What is the non-living stage of a virus's life called? Is a virus a living organism or not? Let's try to figure it out together

Viruses were discovered by D.I. Ivanovsky (1892, tobacco mosaic virus).

If viruses are isolated in their pure form, then they exist in the form of crystals (they do not have their own metabolism, reproduction and other properties of living things). Because of this, many scientists consider viruses to be an intermediate stage between living and nonliving objects.

Viruses are non-cellular life forms. Viral particles (virions) are not cells:

• viruses are much smaller than cells;
• viruses are much simpler in structure than cells - they consist only of nucleic acid and a protein shell, consisting of many identical protein molecules.
• viruses contain either DNA or RNA.

Synthesis of virus components:

• The nucleic acid of the virus contains information about viral proteins. The cell makes these proteins itself, on its ribosomes.
• The cell reproduces the nucleic acid of the virus itself, using its enzymes.
• Then the self-assembly of viral particles occurs.

Virus meaning:

• cause infectious diseases (flu, herpes, AIDS, etc.)
• Some viruses can insert their DNA into the chromosomes of the host cell, causing mutations.

AIDS

The AIDS virus is very unstable and is easily destroyed in air. You can become infected with it only through sexual intercourse without a condom and through a transfusion of contaminated blood.

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Establish a correspondence between the characteristics of a biological object and the object to which this characteristic belongs: 1) bacteriophage, 2) E. coli. Write numbers 1 and 2 in the correct order.
A) consists of nucleic acid and capsid
B) cell wall made of murein
C) outside the body is in the form of crystals
D) can be in symbiosis with humans
D) has ribosomes
E) has a tail canal

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Choose one, the most correct option. Science studies precellular life forms
1) virology
2) mycology
3) bacteriology
4) histology

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Choose one, the most correct option. The AIDS virus infects human blood
1) red blood cells
2) platelets
3) lymphocytes
4) blood platelets

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Choose one, the most correct option. The cells of which organisms are affected by the bacteriophage?
1) lichens
2) mushrooms
3) prokaryote
4) protozoa

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Choose one, the most correct option. The immunodeficiency virus primarily affects
1) red blood cells
2) platelets
3) phagocytes
4) lymphocytes

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Choose one, the most correct option. In what environment does the AIDS virus usually die?
1) in the lymph
2) in breast milk
3) in saliva
4) in the air

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Choose one, the most correct option. Viruses have such signs of living things as
1) food
2) growth
3) metabolism
4) heredity

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1. Establish the correct sequence of stages of reproduction of DNA viruses. Write down the corresponding sequence of numbers in the table.
1) release of the virus into the environment
2) virus protein synthesis in the cell
3) introduction of DNA into the cell
4) synthesis of viral DNA in the cell
5) attachment of the virus to the cell

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2. Establish the sequence of stages of the bacteriophage life cycle. Write down the corresponding sequence of numbers.
1) biosynthesis of DNA and bacteriophage proteins by a bacterial cell
2) rupture of the bacterial membrane, release of bacteriophages and infection of new bacterial cells
3) penetration of bacteriophage DNA into the cell and its integration into the circular DNA of the bacterium
4) attachment of the bacteriophage to the bacterial cell membrane
5) assembly of new bacteriophages

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1) have an unformed core
2) reproduce only in other cells
3) do not have membrane organelles
4) carry out chemosynthesis
5) capable of crystallizing
6) formed by a protein shell and nucleic acid

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Choose three correct answers out of six and write down the numbers under which they are indicated. Viruses as opposed to bacteria
1) have a cellular structure
2) have an unformed core
3) formed by a protein shell and nucleic acid
4) belong to free-living forms
5) reproduce only in other cells
6) are a non-cellular form of life

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1. Establish a correspondence between the characteristic of an organism and the group for which it is characteristic: 1) prokaryotes, 2) viruses.
A) cellular structure of the body
B) the presence of its own metabolism
B) integration of one's own DNA into the DNA of the host cell
D) consists of a nucleic acid and a protein shell
D) reproduction by division in two
E) the ability to reverse transcription

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Choose two correct answers out of five and write down the numbers under which they are indicated. Metabolism as a property of living things is characteristic of
1) plant viruses
2) protozoa
3) soil bacteria
4) animal viruses
5) bacteriophages

Answer

© D.V. Pozdnyakov, 2009-2019

Are viruses a creature or a substance?

Over the past 100 years, scientists have repeatedly changed their understanding of the nature of viruses, microscopic carriers of disease.

