The structure of chromosomes - an urgent topic for research for decades to come.

To date, the genetic characteristics of organisms, which are the subject of research by all biology scientists of the world, remain not fully understood. Every day new interesting facts are revealed. Thanks to the improvement of technologies, methods of analysis and modern equipment, scientists are penetrating deeper into the riddles of the chromosome system, studying its molecular and supramolecular structure.

However, today mankind has achieved much in the study of genetics and microbiology. Each interested person, having opened a textbook, can study the structure of chromosomes, their composition and functions in a living organism. About this and talk. According to the type of structure, the chromosomes are divided into:

• Body-centric,
• Acrocentric,
• Submetacentric,
• Metacentric.

The telocentric ones are rod-shaped and contain a centromere from which two strands emanate. The acrocentric ones also have a rod-shaped structure, but one "shoulder" is small, almost imperceptible. (The shoulder is the site of the chromosome, which emanates in one direction from the centromere). The submetascent structure is a chromosome with long or short shoulders. And the metacentric type of structure includes V-shaped chromosomes, which have the same length of shoulders.

Chromosomes of non-nuclear organisms: viruses and bacteria
Chromosomes of each organism are strictly individual. The structure of the chromosome of bacteria, viruses and certain species of algae is the simplest. The bacterial chromosome consists of a naked DNA molecule of double helix type, which can be linear or annular. The structure of the chromosome apparatus of viruses differs from bacterial DNA molecules. For example, the length of the DNA molecule of the virus varies from one to one hundred micrometers, and the DNA molecule of the bacterium reaches a length of two thousand micrometers. Dividing, that is, the synthesis of the daughter molecule (replication) of the chromosomes of viruses starts from one point of departure and runs along its entire length, and in bacteria it goes in both directions from the point of origin, where two forks of bifurcation of DNA are formed. The virus chromosome containing RNA has a single RNA molecule in the form of a filament, although two-stranded molecules are also found among them. By size, these chromosomes are much smaller than those containing DNA.

Chromosomes of nuclear organisms
The structure of the chromosome of a eukaryotic cell, which has a nucleus, is considered one of the most complex. It is based on a linear DNA molecule of considerable length, which can reach 5 cm! Such specimens can be found by studying the structure of human chromosomes. In addition to the DNA molecule, the chromosome is also made up of specialized proteins - histones. There are five of them: H1, H2A, H3, H4 are the main proteins. In addition, the molecule contains non-histone proteins. The structure of chromosomes of eukaryotes is very difficult and has the form of beads.

There are several more types of chromosomes that are less common. These include giant chromosomes, polytene chromosomes and chromosomes such as tube brushes.

• Gigantic chromosomes are huge in size. They can be found at certain stages of the development of the cell cycle - the period of cell life between the divisions. They are found in the cells of some insect larvae, as well as vertebrates and invertebrates.

• The polytene chromosomes are multiple daughter filaments that depart from the maternal in large numbers, but without being in a chaotic order, but unifying into a single spiral. They are contained in the cells of the internal organs of living organisms, for example, in cells of the intestine, fatty body, salivary glands, trachea. Also, polytene chromosomes can be found in the vessels of the larvae of Diptera insects.

• Chromosomes such as tube brushes are giant chromosomes longer than polythene, which are found in oocytes (ovules) of vertebrates. The structure of chromosomes such as tube brushes differs by a large number of different in size and length of lateral loops on which RNA synthesis occurs.

As you can see, there are many types of chromosomes. And in all organisms they are different. And the most interesting is that the mechanism of this molecular system still remains unexplored until the end. The structure of chromosomes, the number, structure and its violation, leading to mutations of organisms - all this is an open topic of genetic scientists.