Which organelle is primarily responsible for ribosome synthesis and assembly in eukaryotic cells?

Which organelle is primarily responsible for ribosome synthesis and assembly in eukaryotic cells?

• A. Nucleolus
• B. Mitochondrion
• C. Ribosome
• D. Golgi apparatus

Answer: (A)

Ribosome production happens inside the nucleolus, a specialized region within the nucleus. There, ribosomal RNA genes are transcribed by RNA polymerase I, the pre-rRNA is processed, and ribosomal proteins imported from the cytoplasm join with the rRNA to form the large and small ribosomal subunits. These subunits are then exported to the cytoplasm to assemble into functional ribosomes for protein synthesis. The mitochondrion does contain its own ribosomes, but it’s not the primary site for making ribosomes used by the cell as a whole. A ribosome is the particle itself, not the site where ribosome components are assembled. The Golgi apparatus handles protein modification and trafficking, not ribosome assembly.

Ribosome production happens inside the nucleolus, a specialized region within the nucleus. There, ribosomal RNA genes are transcribed by RNA polymerase I, the pre-rRNA is processed, and ribosomal proteins imported from the cytoplasm join with the rRNA to form the large and small ribosomal subunits. These subunits are then exported to the cytoplasm to assemble into functional ribosomes for protein synthesis. The mitochondrion does contain its own ribosomes, but it’s not the primary site for making ribosomes used by the cell as a whole. A ribosome is the particle itself, not the site where ribosome components are assembled. The Golgi apparatus handles protein modification and trafficking, not ribosome assembly.