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The Cytoskeleton Flashcards

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1
Q

What are the major functions of the cytoskeleton?

A
  • Maintains cell shape
  • Responds to environment
  • Aids cellular movement
  • Intracellular / organelle movement
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2
Q

Explain what the cytoskeleton is

A

A microscopic network of protein filaments and tubules in the cytoplasm of living cells, giving them shape and coherence

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3
Q

What is G-actin?

A

Globular actin - a protein monomer

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4
Q

Which is the thinnest class of cytoskeleton filaments?

A

F actin (7nm)

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5
Q

Which 3 polymers is the cytoskeleton composed of?

A

Actin Filaments
Intermediate Filaments
Micro tubules

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6
Q

Outline how the filament monomers are able to polymerise and depolymerise

A
  1. Cell receives signal via receptors
  2. Existing filaments depolarise to form free monomers in the cell
  3. Monomers diffuse rapidly
  4. Reassemble at new site
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7
Q

What are accessory proteins?

A

Proteins ensuring correct protein folding in the right location

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8
Q

Describe the structure of intermediate filaments

A 
Rope-like structure 
Many long strands twisted together  
Composed of different sub units 
Forms a network throughout cytoplasm 
Joins at desosomes
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9
Q

How is F-actin formed?

A

G-actin monomers join together to form filaments

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10
Q

Describe the structure of microtubules

A 
Hollow tubules made of tubulin 
Rigid 
Long straight chains 
Polarised
Dynamic structure
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11
Q

Why is F actin polar?

A

Shows structural polarity due to fast growing +ve end

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12
Q

What are ABPs?

A

Actin Binding Proteins

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13
Q

What type of actin is found in muscle cells?

A

ɒ actin

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14
Q

Explain the advantage of intermediate filaments being so tough?

A

Withstands mechanical stress when cell is stretched

strengthens nuclear envelope

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15
Q

What do Synamin and plectin collectively do?

A

( Bind desmind and vimentin together )

Links Intermediate fiaments to other compounds

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16
Q

Why is the centrosome the optimal MTOC?

A

Contains ɣ tubulin ring that initiates micro tubule growth

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17
Q

What is the function of Plakins?

A

Maintains contact between desosomes of epithelial cells

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18
Q

How many different isoforms of G-actin are there?

A

there are 3 different isoforms

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19
Q

What do accessory proteins regulate?

A
  • Nucleation (site & rate of protein filament formation)
  • De/polymerisation
  • Protein function
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20
Q

Which of the cytoskeleton filaments is the toughest?

A

Intermediate filaments are the toughest - resistant to detergent & high salts

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21
Q

Where is the MTOC of most cells?

A

Centrosomes in percinucleur region

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22
Q

Which cells are IFBPs found in?

A

All nucleated eukaryotic cells

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23
Q

What is the difference between the 3 different isoforms of G-actin?

A

They each have different isoelectric points

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24
Q

Which functions are carried out by the cytoskeleton microtubules ?

