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Cell Cytoskeleton

• provides structural support to the cell and determines its shape.

• is a network of fibrillar proteins.

• These fibrilar proteins are synthesized by polymerization of precursor molecules → if not needed anymore → disassemble → reassemble where and where needed → thus the cytoskeleton can be dynamic as needed.

• Components:

  • Microtubules

  • Filaments

    • Thin filaments

    • Thick filaments

    • Intermediate filament

Microtubules

• polymer of tubulin.

• have a hollow lumen at the center.

• 20-30 nm in diameter.

Functions

• Form and move structures like:

  • Cilia

  • Flagella

  • Centrioles

  • Mitotic spindle

• Form a track for intracellular organelles to move from one area of the cell to the other

Thin & Thick Filaments

• Thin filaments are made up of actin

• Thick filaments are made up of myosin

Functions: They play role in...

• Muscle contraction

• Cell movement e.g. gliding, cytokinesis

• Extend process from cell e.g.

  • Formation of axon in neuron

  • Formation of microvilli in epithelial cells

Intermediate Filaments

• There is a large variety of subunit proteins that can form intermediate filaments.

• Expression of different subunits in different cells results in formation of different intermediate filaments in different cells. For example:

  • Epithelial cells have keratins

  • Nerve cells have neurofilaments

  • Muscle cells have desmin

Functions

• Radiate from the cell area subject to tensile stress → Reinforce such area against tensile stress.

• In epithelial cells, they insert at the desmosomal junctions that attach neighboring cells to one another.

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▶️ Endocytosis