The basic postulates of cell theory have been formed. Creation of cell theory. Structural components of a cell

Cell theory - one of the generally accepted biological generalizations that affirm the unity of the principle of structure and development of the world of plants, animals and other living organisms with a cellular structure, in which the cell is considered as a single structural element of living organisms.

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  Cell theory is a fundamental theory for biology, formulated in the middle of the 19th century, which provided the basis for understanding the laws of the living world and for the development of evolutionary teaching. Matthias Schleiden and Theodor Schwann formulated cell theory, based on a lot of research about the cell (). Rudolf Virchow later () supplemented it with the most important position (every cell comes from another cell).

  To isolate the substances it produces. Eliminate yourself if it is damaged. On the other hand, if you cut the cell into pieces, you will only get a mixture of inert chemicals, nothing living. Some living things consist of only one cell, while others contain thousands of billions.

  Cell theory at the time of its proclamation revolutionized the idea that we have always had in life. In accepting this theory, biologists had to recognize three completely new concepts at the time. Unity of life: living beings are much more similar than we thought; humans are not so different from animals and even plants.

  Schleiden and Schwann, summarizing the existing knowledge about the cell, proved that the cell is the basic unit of any organism. Animal, plant and bacterial cells have a similar structure. Later, these conclusions became the basis for proving the unity of organisms. T. Schwann and M. Schleiden introduced into science the fundamental concept of the cell: there is no life outside cells. The cell theory was supplemented and edited every time.

  Homeostasis: a person's survival and health correspond to his ability to provide a living environment favorable to his life. There is no definite limit between life and death. Not only are all living things made up of cells, but also, from one living thing to another, cells are very similar. There are several differences, for example, between mosquito neurons and mosquito neurons. Likewise, under a microscope it is impossible to detect liver cells from a human, cat or even a fish. Although they may have different shapes and size, all cells have the same basic structure, they are formed from the same organelles: membrane, nucleus, vacuoles, ribosomes, endoplasmic reticulum, etc. from some types of elementary bricks, different types cells, you can build an infinite variety of living forms.

  Provisions of the Schleiden-Schwann cell theory

  The creators of the theory formulated its main provisions as follows:

  1. All animals and plants are made up of cells.
  2. Plants and animals grow and develop through the emergence of new cells.
  3. The cell is the smallest unit of living things, and whole organism is a collection of cells.

  Basic provisions of modern cell theory

  Link and Moldnhower established the presence of independent walls in plant cells. It turns out that the cell is a certain morphologically separate structure. In 1831, G. Mol proved that even such seemingly non-cellular plant structures as water-bearing tubes develop from cells.

  In addition, it was later discovered that the mode of operation of cells, all the chemical reactions that occur, are essentially the same, regardless of the type of cell. There are not many differences between a tomato cell and a human cell, and very a large number of chemical reactions events that occur in one cell also occur in another.

  A cell can only survive if it is immersed in a liquid with physicochemical and chemical characteristics that exactly suit her needs. It's the same inside the body. Cells need to be in a stable environment that provides them with everything they need. The sugar content in the fluid that bathes the cells, for example, must remain strictly stable. It is called "homeostasis", which ensures stability internal environment, which manages to hold living beings.

  F. Meyen in “Phytotomy” (1830) describes plant cells, which “are either single, so that each cell represents a special individual, as is found in algae and fungi, or, forming more highly organized plants, they are combined into more or less significant masses.” Meyen emphasizes the independence of metabolism of each cell.

  Homeostasis is a dynamic equilibrium where cells are constantly changing their environment, drawing from it and rejecting it, which also changes with food intake and the environment in which it is found. systems must therefore continually respond to restore the ever-disturbed balance. The content of homeostasis is constant struggle which should never stop.

  With cell theory, the concept of disease became completely new meaning. From now on, we will consider disease as a defect in homeostasis, and it is the proper functioning of each of the body's cells that allows us to maintain this homeostasis, which is necessary for the survival of each of them.

