cell bio module 7

• Cytoskeleton


  A network of protein-based filaments that provides a scaffolding structure to the cell
• Cytoskeleton


  • It is not a static scaffold, but rather a dynamic network that allows cell movement, growth, and differentiation
• Types of cytoskeletal fibers

  • Actin filaments
  • Microtubules
  • Intermediate filaments
• Cytoskeleton


  • It is essential for the shape and function of specialized structures in differentiated cells, such as the microtubules in cilia and the actin filaments in the microvilli of epithelial cells
• Cytoskeleton


  • It is dynamic, allowing for cell migration and cell division
• Actin filaments


  Also called microfilaments, they are the thinnest cytoskeletal fibers, made up of monomeric actin subunits
• Actin filaments


  • They are polar, with a "plus" end that grows more quickly and a "minus" end that grows more slowly
• Actin filament assembly and disassembly

  Regulated by the binding and hydrolysis of ATP
• Critical concentration of actin monomers


  Determines whether the plus end will grow or shrink
• Actin-binding proteins


  Profilin and thymosin regulate the dynamics of actin polymerization and depolymerization
• Treadmilling


  The process where there is no net increase in actin filament length because the rate of polymerization at the plus end equals the rate of depolymerization at the minus end
• Actin filament reorganization


  Powers the formation of lamellipodia and filopodia, which drive cell movement and migration
• Myosin motor proteins


  Move along actin filaments and power intracellular cargo trafficking
• Myosin II


  • Forms bipolar thick filaments that interact with actin filaments to generate contractile forces, as seen in muscle sarcomeres
• Myosin V


  Transports cargo like melanosomes along actin filaments
• Movement of myosin along actin

  Driven by the cyclic binding and hydrolysis of ATP
• Microtubules


  Hollow tubes composed of 13 protofilaments of α- and β-tubulin dimers
• Microtubules


  • Exhibit dynamic instability, cycling between growth (polymerization) and shrinkage (depolymerization) phases
• Microtubule-associated proteins (MAPs)


  Regulate microtubule dynamics by stabilizing or destabilizing the filaments
• Microtubule organizing center (MTOC)


  Also called the centrosome in animal cells, it is where microtubules are nucleated
• γ-tubulin ring complexes (γ-TuRCs)


  Serve as templates for new microtubule growth at the MTOC
• During mitosis


  The mitotic spindle is formed from microtubules that attach to and separate the replicated chromosomes
• Microtubule-targeting drugs


  Colchicine and taxol can inhibit microtubule dynamics and disrupt cell division
• Kinesin motor proteins


  Move cargo towards the plus end of microtubules, typically towards the cell periphery
• Dynein motor proteins


  Move cargo towards the minus end of microtubules, typically towards the MTOC at the cell center
• Opposing movements of kinesin and dynein


  Can result in bidirectional transport of cargo along microtubules