The Question is from neet-zoology locomotion-and-movement muscles, and it was created by the author K SUNKANNA

Question

A patient presents with muscle weakness and fatigue.  Biochemical analysis reveals a defect in the calcium-binding protein crucial for muscle contraction, specifically within the thin filaments. Which protein is MOST likely affected?

K SUNKANNA · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
	**Primary Concept**: Muscle Contraction Mechanism
	**Related Topics**: Thin filaments, Calcium's role in muscle contraction, Troponin complex
	**Prerequisites**: Understanding of the sliding filament theory and the roles of different proteins in muscle contraction.
## SOLUTION PATHWAY
**Given Information**:
		Muscle weakness and fatigue.
		Defect in calcium-binding protein within thin filaments.
**Method & Steps**:
	1. **Identify the thin filament components:** The thin filaments of muscle fibers are composed of actin, tropomyosin, and the troponin complex (Troponin T, Troponin I, and Troponin C).
	2. **Determine the calcium-binding protein:**  Calcium ions ($Ca^{2+}$) play a crucial role in muscle contraction.  Troponin C is the calcium-binding subunit of the troponin complex.  It binds $Ca^{2+}$ which triggers a conformational change, moving tropomyosin and allowing myosin to interact with actin.
	3. **Relate the defect to the symptoms:** A defect in Troponin C would impair the ability of the thin filaments to bind calcium, thus disrupting the normal muscle contraction process. This would lead to muscle weakness and fatigue.
		Result: Troponin C
		Verification: The symptoms and the location of the defect (thin filaments) strongly suggest a problem with the calcium-binding protein within the troponin complex.
## OPTION ANALYSIS
A :x: Tropomyosin is a protein that regulates the interaction between actin and myosin, but it does not directly bind calcium.
B :x: Troponin T anchors the troponin complex to tropomyosin.
C :x: Troponin I inhibits the interaction between actin and myosin in the absence of calcium.
D ✓: Troponin C binds calcium, initiating the conformational changes that lead to muscle contraction. A defect in Troponin C would directly impair this process, causing the observed symptoms.
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing the roles of different troponin subunits: Understanding the specific function of each troponin subunit is crucial for accurate diagnosis.
		2. Overlooking the location of the defect: The question specifically mentions the defect is within the thin filaments, which helps narrow down the possible proteins involved.
	**Quick Tips**:
		1. Remember the key role of calcium in muscle contraction and its interaction with Troponin C.
		2. Visualize the structure of the thin filament and the arrangement of actin, tropomyosin, and the troponin complex.

K SUNKANNA · Answer

Tropomyosin

K SUNKANNA · Answer

Troponin T

K SUNKANNA · Answer

Troponin I

K SUNKANNA · Answer

The correct Option is "Troponin C"

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