Here's why:
* Nucleolus: The nucleolus is a dense, spherical structure within the nucleus. It's not membrane-bound, but it's a distinct region where rRNA synthesis and assembly occur.
* rRNA Genes: The genes that code for rRNA are located within the nucleolus. These genes are transcribed by RNA polymerase I, which produces rRNA precursor molecules.
* Assembly: The rRNA precursor molecules then associate with ribosomal proteins, which are synthesized in the cytoplasm and transported into the nucleolus. This assembly process forms the large and small subunits of ribosomes.
Therefore, the nucleolus acts as the central factory for producing the essential components of ribosomes.
