• Three types of cytoskeletal filaments (actin filaments, microtubules and intermediate filaments) exist in cells, and their networks extends throughout the cytoplasm.
  • While the three types of cytoskeletal filaments have unique structures, they are all polymers of unit protein.
  • Three types of filaments are dynamic as they frequently repeat polymerization and depolymerization. Actin filaments and microtubules in particular perform their functions by frequently repeating degradation and reconstruction of their networks.
  • Many functions of cytoskeleton are performed through collaboration with binding proteins.
  • Proteins that play important roles by binding to cytoskeleton include regulatory proteins (which regulate polymerization and depolymerization) and motor proteins (which carry cargo using the cytoskeleton as a road).
  • Motor proteins move along actin filaments or microtubules like walking on two legs by using the energy of ATP hydrolysis. The direction of movement is related to that of the actin filaments and microtubules.
  • The contractile motion of cells occurs through a mechanism similar to that of motor proteins that transport materials in cells. Both move by changing the structure of proteins using the energy obtained from ATP hydrolysis.
  • Cytoskeletal functions are diverse, and include maintenance of cell shape, arrangement of organelles, contraction of muscle cells, migration of cells, intracellular transport and segregation of chromosomes. They occur mainly through the degradation and reconstruction of filament structures and collaboration with motor proteins.

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