Here's a breakdown:

* Nucleus: The control center of the cell, containing the cell's genetic material (DNA).

* Nucleolus: A dense region within the nucleus where ribosomal RNA (rRNA) is synthesized and assembled with proteins to form ribosomes. Ribosomes are essential for protein synthesis.

So, while the nucleus is the control center, the nucleolus is the busy factory within it, producing the machinery for building proteins.