All organisms consist of cells - the smallest structural and functional units of the structure. But there are non-cellular life forms: viruses and bacteriophages. What structural features allowed them to occupy their worthy niche among the kingdoms of wildlife? Let's find out more.
Viruses - non-cellular life forms
Translated from the Greek language, the name of these organisms translates as "poison." And this is no coincidence. No one has ever seen them with the naked eye, but almost everyone has transferred their influence to themselves. After all, the symptoms of flu in the winter are knocking at our house without demand.
It is now known that viruses are a non-cellular form of life. The biology of these organisms has remained a mystery for many centuries. And only at the end of the 19th century, the Russian physiologist Dmitry Iosifovich Ivanovsky proved that it is viruses that cause many diseases. A scientist examined a tobacco plant that was hit by a tobacco mosaic. He noticed that if the juice of a diseased plant penetrates into a healthy one, then its defeat will occur.
The structure of viruses
Why are viruses non-cellular life forms? The answer is simple: their body is not composed of cells. It is a nucleic acid molecule surrounded by a protein shell - a capsid. Distinguish between DNA and RNA viruses.
Non-cellular life forms - viruses - are divided into simple and complex, depending on the structural features. The former have a classic structure of nucleic acids and proteins. And the second additionally attach part of the plasma membrane during assembly. It serves as an additional protective shell.
Why are they alive?
So, viruses - non-cellular life forms, do not have the usual membrane and organelles - permanent cell structures that perform certain functions. What are their attributes to living organisms? They are capable of the process of reproduction. Moreover, being outside the host organism, they do not show any signs of existence. As soon as the virus enters the cell, it begins to synthesize its proteins. At the same time, the process of suppressing the product of the body's own protein molecules begins.
Viral proteins act as enzymes - biologically active substances. They accelerate the reproduction of nucleic acids. Thus, the number of foreign particles increases, and the own synthesis processes stop. As a result, the body becomes ill, because the virus needs energy and organic matter from the host cells to start the process of reproduction .
Bacteriophages
Viruses are non-cellular life forms that can parasitize in any organism. And unicellular prokaryotic bacteria are no exception.
The “eaters” of these organisms are called bacteriophages. To enter the host cell, they simply inject their own nucleic acid molecule through the membrane into the cytoplasm of the cell. Within half an hour in one bacterium more than a hundred viral particles are formed.
How does a bacteriophage find its prey in nature? The fact is that for this the viral particle has special receptors that recognize the prokaryotic organism.
Routes of entry of viruses into the body
Non-cellular life forms - viruses, having a primitive structure, are able to penetrate the host organism in many ways. They depend on the features of its structure. For humans, the most common of them are the airborne droplet, penetration through the mucous membranes, food and water.
The carriers of such dangerous diseases as encephalitis and yellow fever are animals. In this case, ticks and mosquitoes, respectively. During sexual contact, infection with hepatitis B and C, HIV and herpes is possible.
In nature, viruses that infect plants and fungi are also widespread. Penetration into these organisms occurs through damage sites in the cell wall.
An important feature of viruses is their selectivity. This means that particles that infect humans do not affect plant and bacterial organisms and vice versa.
Viruses: benefit or harm
What benefits can these organisms bring if they cause dangerous deadly diseases: rabies, flu, smallpox and others. The fact is that it is the viruses - non-cellular forms of life - that form the immune system. This concept means the body's ability to resist infections. Immunity is innate, which is represented by blood antibodies, and acquired.
The latter is divided into natural and artificial. When infectious diseases are transferred, the memory of viral particles remains in special blood cells - antibodies. When foreign organisms re-enter, they recognize the virus and destroy it by intracellular digestion - phagocytosis. Artificial immunity is acquired as a result of vaccination. Its essence lies in the fact that the human body is infected with a weakened virus and antibodies begin to fight it, forming an immune memory.
Thanks to various forms of immunity, the body remains viable from the first breath of a baby throughout its life. Every minute a lot of viral particles enter the bloodstream. If the amount of antibodies is sufficient for their complete destruction, the person remains healthy. The disease occurs in another case, when the viral particles prevail and the resources of the immune system are insufficient to neutralize them.
Non-cellular life forms - viruses and phages - are representatives of a separate kingdom of wildlife called Vira. In recent decades, the main task of epidemiologists is to create new vaccines against many dangerous viral diseases. The fact is that in the process of self-assembly, mutation and the formation of new viruses occur. This is especially true of HIV, which affects the immune system itself, completely making the body defenseless. This is a serious problem for modern science. We hope it will be resolved in the near future.