To date, the genetic characteristics of organisms, which are the subject of research by all biologists and scientists of the world, have not been fully studied. Every day new interesting facts are revealed. Thanks to the improvement of technologies, analysis methods and modern equipment, scientists are penetrating deeper and deeper into the mysteries 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 the textbook, can study the structure of chromosomes, their composition and functions in a living organism. We’ll talk about this. According to the type of structure, chromosomes are divided into:
- telecentric
- acrocentric
- submetacentric
- metacentric.
Telocentric have a rod-shaped form and contain a centromere, from which two threads emanate. Acrocentric also have a rod-shaped structure, but one of them has a small, almost invisible shoulder. (The shoulder is the part of the chromosome that comes in one direction from the centromere). The submetacentric structure is a chromosome with long or short shoulders. And the meta-centric type of structure includes V-shaped chromosomes that have the same length shoulders.
Chromosomes of Nuclear-Free Organisms: Viruses and Bacteria
The chromosomes of each organism are purely individual. The chromosome structure of bacteria, viruses and some types of algae is the simplest. The bacterial chromosome consists of a double-stranded naked DNA molecule, which can be linear or ring-shaped. The structure of the chromosomal 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. Bifurcation, that is, the synthesis of a daughter molecule (replication) of virus chromosomes, starts from one starting point and runs along its entire length, and in bacteria it goes both sides from the start point, where two forks of DNA split form. The virus chromosome containing RNA has a single RNA molecule in the form of a strand, although double-stranded molecules are also found among them. In size, these chromosomes are much smaller than those containing DNA.
Chromosomes of nuclear organisms
The chromosome structure of a eukaryotic cell having 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 instances can be found by studying the structure of human chromosomes. In addition to the DNA molecule, specialized proteins, histones, also make up the chromosome. There are five of them: H1, H2A, H3, H4 - these are the main proteins. In addition to them, the molecule contains non-histone proteins. The structure of the chromosomes of eukaryotes is very complex and has the appearance of a bead.
There are several types of chromosomes that are less common. These include giant chromosomes, polytene chromosomes, and lamp brush type chromosomes.
- Giant chromosomes are huge. They can be found at certain stages of the development of the cell cycle - the period of cell life between divisions. They are found in the cells of some insect larvae, as well as vertebrates and invertebrates.
- Polytene chromosomes are multiple daughter strands that depart from the mother in large numbers, but not located in a chaotic order, but combined in a single spiral. They are contained in the cells of the internal organs of living organisms, for example, in the cells of the intestine, adipose body, salivary glands, trachea. Also polytene chromosomes can be found in the vessels of dipterous insect larvae.
- Chromosomes such as lamp brushes are giant chromosomes that are longer than polytene chromosomes that are found in vertebrate oocytes (oocytes). The structure of chromosomes like lamp brushes differs in a large number of lateral loops of various sizes and lengths 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 thing is that the mechanism of this molecular system is still not fully understood. The structure of chromosomes, the number, structure and its violation, leading to mutations of organisms - all this is an open topic for genetic scientists.