The Cytoskeleton is the internal network of protein filamentsand microtubules in eukaryotic cells that are responsible for controlling the cell's movement, providing mechanical strength, establishing the shape of the cell, chromosome transportation during cell division, and the intracellular transport of organelles. The cytoskeleton is made up of three protein filaments: actin filaments (also known as microfilaments), intermediate filaments, and microtubules.

Interactive Activity


The above videos will provide you with background information on the cytoplasm and cytoskeleton

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Protein Filament
Description and Fuction
Actin Filament
  • 8 nm in diameter
  • composed of a contractile protein called actin
  • interact with myosin filaments to cause muscle contraction
  • generate locomotion in cells such as white blood cells and the amoeba
  • carry out cellular movements including gliding, contraction, and cytokinesis
  • generates cytoplasmic streaming in some cells
Intermediate Filament
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  • 10nm in diameter
  • several different types with varying functions (ex: lamins stabilize the nuclear envelope, neurofilaments support neurons, vimentins provide mechanical strength to muscle cells)
  • provide a supporting framework of tensile (tension) strength for the cell.

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  • 20-25nm in diamter
  • straight, hollow cylinders made up of a ring of 13 "protofilaments";
  • composed of subunits of the protein tubulin termed alpha and beta
  • determine cell shape and are responsible for most cell functions involving motion
  • are found in both animal and plant cells.
  • motion is driven by microtubule "motors" that run on ATP
  • kinesin motors move towards the "plus" (active) end, while dyenin motors move towards the "minus" (inactive) end
  • In plant cells, microtubules are created at many sites throughout cell. In animal cells, the microtubules originate at the centrosome.


Types of Microtubules

  • Centrosome- a region near the nucleus that microtubules grow out ofCentriole.jpg
    • the microtubules are the compression resistant grinders of the cytoskeleton
    • found in both plant and animal cells
  • Centrioles used in cellular division
    • composed of 9 sets of three microtubules arranged in a ring
    • only found in animal cells
    • there are 2 centrioles in each cell
    • During cellular division...
      • each centriole divides; two centrioles move to opposite ends of the cell
      • a mitotic spindle (groups of microtubules) will connect to the centrioles and chromosomesexternal image paramecium.gif
      • chromosomes are split and pulled towards the centriole
      • Cilia - a locomotive appendage that protrudes from a cell
      • usually found in large numbers on the surface of the cell
      • very small: 2 - 20 micrometers
      • work as oars to propel cell through water
      • Flagella - a locomotive appendage that protrudes from a cell
        • found in small amounts on the surface of a cell
        • usually much larger than cilia
        • a flagellum propels a cell in the same direction as its axis
      • Flagella and cilia are constructed similarly
        • has central microtubules
        • has 9 pairs of microtubules arranged in a ring radiating from the central microtubules
        • the protein dynein is used to move the cilia and flagella
        • cilia and flagella are anchored to the cell by a basal body
          • basal bodies are structurally identical to a centrio



The above pictures show the structure of flagella and cilia

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Types of Intermediate Filamentsexternal image moz-screenshot.pngexternal image moz-screenshot-1.pngexternal image moz-screenshot-2.pngintermediatefilament.jpg

  • Keratins

are found in epithelial cells and also form hair and nails;

  • Nuclear lamins

form a meshwork that stabilizes the inner membrane of the

  • Neurofilaments

strengthen the long axons of neurons;

  • Vimentins

provide mechanical strength to muscle (and other) cells.

Quiz on the cytoskeleton, test your knowledge: Cytoskeleton Links
Videos about Cytoskeletons:
Click Here for an interactive site on the cytoskeleton

Go to these great sites for additional information

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  • Cytoplasm is the region between the nucleus and the membrane bounding the cell

  • The cytoplasm is made of a semifluid called cytosol

  • Organelles are located in the cytoplasm

  • Cytosol uses enzymes to break down larger molecules

  • The products are used by organellesexternal image cell.gif

  • Ex: Glucose cannot be used by mitochondria unless it is broken down into pyruvate molecules

Eukaryotic Cells: Cytoplasm

The Cell: Cytoplasm


Campbell, Neil A.. "A Tour of The Cell." Biology. Erin Mulligan. Reading, Massachusetts: Addison Wesley Longman, Inc, 1999. Print.
"Cell Structure." Biology4Kids. Andrew Rader Studios, 2010. Web. 25 Oct 2010. <>.
"Cytoplasm." Student's Corner. Oxford University Press (China) Ltd, n.d. Web. 25 Oct 2010.
"Cytoskelaton." A Video Tour of Cell Motility. N.p., n.d. Web. 27 Oct 2010. <>.
"Cytoskeleton Microtubules | Cell Biology." YouTube - Broadcast Yourself. Web. 27 Oct. 2010. <>.
"Essential Biochemistry - Actin and Myosin." Wiley::Home. Web. 27 Oct. 2010. <>.
"Eukaryotic Cells: Cytoplasm." HowStuffWorksVideos. Web. 25 Oct 2010.
"Flagella and Cillia." YouTube. Web. 26 Oct 2010. <>.
"Flying the Flagella." Charles Darwin & Evolution. Web. 26 Oct 2010. <>.
"Paramecium." Web. 27 Oct 2010. <>.
"The Cell: Cytoplasm." HowStuffWorksVideos. Web. 26 Oct 2010. <>.