Viruses are a form of life that dies some time after entering the environment around the body, that is, it cannot exist outside the body of the carrier. In fact, they can be called intracellular parasites that multiply in cells, thereby causing various diseases. Viruses can infect both RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). DNA-containing viruses are recognized as more conservative in terms of genetics and the least susceptible to any changes.
Theories about the origins
There are several theories about the origin of viruses. Adherents of one theory argue that the origin of viruses occurs spontaneously and is due to a number of factors. Others consider viruses to be descendants of the simplest forms. However, this theory is unsubstantiated and unfounded, since the very parasitic essence of viruses suggests the existence of more highly organized creatures in whose cells they could exist.
Another version of the origin of virusesinvolves the transformation of more complex forms. This theory speaks of the secondary simplicity of the virus, as it is a consequence of adaptation to a parasitic lifestyle. This simplification is characteristic of all parasitic microorganisms. They lose the ability to feed on their own, while acquiring a tendency to reproduce rapidly.
Design and size of DNA-containing viruses
The simplest viruses contain nucleic acid, which acts as the genetic material of both the microorganism itself and its capsid, which is a protein sheath. The composition of some viruses is supplemented with fats and carbohydrates. Viruses lack part of the enzymes that are responsible for the reproductive function, so they can multiply only when they enter the cell of a living organism. The metabolism of the infected cell is then rebuilt to produce viral rather than its own components. Each cell contains certain genetic information, which, under certain circumstances, can be considered as instructions for the synthesis of a particular type of protein within the cell. The infected cell perceives this information as a guide to action.
Sizes
As for the size of DNA and RNA viruses, it is in the range of 20-300 nm. Viruses are mostly smaller than bacteria. Erythrocyte cells, for example, are an order of magnitude larger than viral ones. Capable of infection, a full-fledged infectious viral particle outside a he althy body is called a virion. The virion core contains one or more nucleic acid molecules. The capsid is a protein shell that covers the virion nucleic acid, providing protection from the harmful effects of the environment. The nucleic acid included in the virion is considered the genome of the virus and is expressed in deoxyribonucleic acid, or DNA, as well as ribonucleic acid (RNA). Unlike bacteria, viruses do not have a combination of these two types of acid.
Let's consider the main stages of reproduction of DNA-containing viruses.
Reproduction of viruses
To be able to reproduce, viruses need to infiltrate host cells. Some viruses can exist in a large number of hosts, while others tend to be species-specific. At the initial stage of infection, the virus introduces genetic material into the cell in the form of DNA or RNA. Its reproductive function, as well as the further development of cells, directly depend on the activity and production of genes and proteins of the virus.
For the production of cells, DNA-containing viruses do not have enough of their own proteins, so similar carrier substances are used. Some time after infection, only a small fraction of the original viruses remain in the cell. This phase is called the eclipse. The genome of the virus during this period closely interacts with the carrier. Then, after several stages, the accumulation of virus progeny in the intracellular space begins. This is called the maturation phase. Consider the sequence of stages of reproduction of DNA-containing viruses.
The cycle of life
The life cycle of viruses consists of several mandatory stages:
1. Adsorption on the host cell. This is the initial and important stage in the recognition of target cells by receptors. Adsorption can occur on the cells of organs or tissues. The process triggers the mechanism for further integration of the virus into the cell. Cell binding requires a certain amount of ions. This is necessary to reduce electrostatic repulsion. If penetration into the cell fails, the virus looks for a new target for integration and the process is repeated. This phenomenon explains the certainty in the ways the virus enters the human body.
For example, the mucous membrane of the upper respiratory tract has receptors for the influenza virus. Skin cells, on the other hand, do not. For this reason, it is impossible to catch the flu through the skin, this is possible only by inhaling virus particles. Bacterial viruses in the form of filaments or without processes cannot attach to the cell walls, so they are adsorbed on the fimbriae. At the initial stage, adsorption occurs due to electrostatic interaction. This phase is reversible, since the virus particle is easily separated from the target cell. From the second phase, separation is not possible.