At first, viruses were considered poisonous substances, then - one of the forms of life, then - biochemical compounds. Today it is assumed that they exist between the living and inanimate worlds and are the main participants in evolution.

At the end of the 19th century, it was discovered that some diseases, including rabies and foot-and-mouth disease, were caused by particles similar to bacteria, but much smaller. Since they were biological in nature and were transmitted from one victim to another, causing the same symptoms, viruses began to be considered as tiny living organisms that carry genetic information.

The reduction of viruses to lifeless chemical objects occurred after 1935, when Wendell Stanley first crystallized the tobacco mosaic virus. It was discovered that the crystals consist of complex biochemical components and do not possess the property necessary for biological systems - metabolic activity. In 1946, the scientist received the Nobel Prize for this work in chemistry, and not in physiology or medicine.

Stanley's further research clearly showed that any virus consists of nucleic acid (DNA or RNA) packaged in a protein shell. In addition to protective proteins, some of them have specific viral proteins involved in cell infection. If we judge viruses only by this description, then they really are more similar to chemical substances than to a living organism. But when the virus enters a cell (after which it is called a host cell), the picture changes. It sheds its protein coat and subjugates the entire cellular apparatus, forcing it to synthesize viral DNA or RNA and viral proteins in accordance with the instructions recorded in its genome. Next, the virus self-assembles from these components and a new viral particle appears, ready to infect other cells.

This scheme forced many scientists to take a new look at viruses. They began to be considered as objects located on the border between the living and inanimate worlds. According to virologists M.H.V. van Regenmortel of the University of Strasbourg in France and B.W. Mahy of the Centers for Disease Prevention and Control, this way of living can be called "borrowed living." The following fact is interesting: despite the fact that for a long time biologists viewed the virus as a "protein box" filled with chemical parts, and they used its ability to replicate in a host cell to study the protein coding mechanism. Modern molecular biology owes much of its success to information obtained from the study of viruses.

Scientists have crystallized most cellular components (ribosomes, mitochondria, membrane structures, DNA, proteins) and today view them either as “chemical machines” or as the material that these machines use or produce. This view of the complex chemical structures that ensure the life of a cell is the reason why molecular biologists are not too concerned about the status of viruses. Researchers were interested in them only as agents capable of using cells for their own purposes or serving as a source of infection. The more complex issue concerning the contribution of viruses to evolution remains unimportant for most scientists.

To be or not to be?

What does the word "alive" mean? Most scientists agree that in addition to the ability to reproduce themselves, living organisms must have other properties. For example, the life of any creature is always limited in time - it is born and dies. In addition, living organisms have a certain degree of autonomy in the biochemical sense, i.e. To some extent, they rely on their own metabolic processes, which provide them with substances and energy that support their existence.

A stone, as well as a droplet of liquid in which metabolic processes occur, but which does not contain genetic material and is not capable of self-reproduction, is undoubtedly an inanimate object. A bacterium is a living organism, and although it consists of only one cell, it can generate energy and synthesize substances that ensure its existence and reproduction. What can be said about the seed in this context? Not every seed shows signs of life. However, being at rest, it contains the potential that it received from an undoubtedly living substance and which, under certain conditions, can be realized. At the same time, the seed can be irreversibly destroyed, and then the potential will remain unrealized. In this regard, the virus is more reminiscent of a seed than a living cell: it has certain capabilities that may not come to fruition, but it does not have the ability to exist autonomously.

One can also consider living as a state into which, under certain conditions, a system consisting of non-living components with certain properties passes. Examples of such complex (emergent) systems include life and consciousness. To achieve the appropriate status, they must have a certain level of difficulty. Thus, a neuron (by itself or even as part of a neural network) does not have consciousness; this requires a brain. But an intact brain can be alive in the biological sense and at the same time not provide consciousness. Likewise, neither cellular nor viral genes or proteins themselves serve as living substance, and a cell without a nucleus is similar to a decapitated person in that it does not have a critical level of complexity. The virus is also not capable of reaching this level. So life can be defined as a kind of complex emergent state, including the same fundamental “building blocks” that a virus possesses. If you follow this logic, then viruses, not being living objects in the strict sense of the word, still cannot be classified as inert systems: they are on the border between living and nonliving.

Viruses and evolution

Viruses have their own, very long evolutionary history, going back to the origins of single-celled organisms. Thus, some viral repair systems, which ensure the cutting of incorrect bases from DNA and the elimination of damage caused by oxygen radicals, etc., are found only in individual viruses and exist unchanged for billions of years.

