Cytoskeletal Filaments and Functions
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Questions and Answers

What role does the cytoskeleton primarily serve in maintaining cell shape?

  • It acts as a barrier to external forces.
  • It functions as a rigid structure.
  • It enforces a fixed geometric shape.
  • It provides dynamic support that adapts to changes. (correct)

    • Which cytoskeletal component is primarily involved in cellular locomotion?

  • Intermediate filaments
  • Microtubules
  • Microfilaments (actin filaments) (correct)
  • None of the above

    • How does the cytoskeleton contribute to the positioning of organelles within the cell?

  • By forming permanent connections to organelles.
  • By creating a network of tracks for directed movement. (correct)
  • Through cellular osmosis.
  • Through the use of passive diffusion.

    • What is a key characteristic of the proteins that make up the cytoskeletal filaments?

    <p>They allow rapid assembly and disassembly.</p> Signup and view all the answers

    Which function is NOT associated with the cytoskeleton?

    <p>Directing cell metabolism processes.</p> Signup and view all the answers

    What is the primary function of cadherins in adherens junctions?

    <p>To serve as attachment sites for actin filaments</p> Signup and view all the answers

    Which sequences correctly describe the three stages of cell migration?

    <p>Extension of leading edge, attachment to substratum, retraction of the rear</p> Signup and view all the answers

    What role do stress fibers play in a cell?

    <p>They are bundles of actin filaments involved in cell structure and movement</p> Signup and view all the answers

    Which of the following is NOT a characteristic of microvilli?

    <p>Are involved in cellular locomotion</p> Signup and view all the answers

    What drives the transient protrusions of the plasma membrane (PM) during phagocytosis?

    <p>Growth of actin filaments at the leading edge</p> Signup and view all the answers

    What is the function of the Z disc in muscle fibers?

    <p>It serves as an attachment point for actin filaments.</p> Signup and view all the answers

    During muscle contraction, which of the following occurs?

    <p>Actin filaments slide past myosin filaments towards the center of the sarcomere.</p> Signup and view all the answers

    Which structure corresponds to the region containing only thick filaments?

    <p>H zone</p> Signup and view all the answers

    What components are involved in forming a myofibril?

    <p>Bundles of actin and myosin filaments.</p> Signup and view all the answers

    Which bands in a sarcomere contain only thin filaments?

    <p>I bands</p> Signup and view all the answers

    What is the primary function of actin-binding proteins in the context of actin filament dynamics?

    <p>They initiate and regulate both polymerization and depolymerization of actin filaments.</p> Signup and view all the answers

    What occurs at the plus end of an actin filament during polymerization?

    <p>ATP-actin monomers are added more rapidly.</p> Signup and view all the answers

    During the process of treadmilling in actin filaments, what happens to ADP-actin?

    <p>It dissociates from the filament more efficiently compared to ATP-actin.</p> Signup and view all the answers

    Which type of actin monomer is characterized by a faster rate of filament growth when added to the plus end?

    <p>ATP-bound actin.</p> Signup and view all the answers

    What is the first step in the polymerization of actin filaments?

    <p>Dimer and trimer formation from G actin monomers.</p> Signup and view all the answers

    Study Notes

    Cytoskeletal Filaments

    • Cytoskeletal filaments include actin, microtubules, and intermediate filaments.
    • Actin filaments are long, thin protein fibers, crucial for cell structure and movement.
    • Microtubules are hollow tubes composed of protein subunits, forming a dynamic scaffold.
    • Intermediate filaments provide mechanical strength and support to cells.

    Functions of Cytoskeleton

    • Cytoskeleton acts as a scaffold supporting cell shape.
    • It positions organelles within the cell.
    • Transports cellular materials like organelles, vesicles, and mRNA.
    • It's an apparatus generating force for cell movement.
    • Essential for cell division machinery.

    Microtubules

    • Microtubules are composed of tubulin heterodimers
    • Characterized by dynamic instability, rapidly growing and shrinking.
    • Microtubule growth is initiated by microtubule-associated proteins (MAPs).
    • MAPs regulate microtubule organization.

    Actin Filaments

    • Actin filaments are composed of actin monomers.
    • Actin filaments polymerize to form microfilaments.
    • Actin filaments growth at their plus ends is faster.
    • Actin filaments are stabilized by actin-binding proteins.
    • Actin polymerization and depolymerization are regulated by actin-binding proteins.

    Myosin Motors

    • Myosin II is vital in muscle contraction.
    • Myosin is attached to the actin filament and moves along it.
    • ATP binding and hydrolysis drive myosin's movement.
    • Myosin's head's conformational changes are essential for sliding filaments during muscle contraction.

    Actin Bundles & Networks

    • Actin bundles are stabilized and organized into bundles or networks by actin-binding proteins, like cross-linking proteins
    • Actin filaments, projecting from the cell surface, are involved in cell surface projections like microvilli, filopodia, and cell locomotion.

    Cell Migration

    • Cell movement across a surface involves three steps: leading edge extension, attachment to the substratum, and retraction of the trailing edge.

    Focal Adhesions and Adherens Junctions

    • Focal adhesions attach stress fibers to the plasma membrane.
    • Integrins bind to an extracellular matrix, facilitating cell attachment and spreading.
    • Adherens junctions connect cells to each other, providing cell-cell contact.
    • Actin bundles are anchored to adherens junctions via cadherins.

    Microvilli

    • These are actin-based cell protrusions.
    • They're common in epithelial cells lining the gut.
    • They significantly increase the surface area for nutrient absorption.

    Structure of Spectrin

    • Spectrin is a tetramer, composed of two α and two β polypeptide chains.
    • Each β-chain has an actin-binding domain (ABD) at its amino terminus.
    • The α and β chains contain multiple a-helical spacer domains, providing structural stability to the network.

    Stress Fibers and Focal Adhesions

    • Many cells have specialized plasma membrane regions for forming contacts with the extracellular matrix.
    • These regions, called focal adhesions, are crucial attachments for stress fiber bundles of actin filaments.
    • Stress fibers attach cells to their surroundings.

    Filament Severing by Cofilin

    • Cofilin binds to and severs actin filaments, crucial for cell motility.
    • The newly formed filament ends are available for polymerization or depolymerization.
    • This process is essential for cell motility and division.

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    Cytoskeletal Filaments PDF Lecture Notes

    Description

    This quiz covers the essential components and functions of cytoskeletal filaments, including actin filaments and microtubules. Learn how these structures play a critical role in cell shape, movement, and organelle organization. Test your understanding of the dynamic properties and regulatory mechanisms involved in cytoskeleton dynamics.

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