What does cytology study?

Cytology is the science of cells. It emerged from other biological sciences almost 100 years ago. For the first time, generalized information about the structure of cells was collected in a book by J.-B. Carnoy's Biology of the Cell, published in 1884. Modern cytology studies the structure of cells, their functioning as elementary living systems: the functions of individual cellular components, the processes of cell reproduction, their repair, adaptation to environmental conditions and many other processes are studied, allowing one to judge the properties and functions common to all cells. Cytology also examines the structural features of specialized cells. In other words, modern cytology is the physiology of the cell. Cytology is closely associated with scientific and methodological achievements of biochemistry, biophysics, molecular biology and genetics. This served as the basis for an in-depth study of the cell from the standpoint of these sciences and the emergence of a certain synthetic science about the cell - cell biology, or cell biology. Currently, the terms cytology and cell biology coincide, since their subject of study is the cell with its own patterns of organization and functioning. The discipline “Cell Biology” refers to the fundamental sections of biology, because it studies and describes the only unit of all life on Earth – the cell.

The idea that organisms are made up of cells.

A long and careful study of the cell as such led to the formulation of an important theoretical generalization that has general biological significance, namely the emergence of the cell theory. In the 17th century Robert Hooke, a physicist and biologist, distinguished by great ingenuity, created a microscope. Examining a thin section of cork under his microscope, Hooke discovered that it was built from tiny empty cells separated by thin walls, which, as we now know, consist of cellulose. He called these small cells cells. Later, when other biologists began to examine plant tissues under a microscope, it turned out that the small cells discovered by Hooke in a dead, withered plug were also present in living plant tissues, but they were not empty, but each contained a small gelatinous body. After animal tissues were subjected to microscopic examination, it was found that they also consisted of small gelatinous bodies, but that these bodies were only rarely separated from each other by walls. As a result of all these studies, in 1939, Schleiden and Schwann independently formulated the cell theory, which states that cells are the elementary units from which all plants and all animals are ultimately built. For some time, the double meaning of the word cell still caused some misunderstandings, but then it became firmly established in these small jelly-like bodies.

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Cytology is the science of the structure, functions and development of animal and plant cells, as well as single-celled organisms and bacteria.

Etymology of the term cytology: (Greek language) kytos - container, cell + logos teaching.

Cytological studies are essential for the diagnosis of human and animal diseases.

There are general and specific cytology.

General cytology(cell biology) studies the structures common to most types of cells, their functions, metabolism, responses to damage, pathological changes, reparative processes and adaptation to environmental conditions.

Private cytology explores the characteristics of individual cell types in connection with their specialization (in multicellular organisms) or evolutionary adaptation to the environment (in protists and bacteria).

The development of cytology is historically associated with the creation and improvement of the microscope and histological research methods. The term “cell” was first used by B. Hooke (1665), who described the cellular structure (more precisely, cellulose cell walls) of a number of plant tissues. In the 17th century, Hooke's observations were confirmed and developed by M. Malpighi and N. Grew, (1671), A. Leeuwenhoek. In 1781, F. Fontana published drawings of animal cells with nuclei.

In the first half of the 19th century, the idea of ​​the cell as one of the structural units of the body began to take shape. In 1831, R. Brown discovered a nucleus in plant cells, gave it the name “nucleus” and assumed the presence of this structure in all plant and animal cells. In 1832, V. S. Dumortier, and in 1835, H. Mohl, observed the division of plant cells. In 1838, M. Schleiden described the nucleolus in the nuclei of plant cells.

The prevalence of cellular structure in the animal kingdom was shown by the studies of R. J. N. Dutrochet (1824), F. V. Raspail (1827), and the schools of J. Purkinje and I. Müller. J. Purkinje was the first to describe the nucleus of an animal cell in 1825, developed methods for staining and clearing cell preparations, used the term “protoplasm”, and was one of the first who tried to compare the structural elements of animal and plant organisms (1837).

In 1838-1839 T. Schwann formulated the cell theory, in which the cell was considered as the basis of the structure, life activity and development of all animals and plants. T. Schwann's concept of the cell as the first stage of organization, possessing the entire complex of properties of living things, has retained its significance in the past.

The transformation of cell theory into a universal biological doctrine was facilitated by the discovery of the nature of protozoa. In 1841-1845 S. Th. Siebold formulated the concept of single-celled animals and extended the cell theory to them.

