Here's a breakdown:
* Nucleolus: This is a dense, spherical structure located within the nucleus of a eukaryotic cell. It is not membrane-bound, but rather a specialized region of the nucleus.
* rRNA synthesis: rRNA is transcribed from DNA by RNA polymerase I. This transcription occurs within the nucleolus.
* Ribosome assembly: After transcription, the rRNA molecules associate with ribosomal proteins, also synthesized in the cytoplasm and imported into the nucleus. This assembly process leads to the formation of the two ribosomal subunits (large and small) that will eventually join together to form functional ribosomes.
In summary: The nucleolus is the "factory" for rRNA synthesis and the initial assembly of ribosomes in a cell.