A

Organelle positioning

Intracellular transport

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25
Describe the structure of actin filaments
Helical polymers made of actin Flexible chain of globular actin (G-actin) Organised into 2D networks and 3D gels
26
Where are majority of ABPs found?
Many ABPs in F actin
27
Explain how the cytoskeleton is dynamic
The filament monomers continuously polymerise and depolymerise
28
What are intermediate filaments?
Heterogenous group of filamentous proteins
29
What are the various filaments made of?
monomers
30
Where is Β actin found?
In non muscles
31
What are the functions of actin in non muscle cells?
cell cortex - forms thin sheath beneath plasma membrane associated with myosin - forms a purse string resulting in cleavage of mitotic cells cytokinesis - involves actin-myosin ring
32
Describe the structure of an intermediate filament
NH2 group on one end COOH group on other end ɒ helical region in monomer
33
Which 2 ABPs control the levels of G actin?
Profilin - facilitates actin polymerisation | Thymosin b4 - Prevents actin monomer addition to F actin
34
How do filaments allign with Actin Bundling proteins ?
F actin kept in parallel bundles | e.g. microvilli in epithelial cells
35
What is the significance of the intermediate filaments in the cytoskeleton?
They provide mechanical strength
36
What is the length of F actin determined by?
G actin concentration | ABP presence
37
What is the significance of ABPs?
Determine how the filaments form
38
How does cell migration occur?
1. Cell forms protrusions at its front calles lamellipodia and filopodia 2. Actin polymerisation occurs 3. Protrusions adhere to surface 4. Integrins link actin filaments to extra cellular matrix surrounding cell 5. cell contraction and retraction of rear of cell 6. Interaction of actin and myosin
39
How is actin arranged in skeletal muscle?
In a para-crystalline array integrated with different ABPs
40
What are the 2 ABPs responsible for the filament structure?
- Actin Bundling Proteins | - Cross Linking Proteins
41
What is the functions of actin in skeletal muscle?
Interacts with myosin allowing muscle contraction
42
What are the various sub units forming an intermediate filament?
- N-terminal globular head - C-terminal globular tail - Central elongated rod
43
What is the MTOC?
Micro tubules organising centre | Specialised protein complexes where micro tubule assembly starts
44
What type of structure do intermediate filaments form in the cell nucleus?
A mesh structure
45
What are the functions of the cytoskeleton actin filaments?
Cell shape Organelle shape Cell migration
46
How do the ABPs work?
They bind to the monomers to cause their respective effects
47
How are filaments aligned with cross linking proteins?
Maintain F actin in a gel like mesh work | e.g. Cell cortex under plasma membrane
48
What tubulin structures cause the development of the microtubules?
ɒ and Β heterodimers of tubulin constitute the micro tubule
49
What is the role of Filagrin IFBP?
Binds keratin filaments into bundles
50
Why are the sub units forming intermediate filaments significant?
These sub units form stable dimers
51
Explain what the function is of motor proteins (myosin)
Transport vesicles / organelles through actin filaments
52
Where in the nucleus are Intermediate filaments and IFBPs found?
They line the inner face of the nuclear envelope
53
How do microtubules allow the motility of flagella and cilia?
They have highly organised micro tubule cores
54
What are IFBPs?
Intermediate Filament Binding Proteins
55
What happens to the intermediate filaments during cell division?
Disassemble and reform at each cell division as nuclear envelope disintegrates
56
What is the role of F actin severing proteins?
Break F actin into smaller filaments
57
Is the micro tubule growth favoured at either end of the tubule?
There is polarised growth due to faster growth of the positive end
58
Name some cytoplasmic IFBPs
Filagrin Synamin Plectin Plakins
59
What is the reassembly and disassembly of intermediate filaments controlled by?
By post translational modifications (mainly phosphorylation and dephosphorylation)
60
What are the functions of microtubules?
- intracellular transport - organises organelle positioning - provides cell polarisation - causes rhythmic beating of cilia and flagella
61
How does a motor operate on the microtubules?
Each motor carries a different specific cargo in one direction only
62
Where is flagella present in the body?
On sperm cells to aid transport
63
What controls the assembly of the axoneme ?
The basal body at the base of the tubule
64
Name the motor protein involved in the movement of flagella and cilia
Dynein protein
65
Is the nuclear or cytoplasmic form of IBPs more stable?
Cytoplasmic IFBPs are more stable than the nuclear form
66
What is a micro tubule core comprised of?
Each core consists of 9 pairs (18) microtubules around 2 central microtubules (axoneme)
67
Give an example of where cilia are present in the body?
In the respiratory tract
68
What is the advantage of microtubules having a track like structure?
Allows molecular motors to run along the microtubules
69
What are the advantages of having intermediate filaments in the nucleus?
Strengthen nuclear envelope | Provide attachment site for chromatin

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