An important stage in the development of cytology was the creation by R. Virchow of the doctrine of cellular pathology. He viewed cells as the material substrate of diseases, which attracted not only anatomists and physiologists, but also pathologists to their study. R. Virchow also postulated the origin of new cells only from pre-existing ones. To a large extent, under the influence of the works of R. Virchow and his school, a revision of views on the nature of cells began. If previously the most important structural element of a cell was considered its shell, then in 1861 M. Schultze gave a new definition of a cell as “a lump of protoplasm, inside which lies the nucleus”; that is, the nucleus was finally recognized as an essential component of the cell. In the same 1861, E. W. Brucke showed the complexity of the structure of protoplasm.

The discovery of cell organelles - the cell center, mitochondria, Golgi complex, as well as the discovery of nucleic acids in cell nuclei contributed to the establishment of ideas about the cell as a complex multicomponent system. Study of mitosis processes [E. Strasburger (1875); P. I. Neremezhko (1878); V. Flemming (1878)] led to the discovery of chromosomes, the establishment of the rule of species constancy of their number (K. Rabl, 1885] and the creation of the theory of chromosome individuality (Th. Boveri, 1887). These discoveries, along with the study of the processes of fertilization, the biological essence of which he found out O. Hertwig (1875), phagocytosis, cell reactions to stimuli contributed to the fact that at the end of the 19th century, cytology became an independent branch of biology. J. B. Carnoy (1884) first introduced the concept of “cell biology” and formulated the idea of ​​cytology as a science. , which studies the form, structure, function and evolution of cells.

G. Mendel’s establishment of the laws of inheritance of characteristics and their subsequent interpretation, given at the beginning of the 20th century, had a great influence on the development of cytology. These discoveries led to the creation of the chromosomal theory of heredity and the formation of a new direction in cytology - cytogenetics, as well as karyology.

A major event in cell science was the development of the tissue culture method and its modifications - the method of single-layer cell cultures, the method of organ cultures of tissue fragments at the boundary of the nutrient medium and the gas phase, the method of culture of organs or their fragments on the membranes of chicken embryos, in animal tissues or in nutrient media. environment. They made it possible to observe the vital activity of cells outside the body for a long time, to study in detail their movement, division, differentiation, etc. The method of single-layer cell cultures, which played a large role in the development of not only cytology, but also virology, as well as receiving a number of antiviral vaccines. The intravital study of cells is greatly facilitated by microfilming, phase-contrast microscopy, fluorescent microscopy, microsurgery, and vital staining. These methods have made it possible to obtain much new information about the functional significance of a number of cellular components.

The introduction of quantitative research methods into cytology led to the establishment of the law of species constancy of cell sizes, later refined by E.M. Vermeule and known as the law of constancy of minimum cell sizes. W. Jacobi (1925) discovered the phenomenon of sequential doubling of the volume of cell nuclei, which in many cases corresponds to a doubling of the number of chromosomes in cells. Changes in the size of nuclei were also identified, associated with the functional state of cells both under normal conditions and in pathology (Ya. E. Hesip, 1967).

Raspail began to use methods of chemical analysis in cytology back in 1825. However, the works of L. Lison (1936), D. Glick (1949), and A. G. E. Perse (1953) were decisive for the development of cytochemistry. B.V. Kedrovsky (1942, 1951), A.L. Shabadash (1949), G.I. Roskin and L.B. Levinson (1957) also made great contributions to the development of cytochemistry.

The development of methods for the cytochemical detection of nucleic acids, in particular the Feilgen reaction and the Einarsop method, in combination with cytophotometry, made it possible to significantly clarify the understanding of cell trophism, the mechanisms and biological significance of polyploidization (V. Ya. Brodsky, I. V. Uryvaeva, 1981) .

In the first half of the 20th century. The functional role of intracellular structures is beginning to be elucidated. In particular, the work of D.N. Nasonov (1923) established the participation of the Golgi complex in the formation of secretory granules. G. Hogeboom proved in 1948 that mitochondria are the centers of cellular respiration. N.K. Koltsov was the first to formulate the idea of ​​chromosomes as carriers of molecules of heredity, and also introduced the concept of “cytoskeleton” into cytology.

The scientific and technological revolution of the mid-20th century led to the rapid development of cytology and a revision of a number of its concepts. Using electron microscopy, the structure was studied and the functions of previously known cell organelles were largely revealed, and a whole world of submicroscopic structures was discovered. These discoveries are associated with the names of K. R. Porter, N. Ris, W. Bernhard and other outstanding scientists. The study of cell ultrastructure made it possible to divide the entire living organic world into eukaryotes and prokaryotes.

