The generation of excitation-contraction coupling involves all the following events except

Options

A. hydrolysis of ATP to ADP
B. Confirmational change in troponin
C. releases of calcium from troponin
D. formation of cross linkages between actin and myosin

Answer

To solve the question regarding the events involved in excitation-contraction coupling in muscle fibers, we need to analyze each option provided in the context of muscle contraction mechanisms.

### Step-by-Step Solution:

1. **Understanding Excitation-Contraction Coupling**:
- Excitation-contraction coupling is the physiological process of converting an electrical stimulus (excitation) into a mechanical response (contraction) in muscle fibers.

2. **Identify Key Components**:
- The main components involved in this process include:
- **Actin and Myosin**: The contractile proteins that interact to cause muscle contraction.
- **Calcium Ions**: Essential for muscle contraction, released from the sarcoplasmic reticulum.
- **Troponin**: A protein that binds calcium and regulates the interaction between actin and myosin.
- **ATP**: The energy source that is hydrolyzed to ADP during muscle contraction.

3. **Analyzing the Events**:
- **Hydrolysis of ATP to ADP**: This is necessary for muscle contraction as it provides the energy for the cross-linking of actin and myosin.
- **Confirmation Change in Troponin**: When calcium binds to troponin, it causes a conformational change that exposes the binding sites on actin for myosin.
- **Release of Calcium from Troponin**: This statement is misleading. Calcium is released from the sarcoplasmic reticulum, not from troponin.
- **Formation of Cross-Linkage Between Actin and Myosin**: This occurs when the binding sites on actin are exposed, allowing myosin heads to attach to actin.

4. **Conclusion**:
- The event that does not occur in excitation-contraction coupling is the **release of calcium from troponin**. Instead, calcium is released from the sarcoplasmic reticulum.

### Final Answer:
The generation of excitation-contraction coupling involves all the following events except the **release of calcium from the troponin**.

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