DNA-containing viruses. The stages of multiplication of DNA-containing viruses
Viruses are a form of life that dies some time after getting into the environment, that is, it can not exist outside the body of the carrier. In fact, they can be called parasites of the intracellular level, which multiply in cells, thus causing various diseases. Viruses can infect both RNA( ribonucleic acid) and DNA( deoxyribonucleic acid).DNA-containing viruses are considered more conservative in terms of genetics and least susceptible to any changes.
Theories about the origin of
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 descendants of the simplest forms. However, this theory is unsubstantiated and unreasonable, since the very parasitic essence of viruses presupposes the presence of more highly organized beings in the cells of which they could exist.
Another version of the origin of viruses involves the conversion of more complex forms. This theory speaks of the secondary nature of the simplicity of the virus, as it is the result of adaptation to the parasitic way of life. This simplification is characteristic of all parasitic microorganisms. They lose the ability to self-feed, while gaining a propensity for rapid reproduction.
The device and dimensions of DNA-containing viruses
The simplest viruses contain a nucleic acid that acts as a genetic material of both the microorganism itself and its capsid, which is a cover made of protein. The composition of some viruses is supplemented with fats and carbohydrates. Viruses lack a part of the enzymes, which is responsible for the reproductive function, so they can multiply only if they get into 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 an instruction for the synthesis of a specific type of protein within the cell. The infected cell perceives this information as a guide to action.
As for the sizes of DNA and RNA-containing viruses, it is in the range of 20-300 nm. Viruses are mostly smaller in size than bacteria. Erythrocyte cells, for example, are an order of magnitude larger than viral cells. Able to infect, a full-fledged infectious viral particle outside a healthy organism is called a virion. The virion core contains one or more nucleic acid molecules. The capsid is a shell of protein that covers the virion nucleic acid, providing protection from the harmful effects of the environment. The nucleic acid that enters the virion is considered a virus genome and is expressed in deoxyribonucleic acid, or DNA, as well as in ribonucleic( RNA).Unlike bacteria, viruses do not have a combination of these two kinds of acid.
Let's consider the main stages of the multiplication of DNA-containing viruses.
Propagation of viruses
To be able to multiply, viruses need to penetrate into the carrier cells. Some viruses can exist in a large number of hosts, others have a propensity for specific species. At the initial stage of infection, the virus inserts 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.
To produce cells, DNA-containing viruses do not have enough of their own proteins, therefore, similar carrier substances are used. After some time after infection, only a small part of the original virus remains in the cell. This phase is called the eclipse phase. 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 progeny of the virus begins. This is called the maturation phase. Consider the sequence of the stages of multiplication of DNA-containing viruses.
The life cycle of viruses consists of several steps that are mandatory:
1. Adsorption on the carrier cell. This is the initial and important stage of recognition of target cells by receptors. Adsorption can occur on cells of organs or tissues. The process triggers a mechanism for further integration of the virus into the cell. A certain amount of ions is required to bind the cells. This is necessary to reduce electrostatic repulsion. If penetration into the cell fails, the virus is looking for a new target for integration and the process is repeated. This phenomenon explains the certainty in the ways of penetration of the virus into the human body.
So, for example, the mucosa of the upper respiratory tract has receptors for the influenza virus. Skin cells, in contrast, have none. For this reason, it is impossible to get influenza through the skin, it is possible only by inhaling the particles of the virus. Bacterial viruses in the form of filaments or not having shoots can not be attached to the walls of the cell, 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 cell chosen as the target. Since the second phase, separation is not possible.
2. The next stage of multiplication of DNA-containing viruses is characterized by the ingress of an entire virion or nucleic acid that is released inside the cell of the carrier. In the animal organism the virus is integrated easier, since the cells in this case are not provided with a shell. If the virion has a lipoprotein membrane outside it, it collides with a similar protection of the carrier cell and the virus enters the cytoplasm. Viruses penetrating into bacteria, plants and fungi are more difficult to integrate, because in this case they are forced to pass through the rigid wall of the cell. For this, bacteriophages, for example, are provided with a lysozyme enzyme that helps dissolve solid cell walls. Examples of DNA-containing viruses are discussed below.
3. The third stage is called deproteinization. It is characterized by the release of a 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 shell of the virion remains outside the carrier cell. Virion is able to penetrate the cell by capturing the latter. This creates a vacuole-phagosome, which absorbs the primary lysosomes. In this case, the cleavage into enzymes occurs only in the protein part of the viral cell, and the nucleic acid remains unchanged. It is she who subsequently substantially restores the functioning of a healthy cell, forcing her to produce the substances needed by the virus. The virus itself is not necessary for such procedures by mechanisms. There is such a thing as the strategy of the viral genome, which implies the realization of genetic information.
4. The fourth stage of multiplication 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 .First, early mRNA is produced, which will become the basis for the proteins of the virus. The early ones are the molecules that appeared before the release of the nucleic acid. Molecules that are formed after the replication of acid, 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, including specific steps - DNA-RNA-protein. Small viruses are used in the process of transcription of RNA polymerase. Large, such as a smallpox virus, are synthesized not in the cell nucleus, but in the cytoplasm.
