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Cellular Processes > Intro to the Cytoskeleton > Flashcards

Intro to the Cytoskeleton Flashcards

1
Q

How many strands make up an intermediate filament?

A

32

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2
Q

What are the 3 components of the cytoskeleton?

A
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3
Q

What are the properties of intermediate filaments?

A
  • Very strong
  • Very stable
  • Very insoluble
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4
Q

Outline the structure of intermediate filaments

A
  • Dimers form as head to head coiled structures
  • Tetramers form head-to-tail and assemble into rope-like filaments
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5
Q

Describe the structure of intermediate filament proteins

A

Elongated with a central α helical region

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6
Q

What is a dermasome?

A

Connections between epithelial cells

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7
Q

What is a hemidesmasome?

A

Connects cells to underlying extracellular matrix

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8
Q

How do intermediate filaments like keratin support epithelial cells?

A
  • Span epithelial cells forming a framework that supports the cell and links it mechanically to its framework
  • Supports the cell and links it mechanically to its neighbours
  • Mechanically couples cells together so force is spread out along whole skin layer
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9
Q

What causes Epidermolysis Bullosa Simplex?

A

Defects in keratin

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10
Q

What happens in Epidermolysis Bullosa Simplex?

A

Produces weak intermediate fibres so if force is apploed it is not spread out so cells burst and blistering of the skin occurs

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11
Q

What is the basic subunit of actin?

A

G (globular) actin

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12
Q

What is bound centrally in actin?

A

ATP/ADP

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13
Q

What is the polymer of actin?

A

F (filamentous) actin

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14
Q

What is the structure of filamentous actin?

A

A right handed helix made up of two protofilaments

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15
Q

Is F actin symmetrical?

A

No, it is asymmetrical

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16
Q

How does growth of actin occur?

A

By the addition of actin monomers to the plus end

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17
Q

What is the 1st stage of actin polymerisation?

A

Nucleation, formation of the trimer

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18
Q

What is the rate limiting step in actin polymerisation?

A

Formation of the trimer

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19
Q

What is Cc?

A

The critical concentration of G actin, where rates of addition and loss are balanced and there is no net polymerisation

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20
Q

What happens to intermediate filaments at Cc?

A

The filaments are neither growing or shrinking

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21
Q

Where is most actin bound to ATP?

A

At the plus end

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22
Q

Why is most actin ADP bound at the negative end?

A

As the filament gets older there is spontaneous ATP hydrolysis

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23
Q

At a steady state where is actin preferentially lost

A
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24
Q

is koff higher for ATP or ADP actin?

A

ADP-actin

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25
Q

What allows an actin filament to stay the same length but constantly be turning over?

A

2 different rates of depolymerisation at different rates

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26
Q

What is used to visualise the actin cytoskeleton?

A

Phalloidin

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27
Q

How does phalloidin help to visualise the actin cytoskeleton?

A

It binds to F-actin and stabilises filaments

28
Q

What joins actin together to produce a mesh?

A

Filamin

29
Q

Outline the structure of filamin

A
  • It is a dimer
  • Each subunit has an actin binding site
30
Q

How does the actin cytoskeleton give the cell strength?

A
  • Actin cytoskeleton form a cortical cytoskeleton beneath the plasma membrane
  • Anchored by transmembrane proteins
  • Allows force to be spread across the plasma membrane of the whole cell
31
Q

Give the role of actin filaments in red blood cells

A

Actin filaments form a network with spectrin filaments to support the rbc shape

32
Q

How do actin filaments drive membrane protrusion?

A

Actin filaments are cross-linked to form bundles in order to make them more rigid so the actin can push against the membrane with sufficient force

33
Q

What are filopodia?

A

Cytoplasmic projections which sense rhe surroundingof the cell and look for chemotoxic signals

34
Q

What are lamellipodia?

A

Cytoskeletal actin projections on the leading edge of the cell, which are used when the cell wants to move

35
Q

Outline the structure of myosin

A

2 heavy chains intertwined to form a long coiled rail region with two globular heads

36
Q

What is linked to mechanical movement of the myosin head domain?

A

ATP hydrolysis

37
Q

What is the basic subunit of microtubules?

A

αβ tubulin dimer

38
Q

What is bound at the centre of each tubulin dimer?

A

GDP/GTP

39
Q

Are microtubules symmetric?

A

No they are asymmetric

40
Q

Outline the structure of microtubules

A
  • Right handed helical tube of protofilaments
  • Hollow in the centre with a cross section of 13 subunits
41
Q

How does growth of a microtubule occur?

A

By the addition of tubulin dimers to the plus end

42
Q

What is the primary function of microtubules?

A

Form a railway network within the cell

43
Q

What stabilises the growing tip of microtubules?

A

GTP-bound β subunits, this is called a GTP cap

44
Q

Can the GTP on the α tubulin subunit be hydrolysed?

A

No

45
Q

Can the GTP on the β tubulin subunit be hydrolysed?

A

Yes, it spontaneously hydrolyses to GDP

46
Q

What is the effect of the loss of the GTP cap on microtubules?

A

It causes catastrophe, the microtubule to depolymerise

47
Q

Why does loss of the GTP cap in microtubules lead to catastrophe?

A

GDP bound β subunits have a different conformation which induces a curve in the protofilament, this destabilises the microtubule

48
Q

What anchors microtubules?

A

The centrosome

49
Q

Where is the centrosome located in most cell types?

A

Near the nucleus

50
Q

Which end of a microtubule is tethered to the centrosome?

A

The minus end

51
Q

What protein is the centrosome rich in?

A

γ-TuRC

52
Q

Outline the structure of the centrosome

A
  • in the centre 2 centrioles at right angles to each other
  • Matrix contains rings of γ-tubulin which nucleate the growth of new microtubules
53
Q

Where is γ-tubulin found?

A

Only in the centrosome

54
Q

What are centrioles?

A

Central short microtubues with accessory pigments

55
Q

How does γ-tubulin nucleate the growth of new microtubules?

A

γ tubulin forms 1st ring of tubulin, αβ dimers can then join on

56
Q

What are the 2 families of motor proteins that microtubules interact with?

A

Kinesin and dynein

57
Q

Which direction do kinesins travel?

A

Towards the plus end of the microtubule

58
Q

What direction do dyneins travel?

A

Towards the minus end of the microtubule

59
Q

How do motor proteins bind to vesicles and organelles?

A

Through their tails

60
Q

How do kinesins and dyneins recognise microtubules?

A

Through their head regions

61
Q

How do motor proteins track along the microtubule?

A

They hydrolyse ATP in their heads

62
Q

What happens to microtubules at interphase?

A

Microtubules break down and the centrosome is duplicated

63
Q

What kind of microtubules attach to the chromosome pairs?

A

Kinetochore microtubules

64
Q

What is the function of astral microtubules?

A

they help orientate and position the spindle in the centre of the cell so can alter the axes of division

65
Q

What is the role of motor proteins in cell division?

A

They interact with the spindle to regulate shape and position of the chromosomes

66
Q

How do microtubules ensure they are attached to something during cell division?

A

Each microtubule will tug on each chromosome

Cellular Processes (22 decks)

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