Signs of the living and nonliving in viruses

(ORDO NEWS) — Viruses evolve, mutate and multiply. Like complex organisms like humans, viruses are also subject to natural selection. However, outside the cells, they are nonviable and rapidly destroyed. About whether the virus is a transitional form between the world of the living and nonliving, PostScience asked the virologist Leonid Margolis.

Before talking about whether the virus is alive, it is worth saying that the boundary between living and nonliving is not so unambiguous. An indisputable sign of the living is the ability to produce offspring. However, many animals and people do not pass on their genetic material to future generations. Does this mean that they are not alive? Another sign of the living is the ability to adapt to the environment. When falling, a stone can change its shape, and formally it is adaptation to the environment. In addition, the stone at the same time spends energy, and energy exchange is another sign.

Whether the virus is alive or inanimate, scientists have been arguing for a very long time. The fact is that the virus does not possess all the signs of living, therefore it is impossible to categorically attribute it to this category. For example, the structure of viruses is non-cellular, and they are not able to live autonomously. For reproduction, viruses use a living cell along with its resources. Metaphorically speaking, the virus resembles a letter sealed in an envelope from the commander in chief. It is not alive in itself, but the orders it contains set in motion a huge number of soldiers and units. Similarly, some viruses can change the life of a cell or even an organism.

A cell is an independent organism. The cells in our body are in close interaction with other cells, but they, in principle, can live apart. At the beginning of the 20th century, American biologist Ross Harrison and French surgeon Alexis Carrel, who at that time was a Nobel laureate, began to cultivate individual animal cells, starting with chicken cells. They proved that in a special nutrient solution the animal’s cell can multiply and perform some functions, for example, crawl when it comes to bacteria or protozoa. The same was true for human cells.

The virus, in contrast, is a non-autonomous system. Despite the variety of forms of viruses, their structure is more or less the same: nucleic acid (DNA or RNA) and capsid – a set of proteins in the lipid membrane. Some viruses, such as bacteriophages, have processes by which they inject their genetic material into the cells. Regardless of the structure of the virus, its construction is ten times simpler than the construction of a cell. In addition, viruses are not able to produce and accumulate energy, as well as maintain the internal environment, because it simply does not exist. These three parameters distinguish a living cell from an inanimate virus.

On the other hand, viruses are capable of self-replicating and developing, if development is understood to mean the entire life cycle of a virus. Moreover, viruses change the stages of their life cycle under the influence of the environment. They are also able to pass on genetic information to future generations and evolve.

And at the same time, viruses are very fragile creatures. For example, coronavirus lives on some surfaces for only a few days, and then collapses. The HIV virus maintains its integrity outside the body for only about an hour. The situation with the cold is different: in the conditions of deep freezing (around -80 ° C), viruses are able to remain infectious for a long time. However, other environments make viruses very vulnerable.

Life is relatively discrete, and there are no transitional forms. However, relatively recently, scientists found that all cells release vesicles – extracellular vesicles, inside which is part of the cell’s genome, and their membranes are very similar to viral ones: they consist of lipids, fats and proteins. Some cells that absorb these vesicles change the function of their RNA. This discovery led to serious controversy: is extracellular vesicle a precursor of the virus, or is it a primitive form of the virus that has lost many of its properties? It is obvious that viruses are one of the most successful forms of the existence of a gene because of its simplicity, and therefore viruses are a very beneficial form of life. And many successful mutations, as we know, evolution preserves.


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