Researchers do not deny that viruses played some role in evolution. But, considering them to be inanimate matter, they put them on a par with factors such as climatic conditions. Such a factor influenced organisms that had changing, genetically determined characteristics from the outside. Organisms that were more resistant to this influence successfully survived, reproduced, and passed on their genes to subsequent generations.

However, in reality the viruses affected the genetic material living organisms not indirectly, but in the most direct way possible - they exchanged their DNA and RNA with him, i.e. were players on the biological field. The big surprise for doctors and evolutionary biologists was that most of the viruses turned out to be completely harmless creatures not associated with any diseases. They quietly sleep inside the host cells or use their apparatus for their leisurely reproduction without any damage to the cell. Such viruses have a lot of tricks that allow them to escape the watchful eye of the cell’s immune system - for each stage of the immune response, they have a gene that controls or modifies this stage in their favor.

Moreover, during the cohabitation of the cell and the virus, the viral genome (DNA or RNA) “colonizes” the genome of the host cell, supplying it with more and more new genes, which ultimately become an integral part of the genome of a given type of organism. Viruses have a faster and more direct effect on living organisms than external factors that select genetic variants. The large number of virus populations, coupled with their high speed replication and high frequency mutations make them the main source of genetic innovation, constantly creating new genes. Some unique gene of viral origin, traveling, passes from one organism to another and contributes to the evolutionary process.

A cell whose nuclear DNA has been destroyed is truly “dead”: it is deprived of genetic material with instructions for activity. But the virus can use the remaining intact cell components and cytoplasm for its replication. It subjugates the cellular apparatus and forces it to use viral genes as a source of instructions for the synthesis of viral proteins and replication of the viral genome. The unique ability of viruses to develop in dead cells is most clearly demonstrated when the hosts are single-celled organisms, primarily those inhabiting the oceans. (The vast majority of viruses live on land. According to experts, there are no more than 1030 viral particles in the World Ocean.)

Bacteria, photosynthetic cyanobacteria and algae, potential hosts of marine viruses, are often killed by ultraviolet radiation, which destroys their DNA. At the same time, some viruses (“residents” of organisms) turn on the mechanism for the synthesis of enzymes that restore damaged molecules of the host cell and bring it back to life. For example, cyanobacteria contain an enzyme that is involved in photosynthesis, and when exposed to excess light, it is sometimes destroyed, leading to cell death. And then viruses called cyanophages “switch on” the synthesis of an analogue of the bacterial photosynthetic enzyme, which is more resistant to UV radiation. If such a virus infects a newly dead cell, a photosynthetic enzyme can bring it back to life. Thus, the virus plays the role of a “gene resuscitator.”

Excessive doses of UV radiation can lead to the death of cyanophages, but sometimes they manage to return to life with the help of multiple repairs. There are usually several viruses present in each host cell, and if they are damaged, they can assemble the viral genome piece by piece. Various parts of the genome a are capable of serving as suppliers of individual genes, which, together with other genes, will restore the functions of the genome a in full without creating a whole virus. Viruses are the only living organisms that, like the Phoenix bird, can be reborn from the ashes.

According to the International Human Genome Sequencing Consortium, between 113 and 223 genes shared between bacteria and humans are missing from well-studied organisms such as the yeast Sacharomyces cerevisiae, the fruit fly Drosophila melanogaster and the roundworm Caenorhabditis elegans, which fall between the two extreme lineages. living organisms. Some scientists believe that yeast, the fruit fly and the roundworm, which appeared after bacteria but before vertebrates, simply lost the corresponding genes at some point in their evolutionary development. Others believe that the genes were transferred to humans by bacteria that entered his body.

Together with colleagues at the University of Oregon Health Sciences Institute for Vaccines and Gene Therapy, we propose that there was a third way: the genes were initially of viral origin, but then colonized members of two different lineages of organisms, such as bacteria and vertebrates. The gene that the bacterium endowed humanity with could have been transmitted to the two lineages mentioned by the virus.

Moreover, we are confident that the cell nucleus itself is of viral origin. The appearance of the nucleus (a structure found only in eukaryotes, including humans, and absent in prokaryotes, such as bacteria) cannot be explained by the gradual adaptation of prokaryotic organisms to changing conditions. It could have been formed on the basis of pre-existing high-molecular-weight viral DNA, which had built a permanent “home” for itself inside the prokaryotic cell. This is confirmed by the fact that the DNA polymerase gene (an enzyme involved in DNA replication) of phage T4 (phages are viruses that infect bacteria) is close in its nucleotide sequence to the DNA polymerase genes of both eukaryotes and the viruses that infect them. In addition, Patrick Forterre from the University of Paris South, who studied the enzymes involved in DNA replication, came to the conclusion that the genes that determine their synthesis in eukaryotes are of viral origin.

