In the twentieth century, five levels of life organization were established: molecular-genetic, ontogenetic, popular-species, ecosystem and biospheric. Elucidation of the phenomenon of life at each level is one of the main tasks of biology.
Molecular genetic level- This is the level of organization of living systems, consisting of proteins and nucleic acids. At this level, the basic unit of an organism is genes. Here biology studies the mechanisms of transmission of genetic information, heredity and variability.
The six most common elements in living organisms are: organogens: carbon, nitrogen, hydrogen, oxygen, phosphorus and sulfur. With the participation of these elements, in the course of chemical evolution, giant biopolymers: carbohydrates, proteins, lipids and nucleic acids. These macromolecules are the basis of living organisms. The monomers of these macromolecules are: monosaccharides, amino acids, fatty acids and nucleotides.
Proteins and nucleic acids are informational» macromolecules, because their properties depend on the connection sequence of 20 amino acids and 4 nucleotides. Carbohydrates and lipids play the role of a reserve of energy and building material. To share proteins accounted for over 50% total dry weight of cells.
genetic information organism is stored in the DNA. It controls almost all biological processes in the body. Proteins and nucleic acids have the property of molecular asymmetry (molecular chirality). Chirality(Greek cheir - hand) manifests itself in the fact that proteins rotate the plane of polarization of light to the left, and nucleic acids right. Chirality lies in their asymmetry with their mirror image, as in the right and left hands, hence the name.
DNA molecules together with proteins form the substance of chromosomes. The proof of the genetic role of DNA was obtained, in 1944, by the scientist O. Avery, in an experiment on bacteria. In 1953, American biochemist James Watson and English biophysicist Francis Crick discovered structure DNA molecules. They showed that DNA consists of two strands twisted into a double helix. DNA contains 10 ÷ 25 thousand nucleotides, and RNA - from 4 to 6 thousand.
In 1941, American scientists J. Beadle and E. Teymut found that protein synthesis depends on the state of DNA genes. Gene A section of a DNA molecule consisting of hundreds of nucleotides. Then there were statements: one gene - one protein. The totality of an organism's genes is called genome. The number of genes in the human body is about 50 ÷ 100 thousand, and the entire human genome contains more 3 billion base pairs. Genes code for the synthesis of proteins.
In 1954 the theoretical physicist Georgy Gamov decoded the genetic code. He found that a combination of three DNA nucleotides is used to encode one amino acid. It is the elementary unit of heredity, encoding one amino acid, and is called codon(triplet). In 1961 Gamow's hypothesis was experimentally confirmed by Crick.
Cellular organelle ribosome is reading» information contained in i-RNA, and in accordance with it synthesizes protein. Codons - triplets consist of three nucleotides, for example, ACH, AGC, GGG and others. The total number of such triplets is 64. Of these, three triplets are stop signals, and 61 triplets encode 20 amino acids. A protein consisting of 200 amino acids is encoded by 200 codons, i.e. 600 nucleotides in mRNA, and 600 base pairs in DNA. This is the size of one gene. The information in DNA is written using nucleotides in the form: A-C-A-T-T-G-A-G-A-T-∙∙∙∙∙∙. This text contains information that defines the specifics of each organism.
Genetic code universal, because the same for all living organisms. This testifies to the biochemical unity of life, i.e. the origin of life on Earth from a single ancestor. Genetic code unique, because it codes for only one amino acid.
Life is characterized by the dialectical unity of opposites: it is both integral and discrete. The organic world is a single whole, since it is a system of interconnected parts (the existence of some organisms depends on others), and at the same time it is discrete, since it consists of separate units - organisms, or individuals. Each living organism, in turn, is also discrete, as it consists of individual organs, tissues, cells, but at the same time, each of the organs, having a certain autonomy, acts as part of the whole. Each cell consists of organelles, but functions as a single unit. Hereditary information is carried by genes, but
none of the genes outside of the totality determines the development of the trait, and so on.
The discreteness of life is associated with various levels of organization of the organic world, which can be defined as discrete states of biological systems characterized by subordination, interconnectedness and specific patterns. At the same time, each new level has special properties and patterns of the previous, lower level, since any organism, on the one hand, consists of elements subordinate to it, and on the other hand, it is itself an element that is part of some kind of macrobiological system.
At all levels of life, its attributes such as discreteness and integrity, structural organization, exchange of matter, energy and information are manifested. The existence of life at higher levels of organization is prepared and determined by the structure of the lower level; in particular, the nature of the cellular level is determined by the molecular and subcellular levels, the nature of the organism - by the cellular, tissue levels, etc.
The structural levels of life organization are extremely diverse, but the main ones are molecular, cellular, ontogenetic, population-species, biocenotic, biogeocenotic and biospheric.
Molecular genetic level
The molecular genetic level of life is the level of functioning of biopolymers (proteins, nucleic acids, polysaccharides) and other important organic compounds that underlie the life processes of organisms. At this level, the elementary structural unit is the gene, and the carrier of hereditary information in all living organisms is the DNA molecule. The implementation of hereditary information is carried out with the participation of RNA molecules. Due to the fact that the processes of storage, change and implementation of hereditary information are associated with molecular structures, this level is called molecular-genetic.
The most important tasks of biology at this level are the study of the mechanisms of transmission of genetic information, heredity and variability, the study of evolutionary processes, the origin and essence of life.
All living organisms contain simple inorganic molecules: nitrogen, water, carbon dioxide. From them, in the course of chemical evolution, simple organic compounds appeared, which, in turn, became the building material for larger molecules. This is how macromolecules appeared - giant mo-
polymer molecules built from many monomers. There are three types of polymers: polysaccharides, proteins and nucleic acids. The monomers for them, respectively, are monosaccharides, amino acids and nucleotides.
Squirrels and nucleic acids are "information" molecules, since the sequence of monomers, which can be very diverse, plays an important role in their structure. Polysaccharides (starch, glycogen, cellulose) play the role of an energy source and building material for the synthesis of larger molecules.
Proteins are macromolecules that are very long chains of amino acids - organic (carboxylic) acids, usually containing one or two amino groups (-NH 2).
In solutions, amino acids can exhibit the properties of both acids and bases. This makes them a kind of buffer on the way of dangerous physical and chemical changes. More than 170 amino acids are found in living cells and tissues, but only 20 of them are included in proteins. It is the sequence of amino acids connected to each other by peptide bonds 1 that forms the primary structure of proteins. Proteins account for over 50% of the total dry mass of cells.
Most proteins act as catalysts (enzymes). In their spatial structure there are active centers in the form of recesses of a certain shape. Molecules, the transformation of which is catalyzed by this protein, enter such centers. In addition, proteins play the role of carriers; for example, hemoglobin carries oxygen from the lungs to the tissues. Muscle contractions and intracellular movements are the result of the interaction of protein molecules, the function of which is to coordinate movement. The function of antibody proteins is to protect the body from viruses, bacteria, etc. The activity of the nervous system depends on proteins that collect and store information from the environment. Proteins called hormones control cell growth and activity.
Nucleic acids. The life processes of living organisms are determined by the interaction of two types of macromolecules - proteins and DNA. The genetic information of an organism is stored in DNA molecules, which serve as a carrier of hereditary information for the next generation and determine the biosynthesis of proteins that control almost all biological processes. So nuk-
1 A peptide bond is a -CO-NH- chemical bond.
Leic acids have the same important place in the body as proteins.
Both proteins and nucleic acids have one very important property - molecular dissymmetry (asymmetry), or molecular chirality. This property of life was discovered in the 1940s and 1950s. 19th century L. Pasteur in the course of studying the structure of crystals of substances of biological origin - salts of tartaric acid. In his experiments, Pasteur discovered that not only crystals, but also their aqueous solutions are capable of deflecting a polarized light beam, i.e. are optically active. Later they were named optical isomers. Solutions of substances of non-biological origin do not have this property, the structure of their molecules is symmetrical.
Today, Pasteur's ideas have been confirmed, and it is considered proven that molecular chirality (from the Greek cheir - hand) is inherent only in living matter and is its integral property. The substance of inanimate origin is symmetrical in the sense that the molecules that polarize light to the left and to the right are always equally divided in it. And in the substance of biological origin there is always a deviation from this balance. Proteins are built from amino acids that polarize light only to the left (L-configuration). Nucleic acids are composed of sugars that polarize light only to the right (D-configuration). Thus, chirality lies in the asymmetry of molecules, their incompatibility with their mirror image, as in the right and left hands, which gave the modern name to this property. It is interesting to note that if a person suddenly turned into his mirror image, then everything would be fine with his body until he began to eat food of plant or animal origin, which he simply could not digest.
Nucleic acids are complex organic compounds that are phosphorus-containing biopolymers (polynucleotides).
There are two types of nucleic acids - deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acids got their name (from the Latin nucleus - nucleus) due to the fact that they were first isolated from the nuclei of leukocytes in the second half of the 19th century. Swiss biochemist F. Miescher. Later it was found that nucleic acids can be found not only in the nucleus, but also in the cytoplasm and its organelles. DNA molecules together with histone proteins form the substance of chromosomes.
In the middle of the XX century. the American biochemist J. Watson and the English biophysicist F. Crick revealed the structure of the DNA molecule. X-ray diffraction studies have shown that DNA consists of two strands twisted into a double helix. The role of the backbones of the chains is played by sugar-phosphate groups, and the bases of purines and pyrimidines serve as jumpers. Each jumper is formed by two bases attached to two opposite chains, and if one base has one ring, then the other has two. Thus, complementary pairs are formed: A-T and G-C. This means that the sequence of bases in one chain uniquely determines the sequence of bases in another, complementary chain of the molecule.
A gene is a section of a DNA or RNA molecule (in some viruses). RNA contains 4-6 thousand individual nucleotides, DNA - 10-25 thousand. If it were possible to stretch the DNA of one human cell into a continuous thread, then its length would be 91 cm.
And yet, the birth of molecular genetics occurred somewhat earlier, when the Americans J. Beadle and E. Tatum established a direct link between the state of genes (DNA) and the synthesis of enzymes (proteins). It was then that the famous saying appeared: "one gene - one protein." Later it was found that the main function of genes is to code for protein synthesis. After that, scientists focused their attention on the question of how the genetic program is written and how it is implemented in the cell. To do this, it was necessary to figure out how just four bases can encode the order in the protein molecules of as many as twenty amino acids. The main contribution to the solution of this problem was made by the famous theoretical physicist G. Gamow in the mid-1950s.
According to him, a combination of three DNA nucleotides is used to encode one amino acid. This elementary unit of heredity, encoding one amino acid, is called codon. In 1961, Gamow's hypothesis was confirmed by F. Crick's research. So the molecular mechanism for reading genetic information from a DNA molecule during protein synthesis was deciphered.
In a living cell, there are organelles - ribosomes that "read" the primary structure of DNA and synthesize protein in accordance with the information recorded in DNA. Each triplet of nucleotides is assigned one of the 20 possible amino acids. This is how the primary structure of DNA determines the sequence of amino acids of the synthesized protein, fixes the genetic code of the organism (cell).
The genetic code of all living things, be it a plant, an animal or a bacterium, is the same. This feature of the genetic code, together with the similarity of the amino acid composition of all proteins, indicates
about the biochemical unity of life, the origin of all living beings on Earth from a single ancestor.
The mechanism of DNA reproduction was also deciphered. It consists of three parts: replication, transcription and translation.
replication is the duplication of DNA molecules. The basis of replication is the unique property of DNA to self-copy, which makes it possible for a cell to divide into two identical ones. During replication, DNA, consisting of two twisted molecular chains, unwinds. Two molecular threads are formed, each of which serves as a matrix for the synthesis of a new thread, complementary to the original one. After that, the cell divides, and in each cell one strand of DNA will be old, and the second will be new. Violation of the sequence of nucleotides in the DNA chain leads to hereditary changes in the body - mutations.
Transcription- this is the transfer of the DNA code by the formation of a single-stranded messenger RNA molecule (i-RNA) on one of the DNA strands. i-RNA is a copy of a part of the DNA molecule, consisting of one or a group of adjacent genes that carry information about the structure of proteins.
Broadcast - this is protein synthesis based on the genetic code of i-RNA in special cell organelles - ribosomes, where transfer RNA (t-RNA) delivers amino acids.
