Viruses (biology deciphers the meaning of this term as follows) are extracellular agents that can reproduce only with the help of living cells. Moreover, they are able to infect not only people, plants and animals, but also bacteria. Bacterial viruses are called bacteriophages. Not so long ago, species were discovered that amaze each other. They are called "satellite viruses".
General Features
Viruses are a very numerous biological form, as they exist in every ecosystem on planet Earth. They are studied by such a science as virology - a section of microbiology.
Each virus particle has several components:
- genetic data (RNA or DNA);
- capsid (protein shell) - performs a protective function;
Viruses have a fairly diverse shape, ranging from the simplest spiral to icosahedral. Standard sizes are about one-hundredth of the size of a small bacterium. However, most of the specimens are so small that they are not even visible under a light microscope.
By their nature, viruses are parasites and cannot reproduce outside of a living cell. But beingoutside the cell, cease to show living signs.
Spread in several ways: viruses living in plants are moved by insects that feed on grass juices; Animal viruses are carried by blood-sucking insects. In humans, viruses are transmitted in many ways: through airborne droplets, through sexual contact, and through blood transfusions.
Origin
Viruses (biology has a huge number of species) have several hypotheses of origin. These parasites have been found on every millimeter of the planet where there are living cells. Therefore, they have existed since the beginning of life.
In our time, there are three hypotheses of the origin of viruses.
- The cellular origin hypothesis states that extracellular agents emerged from RNA fragments and DCHs that could be released from a larger organism.
- The regressive hypothesis shows that viruses were small cells that were parasitic in larger species, but over time lost the genes needed for parasitic existence.
- The co-evolution hypothesis suggests that viruses arose at the same time as living cells appeared, that is, already billions of years ago. And they appeared as a result of the construction of complex complexes of nucleic acids and proteins.
Briefly about viruses (on the biology of these organisms, our knowledge base, unfortunately, is far from perfect) you can read in this article. Each of the above theories has its drawbacks.and unproven hypotheses.
Viruses as a form of life
There are two definitions of the life form of viruses. According to the first, extracellular agents are a complex of organic molecules. The second definition says that viruses are a special form of life.
Viruses (biology implies the emergence of many new types of viruses) are characterized as organisms on the border of the living. They are similar to living cells in that they have their own unique set of genes and evolve based on the method of natural selection. They can also reproduce, creating copies of themselves. Since viruses do not have a cellular structure, scientists do not consider them as living matter.
In order to synthesize their own molecules, extracellular agents need a host cell. The lack of their own metabolism does not allow them to reproduce without outside help.
However, in 2013, a scientific article was published that some bacteriophages have their own adaptive immune system. And this is more proof that viruses are a form of life.
B altimore classification of viruses
What are viruses, biology describes in sufficient detail. David B altimore (Nobel laureate) developed his classification of viruses, which is still a success. This classification is based on how mRNA is formed.
Viruses must form mRNA from their own genomes. This process is necessary for self-nucleic acid replication andprotein formation.
Classification of viruses (biology takes into account their origin), according to B altimore, is as follows:
- Viruses with double-stranded DNA without RNA stage. These include mimiviruses and herpeviruses.
- Single-stranded DNA with positive polarity (parvoviruses).
- Double-stranded RNA (rotaviruses).
- Single-stranded RNA of positive polarity. Representatives: flaviviruses, picornaviruses.
- Single-stranded RNA molecule of double or negative polarity. Examples: filoviruses, orthomyxoviruses.
- Single-stranded positive RNA, as well as the presence of DNA synthesis on an RNA template (HIV).
- Double-stranded DNA, and the presence of DNA synthesis on an RNA template (hepatitis B).
Life span
Examples of viruses in biology are found at almost every turn. But for all the life cycle proceeds almost the same. Without a cellular structure, they cannot reproduce by division. Therefore, they use materials that are inside the cells of their host. Thus, they reproduce a large number of copies of themselves.
The virus cycle consists of several stages that overlap.
At the first stage, the virus is attached, that is, it forms a specific connection between its proteins and the receptors of the host cell. Next, you need to penetrate the cell itself and transfer your genetic material to it. Some species also tolerate proteins. After this, the loss of the capsid occurs, and the genomic nucleic acidreleased.
After the parasite enters the cell, assembly of viral particles and protein modification begin. Finally, the virus leaves the cell. Even if it continues to actively develop, it may not kill the cell, but continue to live in it.
