The%20Cytoskeleton

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The Cytoskeleton
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Objectives

• Define cytoskeleton.
• Explain the general functions of the
  cytoskeleton.
• List the 3 types of cytoskeletal elements and
  their respective functions.
• Describe the structure and function of the
  centrosome.
• Describe the structure and functions of
  centrioles
• List and describe the similarities and
  differences between cilia and flagella.

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The Cytoskeleton

• Prior to 1970s cytosol thought to be unorganized
  mix of organic molecules.
• Electron microscopy reveals organized cytosol
• Immunoflourescence microscopy identified protein
  fibers.

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The Cytoskeleton

• Characteristics
• ? Found in eukaryotes
• ? Network of connected filaments and tubules
• ? Extends from nucleus to plasma membrane
• ? Elements can disassemble and reassemble

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The Cytoskeleton

• Function
• ? Maintains cell shape
• ? Allows organelles to move

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The Cytoskeleton
Composed of 3 Types of Filaments Actin Intermediat
e Microtubules
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Actin Filaments

• Characteristics
• Long, thin about 7 micrometers in diameter
• Occur in bundles or meshlike networks.
• Consist of two chains of globular actin monomers
  twisted to form a helix.

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Actin Filaments

• Functions
• ? Structural
• Form dense complex web just under the plasma
  membrane.
• In microvilli of intestinal cells likely
  shorten or extend cell into intestine.
• In plant cells, they form tracks along with
  chloroplasts circulate.

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Actin Filaments

• Functions
• ? Movement
• Iinteracts with motor molecule myosin
• Similar action accounts for pinching off cells
  during division and for amoeboid movement.

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Intermediate Filaments

• Characteristics
• ? 8-11nm in diameter
• ? Rope-like
• ? Fibrous polypeptides

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Intermediate Filaments

• Functions
• ? Support
• Nuclear envelope
• Plasma membrane
• ? Form cell-to-cell junctions.

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Microtubules

• Description
• ? Ropelike, hollow cylinders (25nm in
  diameter, 0.2 micrometers in length).
• ? Composed of protein (Tubulin) alpha and
  beta
• ? Associated with motor molecules (kinesins)
  kinesin and dynein

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Microtubules

• Functions
• ? Maintain shape of cells
• ? Tracks for vesicle and organelle movement
• ? Different kinesins move different vesicles or
  organelles.

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Centrioles

• Short cylinders with a 90 pattern of
  microtubules triplets.
• Animals cells and most protista, two centrioles
  lying at right angles
• Plant and fungal cells have equivalent of a
  centrosome but does not contain centrioles.
• Centrioles serve as basal bodies for cilia and
  flagella.

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Centrioles

• Serve as basal bodies for cilia and flagella.

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Cilia and FlagellaFlagella (L. flagello, whip) ?
Cilia (L. cilium, eyelash, hair)

• Short, usually numerous hair like projections
  that can move in an undulating fashion.

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Differences

• Flagella longer than cilia, usually fewer
• Flagella are whip-like projections
• Flagella move whip-like (e.g. Sperm cells),
  cilia move swimmer-like/oar-like

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Similarities

• Construction
• Membrane-bounded cylinders
• (92 pattern of micortubules).
• Basal bodies
• Movement
• Microtubules slide past one another.

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Similarities(Contd)

• Growth
• By addition of tubulin to tips
• Movement Mechanism
• Microtubules slide past one another.

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Review

• Define cytoskeleton.
• Explain the general functions of the
  cytoskeleton.
• List the 3 types of cytoskeletal elements and
  their respective functions.
• Describe the structure and function of the
  centrosome.
• Describe the structure and functions of
  centrioles
• List and describe the similarities and
  differences between cilia and flagella.