

A

The concentration of actin monomers in the cytoplasm.

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8
Q

Which one dissociates more readily from the filament? ADP actin or ATP actin?

A

ADP actin

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9
Q

What does very low G-actin concentration encourage?

A

The disassembly of actin filaments.

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10
Q

What does intermediate G-actin concentration encourage?

A

Treadmilling

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11
Q

What is Treadmilling?

A

An equilibrium state where as one G-actin is removed, another is added resulting in zero net growth.

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12
Q

What does high concentration of G-actin encourage?

A

The addition of G-actin at both ends, resulting in growth.

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13
Q

Once actin microfilaments are polymerized, what do they form?

A

A double helical chain.

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14
Q

What are cytochalasins?

A

They block the elongation of actin by binding to barbed ends which inhibits cell movement (mitosis)

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15
Q

What is phalloidin?

A

It prevents dissociation by binding to actin filaments.

Can be labeled with fluorescent dyes so you can see actin filaments.

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16
Q

Even though actin has the same structure in all cells…

A

It has many different functions and their functions are determined by binding proteins.

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17
Q

Arrange the following in ascending order:

Microtubukes, microfilaments, intermediate filaments

A

Microfilaments, intermediate filaments, and microtubules

18
Q

What is the role of the actin binding protein spectrin?

A

Found in RBCs, binds cytoskeleton to cell membrane.

19
Q

What is the role of the actin binding protein dystrophin.

A

Binds the cytoskeleton to the plasma membrane.

20
Q

What do the actin binding proteins villin and fimbrin do?

A

Cross-link actin in microvilli

21
Q

What are the roles of the acting binding proteins calmodulin and myosin 1?

A

Cross-link actin to the plasma membrane in microvilli.

22
Q

What is the role of the actin binding protein alpha actinin?

A

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

23
Q

What is the role of the actin binding protein filamin?

A

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

24
Q

What is the role of thymosin is controlling treadmilling?

A

Captures actin monomers and prevents them from polymerizing.

25
Q

How does profilin control treadmilling?

A

Binds to actin monomers preventing them from being polymerized.
They also facilitate the exchange of ADP for ATP so that the monomer can be added to the chain.

26
Q

How does gelsolin control treadmilling?

A

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 the plus end.

27
Q

How does cofilin control treadmilling?

A

Triggers depolymerization of ADP bound actin at the minus end.

28
Q

How does Arp 2/3 control treadmilling?

A

Initiates growth of F-actin from sides of existing filament causing branching.

29
Q

How does latrunculins control treadmilling?

A

Binds to G-actin and induces F-actin depolymerization.

30
Q

What is the role of intermediate filaments?

A

The cell undergoes mechanical stress and they provide strength to the cells. (Nucleus, neurons, and macula)

31
Q

What is the structure of intermediate filaments?

A

They have a common monomer..a helical rod with heads and tails.
The heads and tails determine the function.

32
Q

How do intermediate filaments form a coiled dimer?

A

The central rod of 2 polypeptides come together aligned head to head and tail to tail.

33
Q

How do dimers associate and why is this important?

A

They associate into a staggered antiparallel fashion to form tetramers.
This doesn’t allow them to have distinct ends and makes them more stable than actin-no treadmilling.

34
Q

What do tetramers assemble to form?

A

Protofilaments

8 protofilaments form a filament.

35
Q

How do intermediate filaments work in the cytoplasm?

A

They connect with other cytoskeleton elements for form structure within the cell.

36
Q

What are the types of intermediate filaments and what is each associated with?

A 
Type I- acidic keratin
Type II- neutral and basic keratin
Type III- vimentin,desmin,glial fibrillary acidic protein, peripherin.
TypeIV- neurofilaments
Type V- nuclear lamins
Type-VI- nestin
37
Q

What are microtubules composed of?

A

Tubulin dimers alpha and beta unit.
Protofilaments are longitudinal rows of Tubulin dimers.
13 protofilaments arranged parallel to form a cylinder with a hollow core = microtubule

38
Q

Protofilaments have a fast growing plus end and a slow growing minus end? True or False?

A

True

39
Q

Explain treadmilling in microtubules

A

GTP bound Tubulin dimers bind to the plus (growing end) end.
* the plus end grows much faster in low Ca conc
After polymerization, the GTP is hydrolyzed to GDP.
Tubulin becomes less stable and dimers dissociate at the minus end.

40
Q

What happens when there are high levels of GTP-tubulin? And what happens when there are low levels?

A

The dimers are added more rapidly than the GTP is being hydrolyzed and dimers are dissociating. The reverse happens at low levels.

41
Q

What factors inhibit microtubule polymerization?

A

Colchicines
Colcemid
Vincristine - anti cancer drug
Vinblastin- used for Hodgkin’s lymphoma

42
Q

What factors stabilize microtubules?

A

Taxol- used for breast cancer

Histology (19 decks)

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