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This website provides an overview of the nucleolus.

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The nucleolus is the distinct structure present in the nucleus of eukaryotic cells. Primarily, it participates in assembling the ribosomes, alteration 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 other components form the structural components. The main components of the nucleolus are ribonucleic acid, deoxyribonucleic acid, and proteins.

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 cells.

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.

Nucleolus Function

The nucleolus is considered as the brain of the nucleus, covering nearly 25% volume of the nucleus. Primarily, it takes part in the production of subunits that unites to form ribosomes. Hence, nucleolus plays an important role in the synthesis of proteins and in the production of ribosomes in eukaryotic cells.

Difference Between Nucleus and Nucleolus

The difference between nucleus and nucleolus is mentioned below:

Large in size

Very small in size

Bound 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

Also Read: Nucleoplasm
For more information on nucleolus, its structure, function and the difference between nucleus and nucleolus, keep visiting BYJU'S website or download BYJU'S app for further reference.

What is the function of nucleolus?

Nucleolus helps in protein synthesis and production of the ribosome in the cells.

Where is the nucleolus located in the cell?

The nucleolus is located inside the nucleus of the eukaryotic cell. It is surrounded by a membrane inside the nucleus.

What does the nucleolus contain?

The nucleolus contains DNA, RNA and proteins. It is a ribosome factory. Cells from other species often have multiple nucleoli.

Is nucleolus an organelle?

The nucleolus is an organelle, and a very unusual one because it is devoid of lipid bilayers, which are characteristic of other organelles.

What would happen if there is no nucleolus in the cell?

If the nucleolus didn't exist, there would be no production of ribosomes and there would be no synthesis of proteins.

Frequently Asked Questions

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Nucleolus - Function, Difference Between Nucleus & Nucleolus

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The nucleolus is the distinct structure present in the nucleus of eukaryotic cells. Primarily, it participates in assembling the ribosomes, alteration 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.

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This video is very helpful for understanding structure and function of nucleolus.

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Within our nucleus, we house a region referred to as the nucleolus. In this tutorial we will discuss how the nucleolus is arranged and the functions it serves in regard to ribosome construction.

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1. Nucleolus is often considered as the non-organelle part of the cells. This is because it lacks lipid bilayer, which is found in the cell membrane. Lipid bilayers are one of the components that are found in every organelle. However, since the nucleolus is inside the nucleus, it does not need an extra cell membrane.
2. Assuming that nucleolus is an organelle, there are some neurodegenerative diseases (diseases caused by a gradual deterioration in the certain nervous system) that can be caused by malfunction of nucleolus such as Alzheimer's and Huntington's disease. For example, nonoperating nucleolus can result in massive cell damage and typical nerve damage of Parkinson's disease.

Considering all these problems, there are more positive aspects of nucleolus!

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Nucleolus is the dark section in the nucleus. Typically, a cell has one or two nucleoli, but it can have more than two depending on the function and type of the cell. It makes up 25% of the nucleus. Nucleolus is called the "brain" of nucleus.

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The first step of protein synthesis occurs in the nucleolus; the nucleolus is in charge of producing ribosomes that synthesizes proteins. Without nucleolus, the entire process of making protein cannot even be initiated. Remember how dynamic roles proteins have in our bodies. Protein is one of the four main macromolecules - protein, carbohydrate, lipids, and nucleic acid - that are essential to human beings. And out of four of them, protein is used in the most versatile molecule that is used to carry out so many functions in our body.

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The function of the nucleolus could be simply defined as producing ribosomes. Specifically, it manufactures the subunits of ribosomes. It does the mixing of water and cement to make concrete blocks that build up stable buildings. Also, it contains rDNA, the genetic information that encodes rRNA, and produces rRNA.

First of all, information on rDNA, with a repetitive pattern of a single type of nucleotide directly adjacent to each other, is copied into rRNA in the fibrillar center. Then, in the dense fibrillar component, the processing of pre-rRNA takes place. Lastly, in the granular component, ribosomal protein enters the nucleolus and is combined with four rRNA. This produces subunits of ribosomes - one large and on small - which are transferred to the cytoplasm and assembled to form ribosomes.

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Before diving into the structure and function of the nucleolus, these are some key terms that you should know.
DNA: It is a type of nucleic acid that contains genetic information.
RNA: It is another type of nucleic acid that transfer such information from the DNA to produce protein. There are three types of RNA: mRNA, tRNA, and rRNA. rRNA is a RNA molecule that is transcripted from rRNA but does not encode proteins. It is essential for comprising ribosomes.

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There are 3 main components of the nucleolus.

1. Fibrillar center:
This is where the code of rDNA is copied into rRNA.
2. Dense fibrillar component:
It is located on the outside of the fibrillar center. This is where pre-rRNAs are processed, which means the unnecessary parts are eliminated to form a mature rRNA.
3. Granular component:
This is where ribosome subunits are produced by joining ribosomal protein and rRNA.