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BMS241 final exam > Topic 9 - Cytoskeleton > Flashcards

Topic 9 - Cytoskeleton Flashcards

1
Q

Define cytoskeleton…

A

intricate network of protein filaments that extends throughout the cytoplasm that gives a cell its shape and allows the cell to organize its internal components

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2
Q

Cytoskeleton present in bacteria?

A

yes - cytoskeletal components

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3
Q

The cytoskeleton is built on a framework of three types of protein filaments. what are they?

A
  • intermediate filaments
  • microtubules
  • actin filaments
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4
Q

Intermediate filaments are found in…?

A

Animals only

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5
Q

Microtubules & actin filaments are found in…?

A

All eukaryotes

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6
Q

Intermediate filaments main function?

A

enable cells to withstand the mechanical stress that occurs when cells are stretched

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7
Q

Why are they called “intermediate”?

A

smooth muscle cells where they were first discovered, their diam- eter (about 10 nm) is between that of the thin actin-containing filaments and the thicker myosin filaments

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8
Q

Intermediate filaments are often anchored to…?

A

plasma membrane at cell–cell junctions (desmosomes)

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9
Q

Intermediate filament (IF) diameter?

A

10nm

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10
Q

As well as spanning the cell cytoplasm, IFs are also found where?

A

Within the nucleus - nuclear lamina -> underlies and strengthens the nuclear envelope in all eucaryotic cells

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11
Q

Intermediate Filaments Are Strong and Ropelike. ie. coiled tetramers of monomers. how many tetramers? monomers?

A

8 tetramers -> i IF

thus 32 monomers make up 1 IF

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12
Q

Structure of a IF monomer…

A

elongated fibrous proteins, each composed of an N-terminal globular head, a C-terminal globular tail, and a central (a-helical) elongated rod domain

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13
Q

T or F - The central rod domains of different intermediate filament proteins are all similar in size and amino acid sequence

A

true

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14
Q

T or F - The globular domains vary greatly in both size and amino acid sequence from one intermediate filament protein to another

A

true

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15
Q

IFs are analogous to…

A

carbon fibre in fibreglass

or steel bars in concrete

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16
Q

Intermediate filaments can be grouped into four classes: what are they? cells found?

A
  • keratins: epithelial cells
  • vimentin and vimentin-related filaments: connective tissue, muscle cells, and glial cells
  • neurofilaments: nerve cells
  • nuclear lamins: nuclear membrane (all animal cells)
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17
Q

T or F - keratins can interact with other classes of IFs

A

false - only with keratins

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18
Q

Specialised keratins are also found in …?

A

hair, rhino horns, feathers, claws (finger nails)

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19
Q

the rare human genetic disease epidermolysis bullosa simplex, in which mutations in a gene causes skin to become highly vulnerable to mechanical injury. which filament is affected?

A

keratin

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20
Q

Plectin aids in…

A

Accessory protein that aids in linking IFs to:

  • other IFs
  • to microtubules
  • actin filaments
  • adhesion structures in desmosomes
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21
Q

Mutations in plectin gene cause…

A

devastating human disease -> mechanical weakness, muscular dystrophy & neuro-degeneration

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22
Q

The intermediate filaments within this tough nuclear lam- ina are constructed from a class of intermediate filament proteins called…?

A

lamins

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23
Q

Electron micrograph image of lattice IF (looks like old wine bottle in a basket) is what?

A

nuclear lamina (frog egg)

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24
Q

Disassembly and reassembly of the nuclear lamina are controlled by which 2 processes…?

A

phosphorylation and dephosphorylation respectively

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25
Q

Defects in particular nuclear lamin cause disorder that …?

A

cause affected individuals to appear to age prematurely

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26
Q

Microtubule characteristics…

A

long, stiff, hollow tubes of protein play crucial organising role in eukaryotic cells

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27
Q

T or F - microtubules (MTs) can rapidly disassemble in one location and reassemble in another

A

true

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28
Q

In a typical animal cell, microtubules grow out from either of which small structures?

A 
centrosome (2 centrioles)
basal bodies (ciliated eukaryotic cell)
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29
Q

Microtubules are built from subunits. what are they?

A

alpha & beta dimers stacked together -> protofilaments

13 protofilaments -> 1 microtubule

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30
Q

MTs have polarity. Which tubulin is the ‘plus end’ & which is the ‘minus end’? What function does polarity of MTs give?

