Viruses (biology deciphers the meaning of this term like this) are extracellular agents that can only be reproduced with the help of living cells. Moreover, they are able to infect not only people, plants and animals, but also bacteria. Bacterial viruses are commonly called bacteriophages. Not so long ago, species that hit each other were discovered. They are called satellite viruses.
General characteristics
Viruses are a very numerous biological form, as they exist in every ecosystem on planet Earth. Their study is engaged in such a science as virology - a branch of microbiology.
Each viral 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 and ending with the icosahedral. Standard sizes are about one hundredth 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 multiply outside of a living cell. But being outside the cell, they cease to show living signs.
Spread in several ways: viruses that live in plants are moved by insects that feed on herbal juices; animal viruses carry blood-sucking insects. In humans, viruses are transmitted in a large number of ways: by airborne droplets or sexually, as well as through blood transfusion.
Origin
Viruses (biology has a huge number of species) have several origin hypotheses. These parasites were found on every millimeter of the planet where there are living cells. Therefore, they exist from the very beginning of the appearance of life.
Nowadays, there are three hypotheses for the origin of viruses.
- The hypothesis of cellular origin reports that extracellular agents emerged from fragments of RNA and DCH, which could be released from a larger organism.
- The regression hypothesis shows that viruses were small cells, leading a parasitic lifestyle in larger species, but eventually lost the genes that are needed for a parasitic existence.
- The co-evolution hypothesis suggests that viruses arose at the same time that living cells appeared, that is, billions of years ago. And they appeared as a result of building 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 reports 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 multiply, while creating their own copies. 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 multiply without assistance.
However, in 2013, a scientific article was published that some bacteriophages have their own immune system, capable of adaptation. And this is extra evidence that viruses are a form of life.
Baltimore virus classification
What viruses are, biology describes in sufficient detail. David Baltimore (Nobel Laureate) has developed his own classification of viruses, which is still successful. This classification is based on the methods of mRNA formation.
Viruses must form mRNA from their own genomes. This process is necessary for the replication of its own nucleic acid and the formation of proteins.
The classification of viruses (biology takes into account their origin), according to Baltimore, is as follows:
- Viruses with double-stranded DNA without RNA stage. These include mimiviruses and herpeviruses.
- Single-stranded DNA with positive polarity (parvoviruses).
- Two-spot RNA (rotaviruses).
- Single-stranded RNA of positive polarity. Representatives: flaviviruses, picornaviruses.
- Single-stranded RNA molecule of double or negative polarity. Examples: filoviruses, orthomyxoviruses.
- Single-chain positive RNA, as well as the presence of DNA synthesis on the RNA matrix (HIV).
- Double-stranded DNA, and the presence of DNA synthesis on an RNA matrix (hepatitis B).
Life span
Examples of viruses in biology are found at almost every step. But for all, the life cycle proceeds almost identically. 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 are mutually overlapping.
At the first stage, the virus attaches, that is, 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 carry proteins. After this, capsid loss occurs and genomic nucleic acid is released.
After the parasite enters the cell, the assembly of viral particles and protein modification begins. And as a result, the virus leaves the cell. Even if it continues to develop actively, 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. One of the simplest human viral diseases is the common cold. 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 cause harm to human health. In medicine, this is called latency. An example of such a virus is herpes. Some latent species can be beneficial. Sometimes their presence causes an immune response against bacterial pathogens.
Some infections may be chronic or lifelong. That is, the virus develops, despite the protective functions of the body.
Epidemics
Viral epidemiology is a science that studies how to control the transmission of viral infections among people. The transmission of parasites can be horizontal, that is, from person to person; or vertical - from mother to child.
Horizontal transmission is the most common 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.
Body protection
The types of viruses in biology that can affect human health are innumerable. The very first defensive reaction is innate immunity. It is composed of special mechanisms that provide non-specific protection. This type of immunity is not able to provide reliable and long-term protection.
When acquired immunity appears in vertebrates, special antibodies are produced that attach to the virus and make it safe.
However, far from all existing viruses, acquired immunity is formed. For example, HIV is constantly changing its amino acid sequence, so it is moving away from the immune system.
Treatment and prevention
Viruses in biology are a very common occurrence, 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 virus replication.
Viruses and bacteria, biology describes mainly as harmful inhabitants of the human body. Currently, with the help of vaccination, more than thirty viruses that have settled in the human body, and even more in animals, can be overcome.
Prevention measures against viral diseases should be carried out on time and efficiently. For this, humanity must lead a healthy lifestyle and try to increase immunity in every possible way. The state must quarantine in time and provide good medical care.
Plant viruses
Forms of viruses, biology is most often considered rounded and rod-shaped. Such parasites are quite a large number. On the farm, they mainly affect productivity, but getting rid of them is economically unprofitable. From plant to plant, such viruses are spread by vector insects. Such species do not affect humans or animals, since they can only reproduce in plant cells.
Green friends of our planet can also protect themselves from them using the mechanism of the resistance gene. Very often, plants affected by the virus begin to produce antiviral substances such as salicylic acid or nitric oxide. The molecular biology of viruses addresses the problems of damage to fertile plants by parasites, 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 to create artificial parasites. The first artificial look was obtained in 2002. In most extracellular agents, the artificial gene introduced into the cell begins to exhibit infectious qualities. That is, they contain all the information that is needed for the formation of new species. This technology is widely used to obtain anti-infectious vaccines.
The ability to create viruses under artificial conditions can have many consequences. The virus cannot completely die out as long as there are bodies sensitive to it.
Viruses are weapons
Unfortunately, infectious parasites can create devastating epidemics, and therefore can be used as biological weapons. This is confirmed by the Spanish flu, which was created in the laboratory. Another example is smallpox. A vaccine from it has already been found, but, as a rule, only medical workers and military personnel are vaccinated, which means that the rest of the population is in the zone of 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 population of living organisms. Very often they form a symbiosis with animals. For example, the poison of some wasps contains components of viral origin. However, their main role in the existence of the biosphere is life in the sea and ocean.
One teaspoon of sea salt contains approximately a million viruses. Their main goal is the regulation of life in aquatic ecosystems. Most of them are absolutely harmless to flora and fauna.
But these are far from all positive qualities. Viruses regulate the process of photosynthesis, therefore, increase the percentage of oxygen in the atmosphere.