Calcium is important in skeletal muscle contraction because it

Options

A. prevents the formation of bonds between the myosin cross bridges and the actin filaments
B. Detaches the myosin head from the actin filament
C. activates the myosin ATPase by binding to it.
D. binds to troponin to remove the masking of active sites on actin for myosin

Answer

**Step-by-Step Solution:**

1. **Understanding Muscle Contraction**: Skeletal muscle contraction involves the interaction between two types of filaments: myosin (thick filaments) and actin (thin filaments). These filaments slide past each other to produce muscle contraction.

2. **Role of Calcium**: Calcium ions play a crucial role in muscle contraction by interacting with specific proteins associated with the actin filament.

3. **Components of Actin Filament**: The actin filament is composed of three main components:
- **G-actin**: This is the globular form of actin that has binding sites for myosin.
- **Tropomyosin**: This protein covers the binding sites on actin in a relaxed muscle.
- **Troponin**: This complex is attached to tropomyosin and consists of three subunits (C, T, and I).

4. **Troponin Subunits**:
- **C subunit**: Binds to calcium ions.
- **T subunit**: Binds to tropomyosin.
- **I subunit**: Inhibits the interaction between actin and myosin.

5. **Mechanism of Action**: In a relaxed muscle, tropomyosin blocks the binding sites on actin, preventing myosin from attaching. When calcium ions are released during muscle activation, they bind to the C subunit of troponin.

6. **Conformational Change**: The binding of calcium to troponin causes a conformational change that moves tropomyosin away from the binding sites on actin, exposing them.

7. **Binding of Myosin**: Once the binding sites on actin are exposed, myosin can attach to actin, leading to muscle contraction through the sliding filament mechanism.

8. **Conclusion**: Therefore, the correct answer to the question is that calcium binds to troponin to remove the masking of the active sites on actin from myosin.

**Final Answer**: Calcium is important in skeletal muscle contraction because it binds to the troponin to remove the masking of the active sites on the actin from myosin.

---