The development of molecular biology has shown the fundamental commonality of the genetic code and the mechanisms of protein synthesis on nucleic acid matrices for the entire organic world, including the kingdom of viruses. New methods for isolating and studying cellular components, development and improvement of cytochemical studies, especially the cytochemistry of enzymes, the use of radioactive isotopes to study the processes of synthesis of cellular macromolecules, the introduction of electron cytochemistry methods, the use of fluorochrome-labeled antibodies to study the localization of individual cellular proteins using luminescent analysis, preparative methods and analytical centrifugation have significantly expanded the boundaries of cytology and led to the blurring of clear boundaries between cytology, developmental biology, biochemistry, molecular biophysics and molecular biology.

From a purely morphological science of the recent past, modern cytology has developed into an experimental discipline that comprehends the basic principles of cell activity and, through it, the foundations of the life of organisms. The development of methods for transplanting nuclei into enucleated cells by J. B. Gurdon (1974), somatic hybridization of cells by G. Barsk (1960), N. Harris (1970), B. Ephrussi (1972) made it possible to study the patterns of gene reactivation and determine the localization of many genes in human chromosomes and come closer to solving a number of practical problems in medicine (for example, analyzing the nature of cell malignancy), as well as in the national economy (for example, obtaining new crops, etc.). Based on cell hybridization methods, a technology for producing stationary antibodies from hybrid cells that produce antibodies of a given specificity (monoclonal antibodies) was created. They are already used to solve a number of theoretical issues in immunology, microbiology and virology. The use of these clones begins to improve the diagnosis and treatment of a number of human diseases, study the epidemiology of infectious diseases, etc. Cytological analysis of cells taken from patients (often after culturing them outside the body) is important for the diagnosis of some hereditary diseases (for example, xeroderma pigmentosum, glycogenosis) and studying their nature. There are also prospects for using the achievements of cytology for the treatment of human genetic diseases, the prevention of hereditary pathologies, the creation of new highly productive strains of bacteria, and increasing plant productivity.

The versatility of the problems of cell research, the specificity and variety of methods for studying it have currently led to the formation of six main directions in cytology:

1. Cytomorphology, which studies the features of the structural organization of a cell, the main research methods of which are various methods of microscopy, both fixed (light-optical, electron, polarization microscopy) and living cells (dark-field condenser, phase-contrast and fluorescent microscopy).
2. Cytophysiology, which studies the vital activity of a cell as a single living system, as well as the functioning and interaction of its intracellular structures; To solve these problems, various experimental techniques are used in combination with the methods of cell and tissue culture, microfilming and microsurgery.
3. Cytochemistry, which studies the molecular organization of the cell and its individual components, as well as chemical changes associated with metabolic processes and cell functions; Cytochemical studies are carried out using light microscopic and electron microscopic methods, cytophotometry, ultraviolet and interference microscopy, autoradiography and fractional centrifugation, followed by chemical analysis of various fractions.
4. Cytogenetics, studying the patterns of structural and functional organization of chromosomes of eukaryotic organisms.
5. Cytoecology, studying the reactions of cells to the influence of environmental factors and the mechanisms of adaptation to them.
6. Cytopathology, the subject of which is the study of pathological processes in cells.

Along with the traditional ones, new areas of cytology are also being developed in our country, such as ultrastructural cell pathology, viral cytopathology, cytopharmacology - evaluation of the effect of drugs using cytological methods on cell cultures, oncological cytology, space cytology, which studies the characteristics of cell behavior in space flight conditions.

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The history of cytology is closely related to the invention, use and improvement of the microscope. This is because the human eye is unable to distinguish objects with dimensions smaller than 0.1 mm, which is 100 micrometers (abbreviated microns or microns). The sizes of cells (and even more so, intracellular structures) are significantly smaller. For example, the diameter of an animal cell usually does not exceed 20 microns, a plant cell - 50 microns, and the length of the chloroplast of a flowering plant - no more than 10 microns. Using a light microscope, you can distinguish objects with a diameter of tenths of a micron. Therefore, light microscopy is the main, specific method for studying cells.

Note. 1 millimeter (mm) = 1,000 micrometers (µm) = 1,000,000 nanometers (nm). 1 nanometer = 10 angstroms (Å). One angstrom is approximately the diameter of a hydrogen atom.

The first optical instruments (simple lenses, glasses, magnifying glasses) were created back in the 12th century. But complex optical tubes, consisting of two or more lenses, appeared only at the end of the 16th century. Galileo Galilei, father and son Jansens, physicist Druebel and other scientists took part in the invention of the light microscope. The first microscopes were used to study a wide variety of objects.