A

beta - plus end (dimers added faster to this end)
alpha - minus end
polarity give direction for intracellular transport

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31
Q

What makes up a centrosome…?

A

2 centrioles
centrosome matrix
hundreds of gamma-tubulin rings (starting point- nucleation - of MTs)

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32
Q

Orientation of MTs forming from centrosomes?plus & minus end…?

A

minus end stays embedded in gamma rings, while plus ends extend outward

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33
Q

MTs can also form permanent structures like …?

A

cilia

flagela

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34
Q

What is dynamic instability? Stability is therefore dependant on what?

A

MTs grow or shrink depending on GTP hydrolysis

Stability is dependant on [heterodimeric tubulin]

35
Q

Know & understand dynamic instability. fairly straighforward

A

figure 17-12 or slide 30

36
Q

Colchicine, colcemid, vinblastine & vincristine do what?

A

binds to MT subunits & prevents polymerisation

37
Q

Taxol does what?

A

binds to MT & prevents it from losing subunits (can still grow but cannot shrink)

38
Q

Together, all of the drugs mentioned (Colchicine, colcemid, vinblastine, vincristine & taxol) clinically do what?

A

inhibit mitosis -> used as anti-cancer agents

39
Q

Re. centrosome fishing analogy…if the fisherman is the centrosome, the fish is the …?

A

capping protein - stabilises MT (fish lure)

40
Q

In differentiated cells, what happens to MT instability? eg?

A

MT instability is supressed by cap proteins (fish in analogy)
eg. neurons

41
Q

MT-associated proteins can do what to MTs?

A
  • stabilise eg. neurons
  • link to cytoskeleton
  • aid in vesicle transport
42
Q

Movement of small membrane organelles along MTs is called what? What are these movements generated by? Energy source?

A

saltatory movement generated by motor proteins that use energy from repeated cycles of ATP hydrolysis

43
Q

The motor proteins that move along cytoplasmic microtubules, such as those in the axon of a nerve cell, belong to two families. they are? which way do they travel?

A

kinesins - travel towards plus end (remember kind people are positive)
dyenins - travel towards minus end (remember dying is negative)

44
Q

Re. organelles that move along microtubules… how does ER increase in size & Golgi move towards middle?

A

kinesins attach and stretch it outwards

dyenins attach and move Golgi inwards

45
Q

How does colchicine alter location of ER & Golgi? Is it reversible?

A

colchicine -> MT disassembly -> ER goes inward while Golgi get dispersed
these actions are reversible by removing the drug

46
Q

How we know: what enabled scientists to study squid axon cytoplasm back in the day (1980s)?

A

video-anhanced microscopy

47
Q

How we know: What did the scientists use to ID motor proteins?

A

ATP analog - AMP-PNP (inhibit translocation by binding to the ATP site)

48
Q

How we know: These squid experiments were called ?

A

in vitro motility assays

49
Q

How we know: which technique discovered that it was 1 molecule of ATP per step?

A

kinesin-coated silica beads

50
Q

Kinesin walking mechanism… watch video again!

A

17.7

51
Q

Cilia and Flagella Contain Stable Microtubules Moved by Dynein

A

cool fact

52
Q

Cilia are like small oars. explain

A

Cilia have a fast power stroke and a slower recovery stroke -> This creates a current that flows over the cell surface

53
Q

Give 2 examples of where cilia act

A

lung cilia -> sweep particles up the oesophagus to the throat (clear bacteria & debris from lungs)
oviduct cilia -> create a current that helps move the egg

54
Q

How do cytoplasmic MTs differ to those of cilia & flagella?

A

cilia & flagella MTs have a “9 + 2” array (nine doublet micro- tubules arranged in a ring around a pair of single MTs)

55
Q

What causes the bending motion in flagella (sperm)?

A

dynein & linking proteins that bind doublet MTs

56
Q

What happens when hereditary defects in ciliary dynein cause Kartagener’s syndrome?

