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Elements of the Cytoskeleton

Objective: Compare and contrast the structure and function of the three types of cytoskeletal elements: actin filaments, intermediate filaments and microtubules

The 3 Elements of The Cytoskeleton

The Cytoskeleton is a system of dynamic protein filaments in eukaryotic cells

  • function:

    1. gives the cell shape

    2. provide mechanical support

    3. allows it to organize its organelles and to move

    4. hold the golgi and other organelles in place within the cytosol

  • cytoskeleton filament is a long chain of protein subunits

    • subunits is in equilibrium with large filaments

  • subunits self-assemble into filaments in vitro

    • dynamic and adaptable

Types of Cytoskeletal Filaments

Intermediate Filaments

Microtubule

Actin Filament

Diameter

10 nm

- outer diameter: 25 nm

7 nm

structure

- rope-like fibers
- made of IF proteins (fibrous)
- depends on the lateral bundling and twisting of coiled coils via hydrophobic amino acids

- long, hollow cylinders

flexible helical polymers

function

- mechanical strength
- cell shape

- determines the positions of membrane-enclosed organelles
- vesicle transport
- involved in cell division (spindle formation)
- cilia and flagella motility

- determine shape of the cell’s surface
- necessary for
cell locomotion (cell crawling)
- cytokinesis

types

- keratin: in epithelia cells (skin)

I. Intermediate Filaments

  • often anchored to the plasma membrane at junctions

  • found in the cytoplasm of cells from vertebrates

  • IF’s are prominent in the cytoplasm of cells that are subjected a lot to mechanical stress

    • ex. epithelial cells

Structure

Intertwined alpha-helices can form coiled-coil dimers → nonpolar side chans will interact with each other, causing them to wrap around each other → the more hydrophillic a.a side chains are exposed to the aq environment

Intermediate filaments assemble through coil-coil interactions (helical domains are coiled together like the strands of a rope)

  1. monomers have the same orientation (N→C)

  2. two dimers associate in head tail fashion to form a tetrameric subunit (made up of two dimers pointing in opposite directions)

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Types of Intermediate Filaments

Tissue specific in terms of their protein composition → diff cells have diff types of intermediate filament proteins

Functions of Intermediate Filaments

A. Hold Epithelial Cells Together

Skin epithelial cells with non-functional intermediate filaments → can’t stretch, will break, rupture

B. Connect Cells and Between Cells and the Basal Lamina

  • maintains connection between cells

C. Form Strong Network in The Cytosol That Links Indirectly to Neighboring Cells in Epithelial Cells

  • strong network = strong tissue

  • desmosomes = indirectly connect neighboring cells

    n Filaments