DNA-containing viruses include hepatitis B viruses, herpes, smallpox viruses, papovaviruses, hepadnaviruses, parvoviruses.
Groups of RNA viruses
Viruses containing RNA are divided into several groups:
1. The first group is arranged most simply. It includes corona, toga and picornaviruses. Transcription in these species of the virus is not carried out, since single-stranded virion RNA independently realizes the function of matrix acid, that is, it is the basis for the production of proteins at the level of cellular ribosomes. Thus, the bioprospecting scheme for them looks like RNA-protein. Viruses of this group are also called positively genomic or metatarsal.
2. The second group of DNA and RNA-containing viruses includes low-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 not suitable for direct translation. For this reason, the transfer of data to the virion RNA occurs first, and the resulting matrix acid will serve as the basis for further development of the virus proteins. Transcription in this case is determined by a ribonucleic acid-dependent polymerase of RNA.This enzyme is brought by the virion, since it is absent from the cell initially. This is due to the fact that the cell does not need to process RNA to obtain another RNA.So, the bioprospecting scheme 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. Biosynthesis takes place along a more complex path. In the initial matrix RNA single-stranded type, at the initial stage, DNA production takes place, which is a unique phenomenon, which has no analogs in nature. The process is under the control of a special enzyme, namely the DNA dependent on RNA polymerase. This enzyme is also called revertase or reverse transcriptase. The DNA molecule, obtained as a result of biosynthesis, receives the form of a ring and is designated as a provirus. Further, the molecule is introduced into the cells of the carrier chromosomes and transcribed several times by RNA polymerase. The created copies perform the following actions: they are an RNA matrix with the help of 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 has a double-stranded form. Their transcription is realized by means of the virus enzyme dependent RNA polymerase RNA.
5. In the fifth group of , the generation of 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. 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 regions of the cell. Complex viruses also create a protective shell of substances entering the plasma membrane.
7. At the final stage, new virus particles are released from the carrier cell. This process occurs in different ways depending on the type of virus. Some cells die after this, since the cell lysis is released. In other embodiments, budding from the cell may be possible, however, this method also does not prevent its further dying off, since the plasma membrane is damaged.
The period before the release of the virus from the cell is called latent. The duration of this interval can range from a few hours to a couple of days.
Genomic viruses containing DNA
Viruses, genomic DNA content is divided into four groups:
1. Such genomes as adeno, papova and herpesviruses are transferred and copied in the carrier's cellular nucleus. These are viruses containing double-stranded DNA.Capsids, hitting the cell, are transferred to the membrane of the cell nucleus, so that later, under the influence of certain factors, the DNA of the virus passed into the nucleoplasm and accumulated there. The viruses use the RNA template and the 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.Polymerase RNA realizes the transfer of DNA, which multiplies by the principle of a rolling ring. Capsid, in turn, arises from g-5 protein. What are the genomes of DNA-containing viruses?
2. Poxviruses are included in the second group. At the initial stage, the actions are carried out in the cytoplasm. There is a release of nucleotides and the beginning of transcription. 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 the polymerase. On both sides of the genome, replication begins in those places where at the initial stage the DNA chains were spliced and split.
3. Parvoviruses are included in the third group. 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 a so-called hairpin structure and acts as a seed.125 first pairs of bases pass from the initial chain to the adjacent one, which serves as a matrix. Thus, an inversion occurs. To synthesize DNA polymerase is needed, due to which transcription of the viral genome occurs.
8. The fourth group includes hepadnaviruses. This includes the DNA-containing hepatitis virus. The DNA of the ring-type virus acts as the basis for the production of the mRNA of the virus and the plus-strand RNA.It, in turn, becomes a matrix for the synthesis of the minus-strand of DNA.
Methods of combating
DNA-containing viruses certainly represent a danger to human health. The main method of combating them can be the implementation of preventive measures aimed at strengthening immunity, as well as regular vaccination.
As a rule, antibodies directed at combating certain viruses are produced as a result of intrusion of harmful microorganisms into the carrier system. However, to increase the production of antibodies can be done in advance by making a prophylactic vaccination.
Types of vaccination
There are several main types of vaccination, including:
1. Introduction to the body of weakened cells of the virus. This provokes the production of an increased number of antibodies, which makes it possible to fight a normal viral strain.
2. Introduction of 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 like the blood of a person who has undergone the disease, against which the vaccine is being vaccinated, and the animal, for example, horses. The sequence of multiplication of DNA-containing viruses was examined.
To avoid infection of the body with various types of viruses that are dangerous to human health, you should protect your body from potential exposure to pathogens. It is quite possible to avoid toxoplasm, 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 has not been infected with the above virus strains, then he develops healthy and strengthened immunity in the adolescent period. The main danger of viruses is not always in the way 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.
The 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.
In addition to a similar viral load, which is sometimes not limited to herpes only, the conditions of modern life are far from ideal, which also affects the protective barriers of the body. In this item you can refer to the forced urban rhythm of life, poor ecology, malnutrition, etc. Against the background of the decline in the general state of human health, his body becomes less resistant to various viruses and, accordingly, frequent illnesses.