Nucleolus: Structure and Function

Robert Brown identified and described nuclei in plant cells in 1833, and they were immediately recognized as a continuous characteristic of all animal and plant cells. M.J. Schleiden mentioned nucleoli in 1838, but Fontana was the first to notice those (1781). Bowman invented the word nucleolus in 1840.

The nucleus is the cell’s heart. Nearly all the cell’s DNA is contained, duplicated and transcribed here. As a result, the nucleus is in charge of the cell’s metabolic and hereditary operations. The Greek word Karyon is a synonym for this organelle. The true nucleus, as contrasted to the nuclear region, prokaryote, or nucleoid of prokaryotic cells, acts as the principal defining factor of eukaryotic cells.

The nucleus can be observed in all eukaryotic cells, including those of plants and animals. Several eukaryotic cells, however, such as:

1. Numerous eukaryotic cells, including higher plant’s mature sieve tubes and mammalian erythrocytes, do not have a nucleus. Although during the initial phases of development, nuclei are contained in such cells.
2. Bacterial prokaryotic cells lack a true nucleus, which is a single, circular, and massive structure.

The nucleus consists of the following structures: nuclear membrane, nuclear sap or nucleoplasm, nucleolus and chromatin fibers or chromatin.

The structure of nucleolus

1. It is a nucleolus that is not enclosed by an outer membrane, i.e., it is membraneless.
2. Their number can vary from one to many in a nucleolus.
3. It is mainly composed of rRNA as well as proteins such as fibrillarin, DNA, nucleostemin and nucleolin.
4. It contains fibrillar centers, pars fibrosa, pars granulosa and nucleolar matrix.
5. It is involved in the synthesis of rRNA and assembly.
6. Except for sperm and some algae, all eukaryotic cells contain spheroidal bodies.
7. They range in number from one to a few, and they stain evenly and deeply.
8. DNA, RNA and proteins are all present.
9. It vanishes during the early stages of the cell cycle and returns in the newly generated daughter nuclei during telophase.
10. It regulates the nucleus’s synthesis activity.
11. As a result, the nucleus and the cytoplasm are interrelated, and this contact is referred to as nucleocytoplasmic interaction.

The function of nucleolus

1. The nucleolus is the location where ribosomes are made.
2. The majority of rRNA molecules are transcribed by ribosomal DNA, and these molecules are processed before being added to 70 different types of ribosomal proteins to form the ribosomal subunits.
3. Certain nucleolar proteins, including nucleostemin, which operate as cell cycle control signalling proteins, are also contained in the nucleolus.