Human Diseases
Biology interprets viruses as the lowest manifestation of life on planet Earth. The common cold is one of the simplest human viral diseases. However, these parasites can also cause very serious diseases such as AIDS or bird flu.
Each virus has a specific mechanism of action on its host. This process involves the lysis of cells, which leads to their death. In multicellular organisms, when a large number of cells die, the whole organism begins to function poorly. In many cases, viruses may not harm human he alth. In medicine, this is called latency. An example of such a virus is herpes. Some latent species can be beneficial. Sometimes their presence triggers an immune response against bacterial pathogens.
Some infections can be chronic or lifelong. That is, the virus develops despite the protective functions of the body.
Epidemics
Viral epidemiology is the science that studies how to control the transmission of viral infections in humans. Transmission of parasites can be horizontal, that is, from person to person; or vertical - from mother to child.
Horizontal gear is the mostcommon type of virus spread among humanity.
The rate of transmission of the virus depends on several factors: population density, the number of people with poor immunity, as well as the quality of medicine and weather conditions.
Protection of the body
The types of viruses in biology that can affect human he alth are innumerable. The very first protective reaction is innate immunity. It consists of special mechanisms that provide non-specific protection. This type of immunity is not able to provide reliable and long-term protection.
When vertebrates develop acquired immunity, special antibodies are produced that attach to the virus and make it harmless.
However, not all existing viruses form acquired immunity. For example, HIV constantly changes its amino acid sequence, so it evades the immune system.
Treatment and prevention
Viruses in biology are a very common phenomenon, so scientists have developed special vaccines containing "killer substances" for the viruses themselves. The most common and effective method of control is vaccination, which creates immunity to infections, as well as antiviral drugs that can selectively inhibit the replication of viruses.
Biology describes viruses and bacteria mainly as harmful inhabitants of the human body. Currently, more than thirty viruses that have settled in the world can be overcome with the help of vaccination.the human body, and even more - in the body of animals.
Prophylactic measures against viral diseases should be carried out on time and with high quality. To do this, humanity must lead a he althy lifestyle and try in every possible way to increase immunity. The state should arrange quarantines in time and provide good medical care.
Plant viruses
Forms of viruses biology considers most often rounded and rod-shaped. There are quite a lot of such parasites. On the farm, they mainly affect the yield, but it is not economically profitable to get rid of them. From plant to plant, such viruses are spread by insect vectors. Such species do not infect humans or animals, as they can only reproduce in plant cells.
Green friends of our planet can also protect themselves from them using the resistance gene mechanism. Very often, plants affected by the virus begin to produce antiviral substances such as salicylic acid or nitric oxide. The molecular biology of viruses deals with the problem of parasitic infestation of fertile plants, and also changes them chemically and genetically, which contributes to the further development of biotechnology.
Artificial viruses
Types of viruses in biology are numerous. It is especially necessary to take into account the fact that scientists have learned how to create artificial parasites. The first artificial species was obtained in 2002. For most extracellular agents, an artificial gene introduced into a cellbegins to show infectious qualities. That is, they contain all the information that is needed for the formation of new species. This technology is widely used to produce anti-infective vaccines.
The ability to create viruses under artificial conditions can have many implications. The virus cannot die out completely as long as there are bodies sensitive to it.
Viruses are weapons
Unfortunately, infectious parasites can create devastating epidemics, so they can be used as biological weapons. This is confirmed by the Spanish flu, which was created in the laboratory. Smallpox is another example. A vaccine has already been found for it, but, as a rule, only medical workers and military personnel are vaccinated, which means that the rest of the population is at potential risk if this type of biological weapon is used in practice.
Viruses and biosphere
At the moment, extracellular agents can "boast" the largest number of individuals and species living on planet Earth. They perform an important function by regulating the number of populations of living organisms. Very often they form symbiosis with animals. For example, the venom of some wasps contains components of a viral origin. However, their main role in the existence of the biosphere is life in the sea and ocean.
One teaspoon of sea s alt contains approximately one million viruses. Their main purpose is to regulate life in aquatic ecosystems. Most of them are absolutely harmless to flora and fauna
But these are not all positive qualities. Viruses regulate the process of photosynthesis, therefore increasing the percentage of oxygen in the atmosphere.