In the late 1950s Russian and French scientists simultaneously put forward a hypothesis that differences in the frequency of occurrence and the order of nucleotides in DNA in different organisms are species-specific. This hypothesis made it possible to study the evolution of living things and the nature of speciation at the molecular level.
There are several mechanisms of variability at the molecular level. The most important of them is the already mentioned mechanism of gene mutation - direct transformation of the genes themselvesnew, located in the chromosome, under the influence of external factors. Mutation-causing factors (mutagens) are radiation, toxic chemicals, and viruses. With this mechanism of variability, the order of the genes in the chromosome does not change.
Another change mechanism is gene recombination. This is the creation of new combinations of genes located on a particular chromosome. At the same time, the molecular basis of the gene itself does not change, but it moves from one part of the chromosome to another or there is an exchange of genes between two chromosomes. Gene recombination occurs during sexual reproduction in higher organisms. In this case, there is no change in the total amount of genetic information, it remains unchanged. This mechanism explains why children only partially resemble their parents -
they inherit traits from both parent organisms that combine randomly.
Another change mechanism is nonclassical recombinationnew- It was opened only in the 1950s. With non-classical gene recombination, there is a general increase in the amount of genetic information due to the inclusion of new genetic elements in the cell genome. Most often, new elements are introduced into the cell by viruses. Today, several types of transmissible genes have been discovered. Among them are plasmids, which are double-stranded circular DNA. Because of them, after prolonged use of any drugs, addiction occurs, after which they cease to have a medicinal effect. Pathogenic bacteria, against which our drug acts, bind to plasmids, which makes the bacteria resistant to the drug, and they stop noticing it.
Migrating genetic elements can cause both structural rearrangements in chromosomes and gene mutations. The possibility of using such elements by humans has led to the emergence of a new science - genetic engineering, the purpose of which is to create new forms of organisms with desired properties. Thus, with the help of genetic and biochemical methods, new combinations of genes that do not exist in nature are constructed. For this, the DNA encoding the production of a protein with the desired properties is modified. This mechanism underlies all modern biotechnologies.
Recombinant DNA can be used to synthesize a variety of genes and introduce them into clones (colonies of identical organisms) for directed protein synthesis. So, in 1978, insulin was synthesized - a protein for the treatment of diabetes. The desired gene was introduced into a plasmid and introduced into a normal bacterium.
Geneticists are working to develop safe vaccines against viral infections, since traditional vaccines are a weakened virus that must cause the production of antibodies, so their administration is associated with a certain risk. Genetic engineering makes it possible to obtain DNA encoding the surface layer of the virus. In this case, immunity is produced, but infection of the body is excluded.
Today, in genetic engineering, the issue of increasing life expectancy and the possibility of immortality by changing the human genetic program is being considered. This can be achieved by increasing the protective enzyme functions of the cell, protecting DNA molecules from various damages associated with both metabolic disorders and environmental influences. In addition, scientists have managed to discover the aging pigment and create a special drug that frees cells from it. In experiments with we-
shami received an increase in their life expectancy. Also, scientists were able to establish that at the time of cell division, telomeres decrease - special chromosomal structures located at the ends of cellular chromosomes. The fact is that during DNA replication, a special substance - polymerase - goes along the DNA helix, making a copy from it. But DNA polymerase does not start copying from the very beginning, but leaves an uncopied tip each time. Therefore, with each subsequent copying, the DNA helix is shortened due to the terminal sections that do not carry any information, or telomeres. As soon as the telomeres are exhausted, subsequent copies begin to shrink the part of the DNA that carries the genetic information. This is the process of cell aging. In 1997, an experiment was carried out in the USA and Canada on artificial lengthening of telomeres. For this, a newly discovered cellular enzyme, telomerase, was used, which promotes the growth of telomeres. The cells obtained in this way acquired the ability to divide many times, completely retaining their normal functional properties and not turning into cancer cells.
Recently, the successes of genetic engineers in the field of cloning have become widely known - the exact reproduction of one or another living object in a certain number of copies from somatic cells. At the same time, the grown individual is genetically indistinguishable from the parent organism.
Obtaining clones from organisms that reproduce through parthenogenesis, without prior fertilization, is not something special and has long been used by geneticists. In higher organisms, cases of natural cloning are also known - the birth of identical twins. But the artificial production of clones of higher organisms is associated with serious difficulties. However, in February 1997, a method for cloning mammals was developed at the laboratory of Jan Wilmuth in Edinburgh, and Dolly the sheep was raised with it. To do this, eggs were extracted from a Scottish black-faced sheep, placed in an artificial nutrient medium, and the nuclei were removed from them. Then they took mammary gland cells of an adult pregnant sheep of the Finnish Dorset breed, carrying a complete genetic set. After some time, these cells were fused with non-nuclear eggs and activated their development by means of an electrical discharge. Then the developing embryo grew in an artificial environment for six days, after which the embryos were transplanted into the uterus of the adoptive mother, where they developed until birth. But out of 236 experiments, only one turned out to be successful - Dolly the sheep grew up.
After that, Wilmut announced the fundamental possibility of human cloning, which caused the most lively discussions.
not only in scientific literature, but also in the parliaments of many countries, since such an opportunity is associated with very serious moral, ethical and legal problems. It is no coincidence that some countries have already passed laws prohibiting human cloning. After all, most cloned embryos die. In addition, the probability of the birth of freaks is high. So cloning experiments are not only immoral, but also simply dangerous from the point of view of preserving the purity of the Homo sapiens species. That the risk is too great is confirmed by information that came out in early 2002, reporting that Dolly the sheep was suffering from arthritis, a disease not common in sheep, after which she had to be euthanized shortly after.
Therefore, a much more promising area of research is the study of the human genome (set of genes). In 1988, on the initiative of J. Watson, the international organization "Human Genome" was created, which brought together many scientists from around the world and set the task of deciphering the entire human genome. This is a daunting task, since the number of genes in the human body is from 50 to 100 thousand, and the entire genome is more than 3 billion nucleotide pairs.
It is believed that the first stage of this program, associated with deciphering the sequence of nucleotide pairs, will be completed by the end of 2005. Work has already been done to create an "atlas" of genes, a set of their maps. The first such map was compiled in 1992 by D. Cohen and J. Dosset. In the final version, it was presented in 1996 by J. Weissenbach, who, studying a chromosome under a microscope, marked the DNA of its various regions with special markers. Then he cloned these sections, growing them on microorganisms, and received DNA fragments - the nucleotide sequence of one strand of DNA that made up the chromosomes. Thus, Weissenbach localized 223 genes and identified about 30 mutations leading to 200 diseases, including hypertension, diabetes, deafness, blindness, and malignant tumors.
One of the results of this program, although not completed, is the possibility of identifying genetic pathologies in the early stages of pregnancy and the creation of gene therapy - a method of treating hereditary diseases with the help of genes. Before the gene therapy procedure, they find out which gene turned out to be defective, get a normal gene and introduce it into all diseased cells. At the same time, it is very important to make sure that the introduced gene works under the control of cell mechanisms, otherwise a cancer cell will be obtained. There are already the first patients cured in this way. True, it is not yet clear how radically they are cured and
whether the disease will return in the future. Also, the long-term consequences of such treatment are not yet clear.
Of course, the use of biotechnology and genetic engineering has both positive and negative sides. This is evidenced by the memorandum published in 1996 by the Federation of European Microbiological Societies. This is due to the fact that the general public is suspicious and hostile towards gene technologies. Fear is caused by the possibility of creating a genetic bomb that can distort the human genome and lead to the birth of freaks; the emergence of unknown diseases and the production of biological weapons.
And, finally, the problem of the widespread distribution of transgenic food products created by introducing genes that block the development of viral or fungal diseases has been widely discussed recently. Transgenic tomatoes and corn have already been created and are being sold. Bread, cheese and beer made with the help of transgenic microbes are supplied to the market. Such products are resistant to harmful bacteria, have improved qualities - taste, nutritional value, strength, etc. For example, in China, virus-resistant tobacco, tomatoes and sweet peppers are grown. Known transgenic tomatoes resistant to bacterial infection, potatoes and corn resistant to fungi. But the long-term consequences of the use of such products are still unknown, primarily the mechanism of their effect on the body and the human genome.
Of course, in twenty years of using biotechnology, nothing that people fear has happened. All new microorganisms created by scientists are less pathogenic than their original forms. There has never been a harmful or dangerous spread of recombinant organisms. However, scientists are careful to ensure that transgenic strains do not contain genes that, when transferred to other bacteria, can have a dangerous effect. There is a theoretical danger of creating new types of bacteriological weapons based on gene technologies. Therefore, scientists must take this risk into account and contribute to the development of a system of reliable international control capable of fixing and suspending such work.
Taking into account the possible danger of using genetic technologies, documents have been developed that regulate their use, safety rules for laboratory research and industrial development, as well as rules for introducing genetically modified organisms into the environment.
Thus, today it is believed that, with appropriate precautions, the benefits of gene technologies outweigh the risk of possible negative consequences.
Cellular level
At the cellular level of organization, the basic structural and functional unit of all living organisms is the cell. At the cellular level, as well as at the molecular genetic level, the same type of all living organisms is noted. In all organisms, biosynthesis and realization of hereditary information are possible only at the cellular level. The cellular level in unicellular organisms coincides with the organism level. The history of life on our planet began with this level of organization.
Today, science has precisely established that the smallest independent unit of the structure, functioning and development of a living organism is a cell.
Cell is an elementary biological system capable of self-renewal, self-reproduction and development, i.e. endowed with all the characteristics of a living organism.
Cellular structures underlie the structure of any living organism, no matter how diverse and complex its structure may seem. The science that studies the living cell is called cytology. It studies the structure of cells, their functioning as elementary living systems, explores the functions of individual cellular components, the process of cell reproduction, their adaptation to environmental conditions, etc. Cytology also studies the features of specialized cells, the formation of their special functions and the development of specific cellular structures. Thus, modern cytology can be called cell physiology. The successes of modern cytology are inextricably linked with the achievements of biochemistry, biophysics, molecular biology and genetics.
Cytology is based on the assertion that all living organisms (animals, plants, bacteria) consist of cells and their metabolic products. New cells are formed by the division of pre-existing cells. All cells are similar in chemical composition and metabolism. The activity of the organism as a whole is made up of the activity and interaction of individual cells.
The discovery of the existence of cells came at the end XVII when the microscope was invented. The cell was first described by the English scientist R. Hooke in 1665, when he examined a piece of cork. Since his microscope was not very perfect, what he saw were actually walls of dead cells. It took almost two hundred years for biologists to understand that it was not the walls of the cell that played the main role, but its internal contents. Among the creators of the cell theory, one should also mention A. Leeuwenhoek, who showed that the tissues of many plant
organisms are built from cells. He also described erythrocytes, unicellular organisms and bacteria. True, Leeuwenhoek, like other researchers of the 17th century, saw in the cell only a shell containing a cavity.
A significant advance in the study of cells occurred at the beginning of the 19th century, when they began to be viewed as individuals with vital properties. In the 1830s the cell nucleus was discovered and described, which drew the attention of scientists to the contents of the cell. Then it was possible to see the division of plant cells. On the basis of these studies, the cell theory was created, which became the greatest event in the biology of the 19th century. It was the cellular theory that gave decisive evidence of the unity of all living nature, served as the foundation for the development of embryology, histology, physiology, the theory of evolution, as well as understanding the individual development of organisms.
Cytology received a powerful impetus with the creation of genetics and molecular biology. After that, new components, or organelles, cells were discovered - the membrane, ribosomes, lysosomes, etc.
According to modern concepts, cells can exist both as independent organisms (for example, protozoa), and as part of multicellular organisms, where there are germ cells that serve for reproduction, and somatic cells (cells of the body). Somatic cells differ in structure and function - there are nerve, bone, muscle, secretory cells. Cell sizes can vary from 0.1 µm (some bacteria) to 155 mm (ostrich egg in shell). A living organism is formed by billions of various cells (up to 10 15), the shape of which can be the most bizarre (spider, star, snowflake, etc.).
It has been established that despite the great variety of cells and the functions they perform, the cells of all living organisms are similar in chemical composition: they contain especially high content of hydrogen, oxygen, carbon and nitrogen (these chemical elements make up more than 98% of the total content of the cell); 2% is accounted for by about 50 other chemical elements.
