The cell nucleus is an obligatory structure of every eukaryotic organism. This organelle performs a wide variety of functions, but its main purpose is to store and transfer hereditary genetic material.
Almost every cell in the human body has a nucleus. The only exceptions are platelets and red blood cells. Most cells are mononuclear, but, for example, muscle fibers and neurons can have several of these organelles. The nucleus in the cell can have different sizes - the largest nuclear structures in the female egg.
Cell nucleus: structure
The nucleus has a rather complex structure and consists of a nuclear membrane, chromatin, nucleolus and nucleoplasm. Let's look at each part of it in more detail.
- A karyotek, or nuclear envelope, is a structure that separates the internal environment of the nucleus from the cytoplasm. This membrane consists of the outer and inner membranes, between which there is the so-called perinuclear space. It is interesting that the outer membrane of the membrane passes directly into the membrane of the granular endoplasmic reticulum; therefore, the cavities of the EPS tanks and the nucleus are interconnected. And the shell has nuclear pores closed by the diaphragm. They are designed to penetrate large molecules, as well as for the metabolism between karyoplasm and cytoplasm.
- Karyoplasma is a homogeneous substance that fills the internal cavity of the nucleus. It contains the nucleolus, as well as chromatin.
- Chromatin is the genetic material of a cell. Its structural unit is the nucleosome, which is a DNA strand wound on a specific protein - histone. In a cell, two states of genetic material are distinguished. Heterochromatin - is a small, dense osmophilic granules. Euchromatin, or loosened chromatin, are areas in which synthetic processes are actively occurring. During cell division, chromatin condenses, forming chromosomes.
- The nucleolus is a small, oval structure that consists of RNA strands and protein molecules. This is where the formation of ribosome subunits occurs. There can be one or more nucleoli in the nucleus, but they can be seen only in non-dividing cells.
Cell nucleus: functions
The functions of the cell nucleus can be determined by looking at its structure. First, the nucleus is responsible for the transmission of a hereditary set of information during cell division, both mitosis and meiosis. During mitosis, daughter cells receive a genome that is identical to the mother cell. With meiosis (the formation of human sex cells), each cell receives only half of the chromosome set - a complete set of chromosomes is formed only after merging with the reproductive cell of another organism.
In addition, the cell nucleus is responsible for one of the most important stages of metabolism - protein synthesis. The fact is that it is in the nucleus that information or matrix RNA is formed. Then it enters the endoplasmic reticulum, joins the ribosome and serves as a model for the formation of the amino acid sequence of the peptide molecule.
And as already mentioned, the synthesis of ribosome subunits is carried out in the nucleus.
Cell Nucleus: Origin
Today, there are several completely different hypotheses with which scientists are trying to explain how exactly the nucleus was formed in the cell. But, unfortunately, none of these statements has yet found actual evidence.
There is a theory that the nucleus as a cell structure was formed as a result of the symbiosis of a bacterial cell and archaea. Other scientists believe that the nucleus is the result of infection of a cell with a specific virus.
The most complete explanation contains the so-called exomembrane hypothesis. According to her, in the process of evolution, another external cell membrane appeared in the cell. In this case, the old, inner membrane turned into a shell of the nucleus - over time, a complex system of pores appeared in it, and then chromatin molecules began to concentrate in its cavity.