Nucleolus Function

The nucleolus is the most important component of nucleus. Chains of RNA and DNA form the structural components of this cell organelle. It is composed of granular and fibrillar components. The fibrillar components are categorized into fibrillar centers and dense fibrillar component. This kind of structural organization of nucleolus is found in eukaryotic cells. The nucleolar vacuole is found only in plant cells. Nucleolus present in the budding form of yeast is bigger than in other cells and covers almost half the nucleus. The nucleolus which is present in nuclear matrix is not surrounded by any membrane. Main components of this cell organelle are ribonucleic acid (RNA), deoxyribonucleic acid (DNA) and proteins. The structure and functions of nucleolus can be studied in a better manner through information presented in this article.

Structure of Nucleolus
It is the largest structure present inside the boundaries of nucleus. The complex structural organization observed in the nucleoli has evolved during the phase of transition of organisms from anamniotes to amniotes. Anamniotes are vertebrates which do not possess amnion; another notable characteristic of these organisms is that they lay eggs in water. Amniotes are organisms (reptiles, birds, etc) that lay eggs and which have adapted themselves to the terrestrial environment. In this transition phase, the rDNA intergenic region saw a considerable amount of rise. Separation of the original fibrillar component took place during this phase; as a result, the FC (fibrillar centers) & DFC (dense fibrillar components) were formed. Now let us delve into the details about different functions of the nucleolus through information presented below.

What is the Function of the Nucleolus?
The main function of nucleolus is the production and assembling of subunits which together form the cell organelle called ribosomes. The ribosomes are a site for proteins synthesis; which is why the nucleolus plays an indirect but crucial role in the synthesis of protein. The nucleolus carries out 50% of the total production of RNA which takes place in cells. This functionality is attributed to hundreds of r-genes present in the nucleolus.

Ribosomal Subunit Assembly
The formation of assembly of ribosomal subunits takes place in the following manner. Nucleolus is the site for transcription of rRNA precursor molecule from DNA. This long rRNA precursor molecule is processed to form 3 mature RNAs. The step that follows the formation of mature RNAs is the one which carries out the process of packaging. These RNAs are packaged with certain specific forms of proteins and finally the ribosomal units are formed. These ribosomal units may vary in size. Raw materials in the form of ribosomal subunits are needed for the process of translation. The assembly of ribosomal subunits gets transported to the cell cytoplasm i.e. out of the nucleolus and then participates in the process of translation (protein synthesis).

mRNA Biogenesis
Nucleoli are known to play an important role in the process of mRNA biogenesis. The nucleolus is also involved in RNA metabolism. Telomerase RNP events and assembly of signal recognition particles are known to be important. Nucleolus is also involved in the events of RNP assembly.

Nucleolus Organizer Region (NOR)
The NOR is a region in which formation of nucleolus takes place around the chromosomes. This region has a circular shape and is surrounded by filaments called pars fibrosa (PF). The pars fibrosa filaments are formed of ribosomal RNA that are newly transcribed. After the division of nucleus, this region gets associated with the nucleus. Several copies of genes of ribosomal RNA constitute this area. Many tandem copies of genes of these ribosomal RNA are found in the NOR. Identification of the NOR is carried out through the karyotype analysis by means of silver nitrate staining. Generally there are 10 NORs found in a single cell.

An attempt to discuss the different functions of nucleolus is made in the article above. Actually, the structure and functioning of nucleolus is far more complicated than what has been studied till date. Efforts are being taken to understand the working of this cell organelle on a molecular level. Studying the related concepts in-depth should help us understand more about macromolecules involved in different functions.