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Actin Filaments quiz #1

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  • What is the role of microfilaments (actin filaments) in cell division?
    Microfilaments, also known as actin filaments, play a crucial role in cell division by facilitating changes in cell shape and enabling cell movement. During cytokinesis, actin filaments form a contractile ring beneath the plasma membrane, which contracts to physically separate the dividing cell into two daughter cells.
  • What are the monomeric and filamentous forms of actin called?
    The monomeric form of actin is called G-actin, while the filamentous form is called F-actin. G-actin monomers polymerize to form F-actin filaments.
  • How does the polarity of actin filaments influence their growth?
    Actin filaments have a plus end and a minus end, with the plus end growing faster due to slower ATP hydrolysis. The minus end hydrolyzes ATP quickly, leading to destabilization and loss of monomers.
  • What is nucleation in the context of actin filament formation?
    Nucleation is the initial and difficult step in actin filament formation where a small stable complex of actin monomers forms. Once nucleation occurs, additional monomers can easily add to the growing filament.
  • Which proteins assist in the nucleation of actin filaments?
    The ARP2 complex and formins are proteins that assist in the nucleation of actin filaments. They help initiate the formation of new actin branches or filaments.
  • What is the function of ADF and cofilin in actin filament dynamics?
    ADF and cofilin bind to actin and enhance the dissociation of ADP-actin, promoting filament turnover. This action helps regulate the stability and remodeling of actin filaments.
  • How does profilin affect actin filament assembly?
    Profilin reverses the action of ADF and cofilin by stimulating the addition of actin monomers into filaments. It promotes actin polymerization and filament growth.
  • What is the difference between actin bundles and actin networks?
    Actin bundles are closely packed parallel arrays of filaments, while actin networks are cross-linked into orthogonal, mesh-like structures. Bundles provide structural support, and networks form gel-like, flexible frameworks.
  • Where is the cell cortex located and what is its composition?
    The cell cortex is located just beneath the plasma membrane and is composed of actin filaments and associated proteins. It helps maintain cell shape and supports membrane dynamics.
  • What cellular structure is formed by actin filaments and is involved in absorption?
    Microvilli are cellular structures formed by actin filaments that extend from the plasma membrane and are involved in absorption. Cells with many microvilli display a brush border appearance.