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Histology > Lecture 6: Cytoskeleton > Flashcards

Lecture 6: Cytoskeleton Flashcards

1
Q

Cytoskeleton is made up of these three specific protein structures

A

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

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2
Q

Characteristics of Actin

A

Highly conserved among eukaryotes
7nm thick, up to 7um in length
Organized into bundles and 3D networks
Bind to specific transmembrane proteins directly or indirectly
Exist as monomers (G-actin) and long chains (F-actin)

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3
Q

Why do actin filaments display polarity

A

Because all actin monomers are oriented in the same direction

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4
Q

First step in actin polymerization

A

Nucleation: a trimer is formed, then additional actin can be added to either side

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5
Q

The growing end is barbed or pointy

A

Barbed

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6
Q

Treadmilling

A

Intermediate concentrations of G-actin favor a dynamic equilibrium between the +/- end. No net growth

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7
Q

Low concentrations of G-actin favor

A

Depolymerization of actin filaments

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8
Q

Higher concentrations of G-actin favor

A

Net addition of actin at both ends, therefore growing the actin filament

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9
Q

Cytochalasins

A

Bind to barbed ends of actin, block elongation

Can inhibit movements (e.g., cell division)

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10
Q

Phalloidin

A

Binds to actin filaments and prevents dissociation

Can be labeled with fluorescent dyes to allow visualization of actin filaments

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11
Q

Diversity of function of actin filaments in a cell is determined by

A

Actin-binding proteins

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12
Q

Spectrin

A

Found in RBCs

Binds cortical cytoskeleton to plasma membrane

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13
Q

Dystrophin

A

Binds cortical cytoskeleton to plasma membrane

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14
Q

Villin and Fimbrin

A

Cross-links actin in microvilli

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15
Q

Calmodulin and Myosin I

A

Cross-links actin to plasma membrane in microvilli

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16
Q

alpha-Actinin

A

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

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17
Q

Filamin

A

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

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18
Q

Thymosin

A

Captures/bind actin monomers, prevents them from being polymerized

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19
Q

Profilin

A

Binds to actin monomers and prevents them from being polymerized
Facilitates exchange of bound ADP for ATP-which favor polymerization

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20
Q

Gelsolin

A

Destabilizes F-actin and caps actin filaments, preventing loss and addition of G-actin
In presence of calcium ion, it fragments actin filaments and stays bound to +end

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21
Q

Cofilin

A

Triggers depolymerization of ADP-bound actin at the minus end

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22
Q

Arp2/3

A

Initiates polymerization of F-actin from sides of existing filament (causes branching)

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23
Q

Latrunculins

A

Binds to G-actin and induces F-actin depolymerization

24
Q

How thick are intermediate filaments

A

8-10nm

25
Q

Intermediate filaments are abundant in cells subjected to

A

Mechanical stress

26
Q

Intermediate filaments strengthen epithelial cells as

A

Desmosomes and hemidesmosomes

27
Q

Intermediate filament central unit

A

Alpha-helical rod flanked by head and tail domains

28
Q

Head and tail domains of intermediate filaments determine

A

Specific functions

29
Q

Intermediate filament functions

A

Form a cytoplasmic network in most cells

Associate with other cytoskeletal elements to form a scaffolding that organizes the internal structure of a cell

30
Q

Dimer

A

Central rod of two polypeptides together

Rods are alined tail-tail, head-head

31
Q

Tetramer

A

Dimers associated in a staggered anti-parallel fashion

32
Q

Why do intermediate filaments not exhibit behaviors such as treadmilling

A

They are more stable than actin because they do not have distinct ends, due to the antiparallel association of dimers

33
Q

Protofilament

A

Tetramers assemble end to end

34
Q

Filament

A

Eight protofilaments wound together

35
Q

Most common type of intermediate filament

A

Keratin

36
Q

Microtubule thickness

A

25nm

37
Q

Microtubules are composed of what units

A

alpha and beta units

38
Q

Protofilaments are

A

longitudinal rows of tubulin dimers

39
Q

How many protofilaments arrange in what orientation for microtubules

A

13 parallel protofilaments

40
Q

____ dimers with ___ bound to the _____ associate with the growing end

A

Tubulin dimers with GTP bound to the beta unit

41
Q

Plus end grows more rapidly than minus end in presence of

A

low calcium ion concentration

42
Q

After polymerization, ___ is hydrolyzed to ___ and the tubulin is ____ stable

A

GTP is hydrolyzed to GTP and tubulin is less stable

43
Q

Dynamic instability

A

Individual microtubules undergo alternate phases of slow growth and rapid depolymerization

44
Q

alpha tubulin associates with the ___ end, beta tubulin associates with the ___ end

A

alpha tubulin=minus end

beta tubulin=plus end

45
Q

Colchicines

A

Inhibit microtubule polymerization

46
Q

Colcemid

A

inhibit microtubule polymerization

47
Q

Vincristine

A

inhibit microtubule polymerization

48
Q

Taxol

A

Stabilize microtubules

49
Q

Vinblastine

A

Inhibit microtubule polymerization

50
Q

Nocodazole

A

Inhibits microtubule polymerization

51
Q

Cytoskeleton functions (7)

A 
Cell movement
Support and strength for cell
Phagocytosis
Mitotic spindle formation
Cytokenisis
Cell-cell, cell-extracellular matrix adherence
Changes in cell shape
52
Q

Kinesin

A

Anterograde transport protein

53
Q

Dynein

A

Retrograde transport protein

54
Q

Raft protein complex

A

May provide a mechanism for transport of multiple cargos

55
Q

Myosin I number of heads, tail binds to what, head binds to what, direction of head motion towards the

A

One head
Tail binds to cell membrane
Head binds to actin
Head motion towards barbed end

56
Q

Myosin II number of heads, tail binds to what, head binds to what, direction of head motion towards the

A

Two heads
Tail binds to Myosin II
Head binds to Actin
Head motion towards barbed end

Histology (24 decks)

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