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MCB 3010 > Cytoskeleton > Flashcards

Cytoskeleton Flashcards

1
Q

Eukaryotic cells have developed these spatial and mechanical functions in an intricate system of filaments called the

A

Cytoskeleton

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2
Q

The cytoskeleton’s varied functions depend on the behavior of three families of protein molecules which assemble to form three main types of filaments

A

1) Microfilaments: Actin,
2) Microtubules: tubulin
3) Intermediate Filaments

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3
Q

Microfilaments determine

A

cell shape and locomotion

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4
Q

For cells to function properly they must (2)

A

organize themselves in space and interact mechanically with their environment.

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5
Q

Microtubules determine

A

positions of organelles and direct intracellular transport

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6
Q

Intermediate filaments provide

A

mechanical strength

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7
Q

Actin is concentrated inside the

A

PM (anchors to PM)

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8
Q

In a happy and heathy cell the MTs will

A

extend all the way through the cell into the cortex

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9
Q

if a cell is not healthy you will see

A

retraction of the MTs.

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10
Q

Stress fibres

A

Thick and bundled actin that the cell can use to generate force for movement.

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11
Q

Cytoskeletal filaments are

A

dynamic and adaptable

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12
Q

Microtubules are often

A

in a star-like pattern emanating from the nucleus to the cell periphery

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13
Q

Microtubules are a major components of:

A

-the mitotic spindle during cell division,
-cilia and flagella for cell motility
-Structural pathways for the transport of materials within the cell

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14
Q

Actin filaments underlie the ________ and provide ______

A

PM, provide strength and shape to the thin lipid bilayer

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15
Q

Actin filaments also form

A

many types of cell-surface projections such as lamellipodia and filopodia that cells use to explore territory.

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16
Q

The actin-based contractile ring assembles to

A

divide cells in two.

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17
Q

Filopodia is used to

A

explore territory, they would have receptors on the tips that can interpret their environment.

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18
Q

Lamelopodia would be

A

a sheath that gives the cell the machinery it needs to move. It does this by polymerizing and depolymerizing

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19
Q

Intermediate filaments form a

A

protective cage for the cell’s DNA at the inner face of the nuclear envelope.

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20
Q

Intermediate filaments are twisted into

A

strong cables that can hold epithelial cell sheets together.

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21
Q

Intermediate filaments allow (2)

A

-nerve cells to extend long sturdy axons
-form tough appendages such as hair and fingernails

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22
Q

An example of an intermediate filament

A

Keratin

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23
Q

Cells that line the intestine and lung contain

A

microvilli and cilia (cytoskeletal-based cell surface protrusions) that maintain a constant location, length, and diameter.

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24
Q

The cytoskeleton also dictates

A

cell polarity during the lifetime of a cell.

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25
Q

Each type of cytoskeletal filament is constructed from

A

smaller protein subunits

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26
Q

What can small protein subunits do that large filaments cannot

A

diffuse rapidly across the cytoplasm

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27
Q

Actin exists in the cell as

A

small soluble subunits and as large polymers

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28
Q

Intermediate filaments are made up of _____ whereas actin filaments and microtubules are made of ________

A

smaller subunits that are themselves elongated and fibrous, subunits that are compact and globular (actin subunits and tubulin subunits)

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29
Q

What interactions hold subunits together

A

Non-covalent

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30
Q

Nucleation is

A

rate-limiting step in the formation of a cytoskeletal polymer

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31
Q

The tubulin and actin subunits assemble __________ to create _________

A

head-to-tail, polar filaments

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32
Q

Tubulin subunits are heterodimers composed of _________ and ________– tightly bound together by _________

A

α-tubulin and β-tubulin, non-covalent bonds.

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33
Q

Both α- and β-tubulin monomers have a GTP binding site, but

A

the GTP in the α-tubulin is trapped at the dimer interface while β-tubulin can have its GTP hydrolyzed to GDP or exchanged for a new GTP. GTP hydrolysis is thus important for microtubule dynamics

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34
Q

Longitudinal contact

A

between α- and β-tubulin

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35
Q

Microtubules are the stiffest and straightest structural elements found in most animal cells due to their

A

high persistence length (the property of a filament describing how long it must be before random thermal fluctuations cause it to bend)

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36
Q

The actin subunit is a _______ rather than a _______

A

Monomoer, dimer

37
Q

Actin subunit binds ____ rather than _____

A

ATP, GTP

38
Q

Because of the polarity of microtubules and actin filaments their ends

A

grow and shrink at different pace

39
Q

The fast growing end, as well as the fast shrinking end, is called the

A

Plus end (+)

40
Q

Whether filaments grow or shrink depend on whether the free subunit concentration is above or below the

A

Critical concentration

41
Q

The critical concentration is. the

A

concentration of subunits where the filament grows and shrinks at the same rate= treadmilling

42
Q

Treadmilling and dynamic instability are consequences of

A

nucleotide hydrolysis by tubulin and actin

43
Q

newly incorporated subunits are in a

A

T form (GTP or ATP containing)

44
Q

The longer a subunit is incorporated into a filament the more likely it is to be hydrolyzed, therefore in

A

D form (ADP- or GDP-containing).