2. The next stage of reproduction of DNA-containing viruses is characterized by the entry of a whole virion or nucleic acid, which is secreted by it inside the host cell. The virus is easier to integrate into the animal body, since the cells in this case do notprovided with a sheath. If the virion has a lipoprotein membrane on the outside, then it collides upon contact with a similar defense of the host cell and the virus enters the cytoplasm. Viruses that penetrate bacteria, plants and fungi are more difficult to integrate, since in this case they are forced to pass through the rigid cell wall. To do this, bacteriophages, for example, are provided with the enzyme lysozyme, which helps dissolve hard cell walls. Below are examples of DNA-containing viruses.
3. The third stage is called deproteinization. It is characterized by the release of nucleic acid, which is the carrier of genetic information. In some viruses, such as bacteriophages, this process is combined with the second stage, since the protein shell of the virion remains outside the host cell. The virion is able to enter the cell by capturing the latter. In this case, a vacuole-phagosome arises, which absorbs the primary lysosomes. In this case, cleavage into enzymes occurs only in the protein part of the viral cell, and the nucleic acid remains unchanged. It is she who subsequently significantly reshapes the functioning of a he althy cell, forcing it to produce the substances necessary for the virus. The virus itself is not provided with the mechanisms necessary for such procedures. There is such a thing as the strategy of the viral genome, which involves the implementation of genetic information.
4. The fourth stage of reproduction of DNA-containing viruses is accompanied by the production of substances necessary for the life of the virus, which is carried out under the influence of nucleic acid.acids. First, early mRNA is produced, which will become the basis for the proteins of the virus. Molecules that arose before the release of the nucleic acid are called early. Molecules that have arisen after acid replication are called late. It is important to understand that the production of molecules directly depends on the type of nucleic acid of a particular virus. During biosynthesis, DNA-containing viruses adhere to a certain scheme, including specific steps - DNA-RNA-protein. Small viruses are used in the process of transcription of RNA polymerase. Large ones, such as the smallpox virus, are not synthesized in the cell nucleus, but in the cytoplasm.
DNA-containing viruses include hepatitis B viruses, herpes, variola viruses, papovaviruses, hepadnaviruses, parvoviruses.
RNA virus groups
Viruses containing RNA are divided into several groups:
1. The first group is the most simple. It includes corona, toga and picornaviruses. Transcription is not carried out in these types of virus, since the single-stranded RNA of the virion independently implements the function of matrix acid, that is, it is the basis for the production of proteins at the level of cellular ribosomes. Thus, their bioproduction scheme looks like an RNA protein. Viruses of this group are also called positive genomic or metatarsal.
2. The second group of DNA and RNA-containing viruses includes minus-strand viruses, that is, they have a negative genome. These are measles, influenza, mumps and many others. They also contain single-stranded RNA, but it is notsuitable for live broadcast. For this reason, data is first transferred to the RNA of the virion, and the resulting matrix acid will later serve as the basis for the production of virus proteins. Transcription in this case is determined by a ribonucleic acid-dependent RNA polymerase. This enzyme is brought by the virion, since it is not present in the cell initially. This is because the cell does not need to recycle RNA to produce other RNA. So, the scheme of bioproduction in this case will look like RNA-RNA-protein.
3. The third group consists of the so-called retroviruses. They are also included in the category of oncoviruses. Their biosynthesis occurs in a more complex way. In the initial messenger RNA of a single-stranded type, DNA is produced at the initial stage, which is a unique phenomenon, which has no analogues in nature. The process is controlled by a special enzyme, namely the RNA-dependent DNA polymerase. This enzyme is also called reverse transcriptase or reverse transcriptase. The DNA molecule obtained as a result of biosynthesis takes the form of a ring and is designated as a provirus. Next, the molecule is introduced into the cells of the carrier's chromosomes and transcribed several times by RNA polymerase. The created copies perform the following actions: they represent an RNA matrix, with the help of which a viral protein is produced, as well as an RNA virion. The synthesis scheme is presented as follows: RNA-DNA-RNA-protein.
4. The fourth group is formed from viruses whose RNA has a double-stranded form. Their transcription is carried out byenzyme virus dependent RNA polymerase RNA.
5. In the fifth group, the production of the constituent particles of the virus, namely capsid proteins and nucleic acids, occurs repeatedly.
