Which of the following molecules binds to troponin during muscle contraction, triggering tropomyosin to move away from the actin-binding sites and allowing the myosin head to form a cross-bridge?
Correct answer: C. Calcium
- A. ATP
- B. ADP
- C. Calcium
- D. Sodium
Explanation
During muscle contraction, the calcium gates of the smooth endoplasmic reticulum open releasing calcium into the cytosol. When a muscle is at rest the tropomyosin is disposed in such a way that it covers the sites on the actin chain where the heads of myosin become attached. when calcium ions bind with the troponin molecules they cause them to move slightly. This has the effect of displacing the tropomyosin and exposing the binding sites for the myosin head. once the myosin head has become attached to the actin filament, ATP is hydrolysed and cross bridges are broken down.
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About Support and Movement
Support and movement covers the axial and appendicular skeleton, bone structure, joints and the arrangement of skeletal muscles. Muscle contraction is explained through actin, myosin, sliding filaments, calcium ions and ATP, while arthritis is distinguished as a disorder of joints rather than a normal part of movement.
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