Retta - L4 part 2
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Questions and Answers

What characteristic distinguishes actin filaments from microtubules?

  • Actin filaments are composed of tubulin.
  • Actin filaments have a smaller diameter. (correct)
  • Actin filaments have a larger diameter.
  • Actin filaments are hollow structures.
  • Which of the following correctly describes the formation of microtubules?

  • Microtubules consist of a single type of monomer.
  • Microtubules are built from alpha and beta tubulin dimers. (correct)
  • Microtubules are formed exclusively from microfilaments.
  • Microtubules do not have any associated subunits.
  • What is the approximate diameter of a microtubule?

  • 10 nm
  • 25 nm (correct)
  • 20 nm
  • 7 nm
  • Which statement correctly describes the proteins forming actin filaments?

    <p>Actin filaments consist of globular subunits of actin.</p> Signup and view all the answers

    Why are intermediate filaments called 'intermediate'?

    <p>Their diameter is between microfilaments and microtubules.</p> Signup and view all the answers

    How are microtubules structurally oriented?

    <p>Microtubules have a hollow cylindrical structure formed by subunits disposed in an ordered manner.</p> Signup and view all the answers

    What type of structure do actin filaments exhibit?

    <p>Twisted chains of filaments</p> Signup and view all the answers

    What are the basic building blocks of actin filaments?

    <p>Globular proteins</p> Signup and view all the answers

    How do actin filaments influence cellular morphology?

    <p>By mediating the intracellular distribution of filaments</p> Signup and view all the answers

    What role do focal adhesions play in cellular attachment?

    <p>They anchor the cell to the extracellular matrix through actin filaments.</p> Signup and view all the answers

    What structural characteristic differentiates microtubules from actin filaments?

    <p>Microtubules are hollow cylindrical structures.</p> Signup and view all the answers

    What is the function of microtubules in neurons?

    <p>They facilitate the movement of vesicles along the axon.</p> Signup and view all the answers

    What happens to a filament when monomers are removed?

    <p>The filament shortens.</p> Signup and view all the answers

    Where do microtubules emanate from within the cell?

    <p>From the MicroTubule Organization Centre (MTOC).</p> Signup and view all the answers

    Which component plays a significant role in muscle contraction?

    <p>Actin filaments</p> Signup and view all the answers

    What is a key function of the actin cytoskeleton?

    <p>Promoting and shaping cellular protrusions.</p> Signup and view all the answers

    Which statement correctly describes the differences between actin filaments, microtubules, and intermediate filaments?

    <p>Actin filaments and microtubules possess polarity while intermediate filaments do not.</p> Signup and view all the answers

    What role do accessory proteins play in regulating cytoskeletal dynamics?

    <p>They facilitate the initial formation of filaments and influence polymerization.</p> Signup and view all the answers

    How do cells respond to environmental changes via their cytoskeleton?

    <p>By rapidly assembling and disassembling components to adapt movement.</p> Signup and view all the answers

    What is the structure and composition of microtubules?

    <p>They consist of cylindrical structures made from dimers of alpha and beta tubulin.</p> Signup and view all the answers

    Why are intermediate filaments described as having mechanical resistance?

    <p>They have a rope-like structure formed from elongated proteins.</p> Signup and view all the answers

    What is the primary role of actin and myosin interactions within the sarcomere?

    <p>To facilitate the contraction and relaxation of the muscle cell</p> Signup and view all the answers

    Which type of intermediate filament is specifically found in muscle cells?

    <p>Desmin</p> Signup and view all the answers

    What is the consequence of the absence of intermediate filaments in stressed cells?

    <p>Cells can detach from one another more easily</p> Signup and view all the answers

    What structure forms during cytokinesis to separate the two daughter cells?

    <p>Contractile ring</p> Signup and view all the answers

    What triggers the movement of neutrophils toward bacteria?

    <p>Chemotactic signals</p> Signup and view all the answers

    Which component is not part of the cytoskeleton?

    <p>Focal adhesions</p> Signup and view all the answers

    What is a notable feature of epidermolysis bullosa related to intermediate filaments?

    <p>Mutations in keratin genes</p> Signup and view all the answers

    How do microtubules contribute during mitosis?

    <p>They pull apart the chromosomes</p> Signup and view all the answers

    Which proteins are responsible for anchoring one cell to another in epithelial tissues?

    <p>Keratins</p> Signup and view all the answers

    What occurs at the leading edge of a migratory cell?

    <p>Extension of filaments pushing the plasma membrane</p> Signup and view all the answers

    What role does the nuclear lamina play in mitosis?

    <p>It must disassemble to allow the process of mitosis to occur.</p> Signup and view all the answers

    Where are microtubules primarily organized in eukaryotic cells?

    <p>From the microtubule organizing center.</p> Signup and view all the answers

    Which motor proteins are responsible for transporting cargo towards the periphery of the cell?

    <p>Kinesins</p> Signup and view all the answers

    What is the primary function of actin filaments in the context of cell migration?

    <p>To push the plasma membrane and form protrusions.</p> Signup and view all the answers

    Identify the structure that separates the front edge of a polarized migrating cell from the rear edge.

    <p>Focal adhesion</p> Signup and view all the answers

    What distinguishes cilia from microvilli?

    <p>Cilia have a motile function, while microvilli increase surface area.</p> Signup and view all the answers

    Which of the following structures is primarily responsible for cell shape and movement?

    <p>Actin filaments</p> Signup and view all the answers

    During cellular processes, how do motor proteins facilitate movement within the cell?

