Prove that viruses are living organisms. Viruses

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.

Answer

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

Answer

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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

Answer

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

Answer

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

Answer

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

Viruses are contagious, tiny, and pretty nasty. But are they alive?

Not really, although it depends on what you mean by "live". Living things such as plants and animals contain cellular machinery that allows them to reproduce themselves. Viruses are free forms of DNA or RNA that cannot reproduce on their own.

"It is likely that viruses must invade a living organism to be able to reproduce," said Dr. Otto Young, professor of medicine and microbiology, immunology and molecular genetics at the University of California, Los Angeles School of Medicine.

Viruses are made of RNA or DNA. They simply copy themselves, hijacking the cells' machinery for their own replication.

Characteristics of life

Countless philosophers and scientists have discussed how to determine whether an object is alive. According to the accepted characterization of life, all living things must be able to respond to stimuli, grow over time, produce offspring, maintain a stable body temperature, metabolize energy, be composed of one or more elementary cells, and adapt to their environment.

However, there is a life form that does not fit each of these characteristics. Most hybrid animals, such as mules (crossbreeds between donkeys and horses), cannot reproduce because they are sterile. Additionally, stones can grow, albeit in a passive way, with new material flowing through them. But this problem of classification goes away when a simpler definition of life is used.

Simple definitions of life

“Take a cat, a plant and a rock and leave them in a room for a few days,” said Amesh Adalja, a physician and researcher at the Johns Hopkins Center for Health Security in Baltimore. “When you return, the cat and the plant will have changed, but the rock will have changed.” will essentially remain the same."

Like stone, most viruses will remain unchanged if left indefinitely in a room. In addition, the scientist noted that living beings are distinguished by self-generated and self-sufficient actions. This means they can look for a livelihood and behave in a way that keeps them safe. In other words, they take the measures necessary to maintain further life. For example, a plant uses its roots to find water, and an animal can go in search of food.

Unlike plants or animals, viruses are not capable of self-generating or self-sufficient actions.

Inert objects

Dr. Adalja believes that viruses cannot be classified as living organisms. They are essentially inert unless they come into contact with a living cell. There are some characteristics of viruses that define their place on the border with living things: they have genetic material - DNA or RNA. Thus, viruses cannot be called non-living, like, for example, a stone, but at the same time, scientists cannot classify them as living beings. In fact, they can't even reach bacteria levels.

It all depends on your point of view

Dr. Yang agrees with these findings. He says that without a cell, the virus cannot reproduce. From this point of view, viruses are truly non-living, if you consider that the main characteristic of life is its ability to reproduce itself independently of other conditions.

However, if your definition of life depends on whether an object can make copies of itself with the help of others, then viruses can definitely be called living.

It is believed that the very first forms of life on Earth were RNA-like molecules. Given the right conditions, they could make copies of themselves. Viruses may have evolved from this ancestor, but have lost the ability to reproduce themselves.

Arguments for being alive:

• The molecular organization is the same as that of a cell of a living organism: NK, proteins, membranes. From a molecular point of view = this is a normal way of life. Nucleotide sequences similar to the nucleotide sequences of viruses are found inside living objects.
• Viruses have almost all the properties of living things except development.

Arguments for the fact that they are not alive:

• They do not have a cellular structure
• If you put a virus under a microscope and watch it, nothing happens. In order for it to “start living”, it must be introduced into the cell. BUT! The cell is the environment of the virus. If you place a living organism in a vacuum, it will die. The virus is exactly the same; for it the air environment is a vacuum. A dry seed of a plant can lie for thousands of years without showing the properties of a living thing, until it falls into water, a frog frozen in ice, a flake dried in a cocoon, all can be revived by placing them in a suitable environment, just like a virus.

A sign of a living thing is a high degree of self-order. Matrix synthesis is the highest degree of order, therefore viruses are alive. However, the most simply structured viruses are DNA molecules; if viruses are living, then DNA is living.

The main meaning of life is the continuation of life! Life continuation is the reproduction of genetic information. This scheme fits well with the fact that DNA is living. Some transposons are capable of reproducing according to the principle of DNA replication (DNA - transcription). The meaning of the existence of a transposon in general is the reproduction of individual sections of genetic information, each section on its own. All this led to the emergence of Selfish DNA - selfish DNA. DNA is capable of intensive reproduction; DNA, in the course of evolution, has developed such an environment to exist - CELL.