The cells of living organisms contain inorganic substances - water (on average up to 80%) and mineral salts, as well as organic compounds: 90% of the dry mass of the cell is biopolymers - proteins, nucleic acids, carbohydrates and lipids. And finally, it is scientifically proven that all cells consist of three main parts:
the plasma membrane, which controls the passage of substances from the environment into the cell and vice versa;
cytoplasm with a diverse structure;
the cell nucleus, which contains the genetic information.
In addition, all animal and some plant cells contain centrioles - cylindrical structures that form cell centers. Plant cells also have a cell wall (shell) and plastids, specialized cell structures that often contain a pigment that determines the color of the cell.
cell membrane consists of two layers of molecules of fat-like substances, between which there are protein molecules. The membrane maintains the normal concentration of salts inside the cell. When the membrane is damaged, the cell dies.
Cytoplasm is a water-salt solution with enzymes and other substances dissolved and suspended in it. Organelles are located in the cytoplasm - small organs, delimited from the contents of the cytoplasm by their own membranes. Among them - mitochondria- sac-like formations with respiratory enzymes, in which energy is released. Also located in the cytoplasm ribosome, consisting of protein and RNA, with the help of which protein synthesis is carried out in the cell. En-preplasmic reticulum- this is a common intracellular circulatory system, through the channels of which the transport of substances is carried out, and on the membranes of the channels there are enzymes that ensure the vital activity of the cell. plays an important role in the cell glueexact center, consisting of two centrioles. It starts the process of cell division.
The most important part of all cells (except bacteria) is core, in which the chromosomes are located - long thread-like bodies, consisting of DNA and a protein attached to it. The nucleus stores and reproduces genetic information, and also regulates metabolic processes in the cell.
Cells reproduce by dividing the original cell into two daughter cells. In this case, a complete set of chromosomes carrying genetic information is transferred to the daughter cells, therefore, before dividing, the number of chromosomes doubles. Such cell division, which ensures the same distribution of genetic material between daughter cells, is called mitosis.
Multicellular organisms also develop from a single cell - the egg. However, during embryogenesis, cells change. This leads to the appearance of many different cells - muscle, nerve, blood, etc. Different cells synthesize different proteins. However, each cell of a multicellular organism carries a complete set of genetic information to build all the proteins needed by the organism.
Depending on the type of cells, all organisms are divided into two groups:
prokaryotes - cells lacking a nucleus. In them, DNA molecules are not surrounded by a nuclear membrane and are not organized into chromosomes. Prokaryotes include bacteria;
eukaryotes- cells containing nuclei. In addition, they have mitochondria - organelles in which the oxidation process takes place. Eukaryotes include protozoa, fungi, plants, and animals, so they can be unicellular or multicellular.
Thus, there are significant differences between prokaryotes and eukaryotes in the structure and functioning of the genetic apparatus, cell walls and membrane systems, protein synthesis, etc. It is assumed that the first organisms that appeared on Earth were prokaryotes. This was considered until the 1960s, when in-depth study of the cell led to the discovery of archaebacteria, the structure of which is similar to both prokaryotes and eukaryotes. The question of which unicellular organisms are more ancient, of the possibility of the existence of a certain first cell, from which all three evolutionary lines later appeared, still remains open.
Studying a living cell, scientists drew attention to the existence of two main types of its nutrition, which allowed all organisms to be divided into two species according to the method of nutrition:
autotrophic organisms - organisms that do not need organic food and are able to carry out their vital activity due to the assimilation of carbon dioxide (bacteria) or photosynthesis (plants), i.e. autotrophs themselves produce the nutrients they need;
heterotrophic organisms are all organisms that cannot do without organic food.
Later, such important factors as the ability of organisms to synthesize the necessary substances (vitamins, hormones, etc.) and provide themselves with energy, dependence on the ecological environment, etc. were clarified. Thus, the complex and differentiated nature of trophic relationships indicates the need for a systematic approach to the study of life and at the ontogenetic level. This is how the concept of functional consistency was formulated by P.K. Anokhin, according to which various components of systems function in concert in unicellular and multicellular organisms. At the same time, individual components contribute to the coordinated functioning of others, thereby ensuring unity and integrity in the implementation of the vital processes of the whole organism. Functional consistency is also manifested in the fact that processes at lower levels are organized by functional links at higher levels of the organization. The functional system character is especially noticeable in multicellular organisms.
ontogenetic level.Multicellular organisms
The main unit of life at the ontogenetic level is an individual, and ontogenesis is an elementary phenomenon. A biological individual can be both a unicellular and a multicellular organism, but in any case it is an integral, self-reproducing system.
Ontogeny called the process of individual development of the organism from birth through successive morphological, physiological and biochemical changes to death, the process of realization of hereditary information.
The minimum living system, the building block of life, is the cell, which is studied by cytology. The functioning and development of multicellular living organisms is the subject of physiology. At present, a unified theory of ontogenesis has not been created, since the causes and factors that determine the individual development of an organism have not been established.
All multicellular organisms are divided into three kingdoms: fungi, plants and animals. The vital activity of multicellular organisms, as well as the functioning of their individual parts, is studied by physiology. This science considers the mechanisms for the implementation of various functions by a living organism, their relationship with each other, the regulation and adaptation of the organism to the external environment, the origin and formation in the process of evolution and individual development of an individual. In fact, this is the process of ontogenesis - the development of an organism from birth to death. In this case, growth, movement of individual structures, differentiation and general complication of the organism occur.
The process of ontogenesis is described on the basis of the famous biogenetic law formulated by E. Haeckel, the author of the term "ontogenesis". The biogenetic law states that ontogeny in brief repeats phylogeny, i.e. an individual organism in its individual development in an abbreviated form goes through all the stages of development of its species. Thus, ontogeny is the implementation of hereditary information encoded in the germ cell, as well as checking the consistency of all body systems during its work and adaptation to the environment.
All multicellular organisms are composed of organs and tissues. Tissues are a group of physically connected cells and intercellular substances to perform certain functions. Their study
is the subject of histology. Tissues can be formed from the same or different cells. For example, in animals, squamous epithelium is built from identical cells, and muscle, nervous, and connective tissues are built from different cells.
Organs are relatively large functional units that combine various tissues into certain physiological complexes. Only animals have internal organs; plants do not have them. In turn, organs are part of larger units - body systems. Among them are the nervous, digestive, cardiovascular, respiratory and other systems.
Actually, a living organism is a special internal environment that exists in the external environment. It is formed as a result of the interaction of the genotype (the totality of the genes of one organism) with the phenotype (the complex of external signs of the organism formed during its individual development). Thus, the body is a stable system of internal organs and tissues that exist in the external environment. However, since a general theory of ontogeny has not yet been created, many processes occurring during the development of an organism have not received their full explanation.
Population-species level
The population-species level is the supra-organismal level of life, the basic unit of which is the population.
population- a set of individuals of one species, relatively isolated from other groups of the same species, occupying a certain territory, reproducing itself for a long time and having a common genetic fund.
Unlike the population view called a set of individuals similar in structure and physiological properties, having a common origin, able to freely interbreed and produce fertile offspring. A species exists only through populations that are genetically open systems. Population biology is the study of populations.
In the conditions of real nature, individuals are not isolated from each other, but are united into living systems of a higher rank. The first such system is the population.
The term "population" was introduced by one of the founders of genetics, V. Johansen, who called it a genetically heterogeneous set of organisms, different from a homogeneous set - a pure line. Later this term became more
The integrity of populations, manifested in the emergence of new properties in comparison with the ontogenetic standard of living, is ensured by the interaction of individuals in populations and is recreated through the exchange of genetic information in the process of sexual reproduction. Each population has quantitative boundaries. On the one hand, this is the minimum number that ensures the self-reproduction of the population, and on the other hand, the maximum number of individuals that can feed in the area (habitat) of this population. The population as a whole is characterized by such parameters as waves of life - periodic fluctuations in numbers, population density, ratio of age groups and sexes, mortality, etc.
Populations are genetically open systems, since the isolation of populations is not absolute and the exchange of genetic information is periodically possible. It is populations that act as elementary units of evolution; changes in their gene pool lead to the emergence of new species.
The population level of life organization is characterized by active or passive mobility of all components of the population. This entails the constant movement of individuals - members of the population. It should be noted that no population is absolutely homogeneous; it always consists of intrapopulation groups. It should also be remembered that there are populations of different ranks - there are permanent, relatively independent geographical populations, and temporary (seasonal) local populations. At the same time, high abundance and stability are achieved only in those populations that have a complex hierarchical and spatial structure, i.e. are heterogeneous, heterogeneous, have complex and long food chains. Therefore, the loss of at least one link from this structure leads to the destruction of the population or the loss of its stability.
Biocenotic level
Populations representing the first supraorganismal level of the living, which are elementary units of evolution, capable of independent existence and transformation, are united in the aggregate of the next supraorganismal level - biocenoses.
Biocenosis- the totality of all organisms inhabiting a section of the environment with homogeneous living conditions, for example, a forest, meadow, swamp, etc. In other words, a biocenosis is a set of populations living in a certain area.
Usually, biocenoses consist of several populations and are an integral component of a more complex system - biogeocenosis.
Biogeocenotic level
Biogeocenosis- a complex dynamic system, which is a combination of biotic and abiotic elements interconnected by the exchange of matter, energy and information, within which the circulation of substances in nature can be carried out.
This means that biogeocenosis is a stable system that can exist for a long time. Equilibrium in a living system is dynamic, i.e. represents a constant movement around a certain point of stability. For the stable functioning of a living system, it is necessary to have feedback between its control and controlled subsystems. This way of maintaining dynamic balance is called homeostasis. Violation of the dynamic balance between the various elements of the biogeocenosis, caused by the mass reproduction of some species and the reduction or disappearance of others, leading to a change in the quality of the environment, is called ecological disaster.
The term "biogeocenosis" was proposed in 1940 by the Russian botanist V.N. Sukachev, who designated by this term the
a set of homogeneous natural phenomena (atmosphere, rocks, water resources, vegetation, wildlife, soil) distributed over a certain extent of the earth's surface, having a certain type of exchange of matter and energy between them and the surrounding elements, representing a contradictory unity. Representing the unity of living and non-living, biogeocenosis is in constant motion and development, therefore it changes over time.
Biogeocenosis is an integral self-regulating system in which several types of subsystems are distinguished:
primary systems - producers(producing) directly processing inanimate matter (algae, plants, microorganisms);
first order consumers- the secondary level, at which matter and energy are obtained through the use of producers (herbivores);
second order consumers(predators, etc.);
scavengers (saprophytes) and saprophages), eating dead animals;
decomposers - This is a group of bacteria and fungi that decompose the remnants of organic matter.
As a result of the vital activity of saprophytes, saprophages and decomposers, mineral substances return to the soil, which increases its fertility and provides plant nutrition. Therefore, scavengers and decomposers are a very important part of food chains.
The cycle of substances passes through these levels in the biogeocenosis - life is involved in the use, processing and restoration of various structures. But the circulation of energy does not occur: about 10% of the energy that has entered the previous level passes from one level to another, higher one. The reverse flow does not exceed 0.5%. In other words, in the biogeocenosis there is a unidirectional energy flow. This makes it an open system, inextricably linked with neighboring biogeocenoses. This connection manifests itself in various forms: gaseous, liquid, solid, and also in the form of animal migration.
Self-regulation of biogeocenoses proceeds the more successfully, the more diverse the number of its constituent elements. The stability of biogeocenoses depends on the variety of components. The loss of one or more components can lead to an irreversible imbalance of the biogeocenosis and its death as an integral system. Thus, tropical biogeocenoses, due to the huge number of plants and animals included in them, are much more stable than temperate or arctic biogeocenoses, which are poorer in terms of species diversity. For the same reason, the lake, which is
Being a natural biogeocenosis with a sufficient variety of living organisms, it is much more stable than a pond created by man and cannot exist without constant care for it. This is due to the fact that highly organized organisms for their existence need simpler organisms with which they are connected by trophic chains. Therefore, the foundation of any biogeocenosis is the simplest and lower organisms, mostly autotrophic microorganisms and plants. They are directly related to the abiotic components of biogeocenosis - the atmosphere, water, soil, solar energy, which is used to create organic matter. They also constitute the living environment for heterotrophic organisms - animals, fungi, viruses, humans. These organisms, in turn, participate in the life cycles of plants - pollinate, distribute fruits and seeds. This is how the circulation of substances occurs in biogeocenosis, in which plants play a fundamental role. Therefore, the boundaries of biogeocenoses most often coincide with the boundaries of plant communities.