45
Q

If the rate of subunit addition is low then the filament tip will be in the

A

D form

46
Q

D form has a ______ critical concentration than the T form.

A

higher

47
Q

what happens when the concentration of free subunits is in an intermediate range? That is, lower than the critical concentration of the D form but higher than that of the T form?

A

Treadmilling

48
Q

In the D form you need ________ subunits available to add to be able to maintain the length

A

more

49
Q

GTP cap

A

the rate of hydrolysis was faster than the rate of subunit addition
(as it grows we begin to hydrolyze the GTP to GDP, and as this happens if we ran out of available soluble subunits ) (Plus end)

50
Q

Loss of GTP cap

A

rapid shrinkage at the plus end- this is called MT Catastrophe
(rate of hydrolysis faster than rate of subunit addition)

51
Q

MT rescue

A

as plus end shrunk it would release tubulin dimers, dimers could exchange their GDP for GTP and the concentration of GTP would increase beyond the CC and we would get rapid growth and the GTP would form again

52
Q

When tubulin is GTP bound it is more

A

stable

53
Q

A GTP bound tubulin specific biochemical structure

A

Straight

54
Q

GDP bound tubulin in the filament causes

A

conformational change, slight curvature

55
Q

A MT is made up of ____ protofilaments

A

13

56
Q

Why continuously spend energy hydrolyzing nucleoside triphosphate?

A

allows cells to maintain a fluid structure that is primed for a rapid response to external stimuli or the environment.

57
Q

Intermediate filament structure depends on

A

Lateral bundling and twisting of coiled coils

58
Q

Actin and tubulin is present in

A

all eukaryotes

59
Q

Intermediate filaments are only present in

A

some metazoans such as vertebrates, nematodes, and mollusks.

60
Q

Intermediate filaments are predominantly found in cells

A

exposed to mechanical stress

61
Q

IF assembly

A

-You have an N terminal and a c terminal, one monomer coils with another monomer, forming a dimer. -Dimer interacts with another dimer forming a staggered tetramer,
-They interact head to tail, in that the first dimers N terminal will be closer to the second dimers C terminal, and they interact in this staggered manner.
-Two tetramers pack closely together and then 8 tetramers twist into a ropelike structure called a filament

62
Q

Is there directionality and polarity in assembled intermediate filaments

A

no (nothing can move along, no way to tell which way to go)

63
Q

A second family of intermediate filaments are the

A

neurofilaments

64
Q

Neurofilaments are found in ____ concentrations along ________

A

high concentrations along axons

65
Q

Adherens proteins and junction

A

connect branched actin to next cell, giving it strength from cell to cell (in epithelial cells)

66
Q

Desosomes

A

Connections between cells via IF, provide stability and strength to cells and therefore lining of bl vessel or intestine

67
Q

Why is minus end of MTs toward apical and plus end towards basal surface

A

Cellular machinary can move things in proper direction
-ex. blood vessel: apical side next to inside of vessel where blood will be, cell needs to move nutrient s from blood into cells and epithelial layer

68
Q

Cytoskeleton maintains _________ of cell that allows specialized cells to perform their functions

A

Polarity

69
Q

Filaments formed from multiple __________ have advantageous properties

A

protofilaments

70
Q

Nucleation experiment what happens to soluble actin subunits when adding salt

A

They polymerize

71
Q

Lag phase

A

Nucleation

72
Q

Growth phase

A

Elongation

73
Q

Equilibrium phase

A

Steady state

74
Q

Steady state

A

same number of subunits coming off the actin filament that you are adding to the other end

75
Q

Concentration at which steady state occurs

A

critical condition

76
Q

What happens if we added oligomers at the neginning (nucleation experiment)

A

Reach critical concentration in less time, same rate of growth, build fibril faster, bypass nucleation step

77
Q

What happens if you fully depolymerize actin

A

The rate at which you could build a new fibril would reduce

78
Q

Lateral contact

A

α-α and β-β

79
Q

What do lateral and longitudinal contacts do

A

Strengthen microtubules

80
Q

Structure of MT: where is GTP present

A

Both the alpha and beta subunit

81
Q

GTP in the alpha subunit(MT)

A

Buried in the core to make the interactions between 2 units very strong

82
Q

GTP in the beta subunit

A

readily accessible for hydrolysis

83
Q

Alpha and beta subunits bind to eachother to form ________ which gives structure

A

protofilaments polarity

84
Q

What do protofilaments have on their ends

A

A plus end and a minus end

85
Q

The GTP of what subunit is readily accessible for hydrolysis

A

beta

86
Q

Polymerization will happen more readily at the

A

plus end

87
Q

It is slower to add a subunit to the minus end because it is in

A

D form

88
Q

What happens to MT when you lose GTP bound cap

A

Fraying, no strength at end (less interactions), less energy needed to break bonds

89
Q

Amyotrophic lateral sclerosis is associated with the

A

Accumulation and abnormal assembly of neurofilaments in motor neuron cell bodies and in the axon

MCB 3010 (20 decks)

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