Result: if we accept that viruses are living, then the cellular theory of living things is rejected; if viruses are alive, then DNA is alive; increasingly complex structures (except DNA) have only one purpose - to facilitate the reproduction of DNA. During evolution, a cell is created and the DNA “realizes” that this is good. Then it would be nice to divide it into compartments - eukaryotes arose. It would be nice to recombine - sexual reproduction. Then multicellular creatures. DNA habitats adapted to the environment, since the relationship with the environment is very complex, then intelligence arose. Consequently, a person lives only to reproduce his own genetic information.

Nominated in 60 years. Some viruses are able to infect a cell in the form of naked DNA, therefore the basis of life is DNA, therefore DNA is living. Arguments for this concept:

1. Existence of viruses
2. In the cells of various living organisms there are nucleotide sequences that are not intended for anything other than their reproduction - transposons; they contain genetic information that is responsible for the movement of the transposon. There are 2 types of transposons:

• Class 1 transposons, retrotransposons. Retrotransposons – mobile genetic elements. They can easily change the sequence of genetic information. They move throughout the genome by reverse transcription from their RNA. They migrate, with the original copy remaining in place and the other being integrated elsewhere. The internal region is very similar to the genetic material of retroviruses, but without the capsid protein coding region. Retroviruses - using the reverse transcription method (DNA from RNA). First there were retroviruses. They were in cells and eventually lost their capsid, becoming transposons. Another point of view is that first there were transposons. But over time, for some reason, a capsid appeared that allowed transposons to exit the cell in the form of retroviruses.

• DNA transposons, cut by proteins and transferred to another location, have only the function of self-propagation.

1. DNA is a living object that builds a suitable environment around itself - a cell. DNA tracks the processes of DNA reproduction without the organism reproducing, such as sterile ants.
2. What matters is how efficiently the DNA is reproduced; the fate of the organism is not important.
3. Weisman's concept: in the body of a higher animal two types of structures can be distinguished:

• The germinal tract is more valuable, from embryonic cells to reproductive cells
• Soma - all other cells, you can do anything with genetic information

In the roundworm, the soma cell releases many DNA fragments - DNA diminution.

Information is the heterogeneity of space, created specifically. Viruses have genetic information that is structured in the same way as other living beings.

In viruses

Developmental biology

Deterministic crushing – crushing, which begins to be visible very early. The most striking example: nematodes. They can count down to the cells how many there are in each segment (the nuclei are counted).

Caenorhabditis ebgans (nematode). In an adult, the number of somatic nuclei is 959. If there is one less or more, it is a developmental mutant. Each cell has a determined fate. Some cells formed from the first ones must die. This phenomenon is called apoptosis. In humans, apoptosis manifests itself as the division of the hand (scapula in the early stages) into fingers. Some cells die, allowing fingers to form.

In mammals, determination is much weaker, there are stem cells, but, having received specialization, they can no longer go back, this is called terminal differentiation.

Ecology

Ecology studies the relationship of living organisms with the environment. Any trophic relationship consists of elementary parts. The central link of any ecological relationship is a variety of biological responses - this is a system of adequate reactions of the body to a certain external or internal signal.

Biology – life science. It is not known who first introduced this term into science. It is believed that this concept was introduced independently of each other by two scientists (one of them was Lamarck). This concept was used before Lamarck, for example, by Linnaeus, but most likely with a different meaning.

Each science can be divided into smaller ones (highly specialized). At the intersection of rows and columns we get real-life science.

There are sciences that do not fit into this method of classification. Sciences that arose on the border of natural sciences.

To some extent, these sciences are synthetic.

Sciences that study all diversity at once, using the methods of all sciences: molecular biology, evolutionary science, systematics - a description of the existing and existing diversity of species and their distribution in the system depending on their phylogeny. The doctrine of evolution, systematics, is a synthetic science.

Sometimes viruses that infect animals and insects come to the aid of humans. More than twenty years ago in Australia, the problem of fighting wild rabbits became acute. The number of these rodents has reached alarming proportions. They destroyed crops faster than locusts and became a real national disaster. Conventional methods of dealing with them turned out to be ineffective. And then scientists released a special virus to fight rabbits, capable of destroying almost all infected animals. But how to spread this disease among shy and cautious rabbits? The mosquitoes helped. They played the role of "flying needles", spreading the virus from rabbit to rabbit. At the same time, the mosquitoes remained completely healthy.

There are other examples of the successful use of viruses to kill pests. Everyone knows the damage caused by caterpillars and sawflies. The former eat the leaves of useful plants, the latter infect trees in gardens and forests. They are fought by the so-called polyhedrosis and granulosis viruses, which are sprayed in small areas, and airplanes are used to treat large areas. This was done in the USA when fighting caterpillars that infect alfalfa fields, and in Canada when destroying the pine sawfly.

