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2 FLC > Cytoskeleton > Flashcards

Cytoskeleton Flashcards

1
Q

What is the cytoskeleton and why does the cell require it?

A

A complex network of protein filaments and tubules that extend throughout the cytoplasm to provide:
Structural integrity,
Organisation
And stability.

It keeps the cell in shape and also modifies it in response to the environmental cues.

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2
Q

Is the cytoskeleton a dynamic structure or is it stationary?

A

It is a dynamic structure.

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3
Q

What is the cytoskeleton made up of? Name the 3 different polymers? What are their individual functions?

A

Its a complex network of 3 polymers:

  1. Actin
  2. Intermediate Filaments
  3. Microtubules
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4
Q

Are the polymers which make up the cytoskeleton covalently linked?

A

NO.

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5
Q

What 3 things do accessory proteins regulate?

A
  1. Site and rate of filament formation (nucleation)
  2. Polymerisation/depolymerisation
  3. Function
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6
Q

What’s the name of the monomer of actin?

A

G-actin

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7
Q

What is F-actin?

A

A twisted chain of G-actin monomers

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8
Q

Actin is the thinnest class of the cytoskeleton filaments. How thin are they (in nm)?

A

7nm.

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9
Q

Actin chains are associated with many proteins (like how DNA is associated with histones). What are these proteins called? how many are there and what are they?

A

Actin-binding proteins (ABP) - 6.

1) Profilin
2) Thymosin beta 4
3) actin bundling protein
4) cross linking protein
5) F-actin severing protein
6) motor proteins, myosin.

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10
Q

There are many forms of the actin monomer (from the first question on actin molecules). What are the 3 isoforms (with different isoelectric points) and where are they mainly found?

A

o Alpha-actin found mainly in muscle cells.

Beta-actin and gamma-actin found in non-muscle cells.

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11
Q

How do actin filaments grow?

A

G-actin add onto the +ve end of the f-actin

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12
Q

What 2 things determine the length of the actin filament?

A
  1. [G-actin]

Presence of ABP (actin binding proteins)

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13
Q

Monomer actin levels are controlled mainly by 2 proteins. Name the 2 proteins and their main functions.

A
  1. Profilin - increases the rate polymerisation

Thymosin beta 4 –prevents the addition of G-actin to F-actin. (so slows the growth of actin filaments).

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14
Q

What do Actin bundling proteins do??

A

keeps filamentous actin in parallel bundles

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15
Q

What do Cross linking proteins do?

A

maintains polyamorous actin in a gel-like meshwork

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16
Q

What do f-actin severing proteins do?

A

breaks polyamorous actin into smaller filaments

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17
Q

What do Motor proteins, myosin do?

A

oversees transporting vesicles or/and organelles through actin filaments

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18
Q

How are actin filaments arranged in non-muscular cells?

A

o Form thin sheath beneath plasma membrane.

o Associated with myosin.

19
Q

Actin-myosin rings are involved in which cell cycle process? What does it cause?

A

Cytokinesis
o Accumulates b/w the poles of the mitotic spindle beneath the plasma membrane.
o Ring contracts and forms an indentation/cleavage furrow, dividing the cell into 2 new daughter cells.

20
Q

Describe the process of cell migration – it is a multistep process – include all the proteins involved in this process.

A
  1. Cell pushes protrusions at its front. Lamellipodia and filopodia (cytoplasmic projections) form, and Profilin is present here to increase the rate of polymerisation.
  2. Protrusions adhere to surface. – Integrins link actin filaments to extracellular matrix surrounding cells.
  3. Cell contraction and retraction of rear part of the cell. – Interaction b/w actin filaments and myosin.
21
Q

They surround the nucleus. How does this affect the strength of the nuclear envelope?

A
  1. Strengthens it nuclear envelope.

2. Provides attachment site for chromatins.

22
Q

Structure of Intermediate Filaments

A
  1. N-terminal globular head
  2. C-terminal globular tail
  3. Central elongated rod-like domain 48nm long
    These units form stable dimers.,
    8-12nm wide
    Toughest filament
    constitute “rope-like” structure.
23
Q

How many units in the rope like structure?