    <p>By moving along cytoskeletal structures.</p> Signup and view all the answers

    In a polarized cell, which would be considered the 'leading edge'?

    <p>The edge that guides migration forward.</p> Signup and view all the answers

    What would happen if the nuclear lamina does not disassemble during mitosis?

    <p>The nuclear structure would remain intact.</p> Signup and view all the answers

    Study Notes

    Microfilaments and Microtubules

    • Actin filaments, known as microfilaments, have a diameter of 7 nm, making them the thinnest cytoskeletal components.
    • Microtubules are larger, with a diameter of 25 nm, and are composed of tubulin proteins.
    • Intermediate filaments are so named because their diameter is between that of microfilaments and microtubules.
    • Microfilaments are made of globular actin subunits that twist to form protofilaments, which further twist to create the filament structure.
    • Microtubules are composed of dimers formed by alpha and beta tubulin subunits arranged in a hollow cylindrical structure.
    • Both microfilaments and microtubules can dynamically elongate or shorten based on the addition or removal of monomeric subunits.

    Cytoskeletal Filaments and Cell Morphology

    • Actin filaments contribute to the structural integrity of the cell, supporting processes like the formation of microvilli.
    • The distribution and dynamics of actin filaments influence cellular shape and morphology, especially during cell migration.
    • Cell attachment to the extracellular matrix is mediated by focal adhesions linked to actin filaments, crucial for tissue stability.
    • Actin filaments are essential in muscle contraction, forming the sarcomere structure, which is key in muscular function.

    Microtubule Organization and Functions

    • Microtubules originate from the Microtubule Organization Centre (MTOC) near the nucleus, extending in star-like patterns throughout the cell.
    • They provide a structural framework for the intracellular transport of various cargo, including vesicles and organelles, in both directions using motor proteins.
    • Kinesin moves cargo toward the cell periphery, while dyneins move it toward the cell center, reflecting the dynamic nature of microtubule function.

    Intermediate Filaments

    • Intermediate filaments are composed of various proteins, including lamins (forming the nuclear lamina), keratins (found in epithelial cells), and vimentin (in connective tissues).
    • They provide mechanical stability through cytoskeletal integrity, helping to resist cellular stress and maintain tissue structure.
    • Diseases such as epidermolysis bullosa arise from mutations in intermediate filament proteins, leading to fragile skin.

    Dynamic Behavior During Cell Division

    • During cell division, microtubules form the mitotic spindle that separates chromosomes, while actin filaments create a contractile ring for cytokinesis, dividing the cytoplasm of the daughter cells.
    • The coordinated action of actin filaments and microtubules enables effective cell division, which includes both mitosis and the cytokinetic phase of division.

    Cellular Organization and Migration

    • The cytoskeleton plays a significant role in determining cellular organization and polarity, enabling cells to respond to external signals for movement.
    • Migratory cells exhibit distinct leading and trailing edges; the leading edge has extensive protrusions for movement, while the rear edge contracts and detaches from the substrate.### Cytoskeleton Overview
    • The cytoskeleton consists of different filament types, providing structural support and organization in epithelial cells.
    • Key components include actin filaments, microtubules, and intermediate filaments; each performing unique functions.

    Cellular Polarity and Attachment

    • Actin filaments and microtubules exhibit polarity with distinct plus and minus ends, aiding in directionality of cellular functions.
    • Intermediate filaments lack polarity, presenting a uniform structure.
    • Epithelial cells utilize the cytoskeleton for anchoring to the extracellular matrix, facilitating adhesion between cells.

    Dynamics of Cytoskeleton

    • Migratory cells exhibit rapid assembly and disassembly of cytoskeletal components, especially actin, enabling swift responses to environmental changes.
    • Actin filaments undergo processes of elongation and shortening, driven by the reassembly of globular actin subunits.

    Microtubule Structure and Function

    • Microtubules are composed of dimeric subunits of alpha and beta tubulin, forming protofilaments that combine into a hollow, cylindrical structure.
    • Microtubules can grow or shrink quickly, responding to cellular needs by adding or removing subunits.

    Intermediate Filament Characteristics

    • Intermediate filaments are unique, forming from elongated proteins in a staggered manner, resulting in a rope-like structure that provides mechanical strength.
    • These filaments associate both longitudinally and laterally for increased stability.

    Accessory Proteins and Regulation

    • Accessory proteins play a critical role in regulating the dynamics of cytoskeletal components, influencing polymerization and depolymerization.
    • Microtubule organizing centers initiate the assembly of microtubules through a nucleation process.

    Types of Accessory Proteins

    • Nucleating proteins help form initial filaments, encouraging growth from nucleated structures.
    • Monomer sequestering proteins prevent premature assembly by binding to monomers.
    • Lateral cross-linking proteins stabilize bundles of filaments, enhancing structural integrity.
    • Motor proteins, such as myosin, facilitate movement by enabling reciprocal sliding of filaments, contributing to cell contractility.
    • Capping proteins regulate filament stability and growth at both ends of the filaments.
    • Severing proteins enhance disassembly by cutting filaments into shorter segments, speeding up the process compared to gradual subunit removal.

    Significance of Cytoskeletal Dynamics

    • The cytoskeleton's adaptability allows cells to sense and respond to environmental signals, including chemotactic cues.
    • Changes in cytoskeletal dynamics can result in cellular movements, attachment stability, and division in response to stimuli.

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    Description

    Explore the two types of cytoskeletal components: actin filaments and microtubules. This quiz covers their diameters, structural differences, and functions in the cytoskeleton. Test your knowledge on these fundamental cellular structures!

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