Biogeocenoses are structural elements of the next superorganismal level of life. They make up the biosphere and determine all the processes occurring in it.
biospheric level
The biospheric level is the highest level of life organization, covering all life phenomena on our planet.
Biosphere- this is the living substance of the planet (the totality of all living organisms of the planet, including humans) and the environment transformed by it.
Biotic metabolism is a factor that unites all other levels of life organization into one biosphere.
At the biosphere level, there is a circulation of substances and the transformation of energy associated with the vital activity of all living organisms living on Earth. Thus, the biosphere is a single ecological system. The study of the functioning of this system, its structure and functions is the most important task of biology. Ecology, biocenology and biogeochemistry are engaged in the study of these problems.
The concept of the biosphere occupies a key place in the system of the modern scientific worldview. The term "biosphere" itself appeared in 1875. It was introduced by the Austrian geologist and paleontologist E. Suess to designate an independent sphere of our planet.
you, in which there is life. Suess defined the biosphere as a collection of organisms limited in space and time and living on the surface of the Earth. But he did not attach importance to the habitat of these organisms.
However, Suess was not a pioneer, since the development of the doctrine of the biosphere has a rather long prehistory. One of the first to consider the question of the influence of living organisms on geological processes was J. B. Lamarck in his book Hydrogeology (1802). In particular, Lamarck said that all the substances that are on the surface of the Earth and form its crust were formed due to the activity of living organisms. Then there was the grandiose multi-volume work of A. Humboldt "Cosmos" (the first book was published in 1845), in which many facts proved the interaction of living organisms with those earthly shells into which they penetrate. Therefore, Humboldt considered the atmosphere, hydrosphere and land with the living organisms living in them as a single shell of the Earth, an integral system.
But nothing has yet been said about the geological role of the biosphere, its dependence on the planetary factors of the Earth, its structure and functions. The development of the doctrine of the biosphere is inextricably linked with the name of the outstanding Russian scientist V.I. Vernadsky. His concept developed gradually, from the first student's work "On the change in the soil of the steppes by rodents" to "Living Matter", "Biosphere" and "Biogeochemical Essays". The results of his reflections were summed up in the works "Chemical Structure of the Earth's Biosphere" and "Philosophical Thoughts of a Naturalist", on which he worked in the last decades of his life. It was Vernadsky who managed to prove the connection of the organic world of our planet, acting as a single inseparable whole, with geological processes on Earth, it was he who discovered and studied the biogeochemical functions of living matter.
The key concept in Vernadsky's concept was the concept living matter, by which the scientist understood the totality of all living organisms on our planet, including humans. It also included in the composition of living matter a part of its external environment, which is necessary for maintaining the normal life of organisms; secretions and parts lost by organisms; dead organisms, as well as organic mixtures outside the organisms. Vernadsky considered the most important difference between living matter and inert matter to be the molecular asymmetry of living matter, discovered at one time by Pasteur (molecular chirality in modern terminology). Using this concept, Vernadsky managed to prove that not only the environment affects living organisms, but life is also able to effectively shape
their habitat. Indeed, at the level of an individual organism or biocenosis, it is very difficult to trace the impact of life on the environment. But, having introduced a new concept, Vernadsky reached a qualitatively new level of analysis of life and living things - the biospheric level.
The biosphere, according to Vernadsky, is the living substance of the planet (the totality of all living organisms on the Earth) and the habitat transformed by it (inert matter, abiotic elements), which includes the hydrosphere, the lower part of the atmosphere and the upper part of the earth's crust. Thus, this is not a biological, geological or geographical concept, but a fundamental concept of biogeochemistry - a new science created by Vernadsky to study geochemical processes taking place in the biosphere with the participation of living organisms. In the new science, the biosphere began to be called one of the main structural components of the organization of our planet and near-Earth outer space. This is the sphere in which bioenergetic processes and metabolism are carried out as a result of the activity of life.
Thanks to the new approach, Vernadsky explored life as a powerful geological force, effectively shaping the face of the Earth. Living matter has become the link that connected the history of chemical elements with the evolution of the biosphere. The introduction of a new concept also made it possible to raise and resolve the issue of the mechanisms of the geological activity of living matter, the sources of energy for this.
Living matter and inert matter constantly interact in the Earth's biosphere - in a continuous cycle of chemical elements and energy. Vernadsky wrote about the biogenic current of atoms, which is caused by living matter and is expressed in the constant processes of respiration, nutrition and reproduction. For example, the nitrogen cycle is associated with the conversion of atmospheric molecular nitrogen into nitrates. Nitrates are absorbed by plants and, as part of their proteins, get to animals. After the death of plants and animals, their bodies end up in the soil, where putrefactive bacteria decompose organic remains to ammonia, which is then oxidized into nitric acid.
On Earth, there is a continuous renewal of biomass (for 7-8 years), while abiotic elements of the biosphere are involved in the cycle. For example, the waters of the World Ocean have passed through the biogenic cycle associated with photosynthesis at least 300 times, the free oxygen of the atmosphere has been renewed at least 1 million times.
Vernadsky also noted that the biogenic migration of chemical elements in the biosphere tends to its maximum manifestation, and the evolution of species leads to the emergence of new species that increase the biogenic migration of atoms.
Vernadsky also noted for the first time that living matter tends to the maximum population of the habitat, and the amount of living matter in the biosphere remains stable throughout entire geological epochs. This value has not changed for at least the last 60 million years. The number of species also remained unchanged. If in some place of the Earth the number of species decreases, then in another place it increases. Today, the disappearance of a huge number of species of plants and animals is therefore associated with the spread of man and his unreasonable activity to transform nature. The population of the Earth is growing due to the death of other species.
Thanks to the biogenic migration of atoms, living matter performs its geochemical functions. Modern science classifies them into five categories:
concentration function- is expressed in the accumulation of certain chemical elements both inside and outside living organisms due to their activities. The result was the emergence of mineral reserves (limestone, oil, gas, coal, etc.);
transport function- is closely related to the concentration function, since living organisms carry the chemical elements they need, which then accumulate in their habitats;
energy function - provides energy flows penetrating the biosphere, which makes it possible to carry out all the biogeochemical functions of living matter. The most important role in this process is played by photosynthetic plants that convert solar energy into biogeochemical energy of the living matter of the biosphere. This energy is spent on all the grandiose transformations of the appearance of our planet;
destructive function - associated with the destruction and processing of organic remains, during which the substances accumulated by organisms are returned to natural cycles, there is a circulation of substances in nature;
environment-forming function- is manifested in the transformation of the environment under the influence of living matter. We can boldly assert that the entire modern appearance of the Earth - the composition of the atmosphere, hydrosphere, upper layer of the lithosphere, most of the minerals, climate - are the result of the action of Life. So, green plants provide the Earth with oxygen and accumulate energy, microorganisms participate in the mineralization of organic substances, the formation of a number of rocks and soil formation.
Despite the grandeur of the tasks that living matter and the Earth's biosphere solve, the biosphere itself (compared to other geospheres) is a very thin film. Today it is generally accepted that microbial life occurs in the atmosphere up to about 20-22 km above the earth's surface, and the presence of life in deep ocean trenches lowers this limit to 8-11 km below sea level. The penetration of life into the earth's crust is much less, and microorganisms were found during deep drilling and in formation waters no deeper than 2-3 km. The composition of the biosphere Vernadsky included:
living matter;
biogenic substance - a substance created and processed by living organisms (coal, oil, gas, etc.);
inert matter formed in processes without the participation of living matter;
substances created by living organisms and inert processes, and their dynamic balance;
substances in the process of radioactive decay;
scattered atoms released from terrestrial matter under the influence of cosmic radiation;
a substance of cosmic origin, including individual atoms and molecules penetrating the Earth from space.
Of course, life in the biosphere is distributed unevenly, there are so-called thickening and rarefaction of life. The most densely populated are the lower layers of the atmosphere (50 m from the earth's surface), the illuminated layers of the hydrosphere, and the upper layers of the lithosphere (soil). It should also be noted that the tropical regions are much more densely populated than the deserts or ice fields of the Arctic and Antarctic. Deeper into the earth's crust, into the ocean, and also higher into the atmosphere, the amount of living matter decreases. Thus, this thinnest film of life covers absolutely the entire Earth, leaving not a single place on our planet where there would be no life. At the same time, there is no sharp boundary between the biosphere and the terrestrial shells surrounding it.
For a long time, Vernadsky's ideas were hushed up, and they returned to them only in the mid-1970s. This was largely due to the work of the Russian biologist G.A. Zavarzin, who proved that the main factor in the formation and functioning of the biosphere was and remains multilateral trophic relationships. They were established no less than 3.4-3.5 billion years ago and since then determine the nature and extent of the circulation of elements in the Earth's shells.
In the early 1980s English chemist J. Lovelock and American microbiologist L. Margulis proposed a very interesting concept of Gaia-Earth. According to it, the biosphere is
It is a single superorganism with a developed homeostasis, making it relatively independent of fluctuations in external factors. But if the self-regulating system of Gaia-Earth falls into a state of stress close to the limits of self-regulation, even a small shock can push it to a transition to a new state or even to the complete destruction of the system. In the history of our planet, such global catastrophes have happened more than once. The most famous of them is the extinction of dinosaurs about 60 million years ago. Now the Earth is again experiencing a deep crisis, so it is so important to think over a strategy for the further development of human civilization.
Literature for self-study
Afanasiev V.G. The world of the living: consistency, evolution and management. M., 1986.
Barg O.A. Living in a single world process. Perm, 1993.
Borzenko V.G., Severtsov A.V. Theoretical biology: reflection on the subject. M., 1980.
Vernadsky V.I. Biosphere and noosphere // Living matter and biosphere. M., 1994.
Vernadsky V.I. Chemical structure of the Earth's biosphere and its environment. M., 1987.
Dubinin N.P. Essays on genetics. M., 1985.
Kemp P, Arms K. Introduction to biology. M., 1988.
Christine de Duve. Journey into the world of the living cell. M., 1987.
Yugay G.A. General theory of life. M., 1985.
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1. Levels of life organization
Levels of life organization:
molecular genetic,
cellular,
fabric,
organ,
organismic,
population-species,
biogeocenotic
biospheric.
A cell is a structural and functional elementary unit of the structure and vital activity of all organisms (except for viruses, which are often referred to as non-cellular life forms), which has its own metabolism, is capable of independent existence, self-reproduction (animals, plants and fungi), or is unicellular organism (many protozoa and bacteria).
3. Molecular-genetic level of life organization. Characteristic
Components: - Molecules of inorganic and organic compounds
Molecular complexes
Main processes:
Combining molecules into special complexes
Encoding and transmission of genetic information
4. The structure of the cell membrane
The cell membrane is a double layer (bilayer) of lipid class molecules, most of which are the so-called complex lipids - phospholipids. Lipid molecules have a hydrophilic (“head”) and a hydrophobic (“tail”) part. During the formation of membranes, the hydrophobic portions of the molecules turn inward, while the hydrophilic portions turn outward. Membranes are invariable structures, very similar in different organisms.
Perhaps some exception is archaea, whose membranes are formed by glycerol and terpenoid alcohols. The membrane thickness is 7--8 nm.
The biological membrane also includes various proteins: integral (penetrating the membrane through), semi-integral (immersed at one end into the outer or inner lipid layer), surface (located on the outer or adjacent to the inner sides of the membrane). Some proteins are the points of contact of the cell membrane with the cytoskeleton inside the cell, and the cell wall (if any) outside. Some of the integral proteins function as ion channels, various transporters, and receptors.
5. Characteristics of the cellular level of life organization. Schleiden-Schwann theory
The cellular level is represented by a variety of organic cells: plant and animal cells are common in origin, cells are the structural and functional basis of all living beings. Schleiden-Schwann theory:
All animals and plants are made up of cells.
Plants and animals grow and develop through the formation of new cells.
A cell is the smallest unit of life, and the whole organism is a collection of cells.
6. Characteristics of the tissue level of life organization
The tissue level is represented by tissues that unite cells of a certain structure, size, location and similar functions. Tissues arose in the course of historical development along with multicellularity. In multicellular organisms, they are formed in the process of ontogeny as a result of cell differentiation. In animals, several types of tissues are distinguished (epithelial, connective, muscle, nervous). In plants, meristematic, protective, basic and conductive tissues are distinguished. At this level, cell specialization occurs.
