Multiple Choice
During skeletal muscle contraction, calcium ions (Ca2+) bind to which protein to initiate the sliding filament process?
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9. Muscle Tissue
Steps of Muscle Contraction
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During the sliding filament process of skeletal muscle contraction, what best describes the power stroke?
A
The myosin head pivots, pulling the actin filament toward the center of the sarcomere after releasing inorganic phosphate
B
ATP is hydrolyzed, cocking the myosin head into a high-energy position before it binds actin
C
Calcium binds to troponin, causing tropomyosin to move away from the myosin-binding sites on actin
D
ATP binds to the myosin head, causing it to detach from actin
Verified step by step guidance1
Understand the context of the sliding filament theory, which explains how skeletal muscle contraction occurs through interactions between actin and myosin filaments within the sarcomere.
Recall that the power stroke is a specific step in the cross-bridge cycle where the myosin head changes position to pull the actin filament toward the center of the sarcomere, causing muscle shortening.
Identify that before the power stroke, ATP is hydrolyzed by the myosin head, which 'cocks' it into a high-energy state, ready to bind to actin.
Recognize that the power stroke itself happens after the myosin head binds to actin and releases inorganic phosphate (Pi), causing the myosin head to pivot and pull the actin filament inward.
Distinguish the power stroke from other steps such as calcium binding to troponin (which exposes binding sites) and ATP binding to myosin (which causes detachment from actin).
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