The structure of the DNA of bacteria. Organization of the genetic material of a bacterial cell. Nucleic acid structure
Nominative vocative.
Basic Nominative Meanings
The nominative case has the following meanings:
nominative subjective;
a noun in this meaning denotes the subject of speech, the subject (producer) of the action, the bearer of the feature, in the sentence is the subject: Mama washes the frame. House is being built by workers.
nominative predicative;
a noun in this meaning denotes a feature of the subject of speech, in a sentence it is a predicate: Moscow - capital Russian Federation. My brother - banker.
nominative object;
the noun denotes the object of the action, the subject of the action is expressed in the instrumental case, the indicated meaning is found in the passive construction: House is being built by workers. Book published by a publishing house.
nominative appositive;
the noun serves as an inconsistent definition (application): There is a lynx huntress gray-haired, running, falling on his paws.
The noun is an address, does not perform a syntactic function: People, be attentive to each other.
The paradigm is considered complete if the noun has 12 case forms: 6 singular and 6 plural forms; since it is only specific nouns that change in numbers, other LGRs have an incomplete number paradigm.
Peritrichs. Flagella are located over the entire surface of the cell wall (bacteria of the Enterobacteriaceae and Bacillaceae families).
Monotrichs. One thick flagellum at one end (vibrios).
Politrichs. A bundle of 2-50 flagella, visible as a single one.
Polar flagella are attached to one or both ends of the bacteria. Lofotrich- a bundle of flagella at one end of a bacterium (Pseudomonas). Amphitrix- bipolar beams (Spirillum).
Microvilli(drank, fimbria) these are protein hairs (from 10 to several thousand) 3-25 nm thick and up to 12 microns long.
A. Ordinary drank. Many gram-negative bacteria have long, thin pili (fimbriae) that begin at the cytoplasmic membrane and penetrate the cell wall. They are formed by proteins of the same type, the molecules of which form a spiral thread. Their the main function is the attachment of bacteria to substrates, for example, the surface of mucous membranes, which is an important factor in colonization and infection. In addition, the increased surface area of the bacterial cell gives it additional advantages in utilizing environmental nutrients.
B. F-drank(fertility factor) - special formations involved in the conjugation of bacteria. They look like hollow protein tubes with a length of 0.5-10 microns. Their formation is encoded by plasmids.
Cell membrane most bacteria consist of a cell wall and an underlying cytoplasmic membrane.
The bacterial cell wall is thin, elastic and rigid, and may be completely absent in some bacteria (for example, L-forms and mycoplasmas). The cell wall protects bacteria from external influences, gives them a characteristic shape, through which nutrients are transported and metabolites are released. A variety of receptors for bacteriophages, bacteriocins and various chemicals are located on its surface. CS maintains the constancy of the internal environment and withstands significant pressure from the inside (for example, the partial pressure of intracellular substances of gram-positive bacteria can reach 30 atmospheres). The structure and composition of CS elements determine the ability to perceive dyes, i.e. their tinctorial properties... One of the basic principles of bacterial differentiation is based on the ability to perceive and retain the coloring complex of gentian violet with iodine inside the cell, or lose it after treatment with alcohol (Gram stain). Accordingly, gram-positive (colored in violet-purple) and gram-negative (red) are distinguished.
The main component of bacterial CS is peptidoglycan (murein). Peptidoglycan is relatively higher in gram-positive bacteria: the share of the murein network with a thickness of about 40 layers is 30-70% of the dry mass of the CS. Gram-negative bacteria contain only 1-2 layers of murein, which makes up about 10% of the dry mass of the CW.
Peptidoglycan is represented by polymeric molecules consisting of repeating disaccharide groups, in the formation of which N-acetylglucosamine and N-acetylmuramic acid, the latter binds disaccharides with oligopeptides (out of 20 known amino acids in the CW of bacteria, only 4 were found - glutamic acid, glycine, lysine, and alanine). The composition of the bacteria's CW also includes unique amino acids, for example, diaminopimelic and D-isomers of glutamic acid and alanine. Lysozyme hydrolyzes peptidoglycan by cleaving the glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acid.
Cross-linking of peptidoglycan consists in the formation of a peptide bond between the terminal residue of the side peptide chain (usually D-alanine) with the penultimate residue of the adjacent side chain (L-lysine or diaminopimelic acid).
Gram-positive bacteria have an easily organized but powerful CS, consisting mainly of multiple layers of peptidoglycan, including unique teichoic acid polymers- chains of 8-50 glycerol or ribitol residues linked by phosphate bridges.
Gram-negative bacteria have a thinner (compared to gram-positive bacteria) CS, which includes a bimolecular layer of peptidoglycan and does not contain teichoic acid.
An additional or outer membrane is located on top of the peptidoglycan layer. Its thickness exceeds the size of a peptidoglycan monolayer.
Components of the outer membrane: phospholipid bilayer, proteins, polysaccharides and LPS, arranged in a mosaic pattern.
Phospholipid bilayer attached to peptidoglycan by lipoproteins crossing the periplasmic space.
Protein, including porins forming transmembrane channels are involved in the transport of ions and hydrophilic compounds from the external environment to the periplasm.
LPS formed from a lipid part (lipid A) saturated with core polysaccharides and side polysaccharide chains. The polysaccharide part of LPS has immunogenic properties and is called O-Ar. The lipid portion is thermally stable and is responsible for the biological effects of endotoxin.
Autolysins... Bacterial KS contain autolysins - enzymes that dissolve the peptidoglycan layer. Their activity is necessary for the processes of CW growth, cell division, sporulation, and achievement of a state of competence during transformation.
Cytoplasmic membrane(otherwise the cell, or plasma membrane) is a physical, osmotic and metabolic barrier between the internal contents of a bacterial cell and the external environment. CPM has a complex three-layer structure, it is characterized by pronounced selective permeability. In some bacteria, the periplasmic space is located between the CPM and the CS - a cavity filled with enzymes (ribonuclease, phosphatase, penicillinase, etc.); in gram-negative bacteria, enzymes are freely poured into the environment. Bacterial CPM is composed of proteins, lipids, carbohydrates, and RNA.
Protein CPM is divided into structural and functional. The latter include enzymes involved in synthetic reactions on the membrane surface, redox processes, as well as some special enzymes (for example, permeases).
The MTC is located electronic bacteria transport system, providing energy needs.
Mesosomes - complex invaginations of the CPM, the functions of which have not yet been fully established. They are known to be associated with the nucleoid and are related to cell division and sporulation.
Removal of the CS that protects the adjacent CPM leads to lysis of bacteria or to the formation of protoplasts and spheroplasts, differing in origin (from gram-positive or gram-negative bacteria, respectively), as well as in osmotic resistance. Staying in an isotonic environment, bacteria lacking KS are capable of absorbing O 2 and emitting CO 2, as well as multiplying.
L-shapes. Under the influence of some external factors, bacteria are able to lose CW, forming L-forms (named after the D. Lister Institute, where they were first isolated). Such transformation can be spontaneous (for example, in chlamydia) or induced (for example, under the action of antibiotics). Allocate stable and unstable L-shapes. The former are not capable of reversion, while the latter are reversed to their original forms after the removal of the causative factor.
Representatives of the mycoplasma group (class Mollicutes) do not have cell walls.
Cytoplasm bacteria - the matrix for the implementation of vital reactions - is separated from the CS by a cytoplasmic membrane. The cytoplasm of most bacteria contains DNA, ribosomes, and storage granules; the rest of the space is occupied by the colloidal phase, its main components are soluble enzymes and RNA (template and transport RNA). Various organelles characteristic of eukaryotic cells are absent in bacteria, and their functions are performed by the bacterial CPM.
DNA... There is no nuclear membrane in a bacterial cell. DNA is concentrated in the cytoplasm in a coil called a nucleoid, or genophore.
Genofor bacteria is represented by a double helical circular covalently closed supercoiled DNA molecule, accounting for 2-3% of the dry mass of the cell (more than 10% by volume). The length of the molecular contour varies from 0.25 to 3 mm. The supercoil of bacterial DNA contains no histones. The amount of genetic information encoded in the genophore differs between species (for example, the Escherichia coli gene encodes approximately 4,000 different polypeptides).
Plasmids... Bacteria may have an additional DNA molecule in the form of extrachromosomal elements or integrated into the genophore. Such inclusions are called plasmids (respectively episomal or integrated). Episome DNA is also characterized by a circular shape, but the episome is smaller in size than the bacterial chromosome. Plasmids carry a number of different genes and often determine the virulence of bacteria, but the information contained in plasmids is not absolutely necessary for the bacterial cell.
Ribosomes bacteria are complex globular formations consisting of various RNA molecules and many proteins associated with them. All education functions as a locus for protein synthesis.
70S ribosome... The diameter of bacterial ribosomes is about 20 nm. Sedimentation coefficient - 70S (Swedberg units). Bacterial ribosomes consist of two subunits with a sedimentation coefficient of 50S for one and 30S for the other. The union of the subunits occurs before the start of protein synthesis. Depending on the intensity of growth, a bacterial cell can contain from 5,000 to 50,000 ribosomes.
Bacteriostatic antibiotics (streptomycin, tetracycline, chloramphenicol) inhibit protein synthesis by blocking some metabolic processes in the ribosomes of bacteria.
Spare pellets contain a temporary excess of metabolites. The presence and number of granules vary depending on the type of bacteria and their metabolic activity. In the form of granules, polysaccharides (starch, glycogen, granulosis) can be stored, fats (triglycerides, similar to the fats of higher animals, are stored in yeast of the genus Candida; wax - in mycobacteria and nocardia; β-hydroxybutyric acid polymers - for example, in Bacillus megaterium cells), polyphosphates (for example, volutin, first discovered in Spirillum volutans), sulfur (in bacteria that oxidize sulfide to sulfate), proteins - for example, protoxin (in Bacillus thuringiensis and related species).
DNA-containing viruses either have their own replication enzymes (in the capsid), or their genome encodes information on the synthesis of viral enzymes that ensure the replication of viral nucleic acid. The amount of these enzymes is different when applied to different viruses. For example, the genome of the bacterial T4 virus encodes information on the synthesis of about 30 viral enzymes. Further, the genome of large viruses encodes nucleases that destroy the DNA of the host cell, as well as proteins, the effect of which on cellular RNA polymerase is accompanied by the fact that “the RNA polymerase processed in this way transcribes different viral genes at different stages of viral infection. In contrast, small DNA viruses are more dependent on host cell enzymes. For example, the synthesis of DNA of adenoviruses is provided by cellular enzymes. [...]
Bacterial DNA is a high-polymer compound consisting of a large number of nucleotides - polynucleotides with a molecular weight of about 4 million. A DNA molecule is a chain of nucleotides, where their location has a specific sequence. In the sequence of the arrangement of nitrogenous bases, the genetic information of each species is encoded. Violation of this sequence is possible with natural mutations or under the influence of mutagenic factors. In this case, the microorganism acquires or loses any property. He inherited traits change, that is, a new form of microorganism appears. In all microorganisms - prokaryotes and eukaryotes - the carriers of genetic information are nucleic acids - DNA and RNA. Only a few viruses are an exception: they have no DNA, and hereditary information is recorded or reflected only in RNA. [...]
In bacterial cells, the total amount of DNA bases is 32-65 mol.% Of guanine and cytosine. [...]
The nucleus of a bacterial cell. Approximately 1-2% of the dry mass of microorganisms is accounted for by DNA, which contains the genetic information of the organism. Most microorganisms have areas (or several areas) in which most of the DNA is concentrated, which have a specific structure (or organelle) and are called the nucleus. The nucleus (or nuclear substance) is associated with the cytoplasmic membrane, regardless of whether it is surrounded by elementary membranes (like in amoeba) or not (like in bacteria and blue-green algae). The nuclear substance is activated during the reproduction period and with the onset of age-related changes associated with cell aging. [...]
A DNA segment (gene) that is intended for molecular cloning must have the ability to replicate when transferred into a bacterial cell, i.e., be a replicon. However, he does not have this ability. Therefore, in order to ensure the transfer and detection of cloned genes in cells, they are combined with so-called genetic vectors. The latter must have at least two properties. First, vectors must be capable of replication in cells, and in multiple copies. Secondly, they must provide the possibility of selecting cells containing the vector, i.e., possess a marker for which it is possible to counterselect cells containing the vector together with the gene to be cloned (recombinant DNA molecules). Plasmids and phages meet these requirements. Plasmids are good vectors for the reason that they are replicons and can contain genes for resistance to any antibiotic, which allows selection of bacteria for resistance to this antibiotic and, therefore, easy detection of recombinant DNA molecules. [...]
In bacteria, DNA is less densely packed than in true nuclei; a nucleoid does not have a membrane, a nucleolus and a set of chromosomes. Bacterial DNA is not bound to the main proteins - histones - and in the nucleo-ide is located in the form of a bundle of fibrils. [...]
The use of recombinant DNA techniques to obtain biological agents for pollution control is at an early stage, but there is a method that may prove useful in the foreseeable future - this is genetic probing. The selection of organisms capable of transforming a new compound is often based on the ability to use the substance as a growth substrate. If the growth is weak or the substrate is only comet-bolized, then the selection methods will be unsuitable for identifying the degrading ability. Therefore, it would be useful to develop genetic probing to determine specific sequences in plasmids and chromosomes, this is necessary to determine the catabolic potential, even if this potential is not expressed. Such probes are designed for TOL plasmids. The method can identify one bacterial colony containing the TOL plasmid among 106 Escherichia coli colonies. Such a powerful tool would go a long way toward isolating latent catabolic functions. [...]
The development of an elegant technique for "cloning" DNA to obtain a large number of exact copies of specific DNA fragments (Fig. 13.4) has recently opened up new horizons in the study of the structure, organization and function of the genome. If a double-stranded DIC is cleaved with one of the “restriction” enzymes (one of the nucleases) that specifically recognize and cleave short nucleotide sequences (4-6 pairs), highly reproducible DNA fragments appear. The ends of two DNA strands are usually displaced relative to each other due to the specificity of the cutting sites of a double-stranded molecule, the chains of which are complementary in base composition. DNA is usually inserted into a plasmid gene important for selection, such as an antibiotic resistance gene, which allows bacteria containing such a plasmid to grow in the presence of an antibiotic. [...]
In bacteria, during replication, many copies of plasmids are formed, and thus it is possible to "grow" large amounts of inserted DNA fragments, and then simply isolate them again by digestion with the same restriction enzyme, with separation of the resulting products by gel electrophoresis. The use of this DNA recombination method has revolutionized the study of genes. [...]
Recently, it was found that the mutagenic effect on bacterial-DNA viruses is exerted by rays with a wavelength of 320-400 nm (the region close to the zone of visible light), which have a low intensity. The possible effect of radiation in this wavelength range on plant viruses has not yet been detected. [...]
The curves of the dependence of reassociation on SOT, obtained for bacterial DNA, are devoid of inflections, and the DIC of eukaryotes reassociates according to a different type (Fig. 13.2). At low DNA concentrations and a short incubation time, a noticeable fraction of single-stranded DNA reates, and with an increase in COT, an additional amount of double-stranded molecules is formed, so that a two-phase curve is obtained. Rapid reaturation at low COT values shows that some sequences in eukaryotes are repeated many times, that is, up to 10,000 times or more. [...]
The absence of CXS can also be imitated in cases where the DNA of the test phages does not contain sites recognized by the restriction enzyme existing in the strain under study. This phenomenon is one of the variants of evolutionary adaptive changes in bacterial viruses designed to help them overcome the CXS barrier. The effect of selection pressure in this particular case is expressed in a statistically significant decrease in the number or even complete elimination of nucleotide sequences in phage DNA that are a substrate of restriction endonucleases characteristic of host cells of a bacterial virus. [...]
Lindegren described the possible stages of the formation of a bacteriophage from the DNA of a prophage, suggesting that a prophage arises as a fragment of foreign bacterial DNA that accidentally entered the cell, which divides synchronously with bacterial DNA in the early stages. The next important stage in the development of the virus would be such a change in the prophage, as a result of which its reproduction independent of the DNA of the host cell would become possible; as a result, the prophage would use. all available nucleotides, thereby disrupting the growth of the host cell. Finally, at some later stage, a protective protein coat could be formed and other proteins arose, which should have ensured the survival of DNA outside the host organism and effective infection of new cells. The detached piece of bacterial DNA apparently first encoded proteins adapted to bacterial functions. Very significant changes in DNA are required in order for objects as complex and specialized as, say, the E. coli T2 phage, to arise, containing, moreover, bases that are absent in the bacterial DIC. [...]
The genetic information of bacteria is not limited to the DNA located in the nucleoid of the bacterial cell. As noted in the previous sections of the book, extrachromosomal elements, which have received the general name of plasmids, also serve as carriers of hereditary properties. Unlike DNA of nuclear equivalents, nucleoids, which are organelles of a bacterial cell, plasmids are independent genetic elements. The loss of plasmids or their acquisition does not affect the biology of the cell (the acquisition of plasmids has a positive effect only on the population as a whole, increasing the viability of the species). Transmissive plasmids are those that initiate donor properties in host cells. At the same time, the latter receive a new quality - the ability to conjugate with recipient cells and give them their plasmids. Receiving cells, acquiring plasmids during conjugation, themselves turn into donors. [...]
The absence of adsorption does not exhaust the variety of variants of interaction between bacterial viruses and microbial cells. They illustrate only one side of this phenomenon, namely, the manifestation of cellular defense mechanisms that phenotypically (by the criterion of lack of growth) imitate restriction. However, there is another variant of the cell-bacteriophage interaction, which can mimic the absence of CXS. Examples of such mechanisms are the synthesis of inhibitors and methylases encoded by phage genes that protect viral DNA from the action of type II restriction endonucleases. [...]
The mechanism of the disinfecting action of chlorine is associated with a metabolic disorder of the bacterial cell in the process of water disinfection. At the same time, the influence on the enzymatic activity of bacteria, in particular, on dehydrogenases, catalyzing redox reactions in a bacterial cell, was revealed. A. M. Skidalskaya (1969) studied the effect of chlorine on the process of decarboxylation of bacterial amino acids in the presence of strictly specific enzymes, decarboxylases, and also determined the nucleotide composition of E. coli DNA after the end of the disinfection process at various levels of bactericidal effect. [. ..]
Bacteriophages of the T-group are in the form of drumsticks measuring 100 x 25 nm. Their genome is DNA. They are virulent phages, because after infection of bacterial cells with them, the latter are lysed with the release of a large number of newly synthesized phage particles. [...]
Bacterial plasmids are genetic structures found in the cytoplasm and are DNA molecules ranging in size from 2,250 to 400,000 base pairs. They exist apart from chromosomes in an amount of from one to several tens of copies per one bacterial cell. [...]
Strain Pseu.dom.onas vug1 aeri. pkaSeoIcola possesses a plasmid 150 kbp long, which can replicate autonomously or integrate into the bacterial chromosome. Subsequent inaccurate excision made it possible to obtain a family of plasmids ranging in length from 35 to 270 kbp, some of which contained large segments of chromosomal DNA. [...]
In the course of evolution, bacteria have developed the ability to synthesize so-called restriction enzymes (endonucleases), which have become part of the cellular (bacterial) restriction-modification system. In bacteria, restriction-modification systems are an intracellular immune defense system against foreign DNA. Unlike higher organisms, in which the recognition and destruction of viruses, bacteria and other pathogens occurs extracellularly, in bacteria protection from foreign DNA (DNA of plants and animals in whose body they live) occurs extracellularly, i.e. when foreign DNA penetrates into the cytoplasm of bacteria. In order to protect bacteria during evolution, they also developed the ability to "label" their own DNA with methylating bases on certain sequences. For this reason, foreign DNA, due to the absence of methyl groups in it on the same sequences, is melted (cut) into fragments by different bacterial restriction enzymes, and then degraded by bacterial exonucleases to nucleotides. We can say that in this way bacteria protect themselves from the DNA of plants and animals, in whose body they live temporarily (as pathogens) or permanently (as saprophytes). [...]
The hereditary properties of bacteria or individual traits are encoded in units of heredity - genes linearly located in the chromosome along the DNA strand. Consequently, a gene is a fragment of a DNA strand. Each trait corresponds to a certain gene, and often an even smaller piece of DNA is a codon. In other words, information about all the properties of bacteria is located in a linear order in a DNA strand. At the same time, bacteria have one more feature. The nuclei of eukaryotes usually contain several chromosomes, their number in the nucleus is constant for each species. The bacterial nucleoid contains only one ring of the DNA strand, that is, one chromosome. However, the amount of hereditary traits of a bacterial cell is not exhausted by the amount of information contained in one chromosome or in a circularly closed double-stranded DNA helix. Plasmids contain DNA, which also carries genetic information, transmitted from the mother cell to the daughter. [...]
Mutations are changes in the genetic apparatus of a cell, which are accompanied by changes in the traits controlled by these genes. Distinguish between macro- and micro-damage to DNA, leading to a change in the properties of the cell. Macro-changes, namely: the loss of a DNA section (division), movement of a separate section (translocation) or rotation of a certain section of the molecule by 180 ° (inversion), are observed relatively rarely in bacteria.Microdamages or point mutations are much more characteristic of them, i.e. qualitative changes in individual genes, for example, replacement of a pair of nitrogenous bases. Mutations can be direct and reverse, or reverse. Direct ones are mutations in wild-type organisms, for example, the loss of the ability to independently synthesize growth factors, that is, the transition from proto- to auxotrophy. Reverse mutations represent a return, or reversion, to the wild type. The ability to reverse is characteristic of point mutations. As a result of mutations, such important features as the ability to independently synthesize amino acids and vitamins (auxotrophic mutants) and the ability to form enzymes change. These mutations are called biochemical mutations. Mutations leading to changes in sensitivity to antibiotics and other antimicrobial substances are also well known. By origin, mutations are divided into spontaneous and induced. Spontaneous arises spontaneously without human intervention and are random in nature. The frequency of such mutations is very low and ranges from 1 X 10 “4 to 1 X 10-10. Induced arise when microorganisms are exposed to physical or chemical mutagenic factors. Physical factors with mutagenic effects include ultraviolet and ionizing radiation, as well as temperature. A number of compounds are chemical mutagens, and among them the most active are the so-called supermutagens. Under natural conditions and experimentally, changes in the composition of bacterial populations can occur as a result of the action of two factors - mutations and autoselection, which occurs as a result of adaptation of some mutants to environmental conditions. Such a process is evidently observed in an environment where the predominant food source is a synthetic substance, for example, a surfactant or caprolactam. [...]
A single E. coli cell is surrounded by a three-layer cell wall about 40 nm thick, which is a "bag" or "envelope", which contains the cellular content in the form of approximately 2 x 10 1N g of protein, 6 x 10 16 g of DNA and 2 x 10 14 g RNA (mainly ribosomal RNA). In a bacterial cell, about 2000 different proteins are synthesized, most of which are contained in the cytoplasm. The concentration of some proteins is 10 “® M, while others are on the order of 2 x 10" 4 M (from 10 to 200,000 molecules per cell). [...]
In unicellular organisms, sexual reproduction takes several forms. Conjugation is also found in ciliates, in which, during this process, the nuclei pass from one individual to another, followed by the division of the latter. [...]
Bacteria: prokaryotes ("prenuclear") unicellular organisms. Their cells do not have a nucleus separated from the cytoplasm. However, the genetic program, like in all living organisms, is encoded as a sequence of nucleotides in DNA and carries information about the structure of proteins. Bacterial cells do not contain organelles such as chloroplasts (specialized for photosynthesis) and mitochondria (specialized for cellular respiration and ATP synthesis). These biochemical processes occur in bacteria in the cytoplasm. [...]
The extremely small cell size is a characteristic, but not the main feature of bacteria. All bacteria are represented by a special type of cells, devoid of a true nucleus, surrounded by a nuclear membrane. The analogue of the nucleus in bacteria is the nucleoid - DNA-containing plasma, not delimited from the cytoplasm by a membrane. In addition, bacterial cells are characterized by the absence of mitochondria, chloroplasts, as well as a special structure and composition of membrane structures and cell walls. Organisms whose cells lack a true nucleus are called prokaryotes (prenuclear) or protocytes (that is, organisms with a primitive organization of cells). [...]
Mycoplasma cells are oval in shape, and their size is about 0.1-0.25 nm in diameter (Fig. 43). They are characterized by the presence of a thin outer plasma membrane (thickness - about 8 nm), which surrounds the cytoplasm containing a DNA molecule sufficient to encode about 800 different proteins, RNA of different types, ribosomes with a diameter of about 20 nm. Their cytoplasm contains various inclusions in the form of proteins, lipid granules and other compounds. Due to insufficient stiffness of the cell, mycoplasma membranes pass through bacterial filters. [...]
It was found that activated amino acids bind on ribosomes and are folded into a polypeptide chain in accordance with genetic information received from the nucleus through informational (matrix) RNA (mRNA), which, as it were, reads the corresponding information from DNA and transmits it to the ribosomes. A number of proteins have been synthesized on isolated ribosomes, and the inclusion of labeled amino acids in them has been noted. The role of the matrix in protein synthesis is played by mRNA, which is attached to the ribosome. On the surface of the latter, an interaction occurs between a complex of amino acids, a transport RNA carrying the next amino acid, and the nucleotide sequence of messenger RNA, which functions once on the ribosome and after synthesis of the polypeptide chain breaks down, and the newly synthesized protein accumulates in the ribosomes. In a bacterial cell, with a regeneration period of 90 minutes, the mRNA turnover rate reaches 4-6 seconds. [...]
Cytoplasm is a colloidal solution, the dispersed phase of which is complex protein compounds and substances close to fats, and the dispersion medium is water. Some forms of bacteria in the cytoplasm contain inclusions - droplets of fat, sulfur, glycogen, etc. Constant components of bacterial cells are special outgrowths of the cytoplasmic membrane - mesosomes, which contain enzymatic redox systems. In these formations, there are mainly processes associated with the respiration of bacteria. In small inclusions - ribosomes containing ribonucleic acid, protein biosynthesis is carried out. Most types of bacteria do not have a separate nucleus. The nuclear substance, represented by DNA, is not separated from the cytoplasm and forms a nucleoid. The transportation of substances necessary for the vital activity of the cell, and the removal of metabolic products is carried out through special channels and cavities, separated from the cytoplasm by a membrane that has the same structure as the cytoplasmic one. This structural formation is called the endoplasmic reticulum (reticulum). [...]
The idea of the variability and heredity of bacteria cannot be formed without knowledge of some provisions of the molecular genetics of the prokaryotic cell. The processes of adaptation of microbial cultures to changing environmental conditions are based on variability and heredity, which are sections of bacterial genetics. In presenting the cytology of a bacterial cell, the structure of DNA and RNA and their role in the life of the cell have already been considered. The characteristic structure of DNA is preserved in each species and is passed on to offspring from generation to generation, like other traits. Bacterial DNA is a double-stranded helix that closes into a ring. The ringed strand of bacterial DNA located in the nucleoid contains no protein. Such a DNA ring corresponds to the chromosome of a eukaryotic cell. It is known that the chromosome of eukaryotic cells, in addition to DNA, always contains a protein component. It follows that the concept of a chromosome in eukaryotes is somewhat different from the concept of a chromosome of bacteria. The DNA strand, which is the chromosome of bacteria, of course, differs from species to species. The sugar-phosphate component of DNA is the same for all types of bacteria; the arrangement of nitrogenous bases and their combination, on the contrary, differ in different species. [...]
The increasing indiscriminate use of antibiotics in livestock, which are used in small doses as growth promoters and as a preventive measure against stress-induced gastrointestinal upset in farm animals, is leading to an increasing prevalence of antibiotic resistance R-factor in microbial populations. transmitted from one bacterial cell to another during conjugation. Transmission occurs through a plasmid, which is circular extrachromosomal DNA capable of replication. [...]
In contrast to virulent phages, so-called mild-acting phages, or simply mild phages, are known. A typical representative of such phages is the X phage, which has also been used and is being used as an experimental model to clarify many questions of molecular genetics. Phage X has two important properties. Like virulent phages, it can infect bacterial cells, multiply vegetatively, producing hundreds of copies in cells, and lyse cells with the release of mature phage particles. However, the DNA of this phage can be incorporated into the bacterial chromosome, turning into a prophage. In this case, the so-called lysogenization of bacteria occurs, and bacteria containing a prophage are called lysogenic. Lysogenic bacterial cells can possess a prophage for an infinitely long time without being lysed. Lysis with the release of new phage particles is noted after exposure of lysogenic bacteria to any factor, for example, UV radiation, which induces the development of a prophage into a phage. The study of lysogenic bacteria made it possible to obtain a number of new data on the role of various proteins in the action of phage genes. [...]
The chloroplast genome of a number of higher plants consists of 120 genes. The chloroplast genome is very similar to the bacterial genome in both organization and function. Introns are probably absent in the human mitochondrial genome, but introns are found in the DNA of chloroplasts of some higher plants, as well as in the DNA of fungal mitochondria. It is believed that the chloroplast genomes of higher plants remain unchanged for about several million years. It is possible that such antiquity is also characteristic of the mitochondrial genomes of mammals, including humans. [...]
Modern schemes illustrating the work of genes are built on the basis of a logical analysis of experimental data obtained using biochemical and genetic methods. The use of fine electron microscopic methods allows you to literally see the work of the hereditary apparatus of the cell. Recently, electron microscopic images have been obtained, which show how on the matrix of bacterial DNA, in those areas where RNA polymerase molecules (an enzyme that catalyzes the transcription of DNA into RNA) are attached to DNA, synthesis of i-RNA molecules occurs. Strands of m-RNA, located perpendicular to a linear DNA molecule, move along the matrix and increase in length. As the RNA strands elongate, ribosomes are attached to them, which, in turn, moving along the RNA strand towards the DNA, carry out protein synthesis. [...]
Transduction is the transfer of genetic material from a donor bacterium to a recipient bacterium using a phage. For the first time, the phenomenon of transduction was discovered in 1951 by Lederberg and colleagues at Salmonella typhimurium. Now distinguish between nonspecific and specific transduction. With nonspecific transduction, phage transfer of any trait from the donor bacterium to the recipient bacterium is possible. The transfer is carried out only by moderate (non-virulent) phages. Moderate phages are capable of infecting bacteria, but they do not multiply in them and do not cause lysis, but are included in the DNA of a bacterial cell and in this non-infectious state in the form of a so-called prophage are transmitted from cell to cell during reproduction. Bacterial cultures containing prophage are called lysogenic. In these cultures, with a low frequency (in one of 102 - 105 cells), spontaneous phage proliferation is observed and cell lysis occurs with the release of phage particles, which are detected using indicator bacteria for which such a phage is virulent. [...]
The experiments were carried out on a three-chamber cell, consisting of a central working chamber and two electrode chambers. In a working chamber measuring 25 X 7 X 37 mm (length X width X height), separated from the electrode by cellophane membranes, 750 mg of cotton wool was placed. The initial solution of the test substances was fed through it from bottom to top at a constant rate. The content of compounds in the initial solutions fed into the working chamber (C0) and in the solutions leaving the chamber (Ci) was monitored by the absorption maxima of proteins and nucleic acids in the range of wave numbers (35.5-38) X 103 cm-1 using a Specord UV-VIS UV spectrophotometer. The electrode chambers were filled with granular activated carbon and distilled water was passed through them with a separate flow.
The carrier of the genetic information of bacterial cells is DNA. It is a double helix composed of two polynucleotide chains. DNA has been compared to a spiral staircase and a double electric cable. The DNA backbone is composed of phosphate groups and deoxyribose. Polypeptide chains are interconnected by hydrogen bonds, which hold complementary nitrogenous bases to each other. The structure of bacterial DNA is similar to that of eukaryotic cells (plants, animals, fungi). Unlike bacteria, viruses in viruses are represented by a single nucleic acid - DNA or RNA. Bacterial cells, in addition to DNA, can have genetically complete formations that function autonomously. It should be emphasized that in addition to DNA, the carriers of bacterial heredity are plasmids and episomes. In this regard, any structure of a bacterial cell capable of self-replication is called a replicon, i.e., replicons of bacteria are nucleotides, plasmids, episomes. Plasmids are not bound to the nucleotide, they reside in the cytoplasm of the cell autonomously, episomes can be in a free state, but most often they replicate along with DNA.
The bacterial chromosome is represented by one double-stranded DNA molecule of a circular shape and is called a nucleotide. The stretched nucleotide is about 1 mm long. A nucleotide is the equivalent of a nucleus. It is located in the center of the bacteria. Unlike eukaryotes, the nucleus of bacteria does not have a nuclear membrane, nucleolus and basic proteins (histones). The nucleotide can be detected under a light microscope. To do this, it is necessary to stain the cell with special methods: according to Fehlgen or according to Romanovsky-Giemsa. Electron microscopic examination showed that one end of the DNA is attached to the cell membrane. Apparently, this is necessary for the DNA replication process.
Growing bacteria in a test tube. Photo: Tess Watson
Unlike eukaryotic cells, prokaryotes lack mitochondria, the Golgi apparatus and the endoplasmic reticulum.
Each DNA strand consists of links - nucleotides. The nucleotide contains one of the nitrogenous bases (adenine, guanine, thymine or cytosine) deoxyribose and phosphoric acid. Approximately 1500 nucleotides make up a medium-sized gene. Thus, a gene is a specific section of DNA responsible for the manifestation and development of a specific trait. Genes in DNA are located linearly, they are discrete, capable of self-replication. The sequence of amino acids in the synthesized protein is determined by the sequence of nucleotides in the gene.
From a functional point of view, genes are subdivided into structural, regulators, promoters, and operator genes.
Structural genes are genes that condition the synthesis of enzymes involved in biological reactions and in the formation of cellular structures.
Regulator genes are responsible for the synthesis of proteins that regulate metabolism. These genes can influence the activity of structural genes.
Promoter genes determine the start of transcription. They are a piece of DNA that recognizes DNA-dependent RNA polymerase.
Operator genes mediate between structural genes, promoter region, and regulator genes.
The collection of genes regulators, promoters, operators and structural genes is called an operon. Consequently, the operon is a functional genetic unit that is responsible for the manifestation of a certain trait of microorganisms.
Distinguish between inducible and repressive operons. For example, an inducible operon is the Lac operon, the genes of which control the synthesis of enzymes that utilize lactose in a microbial cell. If the cell does not need lactose, the operon is kept inactive and vice versa.
An example of a repressive operon is the tryptophan operon, which provides tryptophan production. This operon is usually constantly functioning, and its repressor protein is in a passive state. In the case of an increase in the content of tryptophan in the cell, the amino acid binds to the repressor and activates it. The repressor inhibits the working operon and interrupts tryptophan synthesis.
The most important property of DNA is the ability to replicate. Replication can be theta-type and sigma-type. Theta-type DNA replication begins at a certain point in the form of a "bulge" and spreads along the molecule in two directions, passing through an intermediate structure that resembles the Greek letter theta. With this type of replication, one of the strands of the original DNA molecule is preserved, and the second is synthesized from nucleotides.
Sigma-type DNA replication occurs through an intermediate structure reminiscent of the Greek letter sigma, hence the name of this type. This type of replication is observed during the conjugation of bacteria and some phages. With this type of replication, both DNA strands are completed to double-stranded DNA.
The bacterial genome performs the following functions:
· Ensures the transfer of biological properties by inheritance;
· Programs the synthesis of bacterial protein with specific properties;
· Participates in the processes of bacterial variability;
· Ensures the preservation of the individuality of the species;
· Determines multiple resistance to a number of medicinal substances.
MORPHOLOGY OF BACTERIA
Bacteria- microscopic, usually unicellular organisms of plant nature (microflora); certain types of bacteria are characterized by a certain morphology with sufficient constancy. There are three main forms of bacteria - spherical or oval (cocci), sticks (bacilli) and spiral.
Cocchi subdivided into paired - diplococci(neisseria); tetracocci, arranged in 4 in the form of squares; bag-forming cocci, or sarcins located "floors"; streptococci located in chains; staphylococci, forming shapeless clusters, somewhat reminiscent of bunches of grapes.
Sticks... Among the sticks are single, randomly located bacteria (enterobacteria), diplobacilli, located in pairs (along one line), and streptobacilli, forming chains (anthrax sticks).
Spiral bacteria divided into two groups - vibrios and bacteria similar in shape, the curvature of which does not exceed a quarter of a spiral turn (campylobacter), and spirochetes and spirillae, having bends equal to one or more turns of the spiral (the causative agent of syphilis).
Any bacterium is composed of three components: surface structures, cell membranes, and cytoplasm.
The surface structures of bacteria are capsules, flagella and microvilli.
Capsules surround the cell wall of many bacteria, including pathogenic ones. The capsules lack the ordered organization characteristic of the bacterial cell wall. Microcapsules are isolated, which are detected only by electron microscopy in the form of a layer of mucopolysaccharide microfibrils) and macrocapsules (detected by light microscopy).
Most bacterial capsules are composed of complex polysaccharides. Poi staining according to Burri-Gins, or using the swelling reaction according to Neufeld, are detected. Capsules may contain nitrogen-containing compounds, for example in pneumococci (composed of polysaccharides, glucosamine and glucuronic acid), but they may not contain nitrogen, for example, leukonostok capsules (composed of dextrin, levulan, fructosan, and other polymerized monosaccharides).
The capsules of some bacteria (Bacillus anthracis) are composed of polysaccharides and polypeptides formed by monomers of D-glutamic acid, which protects the bacterium from the proteolytic enzymes of phagocytes.
Flagella are present in many bacteria and provide motility. The flagellum is a spirally curved filament driven into rotation by a "motor" located at the point of its attachment to the membrane. In different bacteria, the thickness of the flagella varies from 12 to 18 nm, the length can reach 20 microns.
Bacterial flagella are composed of a protein (flagellin) and are built from its subunits with a relatively low molecular weight. The filaments of the flagella are set in motion by a membrane hinge-like basal hook, fixed with the help of a basal corpuscle, which in gram-positive bacteria consists of one, and in gram-negative bacteria, of two pairs of rings. The rings act as a "drive disk" and "bearing" on the inner surface of the peptidoglycan layer. The whole structure performs the function of a chemomechanical converter (flagellin motor).
Location.
Peritrichs. Flagella are located over the entire surface of the cell wall (bacteria of the Enterobacteriaceae and Bacillaceae families).
Monotrichs. One thick flagellum at one end (vibrios).
Politrichs. A bundle of 2-50 flagella, visible as a single one.
Polar flagella are attached to one or both ends of the bacteria. Lofotrich- a bundle of flagella at one end of a bacterium (Pseudomonas). Amphitrix- bipolar beams (Spirillum).
Microvilli(drank, fimbria) these are protein hairs (from 10 to several thousand) 3-25 nm thick and up to 12 microns long.
A. Ordinary drank. Many gram-negative bacteria have long, thin pili (fimbriae) that begin at the cytoplasmic membrane and penetrate the cell wall. They are formed by proteins of the same type, the molecules of which form a spiral thread. Their the main function is the attachment of bacteria to substrates, for example, the surface of mucous membranes, which is an important factor in colonization and infection. In addition, the increased surface area of the bacterial cell gives it additional advantages in utilizing environmental nutrients.
B. F-drank(fertility factor) - special formations involved in the conjugation of bacteria. They look like hollow protein tubes with a length of 0.5-10 microns. Their formation is encoded by plasmids.
Cell membrane most bacteria consist of a cell wall and an underlying cytoplasmic membrane.
The bacterial cell wall is thin, elastic and rigid, and may be completely absent in some bacteria (for example, L-forms and mycoplasmas). The cell wall protects bacteria from external influences, gives them a characteristic shape, through which nutrients are transported and metabolites are released. A variety of receptors for bacteriophages, bacteriocins and various chemicals are located on its surface. CS maintains the constancy of the internal environment and withstands significant pressure from the inside (for example, the partial pressure of intracellular substances of gram-positive bacteria can reach 30 atmospheres). The structure and composition of CS elements determine the ability to perceive dyes, i.e. their tinctorial properties... One of the basic principles of bacterial differentiation is based on the ability to perceive and retain the coloring complex of gentian violet with iodine inside the cell, or lose it after treatment with alcohol (Gram stain). Accordingly, gram-positive (colored in violet-purple) and gram-negative (red) are distinguished.
The main component of bacterial CS is peptidoglycan (murein). Peptidoglycan is relatively higher in gram-positive bacteria: the share of the murein network with a thickness of about 40 layers is 30-70% of the dry mass of the CS. Gram-negative bacteria contain only 1-2 layers of murein, which makes up about 10% of the dry mass of the CW.
Peptidoglycan is represented by polymeric molecules consisting of repeating disaccharide groups, in the formation of which N-acetylglucosamine andN-acetylmuramic acid, the latter binds disaccharides with oligopeptides (out of 20 known amino acids in the CW of bacteria, only 4 were found - glutamic acid, glycine, lysine, and alanine). The composition of the bacteria's CW also includes unique amino acids, for example, diaminopimelic and D-isomers of glutamic acid and alanine. Lysozyme hydrolyzes peptidoglycan by cleaving the glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acid.
Cross-linking of peptidoglycan consists in the formation of a peptide bond between the terminal residue of the side peptide chain (usually D-alanine) with the penultimate residue of the adjacent side chain (L-lysine or diaminopimelic acid).
Gram-positive bacteria have an easily organized but powerful CS, consisting mainly of multiple layers of peptidoglycan, including unique teichoic acid polymers- chains of 8-50 glycerol or ribitol residues linked by phosphate bridges.
Gram-negative bacteria have a thinner (compared to gram-positive bacteria) CS, which includes a bimolecular layer of peptidoglycan and does not contain teichoic acid.
An additional or outer membrane is located on top of the peptidoglycan layer. Its thickness exceeds the size of a peptidoglycan monolayer.
Components of the outer membrane: phospholipid bilayer, proteins, polysaccharides and LPS, arranged in a mosaic pattern.
Phospholipid bilayer attached to peptidoglycan by lipoproteins crossing the periplasmic space.
Protein, including porins forming transmembrane channels are involved in the transport of ions and hydrophilic compounds from the external environment to the periplasm.
LPS formed from a lipid part (lipid A) saturated with core polysaccharides and side polysaccharide chains. The polysaccharide part of LPS has immunogenic properties and is called O-Ar. The lipid portion is thermally stable and is responsible for the biological effects of endotoxin.
Autolysins... Bacterial KS contain autolysins - enzymes that dissolve the peptidoglycan layer. Their activity is necessary for the processes of CW growth, cell division, sporulation, and achievement of a state of competence during transformation.
Cytoplasmic membrane(otherwise the cell, or plasma membrane) is a physical, osmotic and metabolic barrier between the internal contents of a bacterial cell and the external environment. CPM has a complex three-layer structure, it is characterized by pronounced selective permeability. In some bacteria, the periplasmic space is located between the CPM and the CS - a cavity filled with enzymes (ribonuclease, phosphatase, penicillinase, etc.); in gram-negative bacteria, enzymes are freely poured into the environment. Bacterial CPM is composed of proteins, lipids, carbohydrates, and RNA.
Protein CPM is divided into structural and functional. The latter include enzymes involved in synthetic reactions on the membrane surface, redox processes, as well as some special enzymes (for example, permeases).
The MTC is located electronic bacteria transport system, providing energy needs.
Mesosomes - complex invaginations of the CPM, the functions of which have not yet been fully established. They are known to be associated with the nucleoid and are related to cell division and sporulation.
Removal of the CS that protects the adjacent CPM leads to lysis of bacteria or to the formation of protoplasts and spheroplasts, differing in origin (from gram-positive or gram-negative bacteria, respectively), as well as in osmotic resistance. Staying in an isotonic environment, bacteria lacking KS are capable of absorbing O 2 and emitting CO 2, as well as multiplying.
L-forms. Under the influence of some external factors, bacteria are able to lose CW, forming L-forms (named after the D. Lister Institute, where they were first isolated). Such transformation can be spontaneous (for example, in chlamydia) or induced (for example, under the action of antibiotics). Allocate stable and unstableL-forms. The former are not capable of reversion, while the latter are reversed to their original forms after the removal of the causative factor.
Representatives of the mycoplasma group (class Mollicutes) do not have cell walls.
Cytoplasm bacteria - the matrix for the implementation of vital reactions - is separated from the CS by a cytoplasmic membrane. The cytoplasm of most bacteria contains DNA, ribosomes, and storage granules; the rest of the space is occupied by the colloidal phase, its main components are soluble enzymes and RNA (template and transport RNA). Various organelles characteristic of eukaryotic cells are absent in bacteria, and their functions are performed by the bacterial CPM.
DNA... There is no nuclear membrane in a bacterial cell. DNA is concentrated in the cytoplasm in a coil called a nucleoid, or genophore.
Genofor bacteria is represented by a double helical circular covalently closed supercoiled DNA molecule, accounting for 2-3% of the dry mass of the cell (more than 10% by volume). The length of the molecular contour varies from 0.25 to 3 mm. The supercoil of bacterial DNA contains no histones. The amount of genetic information encoded in the genophore differs between species (for example, the Escherichia coli gene encodes approximately 4,000 different polypeptides).
Plasmids... Bacteria may have an additional DNA molecule in the form of extrachromosomal elements or integrated into the genophore. Such inclusions are called plasmids (respectively episomal or integrated). Episome DNA is also characterized by a circular shape, but the episome is smaller in size than the bacterial chromosome. Plasmids carry a number of different genes and often determine the virulence of bacteria, but the information contained in plasmids is not absolutely necessary for the bacterial cell.
Ribosomes bacteria are complex globular formations consisting of various RNA molecules and many proteins associated with them. All education functions as a locus for protein synthesis.
70 Sribosomes... The diameter of bacterial ribosomes is about 20 nm. Sedimentation coefficient - 70S (Swedberg units). Bacterial ribosomes consist of two subunits with a sedimentation coefficient of 50S for one and 30S for the other. The union of the subunits occurs before the start of protein synthesis. Depending on the intensity of growth, a bacterial cell can contain from 5,000 to 50,000 ribosomes.
Bacteriostatic antibiotics (streptomycin, tetracycline, chloramphenicol) inhibit protein synthesis by blocking some metabolic processes in the ribosomes of bacteria.
Spare pellets contain a temporary excess of metabolites. The presence and number of granules vary depending on the type of bacteria and their metabolic activity. In the form of granules, polysaccharides (starch, glycogen, granulosis) can be stored, fats (triglycerides, similar to the fats of higher animals, are stored in yeast of the genus Candida; wax - in mycobacteria and nocardia; β-hydroxybutyric acid polymers - for example, in Bacillus megaterium cells), polyphosphates (for example, volutin, first discovered in Spirillum volutans), sulfur (in bacteria that oxidize sulfide to sulfate), proteins - for example, protoxin (in Bacillus thuringiensis and related species).
DNA (deoxyribonucleic acid) is a polymer that performs the functions of storing, transmitting and realizing information on the vital activity of organisms. It serves as an information carrier about the structure of various types of RNA and proteins.
The nucleus of a prokaryotic cell contains circular DNA - a closed polymer that does not have terminal genes. These molecules (nucleotides) are characterized by attachment in cells to the membrane from the inside. Circular plasmids are present in the cells of prokaryotes and lower eukaryotes. Linear DNA contains cells of animals, plants and fungi (eukaryotes).
The beginning of the rapid development of molecular biology provoked the discovery of a double-stranded structure in 1953. Outstanding scientists who made a decisive contribution to this breakthrough Francis Crick, James Watson, Maurice Wilkins were awarded the Nobel Prize in 1962.
Carriers
Some viruses contain circular genomic DNA. In humans, circular DNA is found in the cytoplasm of the mitochondria. The annular carriers are cells of prenuclear organisms - prokaryotes: cellular organelles, mitochondria and plastids; the simplest unicellular bacteria. Prokaryotes are represented by many species.
Circular DNA
Representative phototrophs, chlorophylls and carotenoids, use light as an energy source. Sulfur bacteria, assimilating hydrogen, oxidize hydrogen sulfide to sulfur and sulfates. Cyanobacteria, splitting water, release molecular oxygen. Bacteria - chemoautotrophs use inorganic substances for energy. Nitrites are obtained from ammonia by assimilating carbon. They are capable of oxidizing ferrous to ferric. Bacteria are organotrophs that use the chemical reaction of fermentation as their source of life. They are also called anaerobic.
There are also prokaryotes that have adapted to live in the body of living beings. Among them, there are species that benefit their owners. For example, bacteria that help digestion and assimilation of nutrients. There are species that do neither harm nor benefit.
Another representative of cyanea prokaryotes is blue-green algae. They purify water, help the mineralization of decay products.
Replication
The circular structure of DNA is most effective for its duplication, that is, replication. Ring-type replication is a fairly straightforward process of doubling a molecule. That is, according to the principle of complementarity, there is a division and build-up along another chain. As a result, we get two daughter DNA, identical copies of the original. Replication is nothing more than the growth of a multicellular organism or the multiplication of a unicellular organism. In the case of a circular structure of the molecule, the doubling process proceeds most accurately without error due to the absence of terminal genes.
Application and prospects
A new era in medicine is the invention of vaccines. Much research is currently being done on vaccine development. The purpose of such research is to prevent human morbidity.
DNA vaccines are produced using recombinant DNA techniques. The infecting bacteria is weakened by artificial gene mutations. A similar principle is used for the production of live recombinant vaccines. They are obtained by introducing a gene encoding an immunogenic protein of a cell, and then embedded inside a stable polymer of circular DNA - a plasmid. In addition, elements are inserted into the plasmid for efficient insertion of the gene into the eukaryotic cell and protein synthesis. The converted plasmid is placed in a bacterial propagation medium. After that, plasmid DNA is obtained from the bacteria, purifying from impurities. This is a live vaccine. It promotes immunity to pathogens. These plasmids do not enter human chromosomes.
The ability of live vaccines to develop immunity against pathogens has been proven. 
Genetic engineering provides great opportunities for transforming eukaryotic and prokaryotic cells for protein production. This allows you to analyze the structure and function of proteins for their use as a medicine.
Genes are introduced inside the simplest organisms that produce important proteins for medical purposes. Scientific laboratories use specialized equipment to obtain drugs (antibiotics, enzymes, hormones, vitamins, and other active compounds) from specially bred microorganisms.
Escherichia coli is one example. Its cells are used to reproduce the human hormone insulin. The hormone produced in this way has no impurities, does not give undesirable effects in comparison with animal insulin. E. coli is capable of producing growth hormone. Previously, it was made from cadaveric material, but such a hormone could include viruses. The antiviral drug interferon was born in the laboratory thanks to genetic engineering.
The basis of genotraction is the discovery of the structure of DNA. Fundamental is the correction of genetic material through controlled change.
Today, the task of delivering genetically active material to problem cells containing the defective gene is under development. That is, the main thing is to organize an efficient delivery method and ensure the long-term functioning of the genetic material. One of the ways is the use of pure DNA inserted into a plasmid. The very issue of delivery of corrective material has been practically resolved. But such tasks as stability, controllability, material safety are undergoing a finalization stage.
Gene therapy opens up great prospects in the treatment of hereditary diseases, disorders of the central nervous system, infectious and oncological diseases.
Despite the significant advances in science in the study of structure, many questions remain. The most pressing question is the reason for the presence of circular DNA in the simplest organisms, and linear - in higher organisms.