During contraction of skeletal muscle `Ca^(2+)` bind to

Options

A. actin
B. troponin
C. tropomyosin
D. myosin ATPase

Answer

To solve the question "During contraction of skeletal muscle, `Ca^(2+)` binds to," we can follow these steps:

### Step-by-Step Solution:

1. **Understand Muscle Contraction**: Muscle contraction in skeletal muscles involves a series of biochemical events triggered by the release of calcium ions (`Ca^(2+)`).

2. **Identify Key Proteins**: The key proteins involved in muscle contraction are troponin and tropomyosin. Troponin is a regulatory protein that plays a crucial role in muscle contraction.

3. **Role of Calcium Ions**: When skeletal muscle is stimulated to contract, calcium ions are released from the sarcoplasmic reticulum into the cytoplasm of the muscle cell.

4. **Binding of Calcium**: The released calcium ions bind specifically to troponin, which is part of the thin filament of the muscle fiber.

5. **Conformational Change**: The binding of calcium to troponin causes a conformational change in the troponin complex. This change leads to the movement of tropomyosin, which normally blocks the binding sites on actin filaments.

6. **Exposure of Binding Sites**: As tropomyosin shifts away from the binding sites on actin, myosin heads can now attach to these sites, allowing muscle contraction to occur.

7. **Conclusion**: Therefore, during the contraction of skeletal muscle, `Ca^(2+)` binds to troponin.

### Final Answer:
The correct answer is that during contraction of skeletal muscle, `Ca^(2+)` binds to **troponin**.

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