7. Functions of the cell membrane
· barrier - provides a regulated, selective, passive and active metabolism with the environment. For example, the peroxisome membrane protects the cytoplasm from peroxides that are dangerous for the cell. Selective permeability means that the permeability of a membrane to various atoms or molecules depends on their size, electrical charge, and chemical properties. Selective permeability ensures the separation of the cell and cellular compartments from the environment and supply them with the necessary substances.
· transport - through the membrane there is a transport of substances into the cell and out of the cell. Transport through membranes provides: the delivery of nutrients, the removal of end products of metabolism, the secretion of various substances, the creation of ionic gradients, the maintenance of optimal pH in the cell and the concentration of ions that are necessary for the functioning of cellular enzymes.
Particles that for some reason are unable to cross the phospholipid bilayer (for example, due to hydrophilic properties, since the membrane inside is hydrophobic and does not allow hydrophilic substances to pass through, or due to large sizes), but necessary for the cell, can penetrate the membrane through special carrier proteins (transporters) and channel proteins or by endocytosis.
In passive transport, substances cross the lipid bilayer without energy expenditure along the concentration gradient by diffusion. A variant of this mechanism is facilitated diffusion, in which a specific molecule helps a substance to pass through the membrane. This molecule may have a channel that allows only one type of substance to pass through.
· Active transport requires energy, as it occurs against the concentration gradient. There are special pump proteins on the membrane, including the AT Phase, which actively pumps potassium ions (K+) into the cell and pumps sodium ions (Na+) out of it.
· matrix - provides a certain relative position and orientation of membrane proteins, their optimal interaction.
Mechanical - ensures the autonomy of the cell, its intracellular structures, as well as connection with other cells (in tissues). Cell walls play an important role in ensuring mechanical function, and in animals, the intercellular substance.
energy - during photosynthesis in chloroplasts and cellular respiration in mitochondria, energy transfer systems operate in their membranes, in which proteins also participate;
receptor - some proteins located in the membrane are receptors (molecules with which the cell perceives certain signals).
For example, hormones circulating in the blood only act on target cells that have receptors corresponding to these hormones. Neurotransmitters (chemicals that conduct nerve impulses) also bind to specific receptor proteins on target cells.
enzymatic - membrane proteins are often enzymes. For example, the plasma membranes of intestinal epithelial cells contain digestive enzymes.
· Implementation of the generation and conduction of biopotentials.
With the help of the membrane, a constant concentration of ions is maintained in the cell: the concentration of the K + ion inside the cell is much higher than outside, and the concentration of Na + is much lower, which is very important, since this maintains the potential difference across the membrane and generates a nerve impulse.
cell marking - there are antigens on the membrane that act as markers - "labels" that allow you to identify the cell. These are glycoproteins (that is, proteins with branched oligosaccharide side chains attached to them) that play the role of "antennas". Due to the myriad of side chain configurations, it is possible to make a specific marker for each cell type. With the help of markers, cells can recognize other cells and act in concert with them, for example, when forming organs and tissues. It also allows the immune system to recognize foreign antigens.
8. Characteristics of the organ level of life organization
In multicellular organisms, the union of several identical tissues, similar in structure, origin and functions, forms the organ level. Each organ contains several tissues, but among them one is the most significant. A separate organ cannot exist as a whole organism. Several organs, similar in structure and function, unite to form an organ system, for example, digestion, respiration, blood circulation, etc.
9. Characteristics of the organismic level of life organization
Plants (chlamydomonas, chlorella) and animals (amoeba, infusoria, etc.), whose bodies consist of one cell, are an independent organism. A separate individual of multicellular organisms is considered as a separate organism. In each individual organism, all the vital processes characteristic of all living organisms take place - nutrition, respiration, metabolism, irritability, reproduction, etc. Each independent organism leaves behind offspring. In multicellular organisms, cells, tissues, organs and organ systems are not a separate organism. Only an integral system of organs specialized in performing various functions forms a separate independent organism. The development of an organism, from fertilization to the end of life, takes a certain period of time. This individual development of each organism is called ontogeny. An organism can exist in close relationship with the environment.
10. Characteristics of the population-species standard of living
An aggregate of individuals of one species or a group that exists for a long time in a certain part of the range relatively apart from other aggregates of the same species constitutes a population. At the population level, the simplest evolutionary transformations are carried out, which contributes to the gradual emergence of a new species.
11. Characteristics of the biogeocenotic standard of living
The totality of organisms of different species and organization of varying complexity, adapted to the same environmental conditions, is called a biogeocenosis, or natural community. The composition of biogeocenosis includes numerous types of living organisms and environmental conditions. In natural biogeocenoses, energy is accumulated and transferred from one organism to another. Biogeocenosis includes inorganic, organic compounds and living organisms.
12. Characteristics of the biospheric level of life organization
The totality of all living organisms on our planet and their common natural habitat constitutes the biospheric level. At the biospheric level, modern biology solves global problems, such as determining the intensity of the formation of free oxygen by the Earth's vegetation cover or changes in the concentration of carbon dioxide in the atmosphere associated with human activities. The main role in the biospheric level is played by "living substances", that is, the totality of living organisms that inhabit the Earth. Also at the biosphere level, "bio-inert substances", formed as a result of the vital activity of living organisms and "inert" substances, i.e., environmental conditions, matter. At the biospheric level, the circulation of substances and energy on Earth takes place with the participation of all living organisms of the biosphere.
13. Cellular organelles and their functions
The plasma membrane is a thin film that consists of interacting lipid and protein molecules, delimits the internal contents from the external environment, provides transport of water, mineral and organic substances into the cell by osmosis and active transfer, and also removes waste products. Cytoplasm - the internal semi-liquid environment of the cell, in which the nucleus and organelles are located, provides connections between them, participates in the main processes of life. Endoplasmic reticulum - a network of branching channels in the cytoplasm. It is involved in the synthesis of proteins, lipids and carbohydrates, in the transport of substances. Ribosomes - bodies located on the EPS or in the cytoplasm, consist of RNA and protein, are involved in protein synthesis. EPS and ribosomes are a single apparatus for the synthesis and transport of proteins. Mitochondria are organelles separated from the cytoplasm by two membranes. Organic substances are oxidized in them and ATP molecules are synthesized with the participation of enzymes. An increase in the surface of the inner membrane, on which enzymes are located, due to ATP crist - an organic substance rich in energy. Plastids (chloroplasts, leukoplasts, chromoplasts), their content in the cell is the main feature of the plant organism. Chloroplasts are plastids containing the green pigment chlorophyll, which absorbs light energy and uses it to synthesize organic substances from carbon dioxide and water. Delimitation of chloroplasts from the cytoplasm by two membranes, numerous outgrowths - grana on the inner membrane, in which chlorophyll molecules and enzymes are located. The Golgi complex is a system of cavities separated from the cytoplasm by a membrane. The accumulation of proteins, fats and carbohydrates in them. Implementation of the synthesis of fats and carbohydrates on membranes. Lysosomes are bodies separated from the cytoplasm by a single membrane. The enzymes contained in them accelerate the reaction of splitting complex molecules into simple ones: proteins to amino acids, complex carbohydrates to simple ones, lipids to glycerol and fatty acids, and also destroy dead parts of the cell, whole cells. Vacuoles - cavities in the cytoplasm filled with cell sap, a place of accumulation of reserve nutrients, harmful substances; they regulate the water content in the cell. The nucleus is the main part of the cell, covered on the outside by a two-membrane, pierced nuclear envelope. Substances enter the core and are removed from it through the pores. Chromosomes are carriers of hereditary information about the characteristics of an organism, the main structures of the nucleus, each of which consists of one DNA molecule in combination with proteins. The nucleus is the site of the synthesis of DNA, i-RNA, r-RNA.
14. Lysosomes. Characteristic
They look like a bag. A characteristic feature of lysosomes is that they contain about 40 hydrolytic enzymes: proteinases, nucleases, glycosidases, phosphorylases, phosphatases, sulfitases, the optimum action of which is carried out at pH 5. In lysosomes, the acidic value of the environment is preserved due to the presence of an H + pump in their membranes, dependent on ATP. At the same time, there are carrier proteins in the lysosome membrane for the transport of monomers of split molecules from lysosomes to the hyaloplasm: amino acids, sugars, nucleotides, lipids. Self-digestion of lysosomes does not occur due to the fact that the membrane elements of lysosomes are protected from the action of acid hydrolases by oligosaccharide sites, which are either not recognized by lysosomal enzymes or simply prevent hydrolases from interacting with them. When viewed in an electron microscope, it can be seen that the lysosome fraction consists of a very variegated class of vesicles 0.2–0.4 μm in size (for liver cells), limited by a single membrane (its thickness is about 7 nm), with a very heterogeneous content inside. In the lysosome fraction, there are vesicles with a homogeneous, structureless content, there are vesicles filled with a dense substance, which in turn contains vacuoles, accumulations of membranes and dense homogeneous particles; it is often possible to see inside lysosomes not only sections of membranes, but also fragments of mitochondria and ER. In other words, this fraction turned out to be extremely heterogeneous in morphology, despite the constancy of the presence of hydrolases.
15. Mitochondria. Characteristic
Mitochondria were first discovered as granules in muscle cells in 1850. The number of mitochondria in a cell is not constant. There are especially many of them in cells in which the need for oxygen is high. In their structure, they are cylindrical organelles found in a eukaryotic cell in quantities from several hundred to 1-2 thousand and occupying 10-20% of its internal volume. The size (from 1 to 70 μm) and shape of mitochondria also vary greatly. The width of these organelles is relatively constant (0.5–1 µm). Able to change shape. Depending on which parts of the cell at each particular moment there is an increased energy consumption, mitochondria are able to move through the cytoplasm to the areas of the highest energy consumption, using the structures of the cytoskeleton of the eukaryotic cell for movement. An alternative to many disparate small mitochondria, functioning independently of each other and supplying ATP to small areas of the cytoplasm, is the existence of long and branched mitochondria, each of which can provide energy for distant parts of the cell (for example, in unicellular green algae Chlorella). A variant of such an extended system can also be an ordered spatial association of many mitochondria (chondria or mitochondrion), which ensures their cooperative work and is found in both unicellular and multicellular organisms. This type of chondriome is especially complex in the skeletal muscles of mammals, where groups of giant branched mitochondria are connected to each other using intermitochondrial contacts (IMCs). The latter are formed by outer mitochondrial membranes tightly adjacent to each other, as a result of which the intermembrane space in this zone has an increased electron density. MMCs are especially abundant in cardiac muscle cells, where they bind multiple individual mitochondria into a coordinated working cooperative system.
16. Golgi Complex
it is a complex network of cavities, tubules and vesicles around the nucleus. It consists of three main components: a group of membrane cavities, a system of tubules extending from the cavities, and vesicles at the ends of the tubules. It performs the following functions: Bubbles accumulate substances that are synthesized and transported through the EPS, here they undergo chemical changes. Altered substances are packed into membrane vesicles, which are secreted by the cell in the form of secrets. Some of the vesicles perform the function of lysosomes, which are involved in the digestion of particles that have entered the cell as a result of phago- and pinocytosis.
17. Cell center
The cell center is a non-membrane organoid, the main microtubule organizing center (MCTC) and the regulator of the cell cycle in eukaryotic cells. First discovered in 1883 by Theodore Boveri, who called it "a special organ of cell division." The centrosome plays a critical role in cell division, however, the presence of a cell center in a cell is not necessary for mitosis. In the vast majority of cases, only one centrosome is normally present in a cell. An abnormal increase in the number of centrosomes is characteristic of malignant tumor cells. More than one centrosome is normal in some polyenergetic protozoa and in syncytial structures. In many living organisms (animals and a number of protozoa), the centrosome contains a pair of centrioles, cylindrical structures located at right angles to each other. Each centriole is formed by nine triplets of microtubules arranged in a circle, as well as a number of structures formed by centrin, cenexin, and tectin. In the interphase of the cell cycle, centrosomes are associated with the nuclear membrane. In the prophase of mitosis, the nuclear membrane is destroyed, the centrosome divides, and the products of its division (daughter centrosomes) migrate to the poles of the dividing nucleus. Microtubules growing from daughter centrosomes are attached at the other end to the so-called kinetochores on the centromeres of chromosomes, forming a division spindle. At the end of division, each of the daughter cells contains only one centrosome. In addition to participating in nuclear division, the centrosome plays an important role in the formation of flagella and cilia. The centrioles located in it act as centers of organization for the microtubules of the flagellum axonemes. In organisms lacking centrioles (for example, marsupials and basidiomycetes, angiosperms), flagella do not develop. Planarians and possibly other flatworms do not have centrosomes.