· 1665: R. Hooke, observing for the first time under a microscope a thin section of balsa wood, discovered empty cells, which he called celluli , or cells; in fact, R. Hooke observed only the membranes of plant cells; Subsequently, R. Hooke studied sections of living stems and discovered similar cells in them, which, unlike dead cork cells, were filled with “nutritional juice.” R. Hooke outlined his observations in his work “Micrography, or some physiological descriptions of the smallest bodies using magnifying glasses” (1665);

· 1671: Marcello Malpighi (Italy) and Nehemiah Grew (England), studying the anatomical structure of plants, came to the conclusion that all plant tissues consist of vesicle cells. The term “fabric” (“lace”) was first used by N. Grew. In the works of R. Hooke, M. Malpighi and N. Grew, the cell is considered as an element, as an integral part of the tissue. Cells are separated from each other by common partitions and therefore cannot be thought of outside the tissue, outside the body;

· 1674: Dutch amateur microscopist Antonio van Leeuwenhoek (1680) observed single-celled organisms - “animalcules” (ciliates, sarcoids, bacteria) and other forms of single cells (blood cells, spermatozoa);

During this period, the main part of the cell was considered to be its wall, and only two hundred years later it became clear that the main thing in the cell is not the wall, but the internal contents. In the 18th century Fundamental observations of protozoa were carried out by the German amateur naturalist Martin Ledermüller. However, during this period, new information about the cell accumulated slowly, and in the field of zoology more slowly than in botany, since the real cell walls, which served as the main subject of research, are characteristic only of plant cells. In relation to animal cells, scientists did not dare to apply this term and identify them with plant cells.

Subsequently, as the microscope and microscopy technology improved, information about animal and plant cells also accumulated. Gradually, ideas about the cell as an elementary organism were formed: later the German physiologist Ernst von Brücke (1861) called the cell an elementary organism. By the 30s of the 19th century, a lot of information had accumulated on cell morphology, and it was established that the cytoplasm and nucleus are its obligatory components.

· 1802, 1808: C. Brissot-Mirbet established the fact that all plant organisms are formed by tissues that consist of cells.

· 1809: J.B. Lamarck extended Brissot-Mirbet's idea of ​​cellular structure to animals.

· 1825: J. Purkinė discovered the nucleus in the eggs of birds.

· 1831: R. Brown first described the nucleus in plant cells.

· 1833: R. Brown came to the conclusion that the nucleus is an essential part of the plant cell.

· 1839: J. Purkinė discovered protoplasm(gr. protoss- first and plasma fashioned, shaped) - the semi-liquid gelatinous contents of cells.

· 1839: T. Schwann summarized all the data accumulated by this time and formulated the cell theory.

· 1858: R. Virchow proved that all cells are formed from other cells by division.

· 1866: Haeckel established that the preservation and transmission of hereditary characteristics is carried out by the nucleus.

· 1866-1898: The main components of a cell that can be seen under an optical microscope are described. Cytology takes on the character of an experimental science.

· 1872: Professor of Dorpat (Tartus) University E. Russov,

· 1874: Russian botanist I.D. Chistyakov was the first to observe cell division.

· 1878: W. Fleming introduced the term “mitosis” and described the stages of cell division.

· 1884: V. Roux, O. Hertwig, E. Strasburger put forward the nuclear theory of heredity, according to which information about the hereditary characteristics of a cell is contained in the nucleus.

· 1888: E. Strasburger established the phenomenon of reduction in the number of chromosomes during meiosis.

· 1900: The advent of genetics was followed by the development of cytogenetics, which studies the behavior of chromosomes during division and fertilization.

· 1946: The use of the electron microscope began in biology, making it possible to study the ultrastructures of cells.

Cytology - a science that studies the structure, chemical composition and functions of cells, their reproduction, development and interaction in a multicellular organism.

Subject of cytology- cells of single- and multicellular prokaryotic and eukaryotic organisms.

Objectives of cytology:

1. Study of the structure and functions of cells and their components (membranes, organelles, inclusions, nucleus).

2. Study of the chemical composition of cells, biochemical reactions occurring in them.

3. Study of the relationships between cells of a multicellular organism.

4. Study of cell division.

5. Studying the possibility of cells adapting to environmental changes.

To solve problems in cytology, various methods are used.

Microscopic methods: allow you to study the structure of the cell and its components using microscopes (light, phase-contrast, fluorescent, ultraviolet, electron); light microscopy is based on the flow of light; studies cells and their large structures; electron microscopy - the study of small structures (membranes, ribosomes, etc.) in a beam of electrons with a wavelength shorter than that of visible light. Phase contrast microscopy is a method of obtaining images in optical microscopes, in which the phase shift of an electromagnetic wave is transformed into intensity contrast. Phase contrast microscopy was invented by Fritz Zernike, for which he received the Nobel Prize in 1953. Designed for studying living, non-colored objects.

