Which of the following statement is INCORRECT regarding actin filaments?

Options

A. Each actin filament is made of two G actin
B. Each F actin is a polymer of G actin
C. Troponin is a complex protein distributed at regular intervals on tropomyosin
D. Tropomyosin run close to F -actin along its length

Answer

To determine which statement is INCORRECT regarding actin filaments, we will analyze the properties and components of actin filaments step by step.

### Step 1: Understanding Actin Filaments
Actin filaments, also known as microfilaments, are one of the main components of the cytoskeleton in eukaryotic cells. They are primarily composed of actin, a globular protein that polymerizes to form long, thin fibers.

**Hint:** Actin filaments are made of monomers called G-actin that polymerize to form F-actin.

### Step 2: Composition of Actin Filaments
Actin filaments are formed from two strands of filamentous actin (F-actin), which are polymers of globular actin (G-actin). Each F-actin is made up of many G-actin monomers.

**Hint:** Remember that F-actin is a polymer made from multiple G-actin units.

### Step 3: Role of Tropomyosin and Troponin
Tropomyosin is a protein that runs along the length of the F-actin and helps regulate the interaction between actin and myosin. Troponin is a complex protein that binds to tropomyosin and actin, and it plays a crucial role in muscle contraction by regulating the exposure of the myosin-binding sites on actin.

**Hint:** Tropomyosin and troponin are regulatory proteins associated with actin filaments.

### Step 4: Evaluating the Statements
Now, we will evaluate the provided statements regarding actin filaments to identify the incorrect one:

1. **Each actin filament is made up of two G-actin.**
- This statement is INCORRECT because each actin filament is made up of two F-actin strands, which are themselves composed of many G-actin monomers.

2. **Troponin is a complex protein distributed at regular intervals on the tropomyosin.**
- This statement is CORRECT.

3. **Tropomyosin runs close to the F-actin along its length.**
- This statement is also CORRECT.

### Step 5: Conclusion
Based on the evaluation, the INCORRECT statement regarding actin filaments is the first one: "Each actin filament is made up of two G-actin."

**Final Answer:** The incorrect statement is: "Each actin filament is made up of two G-actin."