What does the nucleolus do?

The nucleolus is the structure within the nucleus of eukaryotic cells. It consists of RNA, DNA, and proteins. The nucleolus is involved in ribosome biogenesis which results in the synthesis of ribosomes. Ribosomal RNA (rRNA) is transcribed from DNA in the nucleolus. rRNA is processed into three mature RNAs and together with proteins form ribosomal subunits. After subunits form the ribosomes, they are transported out of the nucleus to the cytoplasm where they take place in translation.