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BL2301 Cell Biology > The Cytoskeleton > Flashcards

The Cytoskeleton Flashcards

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1
Q

Name 4 functions of the cytoskeleton

A
  • allows cells to take the stress and strain needed to be flexible
  • used for the division of chromosomes and mitosis
  • drives organelle movement
  • provides support for the plasma membrane
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2
Q

What are the 3 components of the cytoskeleton?

A
  • Actin
  • Microtubules
  • Intermediate filaments
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3
Q

What characteristics are shared by all 3 components of the cytoskeleton?

A
  • repetitive subunits of a helical arrangement

- held together by non-covalent bonds

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4
Q

What are microtubules composed of?

A
  • Alpha and beta tubulin dimers

- Each binds to one molecule of GTP, however for beta tubulin this can also be GDP

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5
Q

What are the properties of microtubules?

A
  • Long, straight and rigid

- Made from parallel protofilaments with a hollow centre

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6
Q

How do the two ends of a microtubule differ?

A
  • One end is positively charged, the other negatively charged
  • The + end grows and shrinks however the - end is always unstable and needs additional proteins to be added
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7
Q

What is the MTOC (microtubule organising point)? Give an example

A

The central point from which microtubules are nucleated

e.g centrosoles, + end grows out to form the mitotic spindle

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8
Q

Describe the process of dynamic instability

A
  • Microtubule has rapid growth when capped with GTP
  • When cap is lost the structure of GDP bound dimers breaks down
  • When cap is regained, can start rapid growth again
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9
Q

What behaviour is shown by microtubules in migrating cells?

A
  • Constantly extend towards the leading edge of the cell
  • Via motor proteins
  • Pattern of dynamic instability known as a growth cone
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10
Q

Can microtubules be modified post translation?

A

Yes, this affects the binding of proteins and does not stabilise with age

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11
Q

What are the two types of microtubule associated proteins?

A

Stabilisers (MAD1B, MAD2, tau (alzh), EB1) and motors (dynein, kinesins)
Can link microtubules to actin binding proteins

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12
Q

What is the role of stabiliser protein EB1?

A

Binds the GTP-tubulin cap in microtubules

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13
Q

What are the 3 types of motor associated proteins, how do they work and how do they differ?

A
  1. Myosin, kinesin and dynein
  2. Bind to polarised filaments and use ATP hydrolysis to move
  3. Kinesin move towards positive end and dynein moves towards the negative end, also differ in cargo and filaments they bind to
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14
Q

What is the structure of kinesin?

A
  • 2 helical heavy chains which dimerize to form a ‘stalk’
  • 2 light chains form the flexible ‘neck’
  • tail interacts with cargo
  • two globular heads interact with the microtubule and ATP
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15
Q

How is dyenin different to kinesin?

A
  • can have 2-3 heads
  • large macromolecular assembly
  • needs associated proteins to attach to cargo
  • used for beating of cilia and flagella
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16
Q

Describe the structure of cilia/flagella

A
  • 9 doublet microtubules, one complete and one half which are all fused
  • dyenin bridges
17
Q

How do cilia/flagella move?

A
  • Dyenin uses ATP to move

- As sliding of microtubules is prevented by protein barriers this results in bending

18
Q

What is actin formed from?

A

Helical polymers of monomers of globular actin (G-actin)

19
Q

When does G-actin form F-actin (filamentous)?

A

When is polymarizes

20
Q

What 3 ways can actin exist?

A

ATP-actin ADP-pi-actin and ADP-actin

21
Q

How is an actin filament formed?

A

When a linear chain of actin forms a protofilament which then wraps around another actin protofilament

22
Q

What are the 2 ends of an actin filament?

A

‘pointed’ and ‘barbed’ end with addition at the later and slow dissociation at the prior

23
Q

What change happens as actin ages?

A

ATP-actin hydrolyses to ADP-pi-actin from which phosphate is released to form ADP-actin

24
Q

What are the overall properties of actin?

A

Flexible forming linear bundles and meshworks

25
Q

How is cell movement coordinated?

A
  • adhesion of protrusion
  • traction via motors
  • dissasembly of old cell-substratum contracts
26
Q

What are the 3 forms of F-actin?

A
  1. Meshwork
  2. Tight parallel bundle
  3. Contractile bundle
27
Q

What are the 6 possible roles of actin binding proteins?

A
  1. Bind/sequester actin monomers
  2. Nucleate actin filaments
  3. Cap/uncap barbed/pointed ends
  4. Sever F-actin
  5. Bundle, crosslink, branch or stabilise F-actin
  6. Anchor F-actin to membrane
28
Q

Where are intermediate filaments found?

A

In vertebrates, nematodes and molluscs

29
Q

What is the structure of intermediate filaments?

A

Elongated with central alpha helical domain that forms a coil-coil with another molecule in the same direction. Form a staggered tetramer with a rope-like structure

30
Q

What are the 4 different isoforms of intermediate filaments and their subunits?

A
  1. Nuclear - lamins
  2. Vimentin-like: vimentin, desmin, peripehrin, glial fibrillary acidic protein
  3. Epithelial - keratins
  4. Axonal - neurofilaments
    These can form further parallel bundles

BL2301 Cell Biology (17 decks)

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