  In 1831, Robert Brown describes the nucleus and suggests that it is a constant integral part plant cell.

  Purkinje School

  In 1801, Vigia introduced the concept of animal tissue, but he isolated tissue based on anatomical dissection and did not use a microscope. The development of ideas about the microscopic structure of animal tissues is associated primarily with the research of Purkinje, who founded his school in Breslau.

  A person is actually a colony of several thousand cells that form an organism. But since each of our cells is a separate living being, at what point can we say that a person is dead? Should we wait until the last camera dies before signing the death certificate? The man who was just cut off from his head while still alive? However, his hair and nails continue to grow, many of his muscle cells shrink again, his skin cells still survive by breathing some of the oxygen present in the fluid that surrounds them, etc.

  Purkinje and his students (especially G. Valentin should be highlighted) identified in the first and most general view microscopic structure tissues and organs of mammals (including humans). Purkinje and Valentin compared individual plant cells with individual microscopic tissue structures of animals, which Purkinje most often called “grains” (for some animal structures his school used the term “cell”).

  In short, it is necessary to look at the evidence; there is no definite line between life and death. And this is a whole ethical problem acts such as euthanasia or, to start at the other end of life, abortion. When is life there and when does it stop?

  And the problem is the same in each of the cells. At what point can we say that a cell is dead? A drop, deprived of the elements necessary for its survival, does not die in one fell swoop. Its activity gradually slows down, its structures gradually degrade until a fairly inert mixture is obtained chemical compounds. But when is she dead? For example, trying to define this point is as futile as trying to define the exact boundary between youth and old age.

  In 1837, Purkinje gave a series of talks in Prague. In them he reported his observations on the structure of the gastric glands, nervous system etc. In the table attached to his report, clear images of some cells of animal tissues were given. Nevertheless, Purkinje was unable to establish the homology of plant cells and animal cells:

  Often in biology we move very gradually from one state to another, there is rarely a fixed boundary. Legally, it was necessary to determine the border. At one time it was cardiac arrest. If the heart no longer beats, then we are dead. However, in last years we have learned to leave the heart stopped. Therefore, it is necessary to find another criterion. Currently, death is legally defined by the absence of electrical activity of neurons in the brain. This electrical activity can be demonstrated using small recording electrodes that are placed on the surface of the scalp.

  • firstly, by grains he understood either cells or cell nuclei;
  • secondly, the term “cell” was then understood literally as “a space bounded by walls.”

  Purkinje conducted the comparison of plant cells and animal “grains” in terms of analogy, and not homology of these structures (understanding the terms “analogy” and “homology” in the modern sense).

  Lack of brain activity results in a flat electroencephalogram. Note that this is a legal boundary, but the issue is even more complex: can we still call alive a person who is in a deep and irreversible coma, but whose brain is still weak? do we stop living when quality of life deteriorates beyond a certain level? This is a problem that is no longer the responsibility of biologists. In fact, death itself is a strange phenomenon. Indeed, cells can constantly renew themselves.

  If a structure is destroyed, the cell can create a new one from the molecules it draws in its environment. Because of this constant renewal that occurs in cells, it is believed that every person renews all of their molecules in about seven years. But to multiply cells, it takes another 50 million cells to replace them. In fact, in theory, since we are constantly renewing ourselves, we should not age, but for reasons that are only beginning to be understood, the processes that allow cells to renew and reproduce deteriorate over time.

  Müller's school and Schwann's work

  The second school where the microscopic structure of animal tissues was studied was the laboratory of Johannes Müller in Berlin. Müller studied the microscopic structure of the dorsal string (notochord); his student Henle published a study about intestinal epithelium, in which he gave a description of its various species and their cellular structure.

  The body gradually loses its efficiency to renew itself, deteriorates, ages and dies. Jean-Baptiste Monet Chevalier de Lamarck. Vitalism: Life = vital “life” question. An old concept, now rejected by biology. Modern Concept: Life is explained by the laws of physics and chemistry. There is no non-essential component in the functioning of the living.