Blue tongue virus

Viruses affect absolutely all forms of life on Earth, and often determine their fate. At the same time, they also evolve. Direct evidence comes from the emergence of new viruses, such as the human immunodeficiency virus (HIV), which causes AIDS.

Viruses constantly modify the boundary between the biological and biochemical worlds. The further we progress in the study of the genomes of various organisms, the more evidence we will discover of the presence of genes from a dynamic, very ancient pool. Nobel Prize winner Salvador Luria spoke about the influence of viruses on evolution in 1969: “Perhaps viruses, with their ability to enter and leave the cellular genome, were active participants in the process of optimizing the genetic material of all living things during evolution. Simply We didn't notice it." Regardless of which world - living or inanimate - we attribute viruses to, the time has come to consider them not in isolation, but taking into account their constant connection with living organisms.

ABOUT THE AUTHOR:
Luis Villarreal(Luis P. Villarreal) - Director of the Center for the Study of Viruses at the University of California, Irvine. He received his PhD in biology from the University of California, San Diego, then worked at Stanford University in the laboratory of Nobel laureate Paul Berg. He is actively involved in teaching activities and is currently involved in the development of programs to combat the threat of bioterrorism.

Humanity became acquainted with viruses at the end of the 19th century, after the work of Dmitry Ivanovsky and Martin Beyerinck. Studying non-bacterial lesions of tobacco plants, scientists for the first time analyzed and described 5 thousand types of viruses. Today it is assumed that there are millions of them and they live everywhere.

Alive or not?

Viruses consist of DNA and RNA molecules that transmit genetic information in various combinations, an envelope that protects the molecule, and additional lipid protection.

The presence of genes and the ability to reproduce allows viruses to be considered living, while the lack of protein synthesis and the impossibility of independent development classifies them as non-living biological organisms.

Viruses are also capable of forming alliances with bacteria and. They can transmit information through RNA exchange and evade the immune response, ignoring drugs and vaccines. The question of whether the virus is alive remains open to this day.

The most dangerous enemy

Today, a virus that does not respond to antibiotics is man’s most terrible enemy. The discovery of antiviral drugs has eased the situation a little, but AIDS and hepatitis have not yet been defeated.

Vaccines provide protection only against some seasonal strains of viruses, but their ability to mutate quickly makes vaccinations ineffective the next year. The most serious threat to the Earth's population may be the inability to cope with the next viral epidemic in time.

Flu is only a small part of the viral iceberg. The Ebola virus infection spreading across Africa has led to the introduction of quarantine measures around the world. Unfortunately, the disease is extremely difficult to treat, and the mortality rate is still high.

A special feature of viruses is their incredibly fast ability to reproduce. The bacteriophage virus is capable of reproducing bacterium 100 thousand times faster. Therefore, virologist scientists from all over the world are trying to save humanity from a deadly threat.

Basic preventive measures viral infections are: vaccinations, compliance with personal hygiene rules and timely consultation with a doctor in case of infection. One of the symptoms was high temperature, which is impossible to shoot down on your own.

There is no need to panic if you have a viral disease, but caution can literally save your life. Doctors say that infections will continue to mutate so long that human civilization will exist, and scientists still have to make many important discoveries in the origin and behavior of viruses, as well as in the fight against them.

Cynthia Goldsmith This colorized transmission electron micrograph (TEM) revealed some of the ultrastructural morphology displayed by an Ebola virus virion. See PHIL 1832 for a black and white version of this image. Where is Ebola virus found in nature?

The exact origin, locations, and natural habitat (known as the “natural reservoir”) of Ebola virus remain unknown. However, on the basis of available evidence and the nature of similar viruses, researchers believe that the virus is zoonotic (animal-borne) and is normally maintained in an animal host that is native to the African continent. A similar host is probably associated with Ebola-Reston which was isolated from infected cynomolgous monkeys that were imported to the United States and Italy from the Philippines. The virus is not known to be native to other continents, such as North America.

They fall under the definition of life: they are somewhere in the middle between supermolecular complexes and very simple biological organisms. Viruses contain some structures and exhibit certain activities that are common to organic life, but they lack many other characteristics. They consist entirely of a single strand of genetic information enclosed in a protein shell. Viruses lack much of the internal structure and processes that characterize "life", including the biosynthetic process required to reproduce. In order to (replicate), a virus must infect a suitable host cell.

