Muscle Contraction Mechanism
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Questions and Answers

What is the primary role of intermediate filaments in cytoplasm?

  • Cell movement
  • Organelle organization and movement
  • Actin filament formation
  • Provides tensile strength (correct)

    • In smooth muscle cells, what triggers the phosphorylation of myosin II?

  • A sudden decrease in cytosolic Ca2+
  • An increase in Ca2+ levels (correct)
  • The inhibition of kinesin motor proteins
  • The activation of dynein motor proteins

    • During muscle contraction, what is the primary mechanism by which actin filaments interact with myosin filaments?

  • Actin filaments slide over myosin filaments (correct)
  • Myosin filaments slide over actin filaments
  • Myosin filaments depolymerize to pull actin filaments
  • Actin filaments polymerize to push myosin filaments

    • What is the primary function of motor proteins like dynein and kinesin?

    <p>Organizing microtubules</p> Signup and view all the answers

    What is the primary trigger for muscle contraction in skeletal muscle cells?

    <p>A sudden rise in cytosolic Ca2+</p> Signup and view all the answers

    What is the distance of head displacement along the filament during a power stroke in muscle contraction?

    <p>5 nm</p> Signup and view all the answers

    What is the role of voltage-sensitive proteins in muscle contraction?

    <p>Regulation of calcium channels in the T-tubules</p> Signup and view all the answers

    What is the result of the sudden rise in Ca2+ in muscle contraction?

    <p>Triggering of muscle contraction</p> Signup and view all the answers

    What is the mechanism by which myosin molecules walk along actin filaments?

    <p>Through a cycle of structural changes</p> Signup and view all the answers

    What is the role of the sarcoplasmic reticulum in muscle contraction?

    <p>Storage of calcium ions</p> Signup and view all the answers

    What is the primary mechanism by which Ca2+ triggers muscle contraction?

    <p>Ca2+ binding to troponin, leading to movement of tropomyosin away from the myosin-binding site</p> Signup and view all the answers

    What is the role of the sarcoplasmic reticulum in muscle contraction?

    <p>To store and release Ca2+ ions in response to electrical signals</p> Signup and view all the answers

    How do myosin molecules move along actin filaments during muscle contraction?

    <p>Through a cycle of structural changes, using ATP hydrolysis to generate force</p> Signup and view all the answers

    What is the role of tropomyosin in regulating muscle contraction?

    <p>To regulate the binding of myosin to actin filaments</p> Signup and view all the answers

    What is the initial event that triggers muscle contraction?

    <p>Action potential spreading through the T-tubules</p> Signup and view all the answers

    What is a characteristic feature of myosin II molecules?

    <p>It has two ATPase heads and a tail</p> Signup and view all the answers

    What is the functional unit of contraction in a skeletal muscle cell?

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

    During muscle contraction, what is the movement of actin filaments relative to myosin filaments?

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

    What is the organization of myosin II molecules in skeletal muscle cells?

    <p>They form clusters through their tails</p> Signup and view all the answers

    What is the structure that makes up the bulk of the cytoplasm in a skeletal muscle cell?

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

    Microtubules are involved in the organization of which structure in the cytoplasm?

    <p>Cilia and flagella</p> Signup and view all the answers

    What is the primary mechanism of motor protein movement?

    <p>Conformational change driven by ATP hydrolysis</p> Signup and view all the answers

    What is the function of motor proteins like dynein and kinesin?

    <p>To transport different types of cargo along microtubules</p> Signup and view all the answers

    What is the primary function of myosin motor proteins?

    <p>To drive contraction in muscle cells</p> Signup and view all the answers

    What is the primary mechanism of microtubule dynamics?

    <p>Dynamic instability driven by GTP hydrolysis</p> Signup and view all the answers

    What is the effect of actin monomer binding with ATP to ADP?

    <p>Reduces binding between monomers, thus decreasing polymer stability</p> Signup and view all the answers

    What is the function of phalloidin?

    <p>Binds and stabilizes actin filaments</p> Signup and view all the answers

    What is the characteristic of actin filaments in treadmilling?