  Cellular surface of the skin. Other cellular structures A sac filled with fat. Cell theory. The cell is the basic unit of life. What is life? = A set of properties of matter: Being alive = a structure that can: Restore itself Reproduction Control its functioning in accordance with changes in the environment.

  Theodor Schwann's classic research was carried out here, laying the foundation for the cell theory. Schwann's work was strongly influenced by the school of Purkinje and Henle. Schwann found correct principle comparison of plant cells and elementary microscopic structures of animals. Schwann was able to establish homology and prove the correspondence in the structure and growth of the elementary microscopic structures of plants and animals.

  Life is only a state of matter at a certain level of organization, and not an imposed principle that falls in some sky. Ernest Kahane Life does not exist Man contains something like billions of cells. Each of these cells is a living being.

  Some living things consist of only one cell, such as the amoeba. Unity of life. The cells of all living things are very similar to each other. At the microscopic level there is very little variation between species, and the functioning of cells is for all practical purposes the same from one species to another.

  The significance of the nucleus in a Schwann cell was prompted by the research of Matthias Schleiden, who published his work “Materials on Phytogenesis” in 1838. Therefore, Schleiden is often called the co-author of the cell theory. The basic idea of ​​cellular theory - the correspondence of plant cells and the elementary structures of animals - was alien to Schleiden. He formulated the theory of new cell formation from a structureless substance, according to which, first, a nucleolus condenses from the smallest granularity, and around it a nucleus is formed, which is the cell maker (cytoblast). However, this theory was based on incorrect facts.

  Cells can only survive if the environment in which they bathe remains stable. They undergo very minor changes. Stay alive = maintain your homeostasis. There is no limit between life and death. Life is defined by cellular level. What's happened living cell. At what point can a metazoan be said to be dead?

  According to William Whitman of the University of Georgia, there are five trillion trillion bacteria on Earth, and the total volume of all people corresponds to a cube of about 700 m on each side. Eukaryotic cells: usually 10 to 100 µm. Numerous internal organelles made of membranes. Membrane-bounded gene material = nucleus.

  In 1838, Schwann published 3 preliminary reports, and in 1839 his classic work “Microscopic studies on the correspondence in the structure and growth of animals and plants” appeared, the very title of which expresses the main idea of ​​cellular theory:

  • In the first part of the book, he examines the structure of the notochord and cartilage, showing that their elementary structures - cells - develop in the same way. He further proves that the microscopic structures of other tissues and organs of the animal body are also cells, quite comparable to the cells of cartilage and notochord.
  • The second part of the book compares plant cells and animal cells and shows their correspondence.
  • In the third part, theoretical positions are developed and the principles of cell theory are formulated. It was Schwann's research that formalized the cell theory and proved (at the level of knowledge of that time) the unity of the elementary structure of animals and plants. The main mistake Schwann was the opinion he expressed, following Schleiden, about the possibility of the emergence of cells from structureless non-cellular substance.

  Development of cell theory in the second half of the 19th century

  Since the 1840s of the 19th century, the study of the cell has become the focus of attention throughout biology and has been rapidly developing, becoming an independent branch of science - cytology.

  Prokaryotic cell eukaryotic cells. Levels of organization of matter Matter is formed from atoms. Atoms assemble into molecules, and molecules assemble to form cells. Cells gather into tissues, organs form systems and systems, organisms. At each level, new properties appear: emergent properties. Molecules have properties that the atoms that compose them do not have. Colors have properties that even the most complex molecules do not possess. The brain has properties that the neurons that make it up do not have.

  To further develop cell theory essential it extended to protists (protozoa), which were recognized as free-living cells (Siebold, 1848).

