O core is an important structure found in eukaryotic cellsand absent in prokaryotic cells. It performs different functions, one of them being the control of cell activities. This structure is surrounded by a double membrane called the nuclear envelope, which is full of pores, which ensure the passage of substances from the cytoplasm into the core and vice versa. Inside the nucleus, we observe a matrix called nucleoplasm and chromatin, which, in dividing cells, is condensed, forming chromosomes.
Read too: Differences between prokaryotic and eukaryotic cells
the cell nucleus
The cell nucleus is a structure quite evident in eukaryotic cells. It has a format, usually, rounded or elongated and has about five µm in diameter. A eukaryotic cell normally has a nucleus, however, some cells may have several nuclei, as is the case with those of the muscle tissue skeletal striatum. In addition, some cells do not have a nucleus, such as the Red Cells, who lose it during their maturation.
Cell nucleus components
Next, we'll better understand some important structures that make up the core:
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Nuclear envelope: the cell nucleus is surrounded by a double membrane called the nuclear envelope or caryotheca. Between these membranes, there is a space, from 20 nm to 40 nm, called perinuclear cistern. Each of them has a structure formed by a lipid bilayer with proteins associates. The outermost membrane is in contact with the cell's cytoplasm, it has several ribosomes associated and is, in several places, continuous with the endoplasmic reticulum. The innermost membrane, in turn, maintains contact with the nuclear matrix. In association with the latter, is the nuclear blade, a network of proteins that act to stabilize the nuclear envelope.
The nuclear envelope is rich in circular pores, which are 30 to 100 nanometers in diameter and have their edges formed by the inner and outer membranes of the nuclear envelope. Pores are important to ensure communication between the interior of the nucleus and the cell cytoplasm. However, it is important to make it clear that they are not just spaces for the passage of substances, being a complex structure surrounded by the so-called pore complex, which guarantees a regulation of what enters and leaves the nucleus.
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Nucleoplasm: inside the nucleus, we have the so-called nucleoplasm, a kind of protein gel that has properties similar to those of the cytoplasm. It is in the nucleoplasm that we find the chromatin, defined as DNA associated with histone proteins. Two types of chromatin can be identified, the heterochromatin, where the DNA double helix is very condensed, and the euchromatin, where the DNA is less condensed.
In the process of cell division, this chromatin condenses and forms what we call the chromosomes. When not dividing, chromatin appears to have a diffuse mass, and it is not possible to differentiate the chromosomes. It is important to make it clear that each species has its own number of them. The human species, for example, has 46 chromosomes in its somatic cells, while the fruit fly has eight chromosomes, and the Arabidopsis thaliana (a weed), 10 chromosomes.
Nucleolus: inside the nucleus, when it is not dividing, it is possible to observe a spherical structure called the nucleolus. It shows a large amount of RNA and proteins, as well as some strands of DNA that come out of chromosomes and are known as the nucleolus organizer regions. In this structure, the formation of ribosomal subunits, which, after being formed, leave the nucleus through the pores and go to the cytoplasm, where they will be responsible for forming a ribosome.
Nuclear matrix: it is a fibrillar structure that spreads through the nucleus. Some researchers admit its existence, others don't. Those who do not confirm it believe that it is a structure formed during the preparation for the observation of cells.
Read more:Cytology or cell biology - field of cell studies
Cell nucleus functions
The cell nucleus is extremely important for the cell, performing functions such as:
Control of cell activities, establishing which and when proteins will be produced.
Storage of genetic information, since it is in the nucleus that most of the DNA is present. We specifically say that most of the DNA is in the nucleus, because in the mitochondria and plastos its presence is also observed.
DNA duplication.
Synthesis and processing of messenger, transporter and ribosomal RNA.
By Vanessa Sardinha dos Santos
Biology teacher
Would you like to reference this text in a school or academic work? Look:
SANTOS, Vanessa Sardinha dos. "Cell core"; Brazil School. Available in: https://brasilescola.uol.com.br/biologia/nucleo-das-celulas.htm. Accessed on June 27, 2021.
