It seems like you might be thinking of Nucleoli instead of "Nucleos". Nucleoli are small, dense, and spherical bodies found within the nucleus of eukaryotic cells, including animal cells.

Here's what nucleoli do:

* Ribosome Biogenesis: Nucleoli are the primary sites for the synthesis and assembly of ribosomes. Ribosomes are essential for protein synthesis, so the nucleolus plays a crucial role in cell function.

* Ribosomal RNA (rRNA) Transcription: Nucleoli contain the genes for ribosomal RNA (rRNA), and they transcribe these genes to produce rRNA molecules.

* rRNA Processing: The rRNA transcribed in the nucleolus undergoes processing, including modifications and splicing, before it is assembled into ribosomes.

* Ribosomal Subunit Assembly: The rRNA molecules, along with ribosomal proteins, are assembled into the two subunits of ribosomes: the small subunit and the large subunit. These subunits later exit the nucleus and join to form functional ribosomes in the cytoplasm.

In summary, nucleoli are vital for the production of ribosomes, which are essential for protein synthesis and therefore for all cellular functions.