What are viruses? Biology: types and classification of viruses

Viruses (biology decodes the meaning of this term so) are extracellular agents that can only be reproduced with the help of living cells. And they are capable of hitting not only people, plants and animals, but also bacteria. Viruses of bacteria are 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 the planet Earth. Their study deals with such a science as virology - the division of microbiology.

Each virus particle has several components:

- genetic data (RNA or DNA);

- capsid (protein coat) - performs a protective function;

Viruses have a fairly diverse form, ranging from the simplest spiral and ending with 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 can not reproduce outside the living cell. But being out of the cage, they stop showing live signs.

Distributed in several ways: viruses living in plants are moved by insects feeding on herbal juices; Animal viruses are transmitted by bloodsucking insects. In humans, viruses are transmitted in a large number of ways: by airborne or by sexual route, and by blood transfusion.

Origin

Viruses (biology has a huge number of species) have several hypotheses of origin. 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 of the origin of viruses.

1. The cellular hypothesis reports that extracellular agents emerged from fragments of RNA and DTC that could be released from the larger body.
2. The regressive hypothesis shows that the viruses were small cells that lead a parasitic lifestyle in larger species, but over time lost the genes that are necessary for parasitic existence.
3. The hypothesis of co-evolution suggests that viruses originated at the same time as living cells appeared, that is, billions of years ago. And appeared as a result of the construction of complex complexes of nucleic acids and proteins.

Briefly about the viruses (according to 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 unproved hypotheses.

Viruses as a form of life

There are two definitions of the form of life 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 boundary of the living. They resemble 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, creating their own copies. Since viruses do not have a cellular structure, scientists do not view them as living matter.

In order to synthesize own molecules, extracellular agents need a host cell. Absence 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 immune system capable of adaptation. And this is an extra proof that viruses are a form of life.

Classification of viruses by Baltimore

What are the viruses, biology describes in detail. David Baltimore (Nobel laureate) has developed his classification of viruses, which is still a success. 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 one's own nucleic acid and the formation of proteins.

The classification of viruses (biology takes into account their origin), according to Baltimore, looks like this:

- Viruses with double-stranded DNA without RNA stage. These include mimiviruses and herpesviruses.

- 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, orthomixoviruses.

- Single-stranded positive RNA, as well as the presence of DNA synthesis on the RNA (HIV) matrix.

- Double-stranded DNA, and the presence of DNA synthesis on the RNA matrix (hepatitis B).

Life Span

Examples of viruses in biology are found almost at every step. But at all the life cycle proceeds practically equally. Without a cellular structure, they can not reproduce by division. Therefore, they use materials that are inside the cell of their host. Thus, they reproduce a large number of copies of themselves.

The cycle of the virus consists of several stages, which are inter-overlapping.

At the first stage, the virus is attached, that is, it forms a specific link between its proteins and receptors of the host cell. Next, you need to enter the cell itself and give it your genetic material. Some species also tolerate proteins. After this, a loss of the capsid occurs, and the genomic nucleic acid is released.

After the parasite gets inside the cell, assembly of virus particles and modification of the protein begins. And as a result, the virus exits the cell. Even if he continues to develop actively, he may not kill the cage, but continue to live in it.

Diseases of man

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 cause very serious diseases, such as AIDS or bird flu.

Each virus has a certain mechanism of action on its owner. This process involves lysing the cells, which leads to their death. In multicellular organisms, with the death of a large number of cells, the entire organism begins to function poorly. In many cases, viruses may not harm human health. In medicine, this is called latency. An example of such a virus is herpes. Some latent species are capable of benefiting. Sometimes their presence causes 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 a science that studies how to control 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 mankind.

The rate of transmission of the virus depends on several factors: the density of the population, 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 health are innumerable. The very first defense reaction is innate immunity. It consists of special mechanisms that give nonspecific protection. This type of immunity can not provide a reliable and long-lasting protection.

When vertebrates appear acquired immunity, then special antibodies are produced that join the virus and make it safe.

However, not all existing viruses are formed acquired immunity. For example, HIV constantly changes the amino acid sequence, so it leaves the immune system.

Treatment and prevention

Viruses in biology - this is a very common phenomenon, so scientists have brought out 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 are able to selectively inhibit the replication of viruses.

Viruses and bacteria biology describes mainly as harmful inhabitants of the human body. Currently, with the help of vaccination, you can overcome more than thirty viruses that have settled in the human body, and even more - in the body of animals.

Measures to prevent viral diseases should be carried out on time and in good quality. For this, mankind must lead a healthy lifestyle and try to improve immunity in every possible way. The state must arrange quarantines on time and provide good medical services.

Viruses of plants

Forms of viruses, biology is often considered round and rod-shaped. There are a lot of such parasites. In the economy, they mainly affect the yield, but getting rid of them is economically unprofitable. From a plant to a plant, such viruses spread with the help of insect vectors. Such species do not affect humans or animals, since they can only reproduce in plant cells.

Green friends of our planet can also be protected from them by the mechanism of the resistance gene. Very often, plants affected by a virus begin to produce antiviral substances such as salicylic acid or nitric oxide. Molecular biology of viruses deals with the problem of the destruction of fertile plants by parasites, and also changes them chemically and genetically, which contributes to the further development of biotechnology.

Artificial viruses

The types of viruses in biology are numerous. Especially it is necessary to take into account that scientists have learned to create artificial parasites. The first artificial species 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 produce anti-infectious vaccines.

The ability to create viruses in artificial environments can have many consequences. The virus can not completely die out as long as there are sensitive bodies.

Viruses are weapons

Unfortunately, infectious parasites can create devastating epidemics, so they can be used as biological weapons. Confirmation of this is the Spanish flu, which was created in the laboratory. Another example is smallpox. The vaccine 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 a potential risk zone if this type of biological weapon is used in practice.

Viruses and the biosphere

At the moment, extracellular agents can "boast" the largest number of individuals and species living on planet Earth. They perform an important function, regulating the number of populations of living organisms. Very often they form 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 the ocean.

One teaspoon of sea salt contains about 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 this is by no means all positive qualities. Viruses regulate the process of photosynthesis, therefore increase the percentage of oxygen in the atmosphere.