Cyto- And histochemical methods- based on the selective action of reagents and dyes on certain substances of the cytoplasm; used to establish the chemical composition and localization of various components (proteins, DNA, RNA, lipids, etc.) in cells.

Histological method is a method of preparing microspecimens from native and fixed tissues and organs. The native material is frozen, and the fixed object goes through the stages of compaction and embedding in paraffin. Sections are then prepared from the material being examined, stained, and embedded in Canada balsam.

Biochemical methods make it possible to study the chemical composition of cells and the biochemical reactions occurring in them.

Method of differential centrifugation (fractionation): based on different rates of sedimentation of cell components; first, the cells are destroyed to a uniform (homogeneous) mass, which is transferred into a test tube with a solution of sucrose or cesium chloride and subjected to centrifugation; isolates individual components of the cell (mitochondria, ribosomes, etc.) for subsequent study by other methods.

X-ray diffraction analysis method: after introducing metal atoms into the cell, the spatial configuration (spatial arrangement of atoms and groups of atoms) and some physical properties of macromolecules (protein, DNA) are studied.

Autoradiography method- introduction of radioactive (labeled) isotopes into the cell - most often isotopes of hydrogen (3 H), carbon (14 C) and phosphorus (32 P); The molecules being studied are detected by radioactive labels using a radioactive particle counter or by their ability to expose photographic film, and then their inclusion in substances synthesized by the cell is studied; allows you to study the processes of matrix synthesis and cell division.

Time lapse filming and photography method allows you to trace and record the processes of cell division through powerful light microscopes.

Microsurgical methods- surgical impact on the cell: removal or implantation of cell components (organelles, nucleus) from one cell to another in order to study their functions, microinjection of various substances, etc.

Cell culture method- growing individual cells of multicellular organisms on nutrient media under sterile conditions; makes it possible to study the division, differentiation and specialization of cells, to obtain clones of plant organisms.

Knowledge of the basics of chemical and structural organization, principles of functioning and mechanisms of cell development is extremely important for understanding the similar features inherent in complex organisms of plants, animals and humans. The development of the IVF method is an example of the practical application of cytological knowledge.

Cytology (from Cyto... and...Logia

Development of modern cytology. Since the 50s 20th century C. has entered the modern stage of its development. The development of new research methods and the successes of related disciplines gave impetus to the rapid development of biology and led to the blurring of clear boundaries between biology, biochemistry, biophysics, and molecular biology. The use of an electron microscope (its resolution reaches 2-4 Å, the resolution limit of a light microscope is about 2000 Å) led to the creation of submicroscopic cell morphology and brought the visual study of cellular structures closer to the macromolecular level. Previously unknown details of the structure of previously discovered cellular organelles and nuclear structures were discovered; new ultramicroscopic components of the cell were discovered: the plasmatic, or cellular, membrane that separates the cell from the environment, the endoplasmic reticulum (network), ribosomes (carrying out protein synthesis), lysosomes (containing hydrolytic enzymes), peroxisomes (containing the enzymes catalase and uricase), microtubules and microfilaments (playing a role in maintaining shape and ensuring the mobility of cellular structures); Dictyosomes, elements of the Golgi complex, were found in plant cells. Along with general cellular structures, ultramicroscopic elements and features inherent in specialized cells are revealed. Electron microscopy has shown the special importance of membrane structures in the construction of various cell components. Submicroscopic studies have made it possible to divide all known cells (and, accordingly, all organisms) into 2 groups: eukaryotes (tissue cells of all multicellular organisms and unicellular animals and plants) and prokaryotes (bacteria, blue-green algae, actinomycetes and rickettsia). Prokaryotes - primitive cells - differ from eukaryotes in the absence of a typical nucleus; they lack a nucleolus, a nuclear membrane, typical chromosomes, mitochondria, and the Golgi complex.

