Biology · Support and Movement
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When the muscle is required to contract, then calcium ions bind with which molecule and cause them to move slightly?
- A
A: Tropomyosin
- B
B: Actin
- C
C: Troponin
- D
D: Myosin
Calcium is required by two proteins, troponin and tropomyosin, that regulate muscle contraction by blocking the binding of myosin to filamentous actin. In a resting sarcomere, tropomyosin blocks the binding of myosin to actin. Calcium binds to troponin, causing the conformational shift in tropomyosin that reveals myosin-binding sites on actin. ATP then binds to myosin.
This is incorrect. Tropomyosin is a protein that covers binding sites on actin filaments, preventing myosin from attaching. It only moves when calcium binds to troponin, not directly to tropomyosin.
This is incorrect. Actin is a component of the thin filament and does not directly bind with calcium ions during muscle contraction.
This is correct. Calcium ions bind to troponin, which causes a change in the position of tropomyosin, exposing the binding sites on actin filaments and facilitating muscle contraction.
This is incorrect. Myosin is a component of the thick filament and interacts with actin during contraction, but calcium ions do not bind directly to myosin.
Tagged under Biology · Support and Movement · 2016