A mutation significantly reduces the number of functional gap junction channels between adjacent cardiac muscle cells. Which effect would most directly result?, A. Reduced mechanical attachment between adjacent cardiomyocytes, B. Reduced electrical current flow between adjacent cardiomyocytes, C. Loss of actin and myosin organization within sarcomeres, D. Loss of the plasma membrane surrounding each cardiomyocyte, A drug blocks desmosome formation in cardiac muscle but leaves gap junctions functional. Which outcome is most likely during repeated forceful contractions?, A. Action potentials can no longer form in individual cardiomyocytes, B. Adjacent cells become more likely to separate mechanically, C. Sarcomeres immediately lose the ability to generate contractile force, D. Electrical current can no longer pass between neighboring cells, Which two structures form the boundaries of a single sarcomere?, A. Two M lines, B. Two A bands, C. Two Z discs, D. Two H zones, Which structure is located at the center of the sarcomere and helps organize the thick myosin filaments?, I band, T tubule, Z disc, M line, In skeletal muscle anatomy, a triad consists of which structures?, One Z disc and two T tubules, One T tubule and two terminal cisternae, One myofibril and two terminal cisternae, Two T tubules and one terminal cisterna, Which filament is anchored to the Z disc and extends toward the center of the sarcomere?, Intermediate filament of the sarcolemma, Thick myosin filament, Thin actin filament, Collagen filament, Which region of the sarcomere contains thick myosin filaments but no overlapping thin actin filaments?, Sarcolemma, Z disc, H zone, I band, A mutation alters the globular heads of myosin molecules but leaves the rod-like tails intact. Which muscle function would be most directly impaired?, Propagation of an action potential along the sarcolemma, Storage of calcium in the sarcoplasmic reticulum, Formation of cross-bridges with actin, Anchoring of thin filaments to the Z disc, A myosin head contains two important binding regions. Which pairing correctly identifies what binds to each site?, Actin-binding site → calcium; ATP-binding site → myosin, Actin-binding site → ATP; ATP-binding site → actin, Actin-binding site → actin; ATP-binding site → ATP, Actin-binding site → myosin; ATP-binding site → calcium, Which protein forms the main structural component of the thin filament?, Titin, Myosin, Actin, Troponin, Each G-actin subunit contains a binding site for which protein?, Myosin, Collagen, Titin, Dystrophin, At rest, which protein covers the myosin-binding sites located on actin?, Troponin, Tropomyosin, Titin, Myosin, Which statement correctly distinguishes the binding sites on actin and myosin?, Actin has an ATP-binding site, while myosin has a calcium-binding site., Actin has a myosin-binding site, while the myosin head has an actin-binding site., Actin and myosin both contain only ATP-binding sites., Actin and myosin do not contain sites that bind to each other., Researchers create a mutation in troponin C (TnC) that prevents it from binding Ca²⁺. Which event would be most directly impaired during skeletal muscle activation?, A. Movement of tropomyosin away from myosin-binding sites on actin, B. Hydrolysis of ATP by the myosin head, C. Formation of thick filaments from myosin molecules, D. Propagation of an action potential along the sarcolemma, A mutation prevents troponin T (TnT) from interacting normally with its binding partner. Which protein would be most directly affected by this mutation?, A. Titin, B. Actin, C. Myosin, D. Tropomyosin, A researcher selectively removes troponin I (TnI) from an isolated thin filament while leaving TnC and TnT intact. Which interaction has been most directly disrupted?, Troponin complex interaction with actin, Troponin attachment to tropomyosin, ATP binding to the myosin head, Calcium binding to the troponin complex, A muscle fiber has normal actin, myosin, ATP, and intracellular Ca²⁺, but its troponin complex cannot cause tropomyosin to change position. What would most directly result?, Myosin would have reduced access to its binding sites on actin, Myosin would lose its ATP-binding sites, The sarcomere would lose its Z discs, Actin would be unable to form thin filaments, A patient presents with suspected acute coronary syndrome. Which troponins would be most useful to measure in the blood when evaluating for myocardial cell necrosis?, Troponin C and tropomyosin, Troponin C only, Troponin C and skeletal troponin I, Cardiac troponin I and cardiac troponin T, In a resting skeletal muscle fiber, what prevents the myosin head from binding to actin?, ATP covers the myosin-binding sites on actin, Calcium occupies the myosin-binding sites, Tropomyosin covers the myosin-binding sites on actin, Troponin directly covers the myosin-binding sites, According to the figure, what happens FIRST when Ca²⁺ reaches the thin filament during muscle activation?, A. Ca²⁺ binds to troponin, B. Ca²⁺ binds to the myosin-binding site on actin, C. Ca²⁺ binds directly to myosin, D. Ca²⁺ binds directly to tropomyosin, After Ca²⁺ binds to troponin, which sequence correctly describes what happens next?, A. Tropomyosin moves → myosin-binding sites on actin become exposed → myosin can bind actin, B. Tropomyosin remains in place → myosin-binding sites stay blocked → myosin binds actin, C. Myosin-binding sites close → myosin detaches → calcium binds ATP, D. Actin moves away → tropomyosin binds myosin → contraction stops, A drug allows Ca²⁺ to be released normally inside a skeletal muscle fiber, but prevents Ca²⁺ from binding to troponin. Which outcome is most likely?, A. Tropomyosin remains over the myosin-binding sites, reducing actin-myosin interaction, B. Myosin heads no longer contain ATP-binding sites, C. Myosin-binding sites become exposed because calcium binds directly to actin, D. Tropomyosin moves away normally because calcium is present, During the cross-bridge cycle, what is a cross-bridge?, A. The attachment of tropomyosin to myosin, B. The attachment of calcium to ATP, C. The attachment of a myosin head to actin, D. The attachment of ATP to actin, After the myosin head has attached to actin, release of Pi helps trigger which event?, A. Binding of calcium to troponin, B. Detachment of myosin from actin, C. Power stroke of the myosin head, D. Hydrolysis of a newly bound ATP, What directly causes a myosin head to detach from actin during the cross-bridge cycle?, A. ADP binds to the myosin head, B. Pi binds to actin, C. A new ATP molecule binds to the myosin head, D. Calcium binds directly to the myosin head, What is the main purpose of ATP hydrolysis at the end of the cross-bridge cycle shown in the diagram?, A. Return the myosin head to its energized original orientation, B. Build new actin filaments, C. Cause calcium to leave the sarcoplasmic reticulum, D. Expose the binding sites on actin, A muscle fiber has exposed myosin-binding sites on actin, but no ATP is available. Which part of the cross-bridge cycle would be most directly prevented once myosin has attached to actin?, A. Detachment of the myosin head from actin, B. Initial formation of a cross-bridge, C. Exposure of myosin-binding sites by tropomyosin movement, D. Calcium binding to troponin C

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