Improving methods for isolating cellular components, using methods of analytical and dynamic biochemistry in relation to the tasks of cytology (precursors labeled with radioactive isotopes, autoradiography, quantitative cytochemistry using cytophotometry, development of cytochemical methods for electron microscopy, use of antibodies labeled with fluorochromes to detect localization under a fluorescent microscope individual proteins; the method of hybridization on sections and smears of radioactive DNA and RNA to identify cell nucleic acids, etc.) led to a refinement of the chemical topography of cells and deciphering the functional significance and biochemical role of many components of the cell. This required a broad combination of work in the field of color with work in biochemistry, biophysics, and molecular biology. For the study of genetic functions of cells, the discovery of DNA content not only in the nucleus, but also in the cytoplasmic elements of the cell - mitochondria, chloroplasts, and, according to some data, in basal bodies, was of great importance. To assess the role of the nuclear and cytoplasmic gene apparatus in determining the hereditary properties of a cell, transplantation of nuclei and mitochondria is used. Hybridization of somatic cells is becoming a promising method for studying the gene composition of individual chromosomes (see Somatic cell genetics). It has been established that the penetration of substances into the cell and into cellular organelles is carried out using special transport systems that ensure the permeability of biological membranes. Electron microscopic, biochemical and genetic studies have increased the number of supporters of the hypothesis of the symbiotic (see Symbiogenesis) origin of mitochondria and chloroplasts, put forward at the end of the 19th century.

The main tasks of modern color science are the further study of microscopic and submicroscopic structures and the chemical organization of cells; functions of cellular structures and their interactions; methods of penetration of substances into the cell, their release from the cell and the role of membranes in these processes; cell reactions to nervous and humoral stimuli of the macroorganism and to environmental stimuli; perception and conduction of excitation; interactions between cells; cell reactions to damaging influences; damage repairs and adaptation to environmental factors and damaging agents; reproduction of cells and cellular structures; cell transformations in the process of morphophysiological specialization (differentiation); nuclear and cytoplasmic genetic apparatus of the cell, its changes in hereditary diseases; relationships between cells and viruses; transformation of normal cells into cancer cells (malignization); cell behavior processes; origin and evolution of the cellular system. Along with solving theoretical problems, C. participates in resolving a number of important biological, medical, and agricultural issues. problems. Depending on the objects and methods of research, a number of sections of cytology are developed: cytogenetics, karyosystematics, cytoecology, radiation cytology, oncological cytology, immunocytology, etc.

In the USSR there are special cytological research institutions: the Institute of Cytology of the USSR Academy of Sciences, the Institute of Cytology and Genetics of the Siberian Branch of the USSR Academy of Sciences, the Institute of Genetics and Cytology of the Academy of Sciences of the BSSR. In many other biological, medical and agricultural. Scientific institutions have special cytological laboratories. Work on color is coordinated in the USSR by the Scientific Council on Color Problems at the USSR Academy of Sciences. The journals “Cytology” (USSR Academy of Sciences) and “Cytology and Genetics” (Ukrainian Academy of Sciences) are published. Cytological works are published in journals in related disciplines. More than 40 cytological journals are published around the world. Books of multivolume international publications are periodically published: protoplasmatology (“Protoplasmatologia”) (Vienna) and an international review of cytology (“International Review of Cytology”) (New York). There is the International Society of Cell Biology, which regularly convenes cytological congresses. The International Cell Research Organization and the European Cell Biology Organization create working groups on individual cell problems, organize courses on key cell issues and to study techniques, and ensure the exchange of information. At universities in the USSR, a course in general coloring is taught in the biological and biology-soil faculties. Many universities offer specialized courses on various problems of color. As a section, color is also included in courses on animal histology, plant anatomy, embryology, protistology, bacteriology, physiology, pathological anatomy, which are read in agricultural, pedagogical and medical schools. See also Art. Cage and lit. with her.

Lit.: Katsnelson Z. S., Cell theory in its historical development, L., 1963; Guide to cytology, vol. 1-2, M. - L., 1965-66; De Robertis E., Novinsky V., Saez F., Cell Biology, trans. from English, M., 1973; Brown W. V., Bertke E. M., Textbook of cytology, Saint Louis, 1969; Hirsch G. S., Ruska H., Sitte P., Grundlagen der Cytologie, Jena, 1973.

V. Ya. Alexandrov.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

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Cytology… Spelling dictionary-reference book

- (from cyto... and...logy) the science of cells. Studies the structure and functions of cells, their connections and relationships in organs and tissues of multicellular organisms, as well as unicellular organisms. Studying the cell as the most important structural unit of living things, cytology... ... Big Encyclopedic Dictionary

In modern science, an important role is played by new, young disciplines that have formed into independent sections in the last century and even later. What was not available for research before is now becoming available thanks to technical innovations and modern scientific methods, allowing new results to be obtained regularly. We constantly hear in the media about new discoveries in the field of biology, and specifically genetics and cytology; these related disciplines are now experiencing a real flourishing, and many ambitious scientific projects are constantly providing new data for analysis.

