Cytoskeleton and Cell Motility Quiz
27 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What structural feature allows myosin II to interact with actin during muscle contraction?

  • The neck region
  • The globular heads (correct)
  • The light chains
  • The long rod-shaped tail

    • What role does calcium play in muscle contraction?

  • It releases ADP from the myosin head
  • It activates myosin directly
  • It caps actin filaments
  • It triggers a conformational shift in troponin (correct)

    • Which protein is responsible for stabilizing F-actin by capping its plus end?

  • Cofilin
  • Profilin
  • CapZ (correct)
  • Nebulin

    • How do myosins facilitate muscle contraction?

    <p>By pulling actin filaments toward the center of the sarcomere</p> Signup and view all the answers

    What occurs when ATP binds to the myosin head?

    <p>Myosin is released from actin</p> Signup and view all the answers

    Which of the following proteins helps to prevent tearing of muscle during contraction?

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

    What is the primary function of the Arp2/3 complex?

    <p>To nucleate new branches off existing actin filaments</p> Signup and view all the answers

    What occurs to the muscle when there is no ATP available?

    <p>Muscle enters a state of rigor mortis</p> Signup and view all the answers

    Which structure caps the minus end of actin to regulate its length?

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

    What is the main structural component of a sarcomere?

    <p>Thick and thin filaments</p> Signup and view all the answers

    Which protein binds to ADP-actin and severs filaments to promote depolymerization?

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

    How does profilin help regulate actin polymerization?

    <p>Facilitating the exchange of ADP for ATP</p> Signup and view all the answers

    What is a key characteristic of myosin in the context of muscle contraction?

    <p>It works asynchronously</p> Signup and view all the answers

    What distinguishes intermediate filaments from other cytoskeletal elements?

    <p>Their assembly does not require ATP or GTP.</p> Signup and view all the answers

    Which of the following statements about intermediate filaments is correct?

    <p>They are less sensitive to chemical agents.</p> Signup and view all the answers

    What role do plectin molecules play in the cytoskeleton?

    <p>They serve as a binding site for intermediate filaments.</p> Signup and view all the answers

    What is the primary function of keratins within the intermediate filament family?

    <p>To provide strength to epithelial cells.</p> Signup and view all the answers

    How do actin filaments differ from intermediate filaments in terms of their assembly?

    <p>Actin filaments form polar structures while intermediate filaments do not.</p> Signup and view all the answers

    What happens during the phosphorylation of lamin during prophase?

    <p>It causes the disassembly of the nuclear lamina.</p> Signup and view all the answers

    Which condition is associated with mutations in keratin polypeptides?

    <p>Epidermolysis bullosa simplex.</p> Signup and view all the answers

    What is the basic building block of intermediate filaments?

    <p>Rodlike tetramer.</p> Signup and view all the answers

    Which type of myosin is primarily responsible for muscle contraction?

    <p>Conventional (Type II) myosins.</p> Signup and view all the answers

    What determines the directionality of muscle contraction in myosin II?

    <p>Movement towards the plus end of actin filaments.</p> Signup and view all the answers

    Which accessory proteins influence actin polymerization?

    <p>Actin-binding proteins.</p> Signup and view all the answers

    What characterizes the assembly of actin filaments in vivo?

    <p>Only ATP-actin polymerizes at the plus end.</p> Signup and view all the answers

    How does desmin contribute to muscle cell function?

    <p>It integrates various components of the muscle cell.</p> Signup and view all the answers

    Which structural characteristic is unique to actin filaments?

    <p>They have a flexible helical filament structure.</p> Signup and view all the answers

    Study Notes

    Cytoskeleton and Cell Motility

    • The cytoskeleton is a network of protein filaments that provides structural support and allows for cell motility.

    Actin and Intermediate Filaments

    • Actin filaments (microfilaments) are flexible structures composed of actin monomers. They have a diameter of 5-9 nanometers.

    • Actin filaments are involved in cell motility, shape, structural support, and muscle contraction. They are highly concentrated just beneath the plasma membrane.

    • Intermediate filaments (IFs) are rope-like fibers, strong, and flexible. They have a diameter of 10-12 nanometers.

    • IFs are found in animal cells, providing mechanical strength where cells are subjected to physical stress.

    • IFs are chemically heterogeneous, existing in multiple classes based on various factors (e.g., cell type, biochemical, genetic). About 70 different genes encode them.

    • IF assembly does not involve ATP or GTP hydrolysis.