When researchers first discovered viruses that behaved like , but were much smaller and caused diseases such as rabies and foot-and-mouth disease, it became common knowledge that viruses were biologically “alive.” However, this perception changed in 1935 when the tobacco mosaic virus was crystallized and showed that the particles lacked the machinery necessary for metabolic function. Once it was established that viruses consisted only of DNA or RNA surrounded by a protein shell, the scientific view became that they were more complex biochemical machines than living organisms.

Viruses exist in two different states. When it is not in contact with a host cell, the virus remains completely dormant. At this time, there is no internal biological activity within the virus, and essentially the virus is nothing more than a static organic particle. In this simple, apparently non-living state, viruses are called "virions". Virions can remain in this dormant state for extended periods of time, patiently awaiting contact with an appropriate host. When a virion comes into contact with its corresponding host, it becomes an active virus. From this point on, the virus displays properties typical of living organisms, such as responding to the environment and directing efforts towards self-replication.

What defines life?

There is no clear definition of what separates the living from the nonliving. One definition might be the point at which a subject has self-awareness. In this sense, severe head injury may be classified as brain death. The body and brain may still be functioning at a basic level, and there is noticeable metabolic activity in all the cells that make up the larger organism, but the assumption is that there is no self-awareness and therefore the brain is dead. At the other end of the spectrum, the criterion for defining life is the ability to pass on genetic material to future generations, thereby restoring one's likeness. In the second, more simplified definition, viruses are undoubtedly alive. They are undoubtedly the most efficient on Earth at disseminating their genetic information.

While the jury is still out on whether viruses can be considered living things, their ability to pass on genetic information to future generations makes them major players in evolution.

Virus dominance

Organization and complexity have slowly increased since macromolecules began to assemble in the primordial soup of life. One must think about the existence of an inexplicable principle, directly opposite to the second, which leads evolution to a higher organization. Not only were viruses extremely efficient at spreading their own genetic material, but they were also responsible for the untold movement and mixing of genetic code between other organisms. Variation in the genetic code may be the driving force. Through the expression of variables, organisms are able to adapt and become more efficient in changing environmental conditions.

Final Thought

Perhaps the relevant question is not whether viruses are alive, but rather what their role is in the movement and formation of life on Earth as we perceive it today?

When asked what phenomena characterize life, biologists answer that each living organism has a specific shape and size, external and internal organization, with which the specialization of individual organs is associated; A living organism is characterized by movement, a reaction to external stimuli, growth, the metabolic process and, finally, such an important feature of living organisms as the ability to reproduce. Reproduction is also associated with the possibility of hereditary changes.

However, some of the listed criteria for life can also be found in inanimate nature. We will find in it a certain degree of organization, and movement, and a reaction to irritation, and growth. Table salt crystals have external and internal organizations; the chemical reactions occurring in them are a kind of manifestation of a reaction to irritation, that is, sensitivity; crystals and glaciers grow; all bodies are actually in motion. Even if such movement does not manifest itself clearly, molecules and atoms are constantly moving.

However, non-living things cannot reproduce, therefore they do not have hereditary changes. Thus, living things differ from non-living things primarily in that they can reproduce and change from generation to generation.

Let's look at viruses from this point of view and try to figure out whether they are living or non-living creatures. To a chemist, they resemble large molecules capable of crystallization. They also have features common to living organisms - they can reproduce (but only inside living cells) and, as proven in lately, be subject to hereditary changes. This duality, this combination of properties of both being and substance, was emphasized by T. Rivers when he called them “organules” or “molecisms” (a combination of words: organism and molecule).

So where should viruses be classified as living or non-living entities? Stanley answered this question this way:

“Whether they are living or non-living - one can argue about this ad infinitum, without receiving, in essence, a satisfactory answer to the question posed. In one respect, viruses are similar to living organisms, in another they are similar to ordinary chemical molecules, but they differ from both the former and the latter. Their dual nature and relatively primitive structure, which we are already able to study in some detail, give us the opportunity to see in them, on the one hand, living beings, and on the other, chemical molecules capable of reproduction. Thus, we are getting closer to understanding the chemical essence of the reproduction process that occurs in all other living organisms. In addition, the study of viruses opens up a new perspective for us, since we see not two supposedly sharply separated groups, but only their increasing complexity. From the point of view of structure, we have the opportunity to trace the entire series of closely interconnected objects: from the atom through a simple molecule, macromolecule, virus, bacterium and further through fish and mammals up to humans. From a functional point of view, we can observe the process of using energy from the random movement of various molecules to the ideal harmony of the finest biological rhythms.”