18. Ergastoplasma
Ergastoplasma (from the Greek ergastikуs - active and plasma - basophilic (staining with basic dyes) areas of animal and plant cells rich in ribonucleic acid (for example, Berg's lumps in liver cells, Nissl bodies in neurons). In an electron microscope, these areas are observed as ordered elements of the granular endoplasmic reticulum.
19. Ribosome
The ribosome is the most important non-membrane organelle of a living cell, spherical or slightly ellipsoidal in shape, with a diameter of 15–20 nanometers (prokaryotes) to 25–30 nanometers (eukaryotes), consisting of large and small subunits. Ribosomes serve to biosynthesize protein from amino acids according to a given template based on the genetic information provided by messenger RNA (mRNA). This process is called translation.
20. Organelles
Organelles - in cytology: permanent specialized structures in the cells of living organisms. Each organelle performs certain functions vital for the cell. The term "Organoids" is explained by the comparison of these cell components with the organs of a multicellular organism. Organelles contrast with the temporary inclusions of the cell, which appear and disappear in the process of metabolism. Sometimes only the permanent structures of a cell located in its cytoplasm are considered organelles. Often the nucleus and intranuclear structures (for example, the nucleolus) are not called organelles. The cell membrane, cilia and flagella are also usually not classified as organelles. Receptors and other small, molecular level structures are not called organelles. The boundary between molecules and organelles is not very clear. Thus, ribosomes, which are usually unambiguously referred to as organelles, can also be considered as a complex molecular complex. Increasingly, other similar complexes of comparable size and level of complexity, such as proteasomes, spliceosomes, etc., are also classified as organoids. At the same time, elements of the cytoskeleton of comparable size (microtubules, thick filaments of striated muscles, etc.) are usually not classified as organoids. The degree of constancy of the cellular structure is also an unreliable criterion for classifying it as an organelle. So, the spindle of division, which, although not constantly, but naturally present in all eukaryotic cells, is usually not referred to as organelles, but vesicles, which constantly appear and disappear in the process of metabolism, are referred to.
21. Scheme of energy release from ATP
22. Cell with organelles
23. Chromatin
Chromatin is a substance of chromosomes - a complex of DNA, RNA and proteins. Chromatin is located inside the nucleus of eukaryotic cells and is part of the nucleotide in prokaryotes. It is in the composition of chromatin that the realization of genetic information, as well as DNA replication and repair, takes place. The bulk of chromatin is made up of histone proteins. Histones are a component of nucleosomes, the supramolecular structures involved in chromosome packing. Nucleosomes are arranged quite regularly, so that the resulting structure resembles beads. The nucleosome is made up of four types of proteins: H2A, H2B, H3, and H4. One nucleosome contains two proteins of each type - a total of eight proteins. Histone H1, which is larger than the other histones, binds to DNA at its entry into the nucleosome. A strand of DNA with nucleosomes forms an irregular solenoid-like structure about 30 nanometers thick, the so-called 30 nm fibril. Further packing of this fibril may have different densities. If the chromatin is packed tightly, it is called condensed or heterochromatin, it is clearly visible under a microscope. DNA located in heterochromatin is not transcribed, usually this state is characteristic of insignificant or silent regions. In interphase, heterochromatin is usually located on the periphery of the nucleus (parietal heterochromatin). Complete condensation of chromosomes occurs before cell division. If the chromatin is loosely packed, it is called eu- or interchromatin. This kind of chromatin is much less dense when observed under a microscope and is usually characterized by the presence of transcriptional activity. The packing density of chromatin is largely determined by histone modifications - acetylation and phosphorylation. It is believed that there are so-called functional chromatin domains in the nucleus (the DNA of one domain contains approximately 30 thousand base pairs), that is, each section of the chromosome has its own “territory”. The question of the spatial distribution of chromatin in the nucleus has not yet been sufficiently studied. It is known that telomeric (terminal) and centromeric (responsible for the binding of sister chromatids in mitosis) regions of chromosomes are fixed on nuclear lamina proteins.
24. Chromosomes
Chromosomes are nucleoprotein structures in the nucleus of a eukaryotic cell, in which most of the hereditary information is concentrated and which are designed for its storage, implementation and transmission. Chromosomes are clearly visible under a light microscope only during the period of mitotic or meiotic cell division. The set of all chromosomes of a cell, called a karyotype, is a species-specific trait characterized by a relatively low level of individual variability. The chromosome is formed from a single and extremely long DNA molecule that contains a linear group of many genes. The necessary functional elements of the eukaryotic chromosome are the centromere, telomeres, and the origin of replication. Origins of replication (sites of initiation) and telomeres located at the ends of chromosomes allow the DNA molecule to replicate efficiently, while at the centromeres sister DNA molecules attach to the mitotic spindle, which ensures their precise separation into daughter cells in mitosis. The term was originally proposed to refer to structures found in eukaryotic cells, but in recent decades, bacterial or viral chromosomes have been increasingly spoken of. Therefore, according to D. E. Koryakov and I. F. Zhimulev, a broader definition is the definition of a chromosome as a structure that contains a nucleic acid and whose function is to store, implement and transmit hereditary information. Eukaryotic chromosomes are DNA-containing structures in the nucleus, mitochondria, and plastids. Prokaryotic chromosomes are DNA-containing structures in a cell without a nucleus. Virus chromosomes are a DNA or RNA molecule in the capsid.
25. Eukaryotes and prokaryotes. Characteristic
Eukaryotes, or nuclear, are the domain (superkingdom) of living organisms whose cells contain nuclei. All organisms except bacteria and archaea are nuclear. Animals, plants, fungi, and the group of organisms collectively called protists are all eukaryotic organisms. They can be unicellular and multicellular, but all have a common cell plan. It is believed that all these dissimilar organisms have a common origin, so the nuclear group is considered as a monophyletic taxon of the highest rank. According to the most common hypotheses, eukaryotes appeared 1.5-2 billion years ago. An important role in the evolution of eukaryotes was played by symbiogenesis - a symbiosis between a eukaryotic cell, apparently already having a nucleus and capable of phagocytosis, and bacteria absorbed by this cell - precursors of mitochondria and plastids.
Prokaryotes, or pre-nuclear, are unicellular living organisms that do not (unlike eukaryotes) have a well-formed cell nucleus and other internal membrane organelles (with the exception of flat cisterns in photosynthetic species, for example, in cyanobacteria). Prokaryotic cells are characterized by the absence of a nuclear membrane, DNA is packaged without the participation of histones. The type of nutrition is osmotrophic and autotrophic (photosynthesis and chemosynthesis). The only large circular (in some species - linear) double-stranded DNA molecule, which contains the main part of the cell's genetic material (the so-called nucleoid) does not form a complex with histone proteins (the so-called chromatin). Prokaryotes include bacteria, including cyanobacteria (blue-green algae), and archaea. The descendants of prokaryotic cells are the organelles of eukaryotic cells - mitochondria and plastids. The study of bacteria led to the discovery of horizontal gene transfer, which was described in Japan in 1959. This process is widespread among prokaryotes and also in some eukaryotes. The discovery of horizontal gene transfer in prokaryotes has led to a different look at the evolution of life. Earlier evolutionary theory was based on the fact that species cannot exchange hereditary information. Prokaryotes can exchange genes with each other directly (conjugation, transformation) and also with the help of viruses - bacteriophages (transduction).
26. Karyosome. Characteristic
one). Relatively large, located in the center of the nucleus, spherical nucleolus. 2). Chromatin thickenings and nodules of the nuclear network, giving their substance to developing chromosomes at the beginning of cell division. 3). Rounded dense chromatin bodies, which are individual chromosomes or their groups that remain in the nucleus after the end of cell division. 4). Larger spherical bodies containing at a certain stage the entire chromatin of the nucleus and giving rise to the entire set of chromosomes.
27. Kernel dimensions
The nuclei are usually usually spherical or ovoid in shape; the diameter of the former is approximately 10 μm, and the length of the latter is 20 μm.
The nucleus (lat. Nucleus) is one of the structural components of a eukaryotic cell, containing genetic information (DNA molecules), performing the main functions: storage, transmission and implementation of hereditary information with protein synthesis. The nucleus consists of chromatin, nucleolus, karyoplasm (or nucleoplasm) and nuclear envelope.
29. By whom and when was the core discovered
In 1831, Robert Brown describes the nucleus and suggests that it is a permanent part of the plant cell.
30. Enucleation
Enucleation - (from lat. Enucleo - I take out the nucleus, peel it from the shell) removal of the cell nucleus.
One of the ways to remove tumors and organs.
31. Kernel functions. Differences from nuclear matter
Functions of the nucleus: 1) metabolism; 2) reproduction; 3) storage, processing and transmission of hereditary information; 4) regenerative.
Unlike the formed nucleus, the nuclear substance does not perform two functions: reproduction and regeneration.
32. By whom and when was mitosis discovered
The first descriptions of the phases of mitosis and the establishment of their sequence were undertaken in the 70-80s of the XIX century. In 1878, the German histologist Walter Flemming coined the term "mitosis" to refer to the process of indirect cell division. It was studied in detail by the German histologist Weismann in 1888.
Mitosis is an indirect division, a universal way of dividing immature germ and somatic cells with intermediate doubling of a diploid set of chromosomes to a tetraploid one and its subsequent equivalent distributions among 2 formed daughter cells with an identical maternal diploid set of chromosomes.
34. What is the difference between mitosis and amitosis and endomitosis
Mitosis is a process of indirect division.
Amitosis is the process of direct cell division.
Endomitosis is the process of doubling the number of chromosomes in the cell nuclei of many protists, plants and animals, which is not followed by the division of the nucleus and the cell itself.
35. Characteristics of the interphase of mitosis. Periods: G1, S, G2
Interphase is the phase of relative rest of the cell. The cell at this stage, although not dividing, is actively growing, forming its structures, synthesizing energy-rich chemicals and preparing for the upcoming division.
Period (phase) G1 (G1 period) [Greek. periodos -- circulation; English g(ap) -- interval, interval] -- stage of the cell cycle (interphase stage), during which there is an active growth and functioning of the cell, due to the resumption of transcription and the accumulation of synthesized proteins, as well as preparation for DNA synthesis; the growth phase preceding the period of DNA replication.
Period (phase) S (S period) [Greek. periodos -- circulation; English (synthesis) - synthesis] - stage of the cell cycle (interphase stage), during which DNA replication and doubling of chromosome material occur; precedes period G2
Period (phase) G2 (G2 period) [Greek. periodos -- circulation; English (gap) -- gap, interval] -- stage of the cell cycle, starting after DNA replication (period S) and preceding mitosis; during this period, the cell is preparing for division, the synthesis of spindle proteins is carried out.
36. Image of early and late prophase of mitosis
Number 4 - early prophase
Number 5 - late prophase
37. Image of the metaphase of mitosis
38. Image of anaphase of mitosis
39. Image of telophase of mitosis
40. Image of all phases of mitosis
41. Characteristics of the division spindle
The spindle of division is a rod-shaped system of microtubules in the cytoplasm of a cell during mitosis or meiosis. Chromosomes are attached to the bulge of the spindle (the equator). The spindle causes the chromosomes to separate, causing the cells to divide.
42. The phenomenon of osmosis. Characteristic. osmotic pressure. Definition
Osmosis is the process of one-way diffusion through a semi-permeable membrane of solvent molecules towards a higher concentration of the solute (lower concentration of the solvent).
The phenomenon of osmosis is observed in those media where the mobility of the solvent is greater than the mobility of the dissolved substances. An important special case of osmosis is osmosis through a semipermeable membrane. Semi-permeable membranes are called, which have a sufficiently high permeability not for all, but only for some substances, in particular, for a solvent. (Mobility of dissolved substances in the membrane tends to zero). As a rule, this is due to the size and mobility of the molecules, for example, a water molecule is smaller than most molecules of solutes.
Osmotic pressure (denoted p) is the excess hydrostatic pressure on a solution separated from a pure solvent by a semipermeable membrane, at which diffusion of the solvent through the membrane stops (osmosis). This pressure tends to equalize the concentrations of both solutions due to the counter diffusion of the solute and solvent molecules.
