Every living organism except viruses consists of... Is a virus a living or non-living creature? Additional literature for studying this topic
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.
The main measures to prevent viral infections are: vaccinations, compliance with personal hygiene rules and timely consultation with a doctor in case of infection. One of the symptoms was a high temperature, which cannot be brought 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.
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 observe 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 scaly plant dried in a cocoon, all of them 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 alive. 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 the 60s. 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:
- Existence of viruses
- 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.
- 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.
- What matters is how efficiently the DNA is reproduced; the fate of the organism is not important.
- 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
| No | Eat | No |
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.
According to Lvov, “an organism is a kind of independent unit of integrated and interconnected structures and functions.” In protozoa, that is, in single-celled organisms, it is the cell that is an independent unit, in other words, an organism. And cellular organisms - mitochondria, chromosomes and chloroplasts - are not organisms, because they are not independent. It turns out that if we follow the definition given by Lvov, viruses are not organisms, since they do not have independence: a living cell is needed to grow and replicate genetic material.
At the same time, in multicellular species, whether animals or plants, individual cell lines cannot evolve independently of each other; therefore, their cells are not organisms. For a change to be evolutionarily significant, it must be passed on to a new generation of individuals. In accordance with this reasoning, an organism is an elementary unit of some continuous series with its own individual evolutionary history
And at the same time, we can look at this problem from the point of view of another definition: a material is alive if, being isolated, it retains its specific configuration in such a way that this configuration can be reintegrated, that is, again included in the cycle in which the genetic substance participates : This identifies life with the presence of an independent, specific, self-replicating mode of organization. The specific sequence of nucleic acid bases of a particular gene can be copied; A gene is a certain part of the information reserves that a living organism has. As a test for living, the above definition suggests reproduction in different cell lines and in a number of generations of organisms. The virus, according to this test, is alive in the same way as any other piece of genetic material, that it can be removed from a cell, reintroduced into a living cell and that in doing so it will be copied in it and become, at least for a while, part of its hereditary apparatus. Moreover, the transmission of the viral genome is the main reason for the existence of these forms - the result of their specialization in the selection process. Therefore, the specialization of viruses as carriers of nucleic acids makes it possible to consider viruses “more alive” than any fragments of genetic material, and “more organisms” than any cellular organelles, including chromosomes and genes.
Koch's strict postulates
What are the basic principles formulated by Robert Koch (1843-1910) that a microbiologist must adhere to whenever an unknown pathogen is discovered? What can serve as evidence that it is the cause of this infectious disease? These are the three criteria:
Repeatedly obtaining a pure culture of the pathogen taken from the patient’s body.
The occurrence of exactly the same or similar disease (both in the nature of the course and in the pathological changes it causes) when a healthy organism is infected with a culture of the suspected pathogen.
The appearance in the body of a person or animal after infection with this pathogen is always the same specific protective substances. When immune serum comes into contact with a pathogen from a culture, the latter should lose its pathogenic properties.
Modern virology is characterized by the rapid development and widespread use of a variety of techniques - both biological (including genetic) and physicochemical. They are used in identifying new, hitherto unknown viruses, and in studying biological properties and structures of already discovered species.
Fundamental theoretical research usually provides important information that is used in medicine, in the field of diagnostics, or in an in-depth analysis of viral infection processes. The introduction of new effective methods of virology is usually associated with outstanding discoveries.
For example, the method of growing viruses in the developing chicken embryo, first used by A. M. Woodroffe and E. J. Goodpasture in 1931, was used with exceptional success in the study of the influenza virus.
The progress of physicochemical methods, in particular the centrifugation method, led in 1935 to the possibility of crystallization of the tobacco mosaic virus (TMV) from the juice of diseased plants, and subsequently to the identification of its constituent proteins. This gave the first impetus to the study of the structure and biochemistry of viruses.
In 1939, A. V. Arden and G. Ruska first used an electron microscope to study viruses. The introduction of this device into practice meant a historical turning point in virological research, since it became possible to see - although in those years it was still not clear enough - individual particles of the virus, virions.
In 1941, G. Hirst established that the influenza virus, under certain conditions, causes agglutination (sticking together and precipitation) of red blood cells (erythrocytes). This laid the basis for studying the relationship between the surface structures of the virus and red blood cells, as well as for the development of one of the most effective methods diagnostics
A turning point in virological research occurred in 1949, when J. Enders, T. Weller and F. Robbins managed to multiply the polio virus in the skin and muscle cells of a human embryo. They achieved the growth of pieces of tissue on an artificial nutrient medium. Cell (tissue) cultures were infected with the polio virus, which had previously been studied exclusively in monkeys and only very rarely in a special type of rat.