What happens to a cell if it is infected with not one, but two viruses? If you decided that in this case the cell’s disease would worsen and its death would accelerate, then you were mistaken. It turns out that the presence of one virus in a cell often reliably protects it from the destructive effects of another. This phenomenon was called virus interference by scientists. It is associated with the production of a special protein - interferon, which in cells activates a protective mechanism that can distinguish viral from non-viral and selectively suppress viral. Interferon suppresses the reproduction of most viruses in cells. Interferon, produced as a therapeutic drug, is now used for the treatment and prevention of many viral diseases.

V SOME OF THE MOST KNOWN HUMAN VIRAL DISEASES

Influenza remains the “king” of epidemics. No disease can reach hundreds of millions of people in a short time, and more than a billion people get sick with the flu during a pandemic! This was the case not only during the memorable pandemic of 1918, but relatively recently - in 1957, when the “Asian” flu pandemic broke out, and in 1968, when the “Hong Kong” flu appeared. Several varieties of influenza virus are known - A, B, C, etc. Under the influence of environmental factors, their number may increase. Due to the fact that immunity to influenza is short-term and specific, repeated illness is possible in one season. According to statistics, an average of 20-35% of the population suffers from influenza every year.

Smallpox is one of the oldest diseases. A description of smallpox was found in the Egyptian papyrus of Amenophis I, compiled 4000 BC. Smallpox lesions were preserved on the skin of a mummy buried in Egypt 3000 BC. The mention of smallpox, which the Chinese called “poison from the mother’s breast,” is contained in the oldest Chinese source - the treatise “Cheu-Cheufa” (1120 BC). The first classical description of smallpox was given by the Arab physician Rhazes.

AIDS is a new infectious disease that experts recognize as the first truly global epidemic in known human history. Neither the plague, nor smallpox, nor cholera are precedents, since AIDS is decidedly unlike any of these and other known human diseases.

VI ARE VIRUSES LIVE?

Two points of view are considered:

• if we consider a living structure containing nucleic acids and capable of reproducing itself, then we can accept the point of view that viruses are living;
• If we assume that only a structure that has a cellular structure is alive, then viruses are a nonliving form of matter (polymers).

A. Lehninger in “Biochemistry” considers viruses as structures standing on the threshold of life and representing stable supramolecular complexes containing a nucleic acid molecule and a large number of protein subunits, arranged in a certain order and forming a specific three-dimensional structure. Among the most important properties of viruses, he notes:

• inability to self-reproduce in the form of pure drugs;
• the ability to control its replication (infected cell);
• wide variations of viruses in size, shape and chemical composition.

Viruses are located on the very border between living and non-living. This indicates the existence of a continuous spectrum of increasingly complex organic world, which begins with simple molecules and ends with the most complex systems of cells.

A stone, as well as a drop 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 produce 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.

Neither cellular nor viral genes or proteins themselves serve as living substance, and a cell without a nucleus is similar to a decapitated person, since 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 we 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.

VII FOREVER LIVING

Viruses that occupy an intermediate position between living and nonliving exhibit unexpected properties. Here's one of them. Typically, viruses replicate only in living cells, but they can also grow in dead cells, and sometimes even bring the latter back to life. Surprisingly, some viruses, being destroyed, can be reborn to a “borrowed life.”

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.

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 can serve as suppliers of individual genes, which, together with other genes, will restore the functions of the genome in full without creating a whole virus. Viruses are the only living organisms that can, like the Phoenix, be reborn from the ashes.

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 initially had viral origins, 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 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” inside the prokaryotic cell. This is confirmed by the fact that the DNA polymerase gene 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 Fortere 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.

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 find 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.

CONCLUSION

The fight against viral infections is associated with numerous difficulties, among which the immunity of viruses to antibiotics should be especially noted. Viruses are actively mutating, and new strains regularly appear, against which “weapons” have not yet been found. First of all, this applies to RNA viruses, whose genome is usually larger and, therefore, less stable. To date, the fight against many viral infections is developing in favor of humans, mainly due to universal vaccination of the population for preventive purposes. Such events ultimately led to the fact that, according to experts, the smallpox virus has now disappeared from nature. As a result of universal vaccination in our country, in 1961. Epidemic polio was eradicated. However, nature still tests humans, from time to time, presenting surprises in the form of new viruses that cause terrible diseases. The most striking example is the human immunodeficiency virus, the fight against which humans are still losing. Its spread is already consistent with the pandemic.

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?