Identify the correct match

Options

A. Motor protein -mask and unmask the active site
B. Regulatory protein- Convert chemical energy into mechanical energy
C. Power stroke - Myosin head pulls the actin filaments towards H-zone
D. Recovery stroke - Movement of actomyosin towards M-line

Answer

To solve the question "Identify the correct match," we need to analyze each option provided regarding the functions of motor proteins and regulatory proteins in muscle contraction. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Role of Motor Proteins and Regulatory Proteins
- **Motor Proteins**: Myosin is the primary motor protein involved in muscle contraction. It converts chemical energy (from ATP) into mechanical energy to perform work, specifically pulling actin filaments.
- **Regulatory Proteins**: Troponin and tropomyosin are regulatory proteins that control the binding of myosin to actin. Troponin can mask or unmask the active site on actin, allowing or preventing myosin from binding.

**Hint**: Remember the distinction between motor proteins (like myosin) and regulatory proteins (like troponin and tropomyosin).

### Step 2: Analyze Each Option
1. **Motor protein masks and unmasks the active site**: This is incorrect. It is the regulatory protein (troponin) that masks and unmasks the active site on actin.

**Hint**: Identify which proteins are responsible for masking/unmasking the active site.

2. **Regulatory protein converts chemical energy into mechanical energy**: This is also incorrect. The conversion of chemical energy into mechanical energy is the function of myosin, the motor protein.

**Hint**: Focus on which protein is responsible for energy conversion.

3. **Power stroke: Myosin head pulls the actin filament towards the A zone**: This statement is correct. During the power stroke, the myosin head binds to actin and pulls it towards the A zone.

**Hint**: Recall what happens during the power stroke in muscle contraction.

4. **Recovery stroke: Movement of actomyosin towards the M line**: This is incorrect. The recovery stroke involves the actin filament moving away from the M line, not towards it.

**Hint**: Understand the direction of movement during the recovery stroke.

### Step 3: Identify the Correct Match
After analyzing all the options, the correct match is:
- **Power stroke: Myosin head pulls the actin filament towards the A zone.**

### Final Answer
The correct answer is **option C**: In the power stroke, the myosin head pulls the actin filament towards the A zone.