The nucleolus is one of the main components of nucleus. Chains of RNAs, DNAs and various form the structural components of this component of cell. It is composed of granular and fibrillar components. The fibrillar components are categorized into fibrillar centers and dense fibrillar component. Such kind of structural organization of nucleolus is found in eukaryotic cells. Nucleolar vacuole is the specialty of plant cells. The nucleolus present in budding form of yeast is bigger than in other cells and covers almost half of the nucleus. Present in the nuclear matrix, the nucleolus is not surrounded by a membrane. The main components of nucleolus are ribonucleic acid (RNA), deoxyribonucleic acid (DNA) and proteins. The nucleolus function and structure can be understood with the help of information provided below.
Structure of Nucleolus
The complex organization which is seen in nucleoli has evolved during the phase when anamniotes transitioned into amniotes. The anamniotes are those vertebrates which do not possess amnion and have to lay eggs in water. Amniotes are those organisms (reptiles, birds, etc) which lay eggs that are adapted to terrestrial environments. In this transition phase, the rDNA intergenic region saw a considerable amount of rise. The separation of original fibrillar component took place during this phase and the FC (fibrillar centers) & DFC (dense fibrillar components) were formed. Let us understand the different nucleolus functions are presented through the information provided in following paragraphs.
What is the Function of the Nucleolus?
The main nucleolus function is production of subunits which together form the ribosomes. The ribosomes are known to produce/manufacture proteins and therefore, nucleolus plays an indirect role in protein synthesis. Out of the total production of RNA that takes place in cells, nucleolus is involved in 50% of the RNA synthesis. This functionality of nucleolus is attributed to hundreds of r-genes.
Ribosomal Subunit Assembly
The assembly of ribosomal subunits takes place in the following manner. Transcription of rRNA precursor molecule from DNA takes place in the nucleolus. This long rRNA precursor molecule is processed and 3 mature RNAs are formed. The next step after formation of mature RNAs is that of carrying out the packaging. These RNAs are packaged with certain specific forms of proteins and finally, the ribosomal units are formed. These ribosomal units can vary in size. Read more on DNA transcription.
The process of translation requires ribosomal subunits as the raw material. The ribosomes subunits which are assembled get transported to the cell cytoplasm i.e. out of the nucleolus and then participate in the process of translation (protein synthesis).
The nucleoli are known to play an important role in mRNA biogenesis. The nucleolus is also involved in RNA metabolism. Events such as telomerase RNP and assembly of signal recognition particle are known to be important. Nucleolus is also involved in these RNP assembly events.
Nucleolus Organizer Region
The NOR is region in which formation of nucleolus takes place around chromosomes. After the division of nucleus, this region gets associated with the nucleus. Several copies of genes of ribosomal RNAs are contained in this area.
The different functions of nucleolus are explained in the article above. The structure and functioning of nucleolus is far more complicated than what has been studied till date. Efforts are being taken to study the working of nucleoli on a molecular level. It would help in understanding more about the macromolecules involved in different functions. The above article thus, presents a short account of different nucleolus functions.