COPY: 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 (D)</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+ (D)</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 (A)</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 (C)</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 (D)</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 (B)</p> Signup and view all the answers

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

<p>Storage of calcium ions (B)</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 (C)</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 (A)</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 (B)</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 (A)</p> Signup and view all the answers

What is the initial event that triggers muscle contraction?

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

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

<p>Sarcomere (A)</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 (B)</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 (C)</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 (C)</p> Signup and view all the answers

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

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

What is the primary mechanism of motor protein movement?

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

What is the primary function of myosin motor proteins?

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

What is the primary mechanism of microtubule dynamics?

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

What is the function of phalloidin?

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

What is the function of cytochalasin?

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

What is the function of latrunculin?

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

What is the characteristic of actin filaments in eukaryotic cells?

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

What is the role of actin filaments in animal cells?

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

What is the location of actin filaments in eukaryotic cells?

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

What is the similarity between actin and tubulin?

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

What is the characteristic of actin filaments in cell migration?

<p>They are dynamic and flexible (A)</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 (A)</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 (D)</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 (A)</p> Signup and view all the answers

What is the primary requirement for muscle contraction to occur?

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

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