Nucleolus
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In biology, the nucleolus is, strictly speaking, a "suborganelle" of the cell nucleus, which is an organelle. Only plant and animal nuclei have nucleoluses. Most plant and animal cells have one or more nucleoluses although some do not. No membrane separates the nucleolus from the nucleoplasm. The nucleolus are made of protein and ribonucleic acid (RNA) and contains proteins as well as ribosomal RNA. It is a consequence of ribosomal RNA (rRNA) synthesis: nucleolar organizers, special regions known as nuclear organizing regions (NOR) on some chromosomes that contain multiple copies of the genes encoding for rRNA (which is involved in protein biosynthesis), gather themselves in the same region where they transcribe the rRNA genes. Thus it can be said the nucleolus consists basically of nucleolar organizers and the transcribed rRNA (plus associated proteins). Following synthesis, rRNA molecules are attached to proteins, forming ribosomal subunits, which leave for the cytosol through nuclear pores. These nuclear pores are known as The Nuclear Pore Complex (NPC).
The nucleolus consists of three distinct regions: the fibrillar centres, The dense fibrillar component and the granular component
Known function: Production and maturation of ribosomes
Other functions have been suggested.
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