The virus multiplied well in human cells grown outside the mother's body and caused characteristic pathological changes. The cell culture method (long-term preservation and cultivation of cells isolated from the human and animal body in artificial nutrient media) was subsequently improved and simplified by many researchers and finally became one of the most important and effective for cultivating viruses. Thanks to this more accessible and cheaper method, it became possible to obtain viruses in a relatively pure form, which could not be achieved in suspensions from the organs of dead animals. The introduction of a new method meant undoubted progress not only in diagnosis viral diseases, but also in receiving vaccinations. It also gave good results in biological and biochemical studies of viruses.
In 1956, it was possible to show that the carrier of the infectivity of the virus is the nucleic acid it contains. And in 1957, A. Isaacs and J. Lindeman discovered interferon, which made it possible to explain many biological phenomena observed in the relationship between a virus and a host cell or host organism.
S. Brenner and D. Horn introduced the method of negative contrast staining into electron microscopy, which made it possible to study the fine structure of viruses, in particular their structural elements (subunits).
In 1964, the American virologist Gajduzek, already mentioned earlier, and his colleagues proved the infectious nature of a number of chronic diseases of the central nervous system of humans and animals. He studied recently discovered peculiar viruses, only in some features similar to previously known ones.
At the same time, the American geneticist Baruch Blumberg discovers (through genetic studies of blood proteins) serum hepatitis antigen (Australian antigen), a substance identified by serological tests. This antigen was destined to play a major role in virological studies of hepatitis.
In recent years, one of the greatest successes of virology can be considered the discovery of some molecular biological mechanisms of the transformation of normal cells into tumor cells. No less success has been achieved in the field of studying the structure of viruses and their genetics.
Infectious unit
The smallest amount of virus capable of causing infection in a given experiment is called an infectious unit.
To determine it, two methods are usually used. The first is based on determining the 50% lethal dose, which is designated LD 50 (from the Latin Letatis - lethal, dosis - dose). The second method determines the number of infectious units by the number of plaques formed in the cell culture.
What exactly is the LD 50 value and how is it determined? The viral material being studied is diluted in accordance with decreasing degrees of concentration, say multiples of ten: 1:10; 1:100; 1:1000, etc. Each of the solutions with the indicated concentrations of the virus infects a group of animals (ten individuals) or a cell culture in test tubes. Then they observe the death of animals or changes that have occurred in the culture under the influence of the virus. A statistical method is used to determine the degree of concentration capable of killing 50% of the animals infected with the source material. When using a cell culture, one must find a dose of the virus that produces a destructive effect on 50% of the cultures infected with it. In this case, the abbreviation CPP 50 (cytopathic dose) is used. In other words, we're talking about about such a dose of the virus that causes damage or death of half of the crops infected with it.
Lesson for distance learning.
Teacher Nikandrova N.N.
School No. 576 of Vasileostrovsky district.
Topic: V I R U S S.
VIRUSES ------ WHAT or WHO is this?
LIVING or NON-LIVING?
Let's try to figure this out together.
Target: To develop knowledge about viruses: about the structural features and vital functions, to note diseases caused by viruses, to inform about the danger of infection with the AIDS virus.
You must know:
History of the discovery of viruses
Virus structure
Features of the life of viruses
Negative effects of viruses on living organisms: diseases caused by viruses.
What is a bacteriophage?
1. A little history
Oh, these diseases: flu, measles, hepatitis, smallpox. What unknown microorganisms cause these diseases? How to stop them? This question has faced scientists since ancient times.
that is not even visible in a microscope at its best
high magnification. It's either the smallest
bacteria or toxic substances that
they excrete. But it turned out to be not a bacterium.
Later, scientists were able to establish that
chemical structure they are nucleoproteins
(nucleic acids and proteins).
We managed to see viruses in electronic
microscope 50 years after their discovery.
And it was the tobacco mosaic virus that was the plant infected with the tobacco virus
photographed first. And he gave the mosaic its name.
"VIRUS" - poison - Louis Pasteur.
2. Structure of the virus
Now let’s be a little scientist and try to describe the structure of the virus.Describe the structure of the tobacco mosaic virus.
