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Fundamentals Of Living Cells > The Cytoskeleton > Flashcards

The Cytoskeleton Flashcards

1
Q

General features of the cytoskeleton

A

Made of 3 polymers: -microtubules

  • intermediate filaments
  • actin filaments

Useful for:- shaping of the cell

  • intracellular movements
  • cell movement
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2
Q

Structure of actin filaments

A
  • Twisted chain of units of G-actin which makes up the F-actin
  • very thin (7nm)
  • plus and minus end means its polar
  • associated with a bunch of ABPs
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3
Q

What are the three different isoforms of G-actin and where are they found?

A

Alpha - mainly in muscle cells

Beta and gamma - mainly in non-muscle cells

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4
Q

Which end of actin filaments does G-actin get added to?

A

Plus end is more favourable

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5
Q

What two ABPs control the G-actin level?

A

Profilin facilitates actin polymerisation

Thymosin beta-4 presents the addition of actin monomers to F-actin

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6
Q

What do Actin bundling proteins do?

A

Keep the F-actin in parallel bundles (like in epithelial cells

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7
Q

What do cross-linking proteins do?

A

Maintain F-actin in a gel-like meshwork- like in the cell cortex under the plasma membrane

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8
Q

What do F-actin severing proteins do?

A

Break F-actin into smaller filaments by adding these proteins at the end of the polymers

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9
Q

What do motor proteins (like myosin) do?

A

Transport vesicles and/or organelles through actin filaments

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10
Q

What are the functions of actin filaments in skeletal muscle cells?

A

Arranged in a para-crystalline array, integrated with different ABPs
Interaction with myosin allows for muscle contraction

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11
Q

What are the functions of actin filaments in non-muscle cells?

A

Forms a thin sheath beneath the plasma membrane

Associated with myosin to form a purse sting result in cleavage of mitotic cells (cytokinesis)

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12
Q

What are the steps to cell migration?

A
  • The cell pushes lamellipodia (plural) or filopodia(single) out at its front (actin polymerisation)
  • these protrusions adhere to the surface (integrins line the actin filaments to the extra cellular matrix surrounding the cell)
  • cell contraction and retraction of the rear part of the cell (interaction between actin filaments and myosin)
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13
Q

What do accessory proteins regulate?

A
  • size and rate of filament formation (nucleation)
  • polymerisation/depolymerisation
  • function
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14
Q

Structure of intermediate filaments

A
  • tough
  • rope-like with many long strands twisted together and made up of many subunits
  • medium size (8-12nm)
  • they form a network through the cytoplasm, joining up cell-cell junctions (desmosomes)
  • withstand mechanical stress when cells are stretched
  • they surround and strengthen the nucleus
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15
Q

What is each monomer of the intermediate filaments made up of?

A
  • N-terminal globular head
  • C- terminal globular tail
  • central elongated rod-like domain
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16
Q

What is a dimer?

A

Two units of an intermediate filaments monomer that is very stable

17
Q

What do two dimers form?

A

Tetramear

18
Q

What do tetramears look like when they bind to each other?

A

A rope-like filament

19
Q

What are the types of cytoplasmic intermediate filament and and their localisation?

A
  • keratin(in epithelia)
  • vimentin and vimentin-related (in connective tissue, muscle and neurological cells)
  • neurofilaments (in nerve cells)
20
Q

What is the nuclear intermediate filament and and its localisation?

A

Nuclear lamins (in all nucleated cells)

21
Q

What does IFBP stand for?

A

Intermediate filament binding proteins

22
Q

Examples of IFBPs

A

Fillagrin binds keratin filaments into bundles
Synamin and plectin bind desmin and vimentin
Plakins keep the contact between the desmosomes of epithelial cells

23
Q

What are the functions of the IF in the cytoplasm?

A
  • tensile strength enables the cells to stretch
  • provides structural support by creating a deformable 3D structural framework and reinforcing cell shape and fixing the organelle localisation
24
Q

Functions of the IF in the nucleus

A
  • forms a mesh rather than a rope like structure
  • lines the inner face of the nuclear envelope to strengthen it and provides attachment sites for chromatin
  • disassembles and reforms at each cell division as the nuclear envelope disintergrates (unstable). This is controlled by post-translational modifications (mainly phosphorylation and dephosphorylation)
25
Q

Give the structure of microtubules

A

-hollow tubes made up of the protein tubulin
-relatively stiff (25nm)
-each filament is polarised (has a head/tail direction)
- it has a dynamic structure:
=it can assemble and disassemble in response to cell needs

26
Q

How can microtubules assemble/ disassemble in response to cell needs?

A

Tubulin in cell B is roughly 50:50 as free or in filament.

27
Q

What does MTOC stand for and what is it?

A

MicroTubule Organising Centre

Specialised protein complexes where assembly of tubulin unit starts

28
Q

What is the MTOC in most cells and how does it work?

A

The centrosome. It contains a gamma tubulin ring that initiates the microtubule growth

29
Q

What makes up the microtubule?

A

Heterodimers of alpha and beta tubulin

30
Q

What is polarised growth and does it happen in microtubules

A

There is one end that grows after than the other- yes it does

31
Q

Give the functions of microtubules

A
  • intracellular transport (act like railway tracks on which molecules can run. There are different motors for different molecules and the directionality of filaments is vital)
  • organises position of organelles (which provides the polarisation of cells)
  • rhythmic beating of the flagella
32
Q

How does the beating of cilia and flagella happen?

A
  • core consists of 9 pairs of microtubules around two central microtubules (called an axoneme)
  • bending of cilia and flagella is driven by dynein (a motor protein)
  • the basal body (at the bas of the tubule) controls the assembly of the axoneme

Fundamentals Of Living Cells (41 decks)

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