- A It is sometimes thought to directly and immediately activate the myosin head protein itself, thereby initiating the start of the cross-bridge cycling process from a resting state
- B Calsequestrin is a high-capacity, low-affinity Ca2+-binding protein in the SR lumen that stores large amounts of Ca2+ for rapid release during contraction
- C It is sometimes thought to be simply a minor structural component protein embedded directly within the thin actin filament structure of the muscle sarcomere itself
- D It is sometimes thought to function mainly to add extra phosphate groups onto the troponin protein complex itself to regulate its overall calcium binding affinity level
Correct answer: B. Calsequestrin is a high-capacity, low-affinity Ca2+-binding protein in the SR lumen that stores large amounts of Ca2+ for rapid release during contraction
Explanation: Calsequestrin stores Ca2+ in the SR by binding up to 40-80 Ca2+ ions per molecule. Because free Ca2+ concentration is buffered low, the SR can store much more total Ca2+ without the osmotic consequences of free Ca2+. Associated with ryanodine receptor complex (via junctin, triadin) and modulates RyR gating. Mutations cause catecholaminergic polymorphic ventricular tachycardia (CPVT).
Concept context
Types of movement, muscle contraction, skeletal system, joints, and disorders. Important for Class 11 and NEET.