Groups of viruses by structure
simple complex
consist of nucleic acid - consist of nucleic acid -
DNA or RNA and protein shell DNA or RNA, protein shell,
(capsid) may contain lipoprotein
(tobacco mosaic virus) membrane, carbohydrates and enzymes
(flu virus, herpes)
Viruses include double-stranded DNA and single-stranded RNA; there are single-stranded DNA and double-stranded RNA. The capsid protects the genetic material of the virus from the action of enzymes and ultraviolet radiation.
3. Features of the life of viruses
Work with text. Read the text and fill out the table.
Viruses can only reproduce in the cells of other organisms.
Having penetrated the cell, the virus changes its metabolism, directing all its activity to the production of viral nucleic acid and viral proteins. Inside the cell, self-assembly of viral particles from synthesized nucleic acid molecules and proteins occurs. Before death, a huge number of viral particles manage to be synthesized in the cell. Ultimately, the cell dies, its shell bursts and the viruses leave the host cell.
Comparison of viruses with living and nonliving nature
Diseases of humans, animals and plants caused by viruses.
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Human diseases |
Animal diseases |
Plant diseases |
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Equine infectious anemia Swine and bird plague |
1. Mosaic disease of tobacco, cucumbers, tomatoes, dwarfism, leaf curl, jaundice. |
In recent years, the HIV virus has been discovered - the human immunodeficiency virus, which causes the disease AIDS - acquired immunodeficiency syndrome.
This disease causes damage to the cellular immune system.
The virus that causes AIDS contains 2 RNA molecules. It specifically binds to blood cells, affecting T-lymphocytes. As a result, their functional activity decreases.
5. Bacteriophages.
Viruses are known that inhabit bacterial cells. They are called BACTERIOPHAGES. Bacteriophages completely destroy bacterial cells.
Therefore, they are used to treat bacterial diseases such as dysentery, typhoid fever, and cholera.
The structure of a bacteriophage that has settled into an Escherichia coli cell.
CLOSURE AND LEARNED
1. Compare viruses with a cell and answer the question: What is the difference between a virus and a cell?
2. Choose the correct answer:
1. Viruses are called:
1. eukaryotes
2. noncellular forms life
3. prokaryotes.
4. tiny bacteria
2. Viruses reproduce:
1. independently
2. only in a bacterial cell
3. in the host cell
4. do not reproduce at all
3. The structure of viruses necessarily includes
1. DNA, RNA
4. carbohydrates
4. A bacteriophage is called:
1. A certain type of virus
2. A certain type of bacteria
3. Viruses that have settled in a bacterial cell
4. Bacteria that has settled in the capsid of the virus
5. Disease caused by a virus
1. Hepatitis
3. Dysentery
4. Scoliosis
3. Fill in the missing words: Viruses are considered_________________ forms of life.
They don't consume _______________, they don't produce ________________________________, they don't grow, they don't have _____________________________________. A virus that has settled into a bacterial cell is called _____________________________________.
Additional literature for studying this topic.
A.A. Kamensky, E.A. Kriksunov, V.V. Beekeeper “General Biology” 10-11 grades p. 20 p. 78.
A.O. Ruvinsky “General Biology” for students in grades 10-11. P18, p. 106-112.
Yu.I. Polyansky “General biology” grades 10-11. P. 36.s 144.
D.K. Belyaev. General biology grades 10-11. P.18.p.67.
A.A. Kamensky, E, A. Kriksunov, V.V.Pasechnik “BIOLOGY. Introduction to general
Biology and ecology” pp. 37-39.
Explanatory note.
The lesson on the topic “Viruses” is designed for both 9th grade students and
11th grade students taking into account independent study. Material
study reflects the most basic points of discovery, structure,
vital activity, reproduction of viruses,
the structure of the bacteriophage, diseases transmitted by viruses are listed.
The information is presented in simple language accessible to students.
Information material intersects with a proposal to fulfill certain
other tasks, and at the end of the material, test your knowledge of the topic studied.
To consolidate the material, tasks of different forms are proposed: question with
free answer, questions in the form of a test and biological dictation.
Materials for preparing students for the Unified State Exam
Subject:viruses
1. Part A tasks
1) virus 2) bacteria 3) fungal cell 4) cell organelle
1) bacteriophages 2) chemotrophs 3) autotrophs 4) cyanobacteria
1) blue-green 2) viruses 3) bacteria 4) protozoa
1) viruses 2) bacteria 3) lichens 4) fungi
1) viruses 2) bacteria 3) lichens 4) fungi
4) its DNA is integrated into the DNA of the host cell and synthesizes its own protein molecules
1) influenza 2) rabies 3) polio 4) smallpox
4) do not produce energy
Answers to assignment part A.
