What is a virus and how long does it "live" outside the cell?
Viruses evolve, mutate and multiply. Like complex organisms such as humans, viruses are also subject to natural selection. However, they are not viable outside the cells and are rapidly destroyed. About whether the virus is a transitional form between the living and nonliving worlds. Virologist Leonid Margolis reports.
Before talking about whether the virus is alive, it should be said that the border between the living and the non-living is not so clearly drawn. An unconditional sign of a living being is the ability to produce offspring. However, many animals and humans do not pass on their genetic material to future generations. Does this mean they are not alive? Another sign of living is the ability to adapt to the environment. When a stone falls, it can change its shape, and formally this is adaptation to the environment. In addition, the stone wastes energy at the same time, and energy exchange is another sign.
Whether the virus is alive or inanimate, scientists have been arguing for a long time. The fact is that the virus does not have all the characteristics of a living thing, therefore it cannot be unequivocally attributed to this category. For example, the structure of viruses is non-cellular, and they are not able to live autonomously. To reproduce, viruses use a living cell along with its resources. Metaphorically speaking, the virus resembles a letter from the commander-in-chief sealed in an envelope. By itself, it is not alive, but the orders it contains set in motion a huge number of soldiers and units. Likewise, some viruses are capable of changing the life of a cell or even an organism.
The 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, the American biologist Ross Garrison and the French surgeon Alexis Carrel, who by that time was a Nobel laureate, began to cultivate individual animal cells, starting with chicken cells. They proved that in a special nutrient solution, an 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.
In contrast, a virus 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 a lipid envelope. Some viruses, such as bacteriophages, have processes that inject their genetic material into cells. Regardless of the structure of the virus, its structure is ten times simpler than that of a cell. In addition, viruses are not able to produce and store energy, as well as maintain the internal environment, because it simply does not exist. These three parameters distinguish a living cell from a non-living virus.
On the other hand, viruses are capable of self-reproduction and development, if by development we 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 capable of transmitting genetic information to future generations and evolving.
At the same time, viruses are very fragile creatures. For example, the coronavirus lives on some surfaces for only a few days and then breaks down. The HIV virus retains its integrity outside the body for only about an hour. The situation with the cold is different: in conditions of deep freezing (about -80 ° C), viruses are able to remain infectious for a long time. However, other environments make viruses very vulnerable.
Promotional video:
Life is relatively discrete, and there are no transitional forms. However, relatively recently, scientists have found that all cells release bubbles - extracellular vesicles, inside which there is a part of the cell's genome, and their membranes are very similar to viral ones: they are composed of lipids, fats and proteins. Some cells that take up these vesicles change the function of their RNA. This discovery led to a serious debate: is the extracellular vesicle a precursor of a virus, or is it a primitive form of a virus that has lost many of its properties? It is obvious that viruses are one of the most successful forms of gene existence because of their simplicity, and therefore viruses are a very beneficial form of life. And evolution preserves many successful mutations, as we know.