Name the ion responsible for masking active sites for myosin for cross-bridge activity during muscle contraction

Options

A. calicum
B. Magnesium
C. Sodium
D. Potassium

Answer

To solve the question, "Name the ion responsible for masking active sites for myosin for cross-bridge activity during muscle contraction," we can follow these steps:

### Step-by-Step Solution:

1. **Understand Muscle Contraction Basics**:
- Muscle contraction involves the interaction between two types of filaments: thick filaments (myosin) and thin filaments (actin).

2. **Identify the Role of Active Sites**:
- Myosin heads need to bind to active sites on actin to form cross-bridges, which are essential for muscle contraction.

3. **Recognize the Masking Mechanism**:
- In a resting state, the active sites on actin are masked, preventing myosin from binding. This masking is primarily due to the presence of the troponin-tropomyosin complex.

4. **Determine the Ion Involved**:
- The masking of these active sites is lifted when calcium ions (Ca²⁺) bind to the troponin protein. This binding causes a conformational change that moves tropomyosin away from the active sites.

5. **Conclude the Answer**:
- Since calcium ions are responsible for unmasking the active sites on actin, the answer to the question is that the ion responsible for masking the active sites for myosin during muscle contraction is **Calcium (Ca²⁺)**.

### Final Answer:
The ion responsible for masking active sites for myosin for cross-bridge activity during muscle contraction is **Calcium (Ca²⁺)**.

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