One of the new extremely promising disciplines is cytology, the science of cells. Modern cytology is a complex science. It has the closest connections with other biological sciences, for example, with botany, zoology, physiology, the study of the evolution of the organic world, as well as with molecular biology, chemistry, physics, and mathematics. Cytology is one of the relatively young biological sciences, its age is about 100 years, although the very concept of a cell was introduced into use by scientists much earlier.

A powerful stimulus to the development of cytology was the development and improvement of installations, instruments and tools for research. Electron microscopy and the capabilities of modern computers, along with chemical methods, have been providing new materials for research in recent years.

Cytology as a science, its formation and tasks

Cytology (from the Greek κύτος - bubble-like formation and λόγος - word, science) is a branch of biology, the science of cells, the structural units of all living organisms, which sets itself the task of studying the structure, properties, and functioning of a living cell.

The study of the smallest structures of living organisms became possible only after the invention of the microscope - in the 17th century. The term “cell” was first proposed in 1665 by the English naturalist Robert Hooke (1635–1703) to describe the cellular structure of a cork section observed under a microscope. Examining thin sections of dried cork, he discovered that they “consisted of many boxes.” Hooke called each of these boxes a cell (“chamber”).” In 1674, the Dutch scientist Antonie van Leeuwenhoek discovered that the substance inside the cell is organized in a certain way.

However, the rapid development of cytology began only in the second half of the 19th century. as microscopes develop and improve. In 1831, R. Brown established the existence of a nucleus in a cell, but failed to appreciate the full importance of his discovery. Soon after Brown's discovery, several scientists became convinced that the nucleus was immersed in the semi-liquid protoplasm filling the cell. Initially, the basic unit of biological structure was considered to be fiber. However, already at the beginning of the 19th century. Almost everyone began to recognize a structure called a vesicle, globule or cell as an indispensable element of plant and animal tissues. In 1838–1839 German scientists M. Schleiden (1804–1881) and T. Schwann (1810–1882) almost simultaneously put forward the idea of ​​cellular structure. The statement that all tissues of animals and plants are composed of cells constitutes the essence cell theory. Schwann coined the term "cell theory" and introduced this theory to the scientific community.

According to the cellular theory, all plants and animals consist of similar units - cells, each of which has all the properties of a living thing. This theory has become the cornerstone of all modern biological thinking. At the end of the 19th century. The main attention of cytologists was directed to a detailed study of the structure of cells, the process of their division and elucidation of their role. At first, when studying the details of cell structure, one had to rely mainly on visual examination of dead rather than living material. Methods were needed that would make it possible to preserve protoplasm without damaging it, to make sufficiently thin sections of tissue that passed through the cellular components, and also to stain sections to reveal details of the cellular structure. Such methods were created and improved throughout the second half of the 19th century.

The concept was of fundamental importance for the further development of cell theory genetic continuity of cells. First, botanists and then zoologists (after the contradictions in the data obtained from the study of certain pathological processes were clarified) recognized that cells arise only as a result of the division of already existing cells. In 1858, R. Virchow formulated the law of genetic continuity in the aphorism “Omnis cellula e cellula” (“Each cell is a cell”). When the role of the nucleus in cell division was established, W. Flemming (1882) paraphrased this aphorism, proclaiming: “Omnis nucleus e nucleo” (“Each nucleus is from the nucleus”). One of the first important discoveries in the study of the nucleus was the discovery of intensely stained threads in it, called chromatin. Subsequent studies showed that during cell division these filaments are assembled into discrete bodies - chromosomes, that the number of chromosomes is constant for each species, and in the process of cell division, or mitosis, each chromosome is split into two, so that each cell receives the number of chromosomes typical for that species.

Thus, even before the end of the 19th century. two important conclusions were reached. One was that heredity is the result of the genetic continuity of cells provided by cell division. Another thing is that there is a mechanism for the transmission of hereditary characteristics, which is located in the nucleus, or more precisely, in the chromosomes. It was found that, thanks to the strict longitudinal segregation of chromosomes, daughter cells receive exactly the same (both qualitatively and quantitatively) genetic constitution as the original cell from which they originated.

The second stage in the development of cytology begins in the 1900s, when the laws of heredity, discovered by the Austrian scientist G.I. Mendel back in the 19th century. At this time, a separate discipline emerged from cytology - genetics, the science of heredity and variability, studying the mechanisms of inheritance and genes as carriers of hereditary information contained in cells. The basis of genetics was chromosomal theory of heredity– the theory according to which chromosomes contained in the cell nucleus are carriers of genes and represent the material basis of heredity, i.e. the continuity of the properties of organisms in a number of generations is determined by the continuity of their chromosomes.

