Viruses are a life form that dies some time after it enters the environment, that is, it cannot exist outside the body of the carrier. In fact, they can be called parasites of the intracellular level, which 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 from the point of view of genetics and the least susceptible to any changes.
Theories of Origin
There are several theories about the origin of viruses. Adherents of one theory argue that the emergence 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 unproven and unfounded, since the parasitic essence of viruses itself implies the presence of more highly organized creatures in whose cells they could exist.
Another version of the origin of viruses involves the transformation of more complex forms. This theory speaks of the secondary simplicity of the virus, so it is a consequence of adaptation to the parasitic lifestyle. A similar simplification is common to all parasitic microorganisms. They lose the ability to self-feed, while acquiring a tendency to rapidly reproduce.
The device 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 cover. The composition of some viruses is supplemented with fats and carbohydrates. Viruses lack a part of enzymes that is responsible for reproductive function, therefore they can reproduce only after they get into the cell of a living organism. The metabolism of the infected cell is then rearranged to produce viral rather than its own components. Each cell contains certain genetic information, which under certain circumstances can be considered as an instruction for the synthesis of a specific type of protein inside the cell. The infected cell perceives this information as a guide to action.
Dimensions
As for the size of DNA- and RNA-containing viruses, it is in the range of 20-300 nm. Most viruses are 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 healthy organism is called virion. The core of the virion includes one or more nucleic acid molecules. The capsid is a protein shell that covers virionic nucleic acid, providing protection against the harmful effects of the environment. The nucleic acid entering 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.
Consider the main stages of reproduction of DNA-containing viruses.
Virus propagation
To be able to multiply, viruses need to invade host cells. Some viruses can exist in a large number of hosts, while others have a tendency to specific species. 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 the genes and proteins of the virus.
For the production of cells, DNA-containing viruses may not have enough of their own proteins, therefore, 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 eclipse. The genome of the virus during this period closely interacts with the carrier. Then, after several stages, the accumulation in the intracellular space of the offspring of the virus begins. This is called the ripening phase. Consider the sequence of stages of reproduction of DNA-containing viruses.
Life cycle
The life cycle of viruses consists of several stages that are mandatory:
1. Adsorption on the cell carrier. This is an initial and important step 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 searches for a new target for integration and the process repeats. This phenomenon explains the certainty in the pathways of the virus into the human body.
For example, the mucous membrane of the upper respiratory tract has influenza virus receptors. Skin cells, in contrast, do not. For this reason, it is impossible to get the flu through the skin, it is only possible by inhaling particles of the virus. Bacterial viruses in the form of filaments or lacking appendages cannot attach to cell walls; therefore, they are adsorbed on fimfibria. At the initial stage, adsorption occurs due to electrostatic interaction. This phase is reversible, as a particle of the virus is easily separated from the cell selected as the target. Starting from the second phase, separation is not possible.
2. The next stage of reproduction of DNA-containing viruses is characterized by the ingestion of a whole virion or nucleic acid, which is secreted by it inside the host cell . The virus integrates more easily into the animal’s body, since the cells in this case are not provided with a membrane. If the virion has an external lipoprotein membrane, 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 wall of the cell. For this, bacteriophages, for example, are provided with the enzyme lysozyme, which helps to dissolve solid cell walls. Examples of DNA viruses are described below.
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, for example, bacteriophages, this process is combined with the second stage, since the protein membrane of the virion remains outside the cell of the carrier. Virion is able to penetrate the cell by capturing the latter. In this case, a vacuole-phagosome arises, which absorbs primary lysosomes. In this case, enzyme cleavage occurs only in the protein part of the viral cell, and the nucleic acid remains unchanged. It is she who will subsequently substantially reform the functioning of a healthy cell, forcing it to produce the substances necessary for the virus. The virus itself is not provided with the necessary mechanisms for such procedures. There is such a thing as a viral genome strategy, which involves the implementation of genetic information.
4. The fourth stage of reproduction of DNA-containing viruses is accompanied by the development of substances necessary for the life of the virus, which is carried out under the influence of nucleic acid . First, early mRNA is produced, which will become the basis for virus proteins. Molecules that arose prior to the release of a nucleic acid are called early molecules. Molecules that arise 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. DNA-containing viruses during biosynthesis adhere to a certain scheme that includes specific steps - DNA-RNA protein. Small viruses are used in the process of transcription of RNA polymerase. Large ones, such as smallpox virus, are not synthesized in the cell nucleus, but in the cytoplasm.
DNA viruses include hepatitis B viruses, herpes, smallpox viruses, papovaviruses, hepatadaviruses, parvoviruses.
RNA virus groups
Viruses containing RNA are divided into several groups:
1. The first group has the simplest structure. It includes the corona, toga, and picornaviruses. Transcription in these types of virus is not carried out, since the single-stranded virion RNA independently performs the function of matrix acid, that is, it is the basis for the production of proteins at the level of cellular ribosomes. Thus, their bio-production pattern looks like an RNA protein. Viruses of this group are also called positively genomic or metatarsal.