A

Men with this disorder are infer- tile because their sperm are non-motile, and all those affected have an increased susceptibility to bronchial infections because the cilia that line their respiratory tract are paralyzed and thus unable to clear bacteria and debris from the lungs

57
Q

T or F - actin filaments are present in all eukaryotic cells

A

true

58
Q

Actin filaments allow eukaryotic cells to adopt many shapes and perform diverse functions. what are they? 4…

A
  1. microvilli (intestine)
  2. contractile bundles in the cytoplasm (muscle)
  3. Sheet-like lamellipodia and finger-like filopodia
  4. Contractile ring of mitosis
59
Q

Diameter of actin filament?

A

7nm

60
Q

One monomer interacts with … neighbours?

A

4

61
Q

Actin and Tubulin Polymerize by Similar Mechanisms
Actin filaments can grow by the addition of actin monomers at either end, but the rate of growth is faster at the plus end than at the minus end. A naked actin filament, like a microtubule without associated proteins, is inherently unstable, and it can disassemble from both ends. Which aspect of these two filaments differs?

A

actin uses ATP, while tubulin uses GTP

62
Q

What do toxins cytochalasins & phalloidin do to actin filaments?

A

cytochalasins - prevent actin polymerization

phalloidin - stabilize actin filaments against breakdown

63
Q

What % of cell protein is typically actin?

A

5% - about half of this actin is assembled into filaments, and the other half remains as actin monomers in the cytosol

64
Q

What do small proteins, such as thymosin and profilin do?

A

keeps the actin monomers in cell cytosol from polymerizing totally into filaments

65
Q

Formins & actin-related proteins (ARPs) control …?

A

When actin filaments are needed, other actin-binding proteins (formins & ARPs) promote their assembly

66
Q

Most actin binding proteins bind assembled filaments or monomers?

A

assembled filaments

67
Q

T or F - Like MTs, actin can also form high-ways for intra-cellular cargo transport (esp. in plants)

A

true

68
Q

What are the roles of spectrin and ankyrin ?

A

part of the cell cortex & link the actin meshwork to binding proteins

69
Q

Cell crawling depends on 3 three interrelated processes . What are they?

A

1) The cell pushes out leading edge protrusions
2) these adhere to the surface
3) the rest of the cell drags itself forward by traction on these anchorage points (& contraction of myosin-II)
ALL INVOLVE ACTIN

70
Q

actin-based lamellipodia and filopodia are required for what process?

A

cell migration

71
Q

lamellipodia is …?

A

dense meshwork of actin filaments

Most plus ends close to the plasma membrane

72
Q

Filopodia is…?

A

thin stiff protrusions, mostly at the leading edge

73
Q

What structures introduce chain branches into the filaments? What structures prevent branching?

A

Actin related proteins (ARPs)

Formins prevent branching

74
Q

Transmembrane proteins called integrins do what?

A

allow Lamellipodia and Filopodia to grip the cell exterior

75
Q

Which myosin is the major myosin found in muscle?

A

myosin II

76
Q

Extracellular Signals Control the Arrangement of Actin

Filaments converge on GTP-binding proteins called …?

A

Rho protein family -> produces signals that shape the actin cytoskeleton

77
Q

myosin-II subfamily of myosins have 2 what?

A

ATPase heads

78
Q

Muscle contraction…watch video.

A

youtube

79
Q

Sarcomere is what? Extends from where to where?

A

contractile units of muscle - extend from Z disc to another Z disk

80
Q

Describe in full detail the process of muscle contraction at the level of myosin-II binding to actin… Remember this!!!

A

step 1. myosin-II dimer ‘dangling’ in the air has bound ADP + phosphate (low actin-binding affinity)
step 2. when it docks onto actin subunit, phosphate fucks off -> increases binding affinity & triggers force-generating power stroke that moves the actin filament
step 3. ADP fucks off & ATP binds to the empty nucleotide binding site -> myosin head to detach from actin filament
step 4. On the now-dettached head, ATP is hydrolysed -> ADP + Pi -> re-cocks the lever arm back to its pre-stroke state thus the arm stores energy released by ATP hydrolysis -> cycle repeats

81
Q

Ca2+ release from SR leads to contraction via…?

A

troponin-mediated tropomyosin displacement

82
Q

What are the rods covering actin-binding sites?

A

tropomyosin

83
Q

After APs stop and Ca2+ stops being released, what happens to existing Ca2+ bound to troponin complex?

A

Ca2+ pumps

BMS241 final exam (5 decks)

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