Myosin is attached to m line by
**Core Concept**
Myosin is a key protein involved in muscle contraction, and its attachment to the M-line (also known as the M-disc) is crucial for maintaining the structural integrity and organization of sarcomeres within muscle fibers. The M-line is a dense plaque-like structure in the center of the sarcomere, where myosin molecules are anchored.
**Why the Correct Answer is Right**
Myosin is attached to the M-line via a protein called M-line protein (MLC1). This attachment helps to stabilize the myosin filaments and prevents them from sliding apart during muscle contraction. The M-line protein also plays a role in regulating the assembly and disassembly of myosin filaments. The M-line is rich in M-line protein, which is a member of the spectrin superfamily of proteins.
**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because this option is not specified, and without more information, it's impossible to determine why it's wrong.
* **Option B:** Incorrect because, although it might seem plausible, myosin is not directly attached to the Z-disk (also known as the Z-line), which is a different structure in the sarcomere that provides attachment points for actin filaments.
* **Option C:** Incorrect because, while myosin is indeed a crucial component of muscle contraction, it is not directly attached to the H-zone, which is the region of the sarcomere where myosin filaments are not anchored.
**Clinical Pearl / High-Yield Fact**
Understanding the structural organization of sarcomeres and the attachments of myosin filaments is essential for grasping the pathophysiology of muscle diseases, such as muscular dystrophy, where disruptions in these attachments can lead to muscle weakness and degeneration.
**Correct Answer: D. M-line protein (MLC1)**