Question

Nucleolus is the site for the synthesis of this component in a cell

• A. Nucleosome
• B. Ribosomes
• C. DNA
• D. Chromation

Hint:

The nucleolus is often called the "ribosome factory" of the cell.
Its size and number of nucleoli inside a nucleus increase in cells that are highly active in protein synthesis, such as secretory cells or rapidly growing embryonic tissues.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The nucleolus is a dense, non-membrane-bound sub-nuclear structure located within the nucleus of eukaryotic cells.
It serves as a specialized region dedicated to the transcription and processing of ribosomal RNA (rRNA) and the assembly of ribosomal subunits.

Step 2: Detailed Explanation:
Let us analyze the biological functions of the listed cellular components:
Nucleosomes are the basic packaging units of chromatin consisting of DNA wrapped around histone proteins, which are assembled in the nucleoplasm during DNA replication.
DNA replication takes place throughout the nucleoplasm, not specifically inside the nucleolus.
Chromatin (spelled as "Chromation" in the question paper) refers to the complex of genomic DNA and packaging proteins located throughout the nucleus.
The nucleolus specifically contains the nucleolar organizer regions (NORs) of chromosomes, which carry multiple copies of rRNA genes.
Within the nucleolus, RNA polymerase I transcribes these genes to produce pre-rRNA, which is subsequently cleaved and modified into 18S, 5.8S, and 28S rRNAs.
These rRNAs are then assembled with ribosomal proteins imported from the cytoplasm to form the small (40S) and large (60S) ribosomal subunits.
These subunits are then exported back to the cytoplasm, where they combine to form functional ribosomes during translation.
Therefore, the nucleolus is the primary site of ribosome subunit synthesis and assembly.

Step 3: Final Answer:
The nucleolus is the site of synthesis for ribosomes.
This corresponds to Option (B).