The nucleolus is a largest structure in the nucleus of eukaryotic cell. It is round in shape. Its main function is to make ribosomal subunits from proteins. Hence, it plays an important role in the biogenesis of ribosomes. It is the site of It is the site of ribosomal subunit (40S and 60S) synthesis. It is also involved in biosynthesis of ribosomal RNA (rRNA) and proteins.