Fill up the blanks in the following sentence by selecting the correct option.

Options

A. `{:("(A)",(B),(C),),("(1F)",("troponin"),("tropomyosin"),):}`
B. `{:("(A)",(B),(C),),("(1F)",("tropomyosin"),("troponin"),):}`
C. `{:("(A)",(B),(C),),("(2F)",("troponin"),("tropomyosin"),):}`
D. `{:("(A)",(B),(C),),("(2F)",("tropomyosin"),("troponin"),):}`

Answer

To fill in the blanks in the given sentence about the components of thin filaments in a myofibril, we need to identify the three main proteins associated with actin. Here’s the step-by-step solution:

1. **Identify the first component**: The thin filaments contain **two filamentous actins** (F-actin) that are wound helically around each other. This is the primary structure of the thin filament.

2. **Identify the second component**: The second component is **tropomyosin**. This protein runs along the length of the filamentous actin and plays a crucial role in muscle contraction by regulating the interaction between actin and myosin.

3. **Identify the third component**: The third component is **troponin**. This protein is located at regular intervals on the tropomyosin and is responsible for masking the binding sites for myosin on the actin filament. This masking is essential for muscle relaxation and contraction regulation.

Now, we can fill in the blanks in the sentence:

"The thin filaments contain **two filamentous actins** and two filaments of **tropomyosin** along with **troponin** protein for masking the binding site for myosin."

**Final Answer**:
The correct answer is:
1. two filamentous actins
2. tropomyosin
3. troponin

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