New techniques, especially electron microscopy, the use of radioactive isotopes and high-speed centrifugation, which emerged after the 1940s, allowed even greater advances in the study of cell structure. At the moment, cytological methods are actively used in plant breeding and in medicine - for example, in the study of malignant tumors and hereditary diseases.

Basic principles of cell theory

In 1838-1839 Theodor Schwann and the German botanist Matthias Schleiden formulated the basic principles of cell theory:

1. The cell is a unit of structure. All living things consist of cells and their derivatives. The cells of all organisms are homologous.

2. The cell is a unit of function. The functions of the whole organism are distributed among its cells. The total activity of an organism is the sum of the vital activity of individual cells.

3. The cell is a unit of growth and development. The growth and development of all organisms is based on the formation of cells.

The Schwann–Schleiden cell theory belongs to the greatest scientific discoveries of the 19th century. At the same time, Schwann and Schleiden considered the cell only as a necessary element of the tissues of multicellular organisms. The question of the origin of cells remained unresolved (Schwann and Schleiden believed that new cells are formed by spontaneous generation from living matter). Only the German physician Rudolf Virchow (1858-1859) proved that every cell comes from a cell. At the end of the 19th century. ideas about the cellular level of organization of life are finally formed. The German biologist Hans Driesch (1891) proved that a cell is not an elementary organism, but an elementary biological system. Gradually, a special science of cells is being formed - cytology.

Further development of cytology in the 20th century. is closely related to the development of modern methods for studying cells: electron microscopy, biochemical and biophysical methods, biotechnological methods, computer technology and other areas of natural science. Modern cytology studies the structure and functioning of cells, metabolism in cells, the relationship of cells with the external environment, the origin of cells in phylogenesis and ontogenesis, patterns of cell differentiation.
Currently, the following definition of a cell is accepted. A cell is an elementary biological system that has all the properties and signs of life. The cell is the unit of structure, function and development of organisms.

Unity and diversity of cell types

There are two main morphological types of cells that differ in the organization of the genetic apparatus: eukaryotic and prokaryotic. In turn, according to the method of nutrition, two main subtypes of eukaryotic cells are distinguished: animal (heterotrophic) and plant (autotrophic). A eukaryotic cell consists of three main structural components: the nucleus, the plasmalemma, and the cytoplasm. A eukaryotic cell differs from other types of cells primarily by the presence of a nucleus. The nucleus is the place of storage, reproduction and initial implementation of hereditary information. The nucleus consists of the nuclear envelope, chromatin, nucleolus and nuclear matrix.

Plasmalemma (plasma membrane) is a biological membrane that covers the entire cell and delimits its living contents from the external environment. A variety of cell membranes (cell walls) are often located on top of the plasmalemma. In animal cells, cell walls are usually absent. Cytoplasm is a part of a living cell (protoplast) without a plasma membrane and nucleus. The cytoplasm is spatially divided into functional zones (compartments) in which various processes occur. The composition of the cytoplasm includes: the cytoplasmic matrix, cytoskeleton, organelles and inclusions (sometimes inclusions and the contents of vacuoles are not considered to be the living substance of the cytoplasm). All cell organelles are divided into non-membrane, single-membrane and double-membrane. Instead of the term “organelles,” the outdated term “organelles” is often used.

Non-membrane organelles of a eukaryotic cell include organelles that do not have their own closed membrane, namely: ribosomes and organelles built on the basis of tubulin microtubules - the cell center (centrioles) and movement organelles (flagella and cilia). In the cells of most unicellular organisms and the vast majority of higher (land) plants, centrioles are absent.

Single-membrane organelles include: endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, spherosomes, vacuoles and some others. All single-membrane organelles are interconnected into a single vacuolar system of the cell. True lysosomes are not found in plant cells. At the same time, animal cells lack true vacuoles.

Double-membrane organelles include mitochondria and plastids. These organelles are semi-autonomous because they have their own DNA and their own protein-synthesizing apparatus. Mitochondria are found in almost all eukaryotic cells. Plastids are found only in plant cells.
A prokaryotic cell does not have a formed nucleus - its functions are performed by a nucleoid, which includes a ring chromosome. In a prokaryotic cell there are no centrioles, as well as single-membrane and double-membrane organelles - their functions are performed by mesosomes (invaginations of the plasmalemma). Ribosomes, organelles of movement and membranes of prokaryotic cells have a specific structure.