43. Plasmolysis. Characteristic
Plasmolysis - separation of the protoplast from the shell under the action of a hypertonic solution on the cell. Plasmolysis is characteristic mainly for plant cells that have a strong cellulose membrane.
44. Characteristics of solutions by the concentration of salts in the cytoplasm
1) isotonic solution - a solution whose osmotic pressure is equal to the osmotic pressure of blood plasma; for example, 0.9% sodium chloride solution, 5% aqueous glucose solution.
2) a hypertonic solution is a solution whose osmotic pressure is higher than the osmotic pressure of blood plasma (a solution with a higher concentration of solutes)
3) hypotonic solution - a solution whose osmotic pressure is lower than the normal osmotic pressure of blood plasma (a solution with a lower concentration of dissolved substances)
45. Characteristics of physiological saline
Physiological saline solution is a 0.9% aqueous solution of NaCl (sodium chloride) - the simplest isotonic solution. Saline is needed to replenish body fluids in case of dehydration. An important property of saline is its antimicrobial property. In this regard, it is widely used in the treatment of colds.
46. Hair dryer (sign). Definition
Fen - (from the Greek phaino - I reveal, I discover) (biol.), A discrete, genetically determined sign of an organism.
47. Gen. Definition
A gene is a structural and functional unit of heredity in living organisms. A gene is a section of DNA that specifies the sequence of a particular polypeptide or functional RNA.
48. Phenotype. Definition
Phenotype - a set of characteristics inherent in an individual at a certain stage of development
49. Genotype. Definition
Genotype - a set of genes of a given organism, which, in contrast to the concept of the gene pool, characterizes the individual, not the species.
50. Allele. Definition
Allele (Greek allelon - each other, mutually), or allelomorphs - an alternative form of the structural state of the gene, on which the manifestation of a hereditary trait depends (alleles of homologous chromosomes are located in the same locus).
51. Which traits are called dominant and which are recessive
Dominant trait - a trait that appears in hybrids of the first generation when crossing a pure line.
A recessive trait is a trait that does not appear in heterozygous individuals due to the suppression of the manifestation of the recessive allele.
52. Write
a) genotype consisting of three alleles: AABBCC
b) give the full name to this genotype: homozygous for the dominant trait for three alleles
c) ABC gamete
53. Write
a) any gamete that carries three traits: ABC
b) all variants of the genotypes that form this gamete: AABBCC; AaBBSS; AaBvSS; AaVvSs; AaBBSS; AAVvSS; AAVVSs; AAVvSS;
54. Homozygous and heterozygous state of the genotype. Definition. Examples
Homozygous state of the genotype - it is carried by a diploid organism carrying single alleles in homozygous chromosomes. (ah, ah)
The heterozygous state of the genotype is a condition inherent in any hybrid organism in which its homologous chromosomes carry different alleles of a particular gene. (Aa, Bc)
55. Name the genotype
ААВbСсdd - homozygous state of the genotype for the dominant trait for the first pair of traits (alleles) and for the recessive trait for the fourth allele. Heterozygous state of the genotype for the second and third alleles.
56. Name the genotype
АаВbСсDd - heterozygous state of the genotype for four pairs of traits. (Alleles)
57. Inheritance of a phenotype or genotype
Unlike the phenotype, the genotype is inherited, since it is hereditarily determined (defined)
genetic cell mitosis chromosome
58. What are the sex and non-sex chromosomes called
Gonosomes are sex chromosomes, chromosomes, the set of which distinguishes male and female individuals.
Autosomes are non-sex chromosomes. Chromosomes are not associated with sex characteristics. Available in both male and female bodies.
59. List the types of inheritance
1) Autosomal dominant type of inheritance
2) Autosomal recessive type of inheritance
60. The formula for determining the number of types of gametes formed by the genotype
The number of gamete types is determined by the formula, where n is the number of gene pairs in the heterozygous state.
61. Mendel's First Law
The law of uniformity of hybrids of the first generation: with monohybrid crossing, all offspring in the first generation are characterized by uniformity in phenotype and genotype.
62. Mendel's second law
The law of splitting: when two heterozygous offspring of the first generation are crossed with each other in the second generation, splitting is observed in a certain numerical ratio: according to the phenotype 3:1, according to the genotype 1:2:1.
63. The third law of Mendel
The law of independent inheritance: when crossing two individuals that differ from each other in two (or more) pairs of alternative traits, genes and their corresponding traits are inherited independently of each other and combined in all possible combinations (as in monohybrid crossing).
64. Definition of all three laws of Mendel
The answer is in question 61,62,63.
65. What splitting is observed in the second generation when deriving Mendel's third law
3:1 - phenotype
1:2:1 - genotype
66. The general formula of dominant - dominant and dominant - recessive
The general formula of dominant - dominant: A_B_
The general formula for dominant - recessive: A_vv
67. Patterns in the Punnett lattice
The Punnett lattice is a graphical representation of the results of various crosses. The gametes of one parent are inscribed horizontally, and those of the other parent vertically. In the cells of the table, we enter the genotypes of the offspring, which were obtained by merging the corresponding gametes.
68. "Character" of Mendel's laws
Mendel's laws are statistical in nature: the deviation from the theoretically expected splitting is the smaller, the greater the number of observations. Each genotype corresponds to a certain phenotype (100% penetrance of traits). In all individuals with this genotype, the trait is equally expressed (100% expressivity of traits). The studied traits are not sex-linked. The viability of individuals does not depend on their genotype and phenotype.
69. All possible variants of "yellow-smooth" genotypes
AABB, AaBv, AaBB, AABv, - variants of "yellow-smooth"
70. Additions to Mendel's laws. Characteristic
Far from all the results of crossings found during the research fit into the laws of Mendel, hence the additions to the laws arose.
The dominant feature in some cases may not be fully manifested or even absent. In this case, there is that called intermediate inheritance, when none of the two interacting genes dominates the other, and their action is manifested in the animal's genotype to an equal extent, one trait, as it were, dilutes the other.
An example is the Tonkinese cat. When Siamese cats are crossed with Burmese kittens are born darker than Siamese, but lighter than Burmese - such an intermediate color is called Tonkinese.
Along with the intermediate inheritance of traits, there is a different interaction of genes, that is, genes responsible for some traits can affect the manifestation of other traits:
Mutual influence - for example, the weakening of the black color under the influence of the Siamese color gene in cats that are its carriers.
Complementarity - the manifestation of a trait is possible only under the influence of two or more genes. For example, all tabby colors appear only in the presence of the dominant agouti gene.
Epistasis - the action of one gene completely hides the action of another. For example, the dominant white gene (W) hides any color and pattern, it is also called epistatic white.
Polymeria - a whole series of genes affects the manifestation of one trait. For example - the density of wool.
Pleiotropy - one gene affects the manifestation of a series of traits. For example, the same gene for white color (W) linked to blue eyes provokes the development of deafness.
Linked genes are also a common deviation, which, however, does not contradict the laws of Mendel. That is, a number of traits are inherited in a certain combination. An example is sex-linked genes - cryptorchidism (females are its carriers), red color (it is transmitted only on the X chromosome).
71. General formula for genotypes
Rose-shaped comb;
Pea-shaped comb;
Nut-shaped comb
The mechanism of inheritance of these traits is monogenic. Cleavage is the same among males and females, the gene is not sex-linked.
Unusual comb gene - B
Simple comb gene - in
General formula of genotypes: V_vv
72. Nucleic acids
Nucleic acids are natural high-molecular organic compounds that provide storage and transmission of hereditary (genetic) information in living organisms.
In nature, there are two types of nucleic acids, differing in composition, structure and function. One of them contains deoxyribose and is called deoxyribonucleic acid (DNA). The other contains ribose and is called ribonucleic acid (RNA)
73. By whom and when was the DNA model proposed
The DNA model was proposed in 1953 by J. Watson and F. Crick, for which they were awarded the Nobel Prize.
74. What is a DNA model
The DNA molecule is a double-stranded helix twisted around its own axis. In a polynucleotide chain, adjacent nucleotides are interconnected by covalent bonds that form between the phosphate group of one nucleotide and the 3"-alcohol group of the pentose of another. Such bonds are called phosphodiester bonds. The phosphate group forms a bridge between the 3"-carbon of one pentose cycle and the 5"-carbon of the next .
The backbone of DNA chains is thus formed by sugar-phosphate residues.
The polynucleotide chain of DNA is twisted in the form of a spiral, resembling a spiral staircase, and is connected to another, complementary chain to it using hydrogen bonds formed between adenine and thymine (two bonds), as well as guanine and cytosine (three bonds). Nucleotides A and T, G and C are called complementary. As a result, in any organism, the number of adenyl nucleotides is equal to the number of thymidyl, and the number of guanyl nucleotides is equal to the number of cytidyl. This pattern is called "Chargaff's rule". Due to this property, the sequence of nucleotides in one chain determines their sequence in another. This ability to selectively combine nucleotides is called complementarity, and this property underlies the formation of new DNA molecules based on the original molecule.
75. Characteristics of purine and pyrimidine nitrogenous bases
Purine nitrogenous bases are organic natural compounds, derivatives of purine. These include adenine and guanine. They are directly related to metabolic processes. Pyrimidine nitrogenous bases are a group of natural substances, pyrimidine derivatives. Biologically, the most important pyrimidine bases are uracil, cytosine, and thymine. The nucleotide sequence of one strand of nucleic acid is completely complementary to the nucleotide sequence of the second strand. Therefore, according to the Chargaff rule (Erwin Chargaff in 1951 established patterns in the ratio of purine and pyrimidine bases in a DNA molecule), the number of purine bases (A + G) is equal to the number of pyrimidine bases (T + C).
76. The constituent parts of a nucleotide
A nucleotide consists of 3 components: a nitrogenous base (purine or pyrimidine), a monosaccharide (ribose or deoxyribose), and a phosphoric acid residue.
77. Complementarity. Characteristic
Complementarity is a property of the DNA double helix, according to which thymine always stands against adenine in the opposite chain of the molecule, cytosine against guanine, and vice versa, forming hydrogen bonds. Complementarity is very important for DNA replication.
Complementarity in molecular biology, mutual correspondence that ensures the connection of complementary structures (macromolecules, molecules, radicals) and is determined by their chemical properties. K. is possible, “if the surfaces of the molecules have complementary structures, so that the protruding group (or positive charge) on one surface corresponds to the cavity (or negative charge) on the other. In other words, interacting molecules should fit together like a key to a lock” (J. Watson). K. chains of nucleic acids is based on the interaction of their constituent nitrogenous bases. So, only when adenine (A) is located in one chain against thymine (T) (or uracil - U) in another, and guanine (G) against cytosine (C), hydrogen bonds arise between the bases in these chains. K. - apparently, the only and universal chemical mechanism of matrix storage and transmission of genetic information.
78. Chargaff's Rule
Chargaff's rules are a system of empirically identified rules that describe the quantitative relationships between different types of nitrogenous bases in DNA. They were formulated as a result of the work of a group of biochemist Erwin Chargaff in 1949-1951. The ratios identified by Chargaff for adenine (A), thymine (T), guanine (G) and cytosine (C) were as follows:
The amount of adenine is equal to the amount of thymine, and guanine is equal to cytosine:
The number of purines is equal to the number of pyrimidines:
The number of bases with amino groups in position 6 is equal to the number of bases with keto groups in position 6:
At the same time, the ratio (A+T):(G+C) may be different in DNA of different species. In some, AT pairs predominate, in others - HC.
Chargaff's rules, along with X-ray diffraction data, played a decisive role in deciphering the structure of DNA by J. Watson and Francis Crick.
79. Codon from purine nitrogenous bases and its complementary anticodon
80. Codon. Definition
A codon (coding trinucleotide) is a unit of the genetic code, a triplet of nucleotide residues (triplet) in DNA or RNA, usually encoding the inclusion of one amino acid. The sequence of codons in a gene determines the sequence of amino acids in the polypeptide chain of the protein encoded by that gene.
81. Anticodon. Definition
An anticodon is a triplet (trinucleotide), a site in the transport ribonucleic acid (tRNA), consisting of three unpaired (having free bonds) nucleotides. By pairing with the codon of messenger RNA (mRNA), it ensures the correct arrangement of each amino acid during protein biosynthesis.
82. By whom and when was protein synthesized for the first time
Protein biosynthesis was first artificially carried out by the French scientist Chacob and Mano in 1957.