1. Part A tasks , with a choice of one correct answer.
1. What object is shown in the picture?
1) virus 2) bacteria 3) fungal cell 4) cell organelle
2. The integration of its nucleic acid into the DNA of the host cell is carried out
1) bacteriophages 2) chemotrophs 3) autotrophs 4) cyanobacteria
3. They do not have a cellular structure
1) blue-green 2) viruses 3) bacteria 4) protozoa
4. What forms of life occupy an intermediate position between living and inanimate bodies?
1) viruses
5. Once in the cell of a living organism, the virus changes its metabolism, so it is classified as
6. They function only in the cell of another organism, use its amino acids, nucleotides, enzymes and energy for the synthesis of nucleic acids and proteins –
1) viruses 2) bacteria 3) lichens 4) fungi
7. The virus disrupts the functioning of the host cell because
1) destroys the cell membrane
2) the cell loses its ability to reduplicate
3) destroys mitochondria in the host cell
4) its DNA is integrated into the DNA of the host cell and synthesizes its own protein molecules
8. DNA-containing viruses include the pathogen
1) influenza 2) rabies 3) polio 4) smallpox
9. The science that studies non-cellular life forms.
10. Viruses are similar to non-living structures in that:
1) capable of reproducing 2) capable of developing
3) have heredity and variability
4) do not produce energy
Part B tasks.
.
1. Viruses are life forms that:
consist of individual viral particles - virions.
can cause diseases in plants, animals and humans.
have a nucleus and organelles
1. Unable to grow
2. Capable of reproducing in the host cell
4. They have heredity and variability
5. Unable to grow
6. Synthesize their proteins.
B) synthesis of viral proteins
into an organism cell 2. Viruses
B) integrate their DNA into the DNA of the host cell
B) are prokaryotes
D) have ribosomes
Answers to tasks in part B.
Multiple Choice Questions .
Viruses are life forms that:
can function both outside the cell and once inside the host cell.
consist of individual viral particles - virions.
can cause diseases in plants, animals and humans.
have a nucleus and organelles
cause the disease dysentery.
2. Viruses are similar to living organisms in that:
1. Unable to grow
2. Capable of reproducing in the host cell
3. Form a crystalline form of existence
4. They have heredity and variability
5. Unable to grow
6. Synthesize their proteins.
Establish the sequence of the virus life cycle in the host cell.
A) attachment of the virus with its processes to the cell membrane.
B) penetration of viral DNA into the cell
B) synthesis of viral proteins
D) integration of viral DNA into the DNA of the host cell
D) formation of new viruses
Compliance task
Establish a correspondence between the structure and function of life forms and their representatives
Structure and functions of life forms life forms
A) can function only by entering 1. Bacteria
into an organism cell 2. Viruses
B) integrate their DNA into the DNA of the host cell
B) are prokaryotes
D) have ribosomes
D) the genetic material is surrounded by a capsid
E) cause tuberculosis
Part C assignments with free detailed answers.
Free-response tasks that test your ability to work with text.
What signs are characteristic of viruses?
What is the effect of the AIDS virus on the body?
ABOUTAnswers to tasks in Part C.
Free-response tasks that test your ability to work with text.
1. Find errors in the given text, indicate the numbers of the sentences in which they are made, write down these sentences without errors.
In 1892, V.I. Vernadsky described the properties of viruses.
None of the known viruses is capable of independent existence.
Individual viral particles - virions - are symmetrical bodies consisting of repeating elements.
Inside each virion there is genetic material represented by protein molecules.
The genetic material of the virus is surrounded by a capsid - a lipid shell.
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(other answer options are allowed) |
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Response elements: 1 – In 1092, D.I. Ivanovsky described the properties of viruses. 4 – Inside each virion there is genetic material represented by DNA molecules. 5 – The genetic material of the virus is surrounded by a capsid - a protein shell. |
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All three errors are indicated and corrected in the answer. |
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The answer identifies and corrects two errors, OR indicates three errors but only corrects two of them |
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The answer indicates and corrects 1 error, OR 2–3 errors are indicated, but 1 of them is corrected |
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No errors are listed, OR 1 – 3 errors are listed, but none of them are fixed |
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Maximum score |
What are the characteristics of viruses?
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(other wording of the answer is allowed without distorting its meaning) |
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Response elements: 1) non-cellular life forms; 2) genetic material (DNA or RNA) is surrounded by a protein shell; 4) do not have their own metabolism (can function only in host cells) |
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Wrong answer |
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Maximum score |
What is the effect of the AIDS virus on the body.
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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?
