Myosin and actin filaments are kept in place by –
**Core Concept**
The question is testing the understanding of the structure and function of muscle filaments, specifically the role of proteins that maintain their organization within the muscle cell (sarcoplasm). Myosin and actin filaments are crucial components of the sarcomere, the functional unit of muscle contraction.
**Why the Correct Answer is Right**
The correct answer is tropomyosin. Tropomyosin is a protein that wraps around the actin filament and plays a key role in regulating muscle contraction by blocking or exposing the myosin binding sites on the actin filament. It is maintained in place by its association with troponin, another regulatory protein. When a muscle is stimulated to contract, the troponin-tropomyosin complex shifts, exposing the myosin binding sites on the actin filament, allowing muscle contraction to occur.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because it does not accurately describe a protein involved in maintaining the organization of myosin and actin filaments.
**Option B:** This option is likely incorrect because it does not accurately describe a protein involved in maintaining the organization of myosin and actin filaments.
**Option C:** This option is likely incorrect because it does not accurately describe a protein involved in maintaining the organization of myosin and actin filaments.
**Clinical Pearl / High-Yield Fact**
Tropomyosin and troponin are essential regulators of muscle contraction, and their dysfunction can lead to muscle diseases such as muscular dystrophy.
**Correct Answer:** Tropomyosin