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Cytoskeleton
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Cytoskeleton
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Means “cell skeleton”
Internal framework of cell
Has many functions
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Anchoring cell organelles
Provide cell shape
Aids in cell motility
Response to environmental signals
Comprises
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Microtubules
Microfilaments
Intermediate filaments
Microtubules
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Hollow tubes made of the protein tubulin
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Alternating dimers of  and  tubulin
Largest of cytoskeleton filaments
Is used for:
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Maintenance of cell shape
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Movement of organelles through cell
• Often involves motor molecule
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Often originate from centrosome
Motility
• Flagella or cilia
Centrioles
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Located in centrosome of animal cells
Occur in perpedicular pair
Have 9 triplets of microtubules
Facilitate microtubule assembly and chromosome separation in some cells
Flagellum structure
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Basal body links flagellum or cilia to cell surface
– Basal body looks just like a centriole
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9 +2 arrangement of microtubules
Radial spokes prevent dramatic sliding and only bending
Motor molecules
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Interact with tubulin or actin
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Undulation-used for flagella and cilia movement
– Two microtubules moving relative to one another
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Organelle movement is like a ski lift tram or a monorail
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Cell movement facilitated by flagella or cilia
Are fixed at one end and allowed to move freely at the other end
– Movement is directional
Cell motility
Unlike in prokaryotes, eukaryotic flagella undulate
Cilia are small appendages and they move like a swimmers arm-active stroke and return stroke
How cell movement works
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Dynein is motor molecule that interacts with tubulin
Dynein walks along one microtubule, while bound to another
– This results in bending
– If no radial spokes or organelle coat, then microtubules would walk out of cell
Microfilaments
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Made of two intertwined strands of actin
Helps maintain cell shape
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Actin rearrangements allow engulfment events
Psuedopod formation in ameoba
Promote cytoplasmic streaming in plants
Essential for muscle contraction
Used by invading bacteria to move around cell
Frequently being assembled and disassembled within cell
Microfilaments 2
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Myosin interacts with actin to cause contraction
Cytoplasmic streaming and ameoboid motion are similar
– Cortical cytoplasm around the perimiter of cell contains perpendicular actin (wind fence)
– Streaming portion has parallel actin which facilitates cytoplasm movement
– Plant cell wall prevents amoeboid movement of plant cell
Intermediate Filaments
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Resemble cable in structure
Are made of protein subunits
Help maintain cell shape and keep organelles in place
Are durable and not assembled and disassembled as other cytoskeleton components