    Intermediate Filaments (continued)

    • IFs extend throughout the cytoplasm in a variety of animal cells, often interconnected by wispy cross-bridges.
    • Plectin is a protein involved in cross-bridging IFs to other cytoskeletal filaments.
    • A single plectin molecule has a binding site for an intermediate filament at one end and, depending on the isoform, a binding site for another intermediate filament, microfilament, or microtubule at the other end.
    • IF assembly involves the association of eight tetramers in a lateral arrangement, forming filaments with a length of approximately 60 nanometers.
    • Unit lengths of filaments then associate end-to-end to form longer intermediate filaments.
    • IF assembly does not involve ATP or GTP hydrolysis. Polarity doesn't exist in IFs.

    Actin and Myosin

    • G-actin is the globular form of actin, and F-actin is a filamentous form of actin.
    • In the presence of ATP, G-actin monomers polymerize into F-actin filaments via a flexible helical structure.
    • The ATP binding cleft is oriented in the same direction in all actin subunits (monomers) within the filament.
    • Plus and minus ends of actin filaments have different polymerization rates.
    • The minus end of the filament contains an exposed binding cleft (pointed end) and the plus end (also called the barbed end) is where the minus end of G-actin binds.
    • Only ADP-actin filaments dissociate.
    • In vivo, polymerization only occurs at the plus end of ATP-actin filaments.

    Actin Binding Proteins

    • Many accessory proteins bind to actin, regulating actin polymerization and organization.
    • Cofilin promotes depolymerisation at the minus end of actin filaments.
    • Profilin binds to ADP-actin at the plus end, affecting actin monomer binding.
    • Thymosin sequesters G-actin to prevent polymerization.
    • CapZ caps plus ends, preventing further growth and capping at the minus end prevents loss of subunits during F-actin.

    Myosins

    • Myosins are actin-based motor proteins.
    • All myosins have a characteristic motor domain that have ATPase activity.
    • Different types of myosins are involved in different tasks, such as muscle contraction, cytokinesis, and cell migration.
    • Type II myosins are best studied in muscle contraction.
    • Conventional myosins (Type II) consist of two heavy chains, each with a globular head and a tail; two light chains are part of each heavy chain's head, forming a highly asymmetric structure.
    • Myosin II assembly is into fibers with tails pointing toward the center and globular heads pointing outwards.

    Muscle Organization and Contraction

    • Muscle consists of parallel fibers (cells) joined by tendons.
    • Muscle fibers are multinucleate cells formed during embryogenesis, specializing in contraction.
    • Myofibrils are thinner cylindrical strands composing each muscle fiber.
    • Myofibrils consist of repeating sarcomeres.
    • A sarcomere includes the area between adjacent Z lines.
    • Thin filaments (actin) extend from one Z line to the next, and thick filaments (myosin) are also found between adjacent Z lines.
    • A sarcomere is composed of an A band (where thick filaments are present), and I bands (where thin filaments are located).
    • The H zone is a region of the sarcomere where only thick filaments are present.
    • The M line consists of proteins that connect adjacent thick filaments.
    • Titin is a protein extending through the myosin filaments (thick filaments) and attaches to the Z line, preventing muscle tearing.
    • Tropomyosin blocks myosin binding sites on actin.
    • Troponin is a complex with three subunits (TnT, TnI, TnC) that regulates the interaction of troponin with tropomyosin and actin.

    Calcium ions

    • Calcium ions trigger muscle contraction by binding to troponin.
    • This binding releases the tropomyosin blockage, allowing myosin to bind to actin, initiating contraction.

    Myosin mutations can cause diseases ranging from deafness to familial hypertrophic cardiomyopathy.

    Contractile cycle

    • Myosin head undergoes conformational changes driven by ATP hydrolysis.
    • ATP binding causes the myosin head to detach from actin.
    • Hydrolysis activates the myosin head for a new power stroke.
    • The power stroke causes actin filaments to slide relative to each other.
    • In the absence of ATP, rigor mortis occurs due to the inability for myosin heads to detach from actin filaments.

    ###Actin in endocytosis

    • Actin plays a crucial role in endocytosis, including membrane invagination, pinching, and scission.
    • Components are recycled and the process of endocytosis occurs with different phases.

    Actin polymerization regulation

    • Actin polymerization is regulated by several proteins, allowing for diverse cellular functions and complex organization.

    Rho family GTPases

    • Rho family of small GTPases regulate the actin cytoskeleton, influencing cellular functions like membrane remodeling and motility.
    • GDI (guanine nucleotide dissociation inhibitor) protein associates with these GTPases and may affect their functions at the cellular membrane.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Chapter 9.2 PDF - Cytoskeleton and Cell Motility

    Description

    Test your knowledge on the cytoskeleton, actin filaments, and intermediate filaments. This quiz covers the structure and function of these critical components in cell motility and mechanical strength. Ideal for students studying cell biology.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser