Changing the set of genes. Changing your own genes with just one injection - unless you're lucky, of course
Hereditary information is transmitted from one generation of microorganisms to another by a large number of genes contained in the nucleotide of each cell. The information contained in the gene is read and used to synthesize a specific enzymatic protein. The presence of this enzymatic protein creates the chemical basis for the manifestation of a particular trait in a microorganism. As a result, all hereditary traits of microorganisms are the end products of biochemical processes, which is equally applicable to physiological features and morphological traits.
A single gene may control the inheritance of a single trait, or may determine several or many traits affecting different parts of a microorganism's cell. In other cases, several genes may jointly control the expression of any one trait. In a bacterial chromosome, all genes are arranged in a linear sequence. The genes for certain traits lie at corresponding locations on the chromosome, called loci. Bacteria are usually haploid: they have only one set of genes.
The complete set of genes possessed by a cell of a microorganism is the genotype of that microorganism. The manifestation of inherited morphological features and physiological processes in individuals is called a phenotype (from the Greek faino - to show, show). Microorganisms similar in genotype can differ significantly in phenotype, that is, in the way hereditary traits manifest. Phenotypic differences between microorganisms that are identical in genotype are called modifications (phenotypic adaptations). Thus, the interaction of genetic inclinations with the external environment can be the cause of the emergence of different phenotypes, even if the genotypes are identical. However, the potential range of such phenotypic differences is controlled by the genotype.
Modifications, as a rule, exist as long as the specific factor of the external environment that caused them acts, they are not transmitted to descendants and are not inherited by them. Thus, phenol treatment of bacteria with flagella prevents the development of flagella in these organisms. However, offspring of phenol-treated flagellate-free bacteria grown on a phenol-free medium develop normal flagella.
It has been established that almost all morphological and physiological characteristics of microorganisms are directly or indirectly controlled by the genetic information contained in DNA.
The information that DNA carries is not something absolutely stable and unchanging. If the information transmitted from one generation to another were not capable of change, then the range of reactions of closely related organisms to environmental factors would also be constant, and any sudden change that turned out to be harmful to microorganisms with a frozen genotype could lead to the extinction of the species. . Consequently, the information transmitted from generation to generation is not absolutely stable, which is useful for the survival of the species.
Changes in the genotype, called mutations (from Latin mutare - change), occur spontaneously, that is, by chance. Such mutations cause dramatic changes in single genes responsible for the information contained in the cell. As a rule, rare DNA replication errors are not accompanied by massive changes in information involving a large number of various features. However, organisms have developed other mechanisms that contribute to the emergence of dramatically changed heredity in the offspring. These mechanisms consist in the association and usually in the immediate shuffling (recombination) of genes belonging to closely related, but genotypically different organisms. During genetic recombination, fragments of the chromosome of the microorganism that is the donor are inserted into the chromosome of one microbial cell serving as a recipient.
In microorganisms, the ability to recombine genes can be represented in the form of a diagram.
At present, three types of transfer of traits from a donor to a recipient are known in microorganisms: transformation, conjugation, and transduction. microorganism aerobic iron salt
Mutation: An allele that occurs in a population with a frequency equal to or less than 1%. The reason for the variability of organisms is not only combinational variability, but also mutations. These are such changes in the genome that consist either in the appearance of new alleles (they are called gene mutations), or in the rearrangement of chromosomes, for example, in the transfer of a piece of one chromosome to another (then they are called chromosome mutations), or in changes in the genome (genomic mutations). An example of a genomic mutation is a change in the number of chromosomes in a cell. Individual mutations rarely occur. For example, gene mutations occur in about one gene in hundreds of thousands or even a million. However, since there can be quite a lot of genes, mutations make a significant contribution to variability. Mutations have been discussed above both in connection with DNA and in connection with the work of Morgan. For Morgan, a sign of mutation was some morphological difference in Drosophila, which is inherited. It showed that in the genetic material of the mutant there is a difference from the genome of wild-type flies. Where it comes from, the question was not raised at first. Mutations are randomly occurring persistent changes in the genotype that affect entire chromosomes, their parts or individual genes. Mutations can be large, clearly visible, for example, lack of pigment (albinism), lack of plumage in chickens (Fig. 11), short legs, etc. However, most often mutational changes are small, barely noticeable deviations from the norm. The term "mutation" was introduced into genetics by one of the scientists who rediscovered Mendel's laws - G. de Vries in 1901 (from Latin mutatio - change, change). This term meant newly emerged, without the participation of crosses, hereditary changes. As already mentioned, mutations are divided into gene mutations, chromosome mutations and genomic mutations (Fig. 118). It should be noted that with chromosomal and genomic mutations, no new genes arise in the genome; in fact, it is some shuffling of old genes. At first glance, it would be more logical to attribute such variability to combinational variability. However, when sex is determined, the appearance of an extra X chromosome in the genome can cause radical changes in the phenotype. Therefore, historically there has been a tradition to attribute such changes in the genome to mutations. In addition to classifying mutations according to the way they occur, they are also classified according to other features. 1). Direct mutations are mutations that cause a deviation from the wild type. Back mutations are a return to the wild type. 2). If mutations occur in germ cells, they are called generative mutations (from lat. generatio - birth), and if in other cells of the body - somatic mutations (from the Greek soma - body). Somatic mutations can be transmitted to offspring through vegetative reproduction. 3). According to the results, mutations are divided into beneficial, neutral and harmful (including sterile, semi-lethal and lethal). Semi-lethal mutations are harmful mutations that greatly reduce the viability, but not fatal, but lethal - leading to the death of the organism at one stage or another of development. Sterile mutations are those that do not affect the viability of the organism, but sharply (often to zero) reduce its fertility. Neutral mutations are mutations that do not change the viability of the organism. Normally, DNA is copied exactly during the replication process and remains unchanged between two successive replications. But occasionally errors occur and the DNA sequence changes - these errors are called mutations. A mutation is a stable inherited change in DNA, regardless of its functional significance. This definition implies a change in the primary nucleotide sequence, while changes of a different kind, such as methylation, are usually referred to as epigenetic events. Mutations in somatic cells may cause aging, cancer, and other less significant changes in the body. Mutations in the germ cells of parents are inherited by children. The concept of mutation stability remains generally valid, but the discovery of dynamic mutations due to an increase in the number of trinucleotide repeats shows that some mutations change during division of somatic or germ cells. Some mutations are lethal and cannot be passed on to the next generation, while others are not so dangerous and remain in the offspring. From an evolutionary standpoint, mutations provide enough genetic diversity to allow species to adapt to environmental conditions through natural selection. Each genetic locus is characterized by a certain level of variability, that is, the presence of different alleles, or variants of DNA sequences, in different individuals. In relation to a gene, alleles are divided into two groups - normal, or wild-type alleles, in which the function of the gene is not impaired, and mutant ones, leading to disruption of the gene. In any population and for any gene, wild-type alleles are predominant. Mutation is understood as all changes in the DNA sequence, regardless of their location and impact on the viability of the individual. Thus, the concept of mutation is broader than the concept of a mutant allele. In the scientific literature, variants of gene sequences that are often found in populations and do not lead to noticeable dysfunctions are usually considered as neutral mutations or polymorphisms, while the concepts of "mutation" and "mutant allele" are often used as synonyms. Mutations can capture sections of DNA of different lengths. This may be a single nucleotide, then we will talk about a point mutation, or an extended section of the molecule. In addition, given the nature of the changes, we can talk about nucleotide substitutions, deletions and insertions (insertions) and inversions. The process of mutations is called mutagenesis. Depending on the factors that cause mutations, they are divided into spontaneous and induced. Spontaneous mutations occur spontaneously throughout the life of an organism under normal environmental conditions. Spontaneous mutations in eukaryotic cells occur at a frequency of 10-9-10-12 per nucleotide per cell generation. Mutations that occur as a result of mutagenic influences under experimental conditions or under adverse environmental influences are called induced. Among the most important mutagenic factors, first of all, it is necessary to note chemical mutagens - organic and inorganic substances that cause mutations, as well as ionizing radiation. There are no significant differences between spontaneous and induced mutations. Most spontaneous mutations result from a mutagenic effect that is not recorded by the experimenter. It should be emphasized that the usefulness or harmfulness of mutations depends on the environmental conditions: in some environmental conditions, a given mutation is harmful, in others it is beneficial. For example, a mutation that causes albinism will be beneficial for the inhabitants of the Arctic, providing a white protective coloration, but harmful, unmasking for animals living in other conditions. Variability provides material for the action of natural selection and underlies the evolutionary process. Mutations provide material for the work of breeders. Obtaining and selecting useful (for humans) mutations underlie the creation of new varieties of plants, animals and microorganisms. The classification of mutations is based on the molecular processes of their occurrence.
The history of the formation of microbiology as a science
Microbiology (from the Greek micros. small, bios. life, logos. doctrine) is a science that studies the structure, vital activity and ecology of microorganisms of the smallest forms of life of plant or animal origin, not visible to the naked eye.
Microbiology studies all representatives of the microcosm (bacteria, fungi, protozoa, viruses). At its core, microbiology is a fundamental biological science. To study microorganisms, she uses the methods of other sciences, primarily physics, biology, bioorganic chemistry, molecular biology, genetics, cytology, and immunology. Like any science, microbiology is divided into general and particular. General microbiology studies the patterns of structure and vital activity of microorganisms at all levels. molecular, cellular, population; genetics and their relationship with the environment. The subject of study of private microbiology are individual representatives of the microworld, depending on their manifestation and influence on the environment, wildlife, including humans. Private sections of microbiology include: medical, veterinary, agricultural, technical (section of biotechnology), marine, space microbiology. Medical microbiology studies pathogenic microorganisms for humans: bacteria, viruses, fungi, protozoa. Depending on the nature of the studied pathogenic microorganisms, medical microbiology is divided into bacteriology, virology, mycology, and protozoology. Each of these disciplines considers the following issues: - morphology and physiology, i.e. carries out microscopic and other types of research, studies metabolism, nutrition, respiration, growth and reproduction conditions, genetic characteristics of pathogenic microorganisms; - the role of microorganisms in the etiology and pathogenesis of infectious diseases; - main clinical manifestations and prevalence of the diseases caused; - specific diagnostics, prevention and treatment of infectious diseases; - ecology of pathogenic microorganisms. Medical microbiology also includes sanitary, clinical and pharmaceutical microbiology. Sanitary microbiology studies the microflora of the environment, the relationship of microflora with the body, the influence of microflora and its metabolic products on human health, develops measures to prevent the adverse effects of microorganisms on humans. The focus of clinical microbiology. The role of conditionally pathogenic microorganisms in the occurrence of human diseases, diagnosis and prevention of these diseases. Pharmaceutical microbiology studies infectious diseases of medicinal plants, spoilage of medicinal plants and raw materials under the action of microorganisms, contamination of medicinal products during preparation, as well as finished dosage forms, methods of asepsis and antiseptics, disinfection in the production of medicinal products, technology for obtaining microbiological and immunological diagnostic, prophylactic and medicinal preparations. Veterinary microbiology studies the same issues as medical microbiology, but with reference to microorganisms that cause animal diseases. Microflora of the soil, flora, its influence on fertility, soil composition, infectious diseases of plants, etc. are the focus of agricultural microbiology. Marine and space microbiology studies, respectively, the microflora of the seas and reservoirs and outer space and other planets. Technical microbiology, which is part of biotechnology, develops a technology for obtaining various products from microorganisms for the national economy and medicine (antibiotics, vaccines, enzymes, proteins, vitamins). The basis of modern biotechnology is genetic engineering. Numerous discoveries in the field of microbiology, the study of the relationship between macro- and microorganisms in the second half of the 19th century. contributed to the rapid development of immunology. Initially, immunology was considered as the science of the body's immunity to infectious diseases. At present, it has become a general medical and general biological science. It has been proven that the immune system serves to protect the body not only from microbial agents, but also from any substances that are genetically alien to the body in order to maintain the constancy of the internal environment of the body, i.e. homeostasis. Immunology is the basis for the development of laboratory methods for the diagnosis, prevention and treatment of infectious and many non-communicable diseases, as well as the development of immunobiological preparations (vaccines, immunoglobulins, immunomodulators, allergens, diagnostic preparations). Immunobiotechnology is engaged in the development and production of immunobiological preparations. independent branch of immunology. Modern medical microbiology and immunology have achieved great success and play a huge role in the diagnosis, prevention and treatment of infectious and many non-infectious diseases associated with immune system disorders (oncological, autoimmune diseases, organ and tissue transplantation, etc.).
Iron transformations
In a normal temperate climate, a healthy person needs 10-15 mg of iron per day in food. This amount is quite enough to cover its losses from the body. Our body contains from 2 to 5 g of iron, depending on the level of hemoglobin, weight, sex and age. Especially a lot of it in the hemoglobin of the blood - two-thirds of the total amount contained in the body; the rest is stored in the internal organs, mainly in the liver.
Iron from food is absorbed in the intestines and transferred to the blood vessels, where it is captured by a special transport protein. This protein was first discovered back in 1920 in blood serum. But the methods of analysis that existed at that time did not allow us to accurately determine its structure. Only in 1945 the Swedish scientists K-Holmberg and K.-B. Laurell studied this iron-containing protein in detail, established its nature and gave it the name "transferrin".
Interestingly, a similar protein was also isolated from milk in 1939 and was named lactoferrin. The molecular weights of these proteins are approximately the same and are about 80 thousand. They are able to bind 2 iron atoms, giving them a characteristic reddish color. Lactoferrin was then found in tears, bile and other body fluids. Strictly speaking, transport proteins perform a similar function to hemoglobin, only they do not carry oxygen, but iron, and trivalent iron. It is transported mainly to the bone marrow, a small part goes to the liver and spleen, where it is stored as a reserve fund; a small amount goes to the formation of myoglobin and some enzymes of tissue respiration. The main organs in which iron is exchanged are the bone marrow, liver and small intestine, where there are special receptors that serve to receive transferrin.
In the bone marrow, hemoglobin and red blood cells are formed, the duration of which is about 4 months. After this time, hemoglobin is destroyed, breaking up into heme and globin. Further transformations of these substances go in different ways. Globin is hydrolyzed to amino acids, and heme in the liver is converted into bile pigments - into green biliverdin, which is reduced to bilirubin, which has a yellow-orange or brown color. Only an insignificant part of these pigments enters the blood again, but mostly they are excreted from the body. In liver diseases such as jaundice, an excess amount of bilirubin enters the bloodstream, which gives the characteristic yellow color to the skin and whites of the eyes.
We said above that some of the iron in the body is stored in reserve. Under normal conditions, such storage iron is part of the red-brown water-soluble protein ferritin, which is widely distributed in the plant and animal kingdom. It is found in vertebrates, invertebrates, flowers, and even fungi. This speaks of its universal role and ancient evolutionary origin. For the first time, ferritin was isolated by F. Laufberger in 1937 from the spleen of a horse. Somewhat later, its role as a compound that accumulates iron in the body was established. Ferritin molecules are iron aggregates in the form of complex compounds surrounded by an apoferritic protein with a molecular weight of 480 thousand. Such a complex can contain up to 4.5 thousand iron atoms. If transferrin is similar in its value to hemoglobin, then ferritin is similar in this respect to myoglobin.
So, the main amount of iron circulates in our body, part of it accumulates in ferritin, and a very small amount settles in the form of insoluble hemosiderin protein granules. In ferritin and hemosiderin, iron can be stored for a long time - until it is urgently needed by the body, for example, during blood loss. Then the spare iron is used for the synthesis of hemoglobin. How it is extracted from storage proteins has not yet been precisely established. As it is not established, in all likelihood, a number of substances, one way or another connected with the iron of our body.
Microorganisms and the environment. Physical factors (salt concentration)
In previous chapters, various microorganisms have been described, grouped according to their physiological and biochemical properties. There were also mentions of habitats. The information obtained now allows us to consider the relationship of microorganisms with their environment. We will focus first on the basic concepts and concepts of ecology. This science studies the behavior of organisms in their natural habitats, their relationship with each other and with the environment. The first traces of life date back to more than 3 billion years ago; these were microorganisms that dominated the Earth's biosphere until a period of about 0.5 billion years ago. Thus, prokaryotes not only stand at the origins of earthly life, not only did the whole variety of eukaryotic forms develop from them, but they always existed after that. The higher forms of life throughout their evolution have never been alone; they were constantly either crowded out or supported by the ubiquitous unicellular organisms. Among the modern higher forms of life there are those that have established themselves not only in the fight against their own kind, but also in relationships with microorganisms. Many organisms in the process of evolution have developed tolerant partnerships - mutualistic symbiosis. Microorganisms already existed when the surface of our planet assumed its present form; they were already present at a time when continents were shifting, sediments several thousand meters thick were being created, the earth's crust was sinking and folded many times, deposits of ores, coal, oil and natural gas deposits arose. Microorganisms actively participated in many of these processes. For at least 80% of the entire period of organic evolution, the Earth was inhabited exclusively by microorganisms. If fossil remains of microbes are rarely found, then the data of comparative physiology and biochemistry serve as sufficient support for the classification of prokaryotes according to the type of metabolism. However, when reading the section on the evolution of organisms, one should take into account the fact that there are still many gaps and conjectures in this area. PHYSICAL FACTORS
The mineral water of the Dead Sea has a high thermal conductivity and heat capacity. Thus, the first factor of influence is temperature. The main site of application is the skin. Irritation of the nerve receptors of the skin causes diffuse inhibition in the cerebral cortex, i.e. removal of overvoltage as a result of psychological stress, stress, etc. With intense exposure to heat during bathing, heat transfer is enhanced by sweating, which contributes to the detoxification of the body. In addition, the thermal effect on the muscles contributes to their relaxation. In a Dead Sea salt bath, a column of water 40-50 cm high exerts a pressure of 1/5 of the atmosphere, which stimulates the function of breathing and blood circulation. The vessels of the abdominal organs react to changes in the temperature of the skin: an increase in external temperature, accompanied by an expansion of the vessels of the skin, leads to a narrowing of the vessels of the abdominal organs and vice versa. The exception is the kidneys: vasodilation of the skin leads to vasodilation of the kidneys. To obtain an adequate vascular response, the temperature of all parts of the body must be equal before taking a bath. For example, cold feet should be warmed in a basin or under running hot water. In this case, the vascular reaction will go in the right direction and the effect of the bath will be positive. Based on the foregoing, it is recommended to take baths with Dead Sea salts at a water temperature of 37-39 degrees, lasting from 10 to 15 minutes.
Phosphorus conversion
The phosphorus cycle is much simpler than carbon and nitrogen. It mainly consists of the mineralization of organic phosphorus and the transfer of phosphate salts from less soluble to more soluble salts (phosphorus mobilization). In the body of animals and plants, phosphorus is part of protein substances (nucleoproteins) and some lipoids (lecithins). This phosphorus, after the death of animals and plants, when decomposed by putrefactive and other microbes, mineralizes and turns into phosphoric acid, which quickly binds with bases and turns into sparingly soluble salts of calcium, magnesium, iron, unsuitable for plant nutrition. Further, the transfer of these sparingly soluble salts into soluble ones occurs as a result of biochemical processes accompanied by acid formation. These processes produce acid-forming bacteria, namely nitrifying, sulfur bacteria, thionic, ammonifying, forming large amounts of carbonic acid, especially you. mycoides.
The sparingly soluble tricalcium salt is converted into the easily soluble dicalcium phosphorus salt:
Ca3(PO4)2+2CO2+2H2O=2CaHPO4+Ca(HCO3)2
Ca3(PO4)2+4HNO3=Ca(H2PO4)2+2Ca(NO3)2,
which is taken up by plants.
Under anaerobic conditions, soil bacteria can reduce phosphate salts up to hydrogen phosphide in the presence of organic matter. This results in the loss of valuable phosphate salts. The best remedy against this harmful process is good soil aeration.
Aerobic decomposition of cellulose
Decomposition of cellulose under aerobic conditions. In well-aerated soils, cellulose is decomposed and used by aerobic microorganisms (fungi, myxobacteria, and other eubacteria), and under anaerobic conditions, mainly clostridia. Under aerobic conditions, a significant role in the decomposition of cellulose belongs to fungi. In this respect, they are more effective than bacteria, especially in acidic soils and in the decomposition of cellulose encrusted with lignin (wood). Representatives of two genera, Fusarium and Chaetomium, play an important role in this process. Cellulose is also digested by Aspergillus fumigatus, A. nidulans, Botrytis cinerea, Rhizoctonia solani, Trichoderma viride, Chaetomium globosum and Myrothecium verrucaria. The last three species serve as test organisms for detecting the breakdown of cellulose, as well as for testing agents used to impregnate various materials in order to protect them from the action of cellulose-decomposing microorganisms. Fungi form cellulases, which can be isolated from the mycelium and from the nutrient medium. Cytophaga and Sporocytophaga are aerobic bacteria that decompose cellulose. They are easiest to isolate by the usual method of enrichment culture in liquid media. These two genera, closely related to myxobacteria, include many species. Little is known about the use of cellulose by myxobacteria and their primary effect on it. They failed to detect either extracellular cellulase or any cellulose cleavage products. The cells of these bacteria closely adhere to the cellulose fibers, being parallel to the fiber axis. Apparently, they hydrolyze cellulose only in close contact with the fiber, and the hydrolysis products are immediately absorbed. On agar with cellulose, Cytophaga colonies are never surrounded by a transparent zone in which the products of enzymatic cleavage of cellulose would be located. In addition to Cytophaga species, mixo bacteria of the genera Polyangium, Sporangium and Archangium, forming fruiting bodies, can grow on cellulose. Many of those aerobic bacteria that could be called "omnivores" can also use cellulose as a substrate for growth. Some of them use cellulose, apparently only when there are no other sources of carbon; the synthesis and release of cellulases in such bacteria are regulated by the type of catabolite repression. Some forms similar to Pseudomonas were formerly grouped under Cellvibrio. They are now described as Pseudomonas fluorescens var. cellulosa. Of the coryneform bacteria, Cellulomonas should be mentioned; this bacterium was even supposed to be used to obtain protein from cellulose. Among actinomycetes, only a few cellulose-decomposing species have been described: Micromonospora chalcea, Streptomyces cellulosae, Strepto-sporangium. Decomposition of cellulose under anaerobic conditions. Under anaerobic conditions, cellulose is most often broken down by mesophilic and thermophilic clostridia. The thermophilic species Clostridium thermocellum grows on simple synthetic media, using cellulose or cellobiose as a substrate, and ammonium salts as a source of nitrogen; This bacterium does not utilize glucose and many other sugars. The products of cellulose fermentation are ethanol, acetic, formic and lactic acids, molecular hydrogen and CO2. Outside the cells, cellulose is broken down, probably, only to cellobiose. Fermentation of cellulose by the mesophilic species Clostridium cellobioparum leads to similar products. The long rod of Bacillus dissolvens behaves similarly to the Cytophaga species mentioned above: the cells of this bacterium adhere closely to cellulose fibers and do not release cellulase into the medium.
Respiration is a process that provides the metabolism of living organisms from the environment with oxygen (O2) and removes some of the metabolic products of the body (CO2, H2O, etc.) into the environment in a gaseous state. Respiration is the main form of dissimilation in humans, animals, plants and many microorganisms. During respiration, substances rich in chemical energy belonging to the body are oxidized to energy-poor end products (carbon dioxide and water), using molecular oxygen for this.
The term "anaerobes" was introduced by Louis Pasteur, who discovered butyric fermentation bacteria in 1861. Anaerobic respiration is a set of biochemical reactions that occur in the cells of living organisms when other substances (for example, nitrates) are used as the final proton acceptor and refers to energy metabolism processes (catabolism, dissimilation), which are characterized by the oxidation of carbohydrates, lipids and amino acids to low molecular weight compounds.
Lactic acid fermentation is the anaerobic conversion of sugar by lactic acid bacteria to form lactic acid.
Alcoholic fermentation is a chemical fermentation reaction carried out by yeast, as a result of which one molecule of glucose is converted into 2 molecules of ethanol and 2 molecules of carbon dioxide.
Butyric fermentation is the process of converting sugar by butyric bacteria under anaerobic conditions to form butyric acid, carbon dioxide and hydrogen.
Nitrification is a microbiological process of oxidation of ammonia to nitrous acid or its further to nitric acid, which is associated either with energy production (chemosynthesis, autotrophic nitrification) or with protection from reactive oxygen species formed during the decomposition of hydrogen peroxide (heterotrophic nitrification).
Denitrification (dissimilation nitrate reduction) is the sum of microbiological processes of reduction of nitrates to nitrites and further to gaseous oxides and molecular nitrogen. As a result, their nitrogen returns to the atmosphere and becomes inaccessible to most organisms. It is carried out only by prokaryotes (both bacteria and archaea) under anaerobic conditions and is associated with their energy production.
Nitrogen fixation - fixation of molecular atmospheric nitrogen, diazotrophy. The process of restoring the nitrogen molecule and including it in the composition of its biomass by prokaryotic microorganisms. The most important source of nitrogen in the biological cycle. In terrestrial ecosystems, nitrogen fixers are localized mainly in the soil.
Streptococci. Streptococci are round, small, arranged in chains of various lengths, cocci. Often these chains consist of paired cocci - diplo-streptococci. Streptococci stain for Gram. In sputum, they are with bronchitis, abscess, gangrene of the lungs. Streptococci are considered pathogenic if they are among and within leukocytes.
Staphylococci. Round cocci of various sizes, located in groups, as well as single stained with conventional paints and Gram. Staphylococci are often found inside white blood cells. In sputum, streptococci are often observed simultaneously.
Tetracoccus (micrococcus tetragenus). They have the appearance of oval or round cocci of various sizes, arranged in four and surrounded by a common capsule. Gram-stained. In sputum, they are observed in abscess and gangrene of the lungs, bronchitis, and also as a secondary infection in tuberculosis, more often in the presence of cavities.
SARCINA (from lat. sarcina - a bunch, a knot), spherical bacteria (cocci) that form cubic packet-like clusters. motionless; not pathogenic.
BACILLA (from the Latin bacillum - stick), rod-shaped bacteria. In a narrow sense, bacilli are rod-shaped bacteria that form intracellular spores (resting forms that are resistant to high temperatures, radiation and other adverse effects). Some bacilli cause diseases in animals and humans, such as anthrax, tetanus.
Clostridia (lat. Clostridium) is a genus of gram-positive, obligate anaerobic bacteria capable of producing endospores. Separate cells are elongated sticks, the name of the genus comes from the Greek klptfed (spindle). Many species that were assigned to Clostridia by this morphological trait were later reclassified. Endospores can be located centrally, eccentrically and terminally. The diameter of endospores often exceeds the diameter of the cell.
Spirilla (Novolatin spirilla, diminutive of Latin spira, Greek speira - bend, twist, coil) bacteria that have the shape of spirally convoluted or arcuately curved sticks. Sizes of S. vary in different species over a wide range: width from 0.6-0.8 to 2-3 microns, length from 1-3.2 to 30-50 microns. C. do not form spores, are gram-positive, mobile thanks to a bundle of flagella located at the end of the cell. There are S.'s types which are badly growing on laboratory nutrient media; individual species have not been isolated in pure culture at all. S. - saprophytes; They live in fresh and salt water bodies, they are also found in decaying stagnant water, slurry and the contents of the intestines of animals.
Spirochetes (lat. Spirochaetales) - an order of bacteria with long (3--500 microns) and thin (0.1--1.5 microns) spirally (Greek ureisb "curl") twisted (one or more turns of the spiral) cells .
Actinomycetes (obsolete radiant fungi) are bacteria that have the ability to form branching mycelium at some stages of development (some researchers, emphasizing the bacterial nature of actinomycetes, call them analogues of mushroom mycelium thin filaments) with a diameter of 0.4--1.5 microns, which manifested in them in optimal conditions for existence. They have a gram-positive type of cell wall and a high (60–75%) content of GC pairs in DNA.
Mycobacteria (Mycobacteriaceae) are a family of actinomycetes. The only genus is Mycobacterium. Some representatives of the genus Mycobacterium (eg M. tuberculosis, M. leprae) are pathogenic for mammals (see tuberculosis, mycobacteriosis, leprosy).
Ensiling is one of the ways to preserve and store succulent feed. High-quality silage has a pleasant aromatic smell of pickled vegetables and fruits, light green, yellowish green and brownish green color with an acidity of 3.9-4.2. It is an excellent component of diets in the winter-stall period, it is readily eaten by animals.
silage - dehydration of green plants in order to create a water deficit that prevents the development of unwanted bacteria during storage of the mass without air access. Unlike ensiling, the fermentation processes during the preparation of haylage are inhibited, since the grasses are dried in the field to a moisture content of 45-55%, as a result of which the so-called physiological dryness of the mass is achieved.
Gram-negative bacteria (denoted Gram (-)) are bacteria that, unlike Gram-positive bacteria, become colorless when washed using the Gram stain method. After bleaching, they are usually stained with an additional dye (magenta) pink.
THERMOGENESIS is the production of heat by the body to maintain a constant body temperature and ensure the operation of all its systems, from the functioning of intracellular processes, to ensuring blood circulation, digestion of food, the ability to move, etc.
Pasteurization is a one-time heating process of most often liquid products or substances up to 60 ° C for 60 minutes or at a temperature of 70-80 ° C for 30 minutes. The technology was discovered in the middle of the 19th century by the French microbiologist Louis Pasteur. It is used to disinfect food products, as well as to extend their shelf life.
Sterilization (from lat. sterilis - barren) - the complete release of various substances, objects, food products from living microorganisms.
Gram-positive bacteria (denoted Gram (+)) are bacteria that, unlike Gram-negative bacteria, retain their color, do not discolor when washed using the Gram stain of microorganisms.
Adhesion (from Latin adhaesio - sticking) in physics - adhesion of surfaces of dissimilar solid and / or liquid bodies. Adhesion is due to intermolecular interaction (van der Waals, polar, sometimes - the formation of chemical bonds or mutual diffusion) in the surface layer and is characterized by the specific work required to separate the surfaces. In some cases, adhesion may be stronger than cohesion, i.e. adhesion within a homogeneous material, in such cases, when a tearing force is applied, a cohesive rupture occurs, i.e. a rupture in the volume of the less strong of the contacting materials.
Commensalism (lat. con mensa - literally “at the table”, “at the same table”) is a way of coexistence of two different types of living organisms, in which one population benefits from the relationship, and the other does not receive any benefit or harm (for example , common silverfish and humans).
PHAGIA (from the Greek phagos - a devourer), an integral part of compound words, corresponding in meaning to the words eating, absorbing.
Satelliteism is an increase in the growth of one type of microorganism under the influence of another microorganism. With the joint growth of several types of microbes, their physiological functions can be activated, which leads to a faster effect on the substrate. For example, yeast or sarcin colonies, releasing metabolites into the nutrient medium, stimulate the growth of some other microorganisms around their colonies.
Phytohormones are low molecular weight organic substances produced by plants and having regulatory functions. Low concentrations of phytohormones (up to 10–11 M) are active, while phytohormones cause various physiological and morphological changes in parts of plants that are sensitive to their action.
1. Forms of microorganisms
2. The structure of a bacterial cell
3. Organs of movement of bacteria
4. Microscope device
5. Forms of colonies
6. Colony profiles.
7. The edge of the colonies
8. Nitrogen conversion cycle
9. Phosphorus conversion cycle
10. Sulfur conversion cycle
Variability is the result of the reaction of the genotype in the process of individual development of the organism (ontogenesis) to environmental conditions.
Variability is one of the main factors of evolution. It serves as a source of natural and artificial selection.
Distinguish hereditary And non-hereditary variability. Hereditary variability includes such changes in traits that are determined by the genotype and persist over a number of generations. Hereditary variation results from mutations(mutational variability) or as a result recombination the genetic material of two individuals, such as parents (combinative variability).
Combination variability is the result of recombination of genes and recombination of chromosomes carrying different alleles, and is expressed in the appearance of a variety of organisms - descendants that have received new combinations of genes, already existing on parent forms.
In eukaryotic organisms, combinative variability occurs due to the recombination of the genetic material of the parents during sexual reproduction. Gene recombination is carried out in various ways. This process may be associated with the redistribution of whole chromosomes. Such a mechanism, in accordance with Mendel's third law, ensures the independent inheritance of unlinked genes and traits. Most often, recombination in the narrow sense of the word is associated with crossing over, that is, with the recombination of genes localized in homologous chromosomes.
In bacteria, three mechanisms have been found for combining and recombining genetic material: transformation, conjugation and transduction.
Non-hereditary variability includes changes in the characteristics of an organism that are not preserved during sexual reproduction. This so-called modification variability - the property of organisms to change their phenotype depending on environmental conditions while maintaining the stability of the genotype. Modification changes have a massive adaptive character and disappear when conditions change. They are of no interest to evolution because they are not inherited. The limits within which an organism is able to respond to environmental conditions are called reaction rate. A wide reaction rate provides a good adaptive ability of the body. The reaction rate is determined by the genotype of the individual.
Epigenetic variability associated with a change in gene expression without changing their structure. The set of working genes changes in the course of individual development and in response to external influences. These changes can be either non-inherited or persist for several generations.
mutational variability.
The term "mutation" was proposed at the beginning of the 20th century by G. De Vries. As a result of many years of research on the evening primrose plant, he discovered a number of forms that differed from the main mass, and these differences persisted from year to year. Summarizing his observations, De Vries formulated the mutation theory: "A mutation is a phenomenon of a spasmodic, discontinuous change in a hereditary trait."
The main provisions of the mutation theory.
- Mutations occur suddenly as discrete changes in traits.
- New forms are stable.
- Unlike modifications, mutations do not form a continuous series, they do not group around any middle type. They represent qualitative changes.
- Mutations manifest themselves in different ways and can be both beneficial and harmful.
- The probability of detecting mutations depends on the number of individuals studied.
- Similar mutations can occur more than once.
Subsequently, all the provisions of this theory, except for point 3, were confirmed.
In the modern sense Mutations are inherited changes in genetic material.
There are several types of mutation classification
- By the nature of the changes in the genome: genomic, chromosomal, gene.
- By manifestation in a heterozygote: dominant recessive.
- By deviation from the norm (wild type): direct, reverse.
- Depending on the reasons that caused the mutation: spontaneous, induced.
- By localization in the cell: nuclear, mitochondrial, chloroplast.
- In relation to the possibility of inheritance: generative, somatic.
TO genomic mutations include changes in the number of chromosomes. The minimum set of chromosomes, when each chromosome is represented by one copy, is called haploid. Gametes are haploid. The haploid set of chromosomes is denoted by the letter n. Usually found in somatic cells diploid a set of chromosomes containing a double compared to a haploid set of chromosomes (2 n). In the life cycles of eukaryotes, cases of supernormal multiplication of the number of chromosomes occur. If such changes are proportional (multiple) to the haploid set, then they speak of polyploidization. If the number of copies of only one or several chromosomes of a set changes, then they say about aneuploidy.
Polyploidy is widely and unevenly distributed in nature. Polyploid fungi and algae are known, polyploids are often found among flowering plants. The macronuclei of ciliates are highly polyploid (more than 100 n).
Autopolyploidy- repetition in the cell of the same chromosome set. One of the ways in which polyploids arise is the formation of unreduced gametes. Doubling the number of chromosomes may be the result of endoreduplication of genetic material: cells that were in the original plant in the G2 phase, instead of mitosis, re-enter the S phase. Then such cells with a double number of chromosomes divide and give rise to polyploid clones. Another reason for the appearance of polyploid cells is endomitosis - the process of nondisjunction of chromosomes in anaphase due to dysfunction of the division spindle. For the artificial production of polyploids, agents are used that block the divergence of duplicated chromosomes, for example, colchicine produced by the colchicum plant, vinblastine obtained from another plant - periwinkle, camphor.
Allopolyploids- organisms containing sets of chromosomes of two or more species, obtained as a result of hybridization and polyploidization. Some plant species are natural allopolyploids, for example, the genome of common wheat includes two genomes of related diploid wheats and the genome of Aegilops. An example of an artificial allopolyploid is a hybrid of radish and cabbage obtained in 1927 by G.D. Karpechenko.
Polyploidy often leads to more powerful and productive organisms. However, the fertility of polyploids is reduced due to improper conjugation of chromosomes in meiosis and uneven divergence of chromosomes in gametes, triploids do not give offspring.
Chromosomal mutations associated with chromosome rearrangements aberrations. There are intrachromosomal aberrations (parts of one chromosome are involved) and interchromosomal aberrations (parts of different non-homologous chromosomes are involved).
Intrachromosomal rearrangements:
Defishensi - end shortages;
Deletions - loss of parts of a chromosome that does not affect the telomere;
Duplications - doubling (multiplication) of a part of a chromosome;
Inversions are changes in the alternation of genes in a chromosome as a result of a 180-degree rotation of a section of the chromosome.
Interchromosomal rearrangements- translocations - the movement of part of one chromosome to another, not homologous to it.
A special position is occupied by transpositions, or insertions - changes in the localization of small sections of genetic material, including one or more genes. Transpositions can occur both within the same chromosome and between chromosomes. Therefore, transpositions occupy an intermediate position between intrachromosomal and interchromosomal rearrangements.
Gene (point) mutations These are changes in the sequence of nucleotides in DNA. Point mutations are classified into the following groups:
a) transitions - the replacement of purine by purine; pyrimidine to pyrimidine;
b) transversions - replacement of pyridine by purine and vice versa;
c) insertion of an extra pair of nucleotides;
d) deletion of a pair of nucleotides.
The main reason for the occurrence of mutations is the "three P errors": replication, repair and recombination. Such errors occur when these three processes are dysregulated. A positive correlation has been shown between mutation rates and defects in DNA polymerases and other replication and repair enzymes.
DNA bases can exist in several tautomeric forms. If adenine is in its normal amine form, it pairs with thymine. Being in a rare imine form, adenine pairs with cytosine. This tautomeric transition of adenine during subsequent replication can lead to the transition of AT-HC. The rare enol tautomer of thymine is able to pair with guanine, and this will also lead to a base pair change. All transitions and transversions can be explained by some ambiguity in the correspondence between nucleotides in complementary DNA strands.
The frequency of spontaneous, that is, mutations that have arisen without the influence of external factors, varies from 10 -4 to 10 -10. For example, streptomycin resistance mutations in E. coli occur at a frequency of 4 . 10 -10, and the appearance of white eyes in Drosophila - 4. 10 -5 . In various microorganisms - bacteria, bacteriophages, fungi - the overall frequency of spontaneous mutation in terms of genome replication is approximately the same - about 1%. Several (many) genes can mutate at the same time.
In 1925-1927. The mutagenic effect of X-rays was discovered. In the 1930s, the mutagenic effect of a number of chemicals was discovered. Physical mutagens include, in addition to X-rays, ultraviolet and gamma radiation, and fast neutrons. Chemical mutagens are very diverse in terms of chemical structure and mechanism of action. For example, nitrous acid causes deamination of nucleic acid bases, and alkylating supermutagens cause the addition of methyl or ethyl groups to them. This results in mismatching. Acridine compounds promote the appearance of nucleotide insertions.
Particularly mobile migratory genetic elements have been found in the genomes of many organisms. They were first discovered by the American researcher B. Mack Klintock in 1940. While studying the color mutation of grains in corn, she found an unstable mutation that reverted to the wild type with an increased frequency. Unstable mutations are often accompanied by chromosomal abnormalities. The genes that cause chromosome breaks have been named mobile elements because they could move from one part of the chromosome to another. These elements are characterized by the following properties:
- they can move from one site to another;
- their integration into a given region affects the activity of genes located nearby;
- loss of TE at a given locus transforms a previously mutable locus into a stable one;
- at sites where MEs are present, chromosomal aberrations and chromosome breaks can occur.
The maize genome contains several families of transposable elements. The members of each family can be subdivided into two classes:
Autonomous elements that can be cut and transposed. Their introduction leads to the appearance of unstable alleles.
Non-autonomous elements that can only be activated to transpositions by certain autonomous elements (members of the same family).
In maize, the families Ac-Ds (activator-dissociator), Spm (suppressor-mutator), and Dt are best studied. The Ac element is 4563 bp long and has inverted repeats at the ends. It encodes the enzyme transposase, which transports Ac and Ds. Ds elements result from deletions of internal regions of the Ac gene.
At present, mobile elements have been discovered in many species of plants, animals, and microorganisms. IS elements (insertion sequences) have been found in E. coli. They are characterized by the following characteristic features:
1) at the ends of the IS-elements are inverted (rotated by 180 degrees relative to each other) repeats from several pairs to several tens of base pairs.
2) most IS elements contain the transposase gene, which controls the synthesis of the enzyme responsible for their movement.
3) at the insertion point of each IS-element, on its flanks, a duplication in a straight orientation of 4-9 base pairs is always found.
Typically, the E. coli chromosome contains several IS elements.
Later, more complex TEs were found in bacteria, i.e., transposons, which differ from IS elements in that they include some genes that are not related to the transposition process itself, for example, the gene for resistance to antibiotics, heavy metals, and other inhibitors. Transposons are usually flanked by long straight or inverted repeats, which are often IS elements.
eukaryotic TEs, for example, yeast Ty 1, and multiple dispersed Drosophila genes, are similarly structured.
According to the mechanisms of transposition, MEs are divided into two classes. Elements of the first class are moved using reverse transcriptase, that is, DNA is synthesized on the RNA template of the mobile element. Reverse transcriptase (revertase) not only leads to the synthesis of a DNA strand into RNA, but also carries out the synthesis of a second complementary strand of DNA, and the ZNK matrix decomposes and is removed. Double-stranded DNA is synthesized in the cytoplasm, and then moves to the nucleus and can be integrated into the genome. Such mobile elements are called retrotransposons. Retrotranposons make up more than 2% of the genome in Drosophila and up to 40% in plants. Elements of the second class move directly as DNA elements and are called transposons. They all have short inverted repeats at the ends.
Functional value of mobile elements.
1. Movements and introduction of ME into genes can cause mutations. About 80% of spontaneous mutations in different Drosophila loci are caused by TE insertions. Introducing into the gene, ME can damage the exon by breaking it. In this case, the gene will no longer encode the protein. Getting into the region of protomores or enhancers, the transposable element can damage the regulatory region of the gene and change its expression. Insertion into the intron region may be harmless.
2. The state of gene activity may change. The long terminal repeats of retrotransposons and the retrotransposons themselves contain nucleotide sequences that are transcriptional enhancers. Therefore, the movement of these signals in the genome can change the regulation of gene activity.
3. As a result of crossing over between identically oriented elements, duplication and deletion of the material located between the insertions occurs. If the MEs are oriented in opposite directions, an inversion occurs.
In recent decades, there has been tremendous progress in the study epigenetic variability, which is understood as a variety of heritable, although possibly reversible, changes in gene expression that are not associated with a violation of the structure of the genetic material. It is now clear that epigenetic factors play a significant role in ontogenetic differentiation, and disruption of this system is associated with many pathological conditions. Many genes are regulated by DNA-protein interactions. This applies, in particular, to the control of gene expression by transcription factors, the reverse regulation of the work of a gene by its product or products of other genes when they reach certain concentrations. If, under the influence of some external influences, changes occur in such regulatory proteins, their consequences will be expressed in the form of a violation of the expression of certain genes.
Epigenetic changes can be inherited not only at the cellular level, but also at the level of the whole organism. Gene expression is affected by the nature of chromosome heterochromatinization, which depends not only on endogenous, but also on exogenous factors. This phenomenon was first studied by A. A. Prokofieva-Belgovskaya, who, in the materials of her doctoral dissertation, convincingly showed that “the development of a trait in an organism is not determined only by the presence of a certain gene on a chromosome site, but is also controlled by the state of this site, which is detected at the microscopic level, that is, whether this region of the chromosome is in the interphase in a decondensed state or is it condensed. The activity of many proteins is determined by their post-translational modifications - phosphorylation, acetylation, methylation. In particular, such modifications related to histone proteins or proteins involved in the regulation of gene function can significantly affect their transcription. An important role in the regulation of gene expression is played by spatial relationships between genes and the corresponding regulatory complexes. All these features of the work of genes determine a phenomenon well known to geneticists, called " position effect"- that is, the different nature of the phenotypic manifestation of the gene, depending on its localization in specific regions of the genome. The list of phenomena that can be explained in terms of epigenetic variability can be continued.
One of the most well-studied epigenetic mechanisms is DNA methylation passing, most often, on the 5th carbon of cytosine. This DNA modification plays a significant role in the regulation of eukaryotic gene expression. The 5'-untranslated regions of genes contain sequences enriched in CpG pairs, the so-called CpG islands. In many cases, gene inactivation is achieved by methylation of these sequences, and this state can be stably maintained over many generations of cells. Methyl groups disrupt the interactions between DNA and proteins, thereby preventing the binding of transcription factors. In addition, methylated regions of DNA can interact with transcriptional repressors.
University of Chicago alumnus Dr. Josiah Zayner has created a set of tools and materials that allow CRISPR to edit the genome at home. According to the scientist, an inexpensive set shows that today, intervention in DNA is a common craft, and not an art with an unpredictable result. The scientist himself willingly demonstrates this idea: in his apartment there are many Petri dishes with genetically modified bacteria created in the kitchen using his own kit.
Biologist Josiah Zayner offers a new approach to popularizing the most advanced part of biological science
The CRISPR genome editing tool was invented three years ago and is a simple, fast and precise way to manipulate DNA. However, until now, CRISPR has been used only by qualified specialists in specialized laboratories.
CRISPR technique allows you to edit the genome even in the kitchen
Josiah Zainer was the first to bring to market a simplified and accessible CRISPR toolkit for genome intervention. This is a provocative initiative, because today the way of life and thinking of society is largely shaped by terrorism. As a result, genetic modification of bacteria at home is associated in most cases with the development of lethal strains for bioterrorists.
Scientists also fear that non-professionals may accidentally create super strains of microorganisms that are resistant to antibiotics. Even if such bacteria and fungi appear to be harmless to humans, they can cause unpredictable changes in the environment.
Gene modifications in the kit are safe and allow only minor changes in the external parameters of microorganisms, such as their color
However, according to Zainer, his kit contains only harmless bacteria and yeasts that cannot survive in a harsh environment and do not live long. Gene modification using kit tools allows only minor changes in their properties, such as color or smell.
A kit for home experiments in genetic engineering costs $120
Josiah Zayner believes that through his recruitment, many talented and curious people can be of great help to biology. Interest in genetic engineering is of great value to science, so a cheap Zayner kit can play an even greater role in the history of biology than a few expensive state-of-the-art laboratories.
It should be noted that crowdfunding brought Zayner's project more than $55,000 - 333% more than the developer of the home gene editing kit had planned.
In the fifties of the XX century, scientists were faced with a strange phenomenon. They drew attention to the fact that some viruses infect different strains of the same bacteria in different ways. Some strains - for example, E. coli - became infected easily and quickly spread the infection throughout the colony. Others became infected very slowly or were completely resistant to the viruses. But once having adapted to this or that strain, in the future the virus infected it without difficulty.
It took biologists two decades to figure out this selective resistance of bacteria. As it turned out, the ability of certain strains of bacteria to resist viruses - it was called restriction (that is, "restriction") - is due to the presence of special enzymes in them that physically cut the viral DNA.
The peculiarity of these proteins - restriction enzymes - is that they recognize a small and strictly defined DNA sequence. Bacteria "target" restriction enzymes to rare sequences that they themselves avoid in their genes - but which may be present in viral DNA. Different restriction enzymes recognize different sequences.
Each strain of bacteria has a specific arsenal of such enzymes and thus responds to a specific set of "words" in the virus genome. If we imagine that the genome of a virus is the phrase "mom washed the frame", then the virus will not be able to infect a bacterium that recognizes the word "mom", but a bacterium that targets the word "uncle" will be defenseless. If the virus manages to mutate and turn into, say, a “woman washing a frame,” then the first bacterium will also lose its protection.
Why is the discovery of "bacterial immunity" at the very top of the list of the most important achievements of molecular biology? It's not the bacteria themselves, or even the viruses.
Measure a piece of DNA
The scientists who described this mechanism almost immediately drew attention to the most important detail of this process. Restriction enzymes (more precisely, one of the types of these enzymes) are able to cut DNA at a well-defined point. Returning to our analogy, an enzyme that targets the word "mother" in DNA binds to that word and cuts it, for example, between the third and fourth letter.
Thus, for the first time, researchers have the opportunity to “cut” the DNA fragments they need from genomes. With the help of special "gluing" enzymes, the resulting fragments could be stitched together - also in a certain order. With the discovery of restriction enzymes, scientists had all the necessary tools for "assembling" DNA in their hands. Over time, a slightly different metaphor took root to refer to this process - genetic engineering.
Although there are other methods of working with DNA today, the vast majority of biological research of the last twenty or thirty years would not have been possible without restriction enzymes. From transgenic plants to gene therapy, from recombinant insulin to induced stem cells, any work involving genetic manipulation uses this "bacterial weapon".
Know the enemy by sight
The immune system of mammals - including humans - has both innate and acquired defense mechanisms. The innate components of immunity usually react to something in common that unites many enemies of the body at once. For example, innate immunity can recognize components of the bacterial cell wall that are the same for thousands of different microbes.
Acquired immunity relies on the phenomenon of immunological memory. It recognizes specific components of specific pathogens, "remembering" them for the future. Vaccination is based on this: the immune system “trains” on a killed virus or bacterium, and later, when a living pathogen enters the body, it “recognizes” it and destroys it on the spot.
Innate immunity is a border checkpoint. It protects from everything at once and at the same time from nothing in particular. Acquired immunity is a sniper who knows the enemy by sight. As it turned out in 2012, bacteria have something similar.
If restriction is a bacterial analogue of innate immunity, then the role of acquired immunity in bacteria is performed by a system with a rather cumbersome name CRISPR / Cas9, or "Crisper".
The essence of Crisper's work is as follows. When a bacterium is attacked by a virus, it copies part of the virus's DNA to a special place in its own genome (this "repository" of information about viruses is called CRISPR). Based on these saved "identikit" of the virus, the bacterium then makes an RNA probe capable of recognizing the viral genes and binding to them if the virus tries to infect the bacterium again.
The RNA probe itself is harmless to the virus, but this is where another player comes into play: the Cas9 protein. It is a "scissors" responsible for the destruction of viral genes - like a restriction enzyme. Cas9 grabs onto the RNA probe and, as if on a leash, is delivered to the viral DNA, after which it is given a signal: cut here!
In total, the entire system consists of three bacterial components:
1) DNA storage of "identikit" old viruses;
2) an RNA probe made on the basis of these "identikit images" and capable of identifying a virus by them;
3) protein "scissors" tied to an RNA probe and cutting viral DNA exactly at the point from which the "identikit" was taken last time.
Almost instantly after the discovery of this “bacterial immunity”, everyone forgot about bacteria and their viruses. The scientific literature exploded with enthusiastic articles about the potential of the CRISPR/Cas9 system as a tool for genetic engineering and medicine of the future.
As in the case of restriction enzymes, the Crisper system is able to cut DNA at a strictly defined point. But compared to the "scissors" discovered in the seventies, it has huge advantages.
Restriction enzymes are used by biologists to “mount” DNA exclusively in a test tube: you must first make the desired fragment (for example, a modified gene), and only then introduce it into a cell or organism. "Crisper" can cut DNA on the spot, right in a living cell. This makes it possible not only to manufacture artificially introduced genes, but also to “edit” entire genomes: for example, to remove some genes and insert new ones instead. Until recently, one could only dream of such a thing.
As it became clear over the past year, the CRISPR system is unpretentious and can work in any cell: not only bacterial, but also mouse or human. "Install" it in the desired cell is quite simple. In principle, this can be done even at the level of whole tissues and organisms. In the future, this will make it possible to completely remove defective genes - for example, those that cause cancer - from the adult human genome.
Let's say that the phrase "mom washed the frame" present in your genome causes you to have a painful craving for gender stereotypes. To get rid of this problem, you need a Cas9 protein - always the same - and a pair of RNA probes aimed at the words "mama" and "frame". These probes can be anything - modern methods make it possible to synthesize them in a few hours. There are no restrictions on the number at all: you can “cut” the genome at least at a thousand points at the same time.
Targeting the body
But Crisper's value goes beyond the scissor function. As many authors note, this system is the first tool known to us with which it is possible to organize a "meeting" of a certain protein, a certain RNA and a certain DNA at the same time. This in itself opens up enormous opportunities for science and medicine.
For example, the Cas9 protein can be turned off the "scissor" function, and instead bind to it another protein - say, a gene activator. With the right RNA probe, the resulting pair can be sent to the right place in the genome: for example, to a poorly functioning insulin gene in some diabetics. By organizing the meeting of the activating protein and the disabled gene in this way, it is possible to precisely and finely tune the functioning of the organism.
You can bind not only activators, but anything in general - say, a protein that can replace a defective gene with its “backup copy” from another chromosome. Thus, in the future, it will be possible to cure, for example, Huntington's disease. The main advantage of the CRISPR system in this case is precisely its ability to “send expeditions” to any point in DNA that we can program without much difficulty. What is the task of each particular expedition - is determined only by the imagination of the researchers.
Today it is difficult to say what kind of problems the CRISPR/Cas9 system will be able to solve in a few decades. The global community of geneticists is now reminiscent of a child who was allowed into a huge hall filled to overflowing with toys. The leading scientific journal Science recently published an overview of the latest advances in the field called "The CRISPR Craze" - "Crisper Madness". And yet, it is already obvious now: bacteria and fundamental science have once again given us a technology that will change the world.
In January, there were reports of the birth of the first primates whose genome was successfully modified by the CRISPR/Cas9 system. As a test experiment, the monkeys were introduced with mutations in two genes: one associated with the immune system, and the other responsible for the deposition of fat, which opaquely hints at a possible application of the method to homo sapiens. Perhaps the solution to the problem of obesity by genetic engineering is not such a distant future.
Waiting for the birth of a child is the most wonderful time for parents, but also the most terrifying. Many are worried that the baby may be born with some kind of handicap, physical or mental disabilities.
Science does not stand still, it is possible to check the baby for developmental abnormalities at a short time in pregnancy. Almost all of these tests can show whether everything is fine with the child.
Why does it happen that completely different children can be born to the same parents - a healthy child and a child with disabilities? It is determined by genes. In the birth of an underdeveloped baby or a child with physical disabilities, gene mutations associated with a change in the DNA structure affect. Let's talk about this in more detail. Consider how this happens, what gene mutations are, and their causes.
What are mutations?
Mutations are physiological and biological changes in cells in the structure of DNA. The reason may be radiation (during pregnancy, X-rays should not be taken, for injuries and fractures), ultraviolet rays (long exposure to the sun during pregnancy or being in a room with ultraviolet light lamps turned on). Also, such mutations can be inherited from ancestors. All of them are divided into types.
Gene mutations with a change in the structure of chromosomes or their number
These are mutations in which the structure and number of chromosomes are changed. Chromosomal regions can fall out or double, move to a non-homologous zone, turn one hundred and eighty degrees from the norm.
The reasons for the appearance of such a mutation is a violation in crossover.
Gene mutations are associated with a change in the structure of chromosomes or their number, they are the cause of serious disorders and illnesses in a baby. Such diseases are incurable.
Types of chromosomal mutations
In total, two types of basic chromosomal mutations are distinguished: numerical and structural. Aneuploidies are types according to the number of chromosomes, that is, when gene mutations are associated with a change in the number of chromosomes. This is the emergence of an additional or several of the latter, the loss of any of them.
Gene mutations are associated with a change in structure in the case when chromosomes break and then reunite, violating the normal configuration.
Types of numerical chromosomes
According to the number of chromosomes, mutations are divided into aneuploidy, that is, species. Consider the main ones, find out the difference.
- trisomy
Trisomy is the occurrence of an extra chromosome in the karyotype. The most common occurrence is the appearance of the twenty-first chromosome. It becomes the cause of Down syndrome, or, as this disease is also called, trisomy of the twenty-first chromosome.
Patau's syndrome is detected on the thirteenth, and on the eighteenth chromosome they are diagnosed. These are all autosomal trisomies. Other trisomies are not viable, they die in the womb and are lost in spontaneous abortions. Those individuals who have additional sex chromosomes (X, Y) are viable. The clinical manifestation of such mutations is very small.
Gene mutations associated with a change in number occur for certain reasons. Trisomy most often occurs during divergence in anaphase (meiosis 1). The result of this discrepancy is that both chromosomes fall into only one of the two daughter cells, the second remains empty.
Less commonly, nondisjunction of chromosomes may occur. This phenomenon is called a violation in the divergence of sister chromatids. Occurs in meiosis 2. This is exactly the case when two completely identical chromosomes lodge in one gamete, causing a trisomic zygote. Nondisjunction occurs in the early stages of the cleavage process of an egg that has been fertilized. Thus, a clone of mutant cells arises, which can cover a larger or smaller part of the tissues. Sometimes it manifests itself clinically.
Many associate the twenty-first chromosome with the age of a pregnant woman, but this factor has not yet been unambiguously confirmed. The reasons why chromosomes do not separate remain unknown.
- monosomy
Monosomy is the absence of any of the autosomes. If this happens, then in most cases the fetus cannot be carried, premature birth occurs in the early stages. The exception is monosomy due to the twenty-first chromosome. The reason why monosomy occurs can be both the nondisjunction of chromosomes and the loss of a chromosome during its journey in anaphase to the cell.
For sex chromosomes, monosomy leads to the formation of a fetus with an XO karyotype. The clinical manifestation of such a karyotype is Turner's syndrome. In eighty percent of cases out of a hundred, the appearance of monosomy on the X chromosome is due to a violation of meiosis of the father of the child. This is due to the nondisjunction of the X and Y chromosomes. Basically, a fetus with an XO karyotype dies in the womb.
According to the sex chromosomes, trisomy is divided into three types: 47 XXY, 47 XXX, 47 XYY. is trisomy 47XXY. With such a karyotype, the chances of carrying a child are divided fifty to fifty. The cause of this syndrome may be the nondisjunction of the X chromosomes or the nondisjunction of X and Y of spermatogenesis. The second and third karyotypes can occur in only one out of a thousand pregnant women, they practically do not manifest themselves and in most cases are discovered by specialists quite by accident.
- polyploidy
These are gene mutations associated with a change in the haploid set of chromosomes. These sets can be tripled or quadrupled. Triploidy is most often diagnosed only when a spontaneous abortion has occurred. There were several cases when the mother managed to bear such a baby, but they all died before reaching even a month of age. The mechanisms of gene mutations in the case of triplodia are determined by the complete divergence and non-divergence of all chromosome sets of either female or male germ cells. Also, a double fertilization of one egg can serve as a mechanism. In this case, the placenta degenerates. Such a rebirth is called a cystic skid. As a rule, such changes lead to the development of mental and physiological disorders in the baby, termination of pregnancy.
What gene mutations are associated with a change in the structure of chromosomes
Structural changes in chromosomes are the result of rupture (destruction) of the chromosome. As a result, these chromosomes are connected, violating their former appearance. These modifications can be unbalanced and balanced. Balanced have no excess or lack of material, so they do not appear. They can appear only if there was a gene that is functionally important at the site of the destruction of the chromosome. A balanced set may have unbalanced gametes. As a result, the fertilization of the egg with such a gamete can cause the appearance of a fetus with an unbalanced chromosome set. With such a set, the fetus develops a number of malformations, severe types of pathology appear.
Types of structural modifications
Gene mutations occur at the level of gamete formation. It is impossible to prevent this process, just as it is impossible to know for sure that it can happen. There are several types of structural modifications.
- deletions
This change is associated with the loss of part of the chromosome. After such a break, the chromosome becomes shorter, and its torn off part is lost during further cell division. Interstitial deletions are the case when one chromosome breaks in several places at once. Such chromosomes usually create a non-viable fetus. But there are also cases when babies survived, but because of such a set of chromosomes, they had Wolf-Hirshhorn syndrome, “cat's cry”.
- duplications
These gene mutations occur at the level of organization of doubled DNA sections. Basically, duplication cannot cause such pathologies that cause deletions.
- translocations
Translocation occurs due to the transfer of genetic material from one chromosome to another. If a break occurs simultaneously in several chromosomes and they exchange segments, then this causes a reciprocal translocation. The karyotype of such a translocation has only forty-six chromosomes. The translocation itself is detected only with a detailed analysis and study of the chromosome.
Changing the nucleotide sequence
Gene mutations are associated with a change in the sequence of nucleotides, when they are expressed in a modification of the structures of certain sections of DNA. According to the consequences, such mutations are divided into two types - without a frameshift and with a shift. To know exactly the causes of changes in DNA sections, you need to consider each type separately.
Mutation without frameshift
These gene mutations are associated with the change and replacement of nucleotide pairs in the DNA structure. With such substitutions, DNA length is not lost, but amino acids can be lost and replaced. There is a possibility that the structure of the protein will be preserved, this will serve. Let us consider in detail both variants of development: with and without replacement of amino acids.
Amino acid substitution mutation
Changes in amino acid residues in polypeptides are called missense mutations. There are four chains in the human hemoglobin molecule - two "a" (it is located on the sixteenth chromosome) and two "b" (coding on the eleventh chromosome). If "b" - the chain is normal, and it contains one hundred and forty-six amino acid residues, and the sixth is glutamine, then hemoglobin will be normal. In this case, glutamic acid must be encoded by the GAA triplet. If, due to a mutation, GAA is replaced by GTA, then instead of glutamic acid, valine is formed in the hemoglobin molecule. Thus, instead of normal hemoglobin HbA, another hemoglobin HbS will appear. Thus, the replacement of one amino acid and one nucleotide will cause a serious serious illness - sickle cell anemia.
This disease is manifested by the fact that red blood cells become shaped like a sickle. In this form, they are not able to deliver oxygen normally. If at the cellular level homozygotes have the HbS/HbS formula, then this leads to the death of the child in early childhood. If the formula is HbA / HbS, then the erythrocytes have a weak form of change. Such a slight change has a useful quality - the body's resistance to malaria. In those countries where there is a danger of contracting malaria the same as in Siberia with a cold, this change has a beneficial quality.
Mutation without amino acid substitution
Nucleotide substitutions without amino acid exchange are called Seimsense mutations. If GAA is replaced by GAG in the DNA region encoding the "b" chain, then due to the fact that it will be in excess, the replacement of glutamic acid cannot occur. The structure of the chain will not be changed, there will be no modifications in the erythrocytes.
Frameshift Mutations
Such gene mutations are associated with a change in the length of DNA. The length can become shorter or longer, depending on the loss or gain of nucleotide pairs. Thus, the entire structure of the protein will be completely changed.
Intragenous suppression may occur. This phenomenon occurs when there is room for two mutations to cancel each other out. This is the moment when a nucleotide pair is added after one has been lost, and vice versa.
Nonsense Mutations
This is a special group of mutations. It occurs rarely, in its case, the appearance of stop codons. This can happen both with the loss of nucleotide pairs and with their addition. When stop codons appear, polypeptide synthesis stops completely. This can create null alleles. None of the proteins will match this.
There is such a thing as intergenic suppression. This is such a phenomenon when the mutation of some genes suppresses mutations in others.
Are there any changes during pregnancy?
Gene mutations associated with a change in the number of chromosomes can in most cases be identified. To find out if the fetus has malformations and pathologies, screening is prescribed in the first weeks of pregnancy (from ten to thirteen weeks). This is a series of simple examinations: blood sampling from a finger and a vein, ultrasound. On ultrasound, the fetus is examined in accordance with the parameters of all limbs, nose and head. These parameters, with a strong non-compliance with the norms, indicate that the baby has developmental defects. This diagnosis is confirmed or refuted based on the results of a blood test.
Also under the close supervision of physicians are expectant mothers, whose babies may develop mutations at the gene level, which are inherited. That is, these are women in whose relatives there were cases of the birth of a child with mental or physical disabilities, identified Down syndrome, Patau and other genetic diseases.
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