    <p>The rates of addition and loss are equal</p> Signup and view all the answers

    What is the function of cytochalasin?

    <p>Caps filament plus ends, preventing polymerization</p> Signup and view all the answers

    What is the function of latrunculin?

    <p>Binds actin monomers and prevents their polymerization</p> Signup and view all the answers

    What is the characteristic of actin filaments in eukaryotic cells?

    <p>They are thin and flexible</p> Signup and view all the answers

    What is the role of actin filaments in animal cells?

    <p>They allow cells to migrate</p> Signup and view all the answers

    What is the location of actin filaments in eukaryotic cells?

    <p>Underlying the plasma membrane</p> Signup and view all the answers

    What is the similarity between actin and tubulin?

    <p>They polymerize by similar mechanisms</p> Signup and view all the answers

    What is the characteristic of actin filaments in cell migration?

    <p>They are dynamic and flexible</p> Signup and view all the answers

    What is the primary function of α-actinin molecules in the Z-disc?

    <p>To crosslink actin filaments from adjacent sarcomeres</p> Signup and view all the answers

    During muscle contraction, what is the primary consequence of the sliding filament mechanism?

    <p>The sarcomere shortens without a change in filament length</p> Signup and view all the answers

    What is the primary direction of myosin head movement during muscle contraction?

    <p>Toward the plus end of the adjacent actin filament</p> Signup and view all the answers

    What is the primary requirement for muscle contraction to occur?

    <p>The presence of calcium ions</p> Signup and view all the answers

    Study Notes

    Muscle Contraction

    • Muscle contraction is triggered by a sudden rise in cytosolic Ca2+.
    • Action potential traverses T-tubules, triggering the release of Ca2+ from the sarcoplasmic reticulum.
    • Ca2+ binds to troponin, causing tropomyosin to move away from the myosin-binding site, allowing myosin to bind and walk along the actin filament.
    • Muscle contraction depends on the interaction of actin and myosin II.

    Skeletal Muscle Contraction

    • Skeletal muscle contraction is controlled by troponin and tropomyosin complexes.
    • Ca2+ binding to troponin leads to the movement of tropomyosin, allowing myosin to bind to actin.
    • Myosin II molecules have two ATPase heads and a tail, and they cluster together to form bundles.

    Muscle Cells

    • A skeletal muscle is a huge single cell formed by the fusion of many smaller cells.
    • The bulk of the cytoplasm is made up of myofibrils, which are the contractile elements of the muscle cell.
    • Each myofibril is made up of sarcomeres, which are assemblies of actin filaments and myosin II filaments.

    Actin Filaments

    • Actin filaments are thin and flexible, and they are essential for cell movements and changing cell shape.
    • Actin filaments associate with different proteins to form structures that depend on the type of protein.
    • Many proteins bind to actin and modify its properties.
    • Actin filaments can undergo treadmilling, where the rates of addition and loss are equal, and the filament stays the same length.

    Microtubules

    • Microtubules are hollow tubes with structurally distinct ends.
    • The centrosome is the major microtubule-organizing center in animal cells.
    • Microtubules display dynamic instability, which is driven by GTP hydrolysis.
    • Microtubules organize the cell interior, and motor proteins drive intracellular transport along them.

    Motor Proteins

    • Motor proteins, such as dynein and kinesin, move along microtubules and drive intracellular transport.
    • Myosin is a motor protein that is involved in muscle contraction.
    • ATP hydrolysis and phosphate release drive the movement of motor proteins.

    Cytoskeleton

    • The cytoskeleton is supported by cytoskeleton filaments, including intermediate filaments, microtubules, and actin filaments.
    • Intermediate filaments provide tensile strength, microtubules organize organelles and move them, and actin filaments are involved in cell movement.
    • The cytoskeleton plays a crucial role in maintaining cell shape and allowing cells to move.

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    Cytoskeleton - Chapter 17 - April 24 3rd Exam PDF

    Description

    Learn how muscle contraction occurs through the sliding filament mechanism, triggered by a sudden rise in calcium ions. Understand the role of myosin II and actin filaments in muscle contraction.

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