The nucleolus is a prominent structure within the nucleus of an animal cell. It's not membrane-bound, but rather a densely packed region of RNA, proteins, and DNA. Its primary function is the synthesis of ribosomes.

Here's how it works:

* Ribosomal RNA (rRNA) synthesis: The nucleolus contains the genes that code for rRNA. These genes are transcribed into rRNA molecules, which then associate with ribosomal proteins.

* Assembly of ribosomal subunits: The rRNA and proteins assemble into the two subunits of a ribosome: the small subunit (40S) and the large subunit (60S).

* Export of ribosomes: Once assembled, the ribosomal subunits are transported out of the nucleus through nuclear pores and into the cytoplasm, where they will participate in protein synthesis.

Essentially, the nucleolus is like a factory that produces the machinery needed for protein production. Without a functioning nucleolus, the cell would be unable to synthesize proteins, which are essential for all cellular processes.