A

2 filaments= dimer
2 dimers= tetramer
8 tetramers= rope like structure

24
Q

Intermediate filaments can be found in 2 main areas. Name the 2 areas where they can be found and the associated filaments in the given areas.

A
  1. CYTOPLASM ;
    I. Keratins – in epithelia
    II. Vimentin and vimentin-related – in connective tissue, muscle cells and neurological cells.
    III. Neurofilaments – in nerve cells
  2. NUCLEUS
  3. Nuclear lamins – in all nucleated cells (obviously)
25
Q

What does IFBP stand for? And what is its main function?

A

Intermediate filaments binding proteins (IFBP). They:
• Are linkers of IF structures.
• Stabilise and reinforce IF into 3D networks.

26
Q

What are the 3 IFBP?

A

o Fillagrin
o Synamin and Plectin
o Plakins

27
Q

Function of fillagrin

A

Binds keratin filaments into bundles

28
Q

Function of Synamin and Plectin

A
  • Binds desmin and vimetin

- Links the IF to the other cytoskeleton compounds as well as to cell-cell structures.

29
Q

Function of Plakins

A

Keeps the contact between the desmosomes of the epithelial cells

30
Q

What are the functions of the IF in the cytoplasm?

A
  1. Provides tensile strength
    • Allows the cells to withstand mechanical stress (to stretch!).
  2. Provides structural support
    • Creating a deformable 3D structural framework.
    Reinforcing cell shape and fix organelle localisation.
31
Q

How can the IF support the structure of the cell? - remember SOS

A

Provides structural support
• Creating a deformable 3D structural framework.
• Reinforcing cell shape and fix organelle localisation.
(Structure, Organisation, Strength)

32
Q

What are the functions of the IF in the nucleus?

A
  1. To strengthen it

To provide an attachment site for chromatin.

33
Q

What is the difference in the shape and order of the IF structure when in the nucleus and when in the cytoplasm?

A
  1. In the nucleus, they form a “mesh-like” structure, rather than the “rope-like” structure in the cytoplasm.
  2. Line the inner face of the nuclear envelope, rather than being present throughout (in cytoplasm). Also, cytoplasmic IF join up cell-cell junctions (desmosomes).
  3. In nucleus, they disassemble and reform at each cell division, as a nuclear envelope disintegrates.
    Process controlled by post-transcriptional modifications. – (mainly phosphorylation and dephosphorylation).
34
Q

Are microtubules dynamic? If yes, how so? If no, how does this affect the stability of the cell?

A

Yes, because they assemble and disassemble in response to cell needs.

35
Q

Is each microtubule polymer polarised or is it uncharged? If they are charged, where would the opposing charges be found on the chain?

A

Polarised – the opposing charges are found either end of the polymer.

36
Q

What is the ratio of the monomer to the chains in the cell?

A

50:50 monomer to chain in the cell.

37
Q

What is the centrosome?

A

(in the perinuclear region) – cytoplasmic region just around the nucleus.
• Is the MTOC in most cells.
• Contains gamma-tubulin ring – initiates the microtubule growth.

38
Q

Structure of Micrtotubules

A

> Hollow tubes made of tubulin
Polarized
Width 25nm (thickest of cytoskeleton structures
relatively stiff

39
Q

What are the functions of microtubules?

Remember SOS!

A

1)Intracellular transport
Like motorways for molecular motors
Motors can only travel in 1 direction

2)Organises position of organelles
causes polarisation of cells

3)Rhythmic beating of cilia
9 microtubule pairs around axenome(2 microtubules)
Dynein is the motor protein that allows for bending

40
Q

There are 2 main molecular motors. In which they run?

A

Motor proteins; Dynein and Kinesin.
• Dynein – moves cargo towards the –ve end of microtubules.
• Kinesin – moves cargo towards the +ve ends of microtubules.

41
Q

Give 2 examples of where flagella and where cilia can be found.

A
  1. Cilia in the respiratory tract, sweeping mucus and debris from lungs.
  2. Flagella on spermatozoa
42
Q

Types of tubulin

A

alpha
beta
gamma

43
Q

Once growth is initiated, what process continues the growth?

A

Alternating addition of alpha and beta tubulin to the structure (mostly in the +ve) end.

2 FLC (9 decks)

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