What are the functions of nucleolus?

The primary function of the nucleus is to synthesize both large and small subunits of ribosomes. The three processes that occur in the nucleus include rRNA transcription, rRNA processing and ribosome subunit assembly. These ribosomal subunits are eventually transported out of the nucleolus into the cytoplasm to be assembled into ribosomes. Transcription of rRNA genes in the nucleolus produces the vast majority of RNAs in the cell. After transcription, rRNA molecules become processed through modification, cleavage, and removal of specific sequences to generate mature rRNA molecules. Afterwards, the nucleolus assists in assembling the components of ribosomes through the granular component. The granular component of the nucleolus contains ribonucleoprotein protein particles which have newly transcribed rRNA molecules. Once the ribosomal subunits become assembled in the nucleus, they are exported to the cytoplasm to form functional ribosomes.