83. Necessary structures and components for protein biosynthesis
For direct protein biosynthesis, the following components must be present in the cell:
informational RNA (mRNA) - a carrier of information from DNA to the assembly site of the protein molecule;
ribosomes are organelles where the actual protein synthesis takes place;
a set of amino acids in the cytoplasm;
transfer RNA (tRNA) encoding amino acids and carrying them to the site of biosynthesis on ribosomes;
enzymes that catalyze the process of biosynthesis;
ATP is a substance that provides energy for all processes.
84. Under the action of what enzymes does protein biosynthesis occur?
Protein biosynthesis occurs under the action of the following enzymes: DNA polymerase, RNA polymerase, intetase.
85. Protein biosynthesis. Characteristic. Scheme
Protein biosynthesis is a complex multi-stage process of synthesis of a polypeptide chain from amino acids, occurring on ribosomes with the participation of mRNA and tRNA molecules. The process of protein biosynthesis requires a significant amount of energy.
Protein biosynthesis occurs in two steps. The first stage includes transcription and processing of RNA, the second stage includes translation. During transcription, the RNA polymerase enzyme synthesizes an RNA molecule that is complementary to the sequence of the corresponding gene (DNA region). The terminator in the DNA nucleotide sequence determines at what point transcription will stop. During a series of successive stages of processing, some fragments are removed from mRNA, and nucleotide sequences are rarely edited. After RNA synthesis on the DNA template, RNA molecules are transported to the cytoplasm. In the process of translation, the information recorded in the sequence of nucleotides is translated into a sequence of amino acid residues.
Between transcription and translation, the mRNA molecule undergoes a series of successive changes that ensure the maturation of a functioning template for the synthesis of the polypeptide chain. A cap is attached to the 5' end, and a poly-A tail is attached to the 3' end, which increases the lifespan of the mRNA. With the advent of processing in the eukaryotic cell, it became possible to combine gene exons to obtain a greater variety of proteins encoded by a single sequence of DNA nucleotides - alternative splicing.
In prokaryotes, mRNA can be read by ribosomes into the amino acid sequence of proteins immediately after transcription, while in eukaryotes it is transported from the nucleus to the cytoplasm, where ribosomes are located. The rate of protein synthesis is higher in prokaryotes and can reach 20 amino acids per second. The process of protein synthesis based on an mRNA molecule is called translation.
The ribosome contains 2 functional sites for interaction with tRNA: aminoacyl (acceptor) and peptidyl (donor). Aminoacyl-tRNA enters the acceptor site of the ribosome and interacts to form hydrogen bonds between codon and anticodon triplets. After the formation of hydrogen bonds, the system advances 1 codon and ends up in the donor site. At the same time, a new codon appears in the vacated acceptor site, and the corresponding aminoacyl-t-RNA is attached to it.
During the initial stage of protein biosynthesis, initiation, the methionine codon is usually recognized as a small subunit of the ribosome, to which methionine transfer RNA (tRNA) is attached using protein initiation factors. After recognition of the start codon, the large subunit joins the small subunit and the second stage of translation begins - elongation. With each movement of the ribosome from the 5" to the 3" end of the mRNA, one codon is read through the formation of hydrogen bonds between the three nucleotides (codon) of the mRNA and the complementary anticodon of the transfer RNA to which the corresponding amino acid is attached. The synthesis of the peptide bond is catalyzed by ribosomal RNA (rRNA), which forms the peptidyl transferase center of the ribosome. Ribosomal RNA catalyzes the formation of a peptide bond between the last amino acid of the growing peptide and the amino acid attached to the tRNA, positioning the nitrogen and carbon atoms in a position favorable for the reaction. Aminoacyl-tRNA synthetase enzymes attach amino acids to their tRNAs. The third and final stage of translation, termination, occurs when the ribosome reaches the stop codon, after which the protein termination factors hydrolyze the last tRNA from the protein, stopping its synthesis. Thus, in ribosomes, proteins are always synthesized from the N- to the C-terminus.
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test, added 07/30/2010
Analysis of molecular, cellular, tissue, organ, organism, population-species, biogeocenotic and biospheric levels of life. The study of the structure and functioning of tissues. Research of genetic and ecological features of populations.
presentation, added 09/11/2016
The essence and significance of mitosis - the process of distribution of copied chromosomes between daughter cells. General characteristics of the main stages of mitosis - prophase, metaphase, anaphase and telophase, as well as a description of the features of the separation of cellular chromosomes in them.
presentation, added 12/04/2010
The study of the process of mitosis as an indirect cell division and a common method of reproduction of eukaryotic cells, its biological significance. Meiosis is a reduction cell division. Interphase, prophase, metaphase, anaphase and telophase of meiosis and mitosis.
presentation, added 02/21/2013
A system for encoding hereditary information in nucleic acid molecules in the form of a genetic code. The essence of cell division processes: mitosis and meiosis, their phases. Transfer of genetic information. The structure of DNA, RNA chromosomes. Chromosomal diseases.
test, added 04/23/2013
The essence of the cell cycle is the period of a cell's life from one division to another, or from division to death. Biological significance of mitosis, its main regulatory mechanisms. Two periods of mitotic division. Scheme of activation of cyclin-dependent kinase.
presentation, added 10/28/2014
The cell cycle is the period of existence of a cell from the moment of its formation by dividing the mother cell to its own division or death. Principles and methods of its regulation. Stages and biological significance of mitosis, meiosis, substantiation of these processes.
presentation, added 12/07/2014
Elementary genetic and structural-functional biological system. Cell theory. Types of cellular organization. Structural features of a prokaryotic cell. Principles of organization of the eukaryotic cell. The hereditary apparatus of cells.
Life is a multi-level system (from the Greek. system- association, collection). There are such basic levels of organization of living things: molecular, cellular, organ-tissue, organism, population-species, ecosystem, biospheric. All levels are closely interconnected and arise one from the other, which indicates the integrity of living nature.
Molecular level of organization of living
This is the unity of the chemical composition (biopolymers: proteins, carbohydrates, fats, nucleic acids), chemical reactions. From this level, the life processes of the organism begin: energy, plastic and other exchanges, change and implementation of genetic information.
Cellular level of organization of living
Cellular level of organization of the living. animal cage
The cell is the elementary structural unit of the living. This is the unit of development of all living organisms living on Earth. In each cell, the processes of metabolism, energy conversion take place, the preservation, transformation and transfer of genetic information is ensured.
Each cell consists of cellular structures, organelles that perform certain functions, so it is possible to isolate subcellular level.
Organ-tissue level of organization of living
Organ-tissue level of organization of the living. Epithelial tissues, connective tissues, muscle tissues and nerve cells
Cells of multicellular organisms that perform similar functions have the same structure, origin, and unite into tissues. There are several types of tissues that have differences in structure and perform different functions (tissue level).
Tissues in different combinations form different organs that have a certain structure and perform certain functions (organ level).
Organs are combined into organ systems (system level).
Organismal level of organization of living
Organismal level of organization of living
Tissues are combined into organs, organ systems and function as a single whole - the body. The elementary unit of this level is an individual, which is considered in development from the moment of birth to the end of existence as a single living system.
Population-species level of organization of living
Population-species level of organization of living
A set of organisms (individuals) of the same species, having a common habitat, forms populations. A population is an elementary unit of species and evolution, since elementary evolutionary processes take place in it, this and the following levels are supraorganismal.
Ecosystem level of organization of living
Ecosystem level of organization of living
The totality of organisms of different species and levels of organization forms this level. Here we can distinguish biocenotic and biogeocenotic levels.
Populations of different species interact with each other, form multispecies groups ( biocenotic level).
The interaction of biocenoses with climatic and other non-biological factors (relief, soil, salinity, etc.) leads to the formation of biogeocenoses (biogeocenotic). In biogeocenoses, there is a flow of energy between populations of different species and the circulation of substances between its inanimate and living parts.
Biospheric level of organization of living
Biospheric level of organization of living things. 1 - molecular; 2 - cellular; 3 - organism; 4 - population-species; 5 - biogeocenotic; 6 - biospheric
It is represented by a part of the shells of the Earth where life exists - the biosphere. The biosphere consists of a set of biogeocenoses, functions as a single integral system.
It is not always possible to select the entire set of levels listed. For example, in unicellular organisms, the cellular and organismal levels coincide, but the organ-tissue level is absent. Sometimes additional levels can be distinguished, for example, subcellular, tissue, organ, systemic.
The following levels of life organization are distinguished: molecular, cellular, organ-tissue (sometimes they are separated), organismic, population-species, biogeocenotic, biospheric. Living nature is a system, and the various levels of its organization form its complex hierarchical structure, when the underlying simpler levels determine the properties of the overlying ones.
So complex organic molecules are part of the cells and determine their structure and vital activity. In multicellular organisms, cells are organized into tissues, and several tissues form an organ. A multicellular organism consists of organ systems, on the other hand, the organism itself is an elementary unit of a population and biological species. The community is represented by interacting populations of different species. The community and the environment form a biogeocenosis (ecosystem). The totality of ecosystems of the planet Earth forms its biosphere.
At each level, new properties of living things arise, which are absent at the underlying level, their own elementary phenomena and elementary units are distinguished. At the same time, the levels largely reflect the course of the evolutionary process.
The allocation of levels is convenient for studying life as a complex natural phenomenon.
Let's take a closer look at each level of organization of life.
Molecular level
Although molecules are made up of atoms, the difference between living matter and non-living matter begins to manifest itself only at the level of molecules. Only the composition of living organisms includes a large number of complex organic substances - biopolymers (proteins, fats, carbohydrates, nucleic acids). However, the molecular level of organization of living things also includes inorganic molecules that enter cells and play an important role in their life.
The functioning of biological molecules underlies the living system. At the molecular level of life, metabolism and energy conversion are manifested as chemical reactions, the transfer and change of hereditary information (reduplication and mutations), as well as a number of other cellular processes. Sometimes the molecular level is called the molecular genetic level.
Cellular level of life
It is the cell that is the structural and functional unit of the living. There is no life outside the cell. Even viruses can exhibit the properties of a living being only once they are in the host cell. Biopolymers fully show their reactivity when organized in a cell, which can be considered as a complex system of molecules interconnected primarily by various chemical reactions.
At this cellular level, the phenomenon of life manifests itself, the mechanisms of transmission of genetic information and the transformation of substances and energy are conjugated.
Organ tissue
Only multicellular organisms have tissues. Tissue is a collection of cells similar in structure and function.
Tissues are formed in the process of ontogenesis by differentiation of cells that have the same genetic information. At this level, cell specialization occurs.
Plants and animals have different types of tissues. So in plants it is a meristem, a protective, basic and conductive tissue. In animals - epithelial, connective, muscular and nervous. The fabrics may include a list of subfabrics.
An organ usually consists of several tissues, united among themselves in a structural and functional unity.
Organs form organ systems, each of which is responsible for an important function for the body.
The organ level in unicellular organisms is represented by various cell organelles that perform the functions of digestion, excretion, respiration, etc.
Organismal level of organization of living
Along with the cellular at the organismal (or ontogenetic) level, separate structural units are distinguished. Tissues and organs cannot live independently, organisms and cells (if it is a unicellular organism) can.
Multicellular organisms are made up of organ systems.
At the organismic level, such phenomena of life as reproduction, ontogeny, metabolism, irritability, neuro-humoral regulation, homeostasis are manifested. In other words, its elementary phenomena constitute regular changes in the organism in individual development. The elementary unit is the individual.
population-species
Organisms of the same species, united by a common habitat, form a population. A species usually consists of many populations.
Populations share a common gene pool. Within a species, they can exchange genes, that is, they are genetically open systems.
In populations, elementary evolutionary phenomena occur, ultimately leading to speciation. Living nature can evolve only in supra-organismal levels.
At this level, the potential immortality of the living arises.
Biogeocenotic level
Biogeocenosis is an interacting set of organisms of different species with different environmental factors. Elementary phenomena are represented by matter-energy cycles, provided primarily by living organisms.
The role of the biogeocenotic level consists in the formation of stable communities of organisms of different species, adapted to living together in a certain habitat.
Biosphere
The biospheric level of life organization is a higher-order system of life on Earth. The biosphere encompasses all manifestations of life on the planet. At this level, the global circulation of substances and the flow of energy (covering all biogeocenoses) take place.
