What is a virus? What does it consist of?

Representatives of the realm of viruses are a special group of life forms. They have not only a highly specialized structure, but also are characterized by a specific metabolism. In this article, we will study the non-cellular form of life - the virus. What it consists of, how it multiplies and what role it plays in nature, you will learn by reading it.

The discovery of non-cellular forms of life

Russian scientist D. Ivanovsky in 1892 studied the causative agent of tobacco disease - tobacco mosaic. He found that the pathogenic agent does not belong to bacteria, but is a special form, later called a virus. At the end of the 19th century, high-resolution microscopes were not yet used in biology, so the scientist could not find out what molecules the virus consists of, and also to see and describe it. After the creation of the electron microscope at the beginning of the 20th century, the world saw the first representatives of the new kingdom, who were the cause of many dangerous and difficult to treat diseases of man, as well as other living organisms: animals, plants, bacteria.

The position of non-cellular forms in the systematics of living nature

As mentioned earlier, these organisms are united in the fifth realm of living nature - viruses. The main morphological feature, characteristic of all viruses, is the absence of a cellular structure. Until now, the scientific world has not stopped discussions on whether the non-cellular forms are living objects in the full sense of the term. After all, all the manifestations of metabolism in them are possible only after penetration into a living cell. Up to this point, viruses behave like objects of inanimate nature: they do not have metabolic reactions, they do not reproduce. At the beginning of the 20th century, a whole group of questions arose before scientists: what is a virus, what does its shell consist of, what is inside the virus particle? The answers were received as a result of many years of research and experiments, which served as the basis for a new scientific discipline. It originated at the junction of biology and medicine and is called virology.

Features of the structure

The expression "all ingenious simple" directly relates to non-cellular forms of life. The virus consists of molecules of nucleic acids - DNA or RNA, coated with a protein shell. He does not have his own power and protein-synthesizing apparatus. Without a host cell, viruses do not have any sign of living substance: neither breathing, nor growth, nor irritability, nor reproduction. To all this appeared, only one thing is required: to find the victim - a living cell, to subordinate its metabolism to its nucleic acid and eventually destroy it. As it was said before, the envelope of the virus consists of protein molecules having an ordered structure (simple viruses).

If the composition of the envelope also includes lipoprotein subunits, which are actually part of the cytoplasmic membrane of the host cell, such viruses are called complex (pathogens of smallpox and hepatitis B). Often, the composition of the surface envelope of the virus includes glycoproteins. They perform an alarm function. Thus, like the shell, and the virus itself consists of molecules of the organic component - protein and nucleic acids (DNA or RNA).

How viruses penetrate into living cells

Earlier we considered the features of the structure of the shell of the intracellular parasite. The virus consists of molecules of organic and biological matter, and its surface structure contains special proteins that recognize the plasmalemma of a living cell. Therefore, non-cellular forms affect specific cell types of certain biological species of organisms. For example, viruses of plague dogs do not pose a threat to human health. Inside the cells, the parasite enters several ways:

1. Merging its shell with the cell membrane (influenza virus).
2. By means of pinocytosis (an agent of poliomyelitis of animals).
3. Through damage to the cell wall (plant viruses).

Propagation of viruses

Once the parasite has entered the cell, the molecules of its nucleic acid, wedged into the nucleus genome, transmit information about the structure of protein particles and trigger the process of biosynthesis of their own proteins. In this case, ribosomes, ATP molecules, t-RNA of the host cell are used. Parallel to the infected cell, the hereditary information is reduplicated. Recall that from protein and nucleic acid are viruses, called simple. Their particles contain RNA, which immediately binds to ribosomes subunits of the host cell and induces the biosynthesis of the molecules of the virus proteins.

The result of the attack of the pathogen on the cell becomes the DNA or RNA of the virus with its own protein particles. Thus, the newly formed virus consists of nucleic acid molecules coated with ordered particles of the proteins. The membrane of the host cell is destroyed, the cell dies, and the viruses that have emerged from it enter the healthy cells of the body.

The phenomenon of reverse reduplication

At the beginning of the study of representatives of this kingdom, it was believed that viruses consist of cells, but already D. Ivanovsky's experiments proved that pathogens could not be isolated with the help of microbiological filters: pathogens passed through their pores and appeared in a filtrate that retained virulent properties.

Further studies established the fact that the virus consists of molecules of organic matter and shows signs of living substance only after its direct entry into the cell. In it, it begins to multiply. Most RNA-containing viruses reproduce as described above, but some of them, for example the AIDS virus, in the nucleus of the host cell cause DNA synthesis. This phenomenon is called reverse replication. Then, the i-RNA of the virus is synthesized on the DNA molecule , and the assembly of the viral protein subunits that form its envelope begins on it.

Features of bacteriophages

What is a bacteriophage-cell or virus? What does this non-cellular form of life consist of? The answers to these questions are: it is a virus that affects exclusively prokaryotic organisms - bacteria. Its structure is quite peculiar. The virus consists of molecules of organic matter and is divided into three parts: the head, the stem (the cover), and the tail filaments. In the front - the head - is a DNA molecule. Next is a cover that has a hollow core inside. The tail filaments attached to it ensure the connection of the virus to the receptor loci of the plasma membrane of the bacterium. The principle of action of a bacteriophage resembles a syringe. After contraction of the coat proteins, the DNA molecule enters the hollow core and is then injected into the cytoplasm of the target cell. Now the infected bacterium will synthesize the DNA of the virus and its proteins, which will inevitably lead to its death.

How the body protects itself from viral infections

Nature has created special protective devices that resist the viral diseases of plants, animals and humans. The pathogens themselves are perceived by their cells as antigens. In response to the presence of viruses, the body produces immunoglobulins - protective antibodies. The organs of the immune system - the thymus, lymph nodes - react to the virus invasion and contribute to the development of protective proteins - interferons. These substances inhibit the development of viral particles and inhibit their reproduction. Both kinds of protective reactions, considered above, refer to humoral immunity. Another form of protection is cellular. Leukocytes, macrophages, neutrophils absorb the virus particles and break them down.

Importance of viruses

It's no secret that it is mostly negative. These ultra-small pathogens (from 15 to 450 nm), visible only in the electron microscope, cause a whole bunch of dangerous and intractable diseases of all organisms existing on the Earth, without exception. So, in humans, viruses affect vital organs and systems, for example, nervous (rabies, encephalitis, poliomyelitis) immune (AIDS), digestive (hepatitis), respiratory (influenza, adenoinfections). Animals are infected with the lizard, the plague, and the plants - with various necroses, patches, mosaic.

The diversity of the representatives of the kingdom has not been fully understood. The proof is that until now they discover new types of viruses and diagnose previously not occurring diseases. For example, in the middle of the 20th century, Zika virus was found in Africa. It is found in the body of mosquitoes, which, when bitten, infect humans and other mammals. Symptoms of the disease indicate that the pathogen affects primarily the central nervous system and causes microcephaly in newborns. People who are carriers of this virus should remember that they pose a potential danger to their partners, since in medical practice cases of sexual transmission of the disease have been registered.

The positive role of viruses can be attributed to their use in the fight against pest species, in genetic engineering.

In this paper, we described what a virus is, what its particle consists of, how organisms protect themselves from pathogenic agents. We also determined the role that non-cellular forms of life play in nature.