Nucleous

The nucleolus is a large, heavily dense organelle found in eukaryotic cells. "Unlike other organelles in eukaryotic cells, the nucleolus does not have a membrane". It a collection of ribosomal RNA and proteins along with ribosomal genes and processing enzymes. The role of the nucleolus is to process RNA into ribosomes. This role relates to the presence of ribosomal RNA, genes and processing enzymes. The nucleolus can be seen under a light microscope and the inner components of It can be seen under an electron microscope. (Alberts et al., 2008: 362-363)

Reference:

Alberts,B.,Johnson,A.,Lewis,J.,Raff,M.,Roberts,K. and Walter,P. (2008) Molecular Biology of The Cell, Fifth Edition, New York:Garland Science