6. The sixth group includes virions, which arise as a result of self-assembly based on many copies of proteins and acids. To this end, the concentration of virions must reach a critical value. In this case, the components of the virus particle are produced separately from each other in different areas of the cell. Complex viruses also create a protective shell of substances that make up the plasma cell membrane.
7. At the final stage, new virus particles are released from the host cell. This process occurs in different ways, depending on the type of virus. Some cells then die as cell lysis is released. In other cases, budding from the cell is possible, however, this method does not prevent its further death, as the plasma membrane is damaged.
The period until the virus leaves the cell is called latent. The duration of this interval can vary from a few hours to a couple of days.
Genomic viruses containing DNA
Viruses, DNA content of the genomic species are divided into four groups:
1. Genomes such as adeno-, papova- and herpesviruses are transferred and copied in the cell nucleus of the carrier. These are viruses containing double-stranded DNA. Capsids, having entered the cell, are transferred to the membrane of the cell nucleus, so that later, under the influencecertain factors, the DNA of the virus passed into the nucleoplasm and accumulated there. In this case, viruses use the RNA matrix and the cellular enzymes of the host. A-proteins are transferred first, followed by b-proteins and g-proteins. The RNA template arises from a-22 and a-47. RNA polymerase implements DNA transfer, which propagates according to the rolling ring principle. The capsid, in turn, arises from the g-5 protein. What other DNA virus genomes exist?
2. Poxyviruses are included in the second group. At the initial stage, the actions are carried out in the cytoplasm. There, nucleotides are released and transcription begins. Then an RNA template is formed. In the early stages of production, DNA polymerase and about 70 proteins are created, and double-stranded DNA is cleaved by polymerase. On both sides of the genome, replication begins in those places where the unwinding and splitting of DNA chains was carried out at the initial stage.
3. The third group includes parvoviruses. Reproduction is carried out in the cell nucleus of the carrier and depends on the functions of the cell. In this case, DNA forms the so-called hairpin structure and acts as a seed. The first 125 base pairs are transferred from the initial strand to the adjacent strand, which serves as a template. Thus, an inversion occurs. For synthesis, DNA polymerase is needed, due to which the transcription of the viral genome occurs.
8. The fourth group includes hepadnaviruses. This includes the DNA-containing hepatitis virus. The DNA of the circular type virus works as the basis for the production of the virus mRNA and plus-strand RNA. She, in turn,becomes a template for the synthesis of the negative strand of DNA.
Methods of struggle
DNA - containing viruses, of course, pose a danger to human he alth. The main method of dealing with them can be preventive measures aimed at strengthening immunity, as well as regular vaccination.
As a rule, antibodies aimed at combating certain viruses are produced as a result of the invasion of harmful microorganisms into the carrier's system. However, you can increase the production of antibodies in advance by making a preventive vaccination.
Types of vaccinations
There are several main types of vaccination, including:
1. Introduction of weakened virus cells into the body. This provokes the production of an increased amount of antibodies, which allows you to fight the normal viral strain.
2. The introduction of an already dead virus. The principle of operation is similar to the first option.
3. passive immunization. This method consists in the introduction of already synthesized antibodies. It can be either the blood of a person who has had a disease against which the vaccine is being given, or an animal, for example, horses. We examined the sequence of reproduction of DNA-containing viruses.
To avoid infecting the body with various types of viruses that are dangerous to human he alth, the body should be protected from potential contact with pathogenic microorganisms. It is quite possible to avoid toxoplasma, mycoplasma, herpes, chlamydia and other common forms of the virus, simply by following certainrecommendations. This is especially true for children under 15.
If the child's body was not infected with the above strains of viruses, then he develops he althy and enhanced immunity in adolescence. The main danger of viruses is not always in how they are expressed, but in the effect they have on the protective properties of our body. Examples of DNA- and RNA-containing viruses are of interest to many.
Herpes virus, which is present in the body of 9 out of 10 inhabitants of the Earth, reduces immune properties by about 10 percent throughout life, although it may not manifest itself in any way.
Conclusion
In addition to such a viral load, which is sometimes not limited only to herpes, the conditions of modern life are far from ideal, which also affects the protective barriers of the body. This item includes the forced urban rhythm of life, poor ecology, malnutrition, etc. Against the background of a decrease in the general state of human he alth, his body becomes less resistant to various viruses and, accordingly, frequent diseases.
