Where is nucleolus located? What is role of nucleolus in cell?
Nucleolus is a microscopic structure seen inside eukaryotic nucleus.
Nucleolus is a factory where assembly of ribosomal subunits take place.
Ribosomes are protein manufacturing units, made of small and large subunits. The subunits are made of few ribosomalRNAs and some proteins.
The rRNAs are formed in nucleus (by transcription from DNA) while ribosomal proteins are formed in cytoplasm. Latter migrate inside nucleus through nuclear pores. At the nucleolar area, rRNA and ribosomal proteins are integrated to form ribosomal subunits.
(Ribosomal subunits travel to cytoplasm through nuclear pores. )
Assembly of ribosomal subunits stop during cell division; hence the nucleolus disappears during mitosis/meiosis .
Nucleolus is not surrounded by any membrane. It appears as a dense area within nucleus under light microscope because of presence of large number of ribosomal subunits.
In the following diagram you can study role of nucleolus in cell:
- Transcription of mRNAs carrying codes for ribosomal proteins
- Migration of mRNAs in cytoplasm through nuclear pores
- Production of ribosomal proteins from those mRNAs
- Migration of ribosomal proteins through nuclear pores
- Transcription of rRNAs inside nucleolus
- Integration of rRNAs with ribosomal proteins
- Ribosomal subunits travel to cytoplasm through nuclear pores
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