- In some references, nucleolus is regarded as an organelle, particularly a non-membrane-bound organelle (as opposed to the membrane-bound organelles). Others do not consider nucleolus as an organelle because of its lack of a lipid bilayer membrane. Rather, it is considered as one of the nuclear bodies found within the nucleus.
- Nucleolus is a round and granular structure located inside the nucleus. It is the most prominent subnuclear structure in the nucleus. It is composed of proteins, DNA, and RNA. In higher eukaryotes, three major components are (1) the fibrillar center (FC), the dense fibrillar component (DFC), and the granular component (GC).1 The FC is involved in the transcription of the rDNA. The DFC contains fibrillarin protein associated with rRNA processing. The GC contains the protein nucleophosmin involved in ribosome biogenesis. In plants, another structure is recognizable — a clear area in the center of the nucleolus called the nucleolar vacuole.2 The granular component of nucleolus refers to the area of nucleolus that appears granular as opposed to the pale staining and fibrillar areas in the electron microscope .The granular appearance is due to the presence of 15nm-diameter maturing ribosomes. The nucleolus contains nucleophosmin, which is a protein responsible for the transport of fluid between nucleus and cytoplasm involved in various cellular functions including protein formation, DNA replication and cell cycle. Another protein present in the nucleolus is the nucleolar protein 3, a protein involved inRNA splicing and inhibits apoptosis to down regulate the enzyme activity. The nucleolus organizer region (NOR) is a region in the chromosome around which the nucleolus forms. NORs are located on the satellite stalks of the acrocentric chromosomes.
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