Nucleolus is a main site for synthesis of:-

Answer

**Step-by-Step Solution:**

1. **Understanding the Nucleolus**: The nucleolus is a prominent structure found within the nucleus of eukaryotic cells. It is not surrounded by a membrane and plays a crucial role in cellular functions.

2. **Function of the Nucleolus**: The primary function of the nucleolus is the synthesis of ribosomes. Ribosomes are essential cellular structures responsible for protein synthesis.

3. **Synthesis of Ribosomal RNA (rRNA)**: The nucleolus is the site where ribosomal RNA (rRNA) is synthesized. rRNA is a key component of ribosomes and is necessary for their formation.

4. **Assembly of Ribosomes**: In addition to synthesizing rRNA, the nucleolus is also involved in the assembly of ribosomal subunits. These subunits are then transported to the cytoplasm where they combine to form functional ribosomes.

5. **Regions of the Nucleolus**: The nucleolus consists of three distinct regions that are important for ribosome formation:
- **Fibrillar Center**: This region contains the genes for rRNA and is where rRNA synthesis begins.
- **Dense Fibrillar Component**: Surrounding the fibrillar center, this area is involved in the processing of rRNA.
- **Cortical Granular Component**: This is the outermost region of the nucleolus and plays a role in the final assembly of ribosomal subunits.

6. **Conclusion**: Therefore, the nucleolus is the main site for the synthesis of ribosomes, specifically through the synthesis of rRNA and the assembly of ribosomal components.

**Final Answer**: The nucleolus is the main site for the synthesis of ribosomes.

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