The nucleolus is the distinct structure present in the nucleus of eukaryotic cells. It is mainly involved in assembling the ribosomes, modification of transfer RNA and sensing cellular stress. The nucleolus is composed of RNA and proteins which form around specific chromosomal regions.


It is one of the main components of the nucleus. The chain of RNA and DNA along with various form the structural components of this component of a cell. The main components of the nucleolus are ribonucleic acid, deoxyribonucleic acid, and proteins.

Function of the Nucleolus

The nucleolus is mainly involved in the production of subunits which then together form ribosomes. Therefore, nucleolus plays an important role in protein synthesis and the production of ribosomes in eukaryotic cells.

Structure of the Nucleolus

In eukaryotic cells, nucleolus has a well-ordered structure with four main ultrastructural components. The components can be further identified as:

  • Fibrillar Centers: It is the place where the ribosomal proteins are formed.
  • Granular Components: Before ribosomes are formed, these components have rRNA that binds to ribosomal proteins.
  • Dense Fibrillar Components: It has new transcribed RNA which connects to the ribosomal proteins.
  • Nucleolar vacuoles: It is present only in Plant cell.

The ultrastructure of the nucleolus can be easily visualized through an electron microscope.  The arrangement of the nucleolus within the cell can be clearly studied by the techniques –  fluorescent recovery after photobleaching and fluorescent protein tagging.

The nucleolus of several plant species has very high concentrations of iron in contrast to the human and animal cell nucleolus.

Difference Between Nucleus and Nucleolus

Nucleus Nucleolus
Large in size. Vey small in size.
Bounded by the nuclear envelope. It has no limiting membrane.
It contains chromosomes. It does not hold any chromosomes
It is rich in DNA, the genetic material. It is rich in RNA.

Stay tuned with BYJU’S to learn more about the Nucleolus.

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