2. The second group of DNA and RNA-containing viruses includes minuscule viruses, that is, they have a negative genome. These are measles, flu, mumps and many others. They also contain single-stranded RNA, but it is not suitable for direct translation. For this reason, data is first transferred to the virion RNA, and the resulting matrix acid will serve in the future as the basis for the production of virus proteins. In this case, transcription is determined by ribonucleic acid-dependent RNA polymerase. This enzyme is brought in by the virion, since it is absent in the cell initially. This is due to the fact that the cell does not need to process RNA to obtain another RNA. So, the bio-production scheme in this case will look like an RNA-RNA protein.
3. The third group consists of the so-called retroviruses. They are included in the category of oncoviruses. Their biosynthesis occurs in a more complex way. In the initial single- stranded messenger RNA , DNA is generated at the initial stage, which is a unique phenomenon that has no analogues in nature. The process is controlled by a special enzyme, namely RNA-dependent DNA polymerase. This enzyme is also called revertase or reverse transcriptase. The DNA molecule obtained by biosynthesis takes the form of a ring and is designated as a provirus. Next, the molecule is introduced into the cells of the carrier chromosomes and transcribed several times through RNA polymerase. The created copies perform the following actions: they are an RNA matrix by which a viral protein is produced, as well as an RNA virion. The synthesis scheme is as follows: RNA-DNA-RNA protein.
4. The fourth group is formed from viruses whose RNA is double-stranded. Their transcription is realized through the enzyme of the virus dependent RNA RNA polymerase.
5. In the fifth group, the production of the constituent particles of the virus, namely capsid proteins and nucleic acid, occurs repeatedly.
6. The sixth group includes virions, which arise as a result of self-assembly based on multiple copies of proteins and acid. For this purpose, the concentration of virions should 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 envelope of substances included in 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 embodiments, budding from the cell is possible, however, this method does not prevent its further death, since the plasma membrane is damaged.
The period until the virus leaves the cell is called latent. The duration of this period can range from several hours to a couple of days.
Genomic viruses containing DNA
Viruses, the DNA content of a genomic species are divided into four groups:
1. Genomes such as adeno-, papa- and herpes viruses are transferred and copied in the cell nucleus of the carrier. These are viruses containing double-stranded DNA. Capsids, once in the cell, are transferred to the membrane of the cell nucleus, so that, under the influence of certain factors, the DNA of the virus passes into the nucleoplasm and accumulates there. In this case, viruses use the RNA matrix and cellular enzymes of the carrier. A proteins are transferred first, followed by b proteins and g proteins. The RNA matrix arises on the basis of a-22 and a-47. RNA polymerase implements DNA transfer, which multiplies by the principle of a rolling ring. Capsid, in turn, arises from g-5 protein. What other genomes of DNA viruses exist?
2. Poxiviruses are in the second group. At the initial stage, actions are carried out in the cytoplasm. There is a release of nucleotides and the beginning of transcription. Then an RNA matrix 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, at the initial stage, DNA chains were untwisted and split.
3. The third group includes parvoviruses. Reproduction is carried out in the cell nucleus of the carrier and is dependent 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 go from the initial chain to the adjacent, which serves as the matrix. Thus, inversion occurs. For synthesis, DNA polymerase is needed, due to which the viral genome is transcribed.
8. The fourth group includes hepatadaviruses. This includes DNA-containing hepatitis B virus. Ring type virus DNA acts as the basis for the production of virus mRNA and RNA plus strands. She, in turn, becomes a matrix for the synthesis of the minus chain of DNA.
Methods of struggle
DNA - containing viruses, of course, pose a threat to human health. The main method of dealing with them can be the implementation of preventive measures aimed at strengthening the immune system, 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 system. However, it is possible to enhance the production of antibodies in advance by making a preventive vaccination.
Types of vaccination
There are several main types of vaccinations, including:
1. Introduction to the body of weakened virus cells. This provokes the production of an increased amount of antibodies, which allows you to fight with a normal viral strain.
2. Introduction of an already dead virus. The principle of operation is similar to the first option.
3. Passive immunization. This method consists in introducing already synthesized antibodies. This can be both the blood of a person who has had a disease, against which the vaccine is given, and an animal, for example, horses. The sequence of reproduction of DNA-containing viruses we have examined.
To avoid infection of the body with various types of viruses hazardous to human health, the body should be protected from potential contact with pathogenic microorganisms. It is quite capable of avoiding toxoplasma, mycoplasma, herpes, chlamydia and other common forms of the virus, simply following certain recommendations. This is especially true for children under 15 years old.
If the child’s body was not infected with the above virus strains, then it develops a healthy and enhanced immunity in the teenage period. The main danger of viruses is not always in how they are expressed, but in what effect they have on the protective properties of our body. Examples of DNA and RNA viruses are of interest to many.
The herpes virus, which is present in the body of 9 out of 10 inhabitants of the Earth, reduces the 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 may include the forced urban rhythm of life, poor ecology, malnutrition, etc. Against the background of a decrease in the general state of human health, his body becomes less resistant to various viruses and, accordingly, frequent diseases.