  At this time, the idea of ​​the composition of the cell changes. The secondary significance is revealed cell membrane, which was previously recognized as the most essential part of the cell, and the importance of protoplasm (cytoplasm) and the cell nucleus (Mol, Cohn, L. S. Tsenkovsky, Leydig, Huxley) comes to the fore, which is expressed in the definition of a cell given by M. Schulze in 1861:

  Life's Essential Molecules: Life uses about 25 of the 92 naturally occurring chemical elements, of which four are particularly important: carbon: can form 4 chemical bonds. Hydrogen: forms only one Oxygen bond: can form 2 bonds Nitrogen: can form 3 bonds.

  Almost all molecules in living things are made up of carbon atoms bonded to each other. Linear circuits. Branched chains. We can't impose them. This will also have positive influence for AIDS patients. Valium molecule Cocaine Caffeine. Organic matter = material composed of carbon-containing molecules. Carbon = the only atom that can bond with it many times.

  A cell is a lump of protoplasm with a nucleus contained inside.

  In 1861, Brücko put forward a theory about complex structure cells, which he defines as an “elementary organism,” further elucidates the theory of cell formation from a structureless substance (cytoblastema), developed by Schleiden and Schwann. It was discovered that the method of formation of new cells is cell division, which was first studied by Mohl on filamentous algae. The studies of Negeli and N.I. Zhele played a major role in refuting the theory of cytoblastema using botanical material.

  Tissue cell division in animals was discovered in 1841 by Remak. It turned out that the fragmentation of blastomeres is a series of successive divisions (Bishtuf, N.A. Kölliker). The idea of ​​the universal spread of cell division as a way of forming new cells is enshrined by R. Virchow in the form of an aphorism:

  "Omnis cellula ex cellula."
  Every cell from a cell.

  In the development of cell theory in the 19th century, contradictions arose sharply, reflecting the dual nature of cellular theory, which developed within the framework of a mechanistic view of nature. Already in Schwann there is an attempt to consider the organism as a sum of cells. This tendency receives special development in Virchow’s “Cellular Pathology” (1858).

  Virchow’s works had a controversial impact on the development of cellular science:

  • He extended the cell theory to the field of pathology, which contributed to the recognition of the universality of cellular theory. Virchow's works consolidated the rejection of the theory of cytoblastema by Schleiden and Schwann and drew attention to the protoplasm and nucleus, recognized as the most essential parts of the cell.
  • Virchow directed the development of cell theory along the path of a purely mechanistic interpretation of the organism.
  • Virchow elevated cells to the level of an independent being, as a result of which the organism was considered not as a whole, but simply as a sum of cells.

  XX century

  Cell theory from the second half of the 19th century centuries acquired an increasingly metaphysical character, strengthened by Verworn’s “Cellular Physiology”, which considered any physiological process occurring in the body as simple sum physiological manifestations of individual cells. At the end of this line of development of cell theory, the mechanistic theory of the “cellular state” appeared, including Haeckel as a proponent. According to this theory, the body is compared to the state, and its cells are compared to citizens. Such a theory contradicted the principle of the integrity of the organism.

  The mechanistic direction in the development of cell theory was subjected to severe criticism. In 1860, I.M. Sechenov criticized Virchow’s idea of ​​the cell. Later, the cell theory was criticized by other authors. The most serious and fundamental objections were made by Hertwig, A. G. Gurvich (1904), M. Heidenhain (1907), Dobell (1911). The Czech histologist Studnicka (1929, 1934) made extensive criticism of the cellular theory.

  In the 1930s, Soviet biologist O. B. Lepeshinskaya, based on her research data, put forward a “new cell theory” as opposed to “Vierchowianism.” It was based on the idea that in ontogenesis cells can develop from some non-cellular living substance. A critical verification of the facts put forward by O. B. Lepeshinskaya and her adherents as the basis for the theory she put forward did not confirm the data on the development cell nuclei from nuclear-free “living matter”.

  Modern cell theory

  Modern cellular theory proceeds from the fact that cellular structure is the most important form of existence of life, inherent in all living organisms, except viruses. Improving cellular structure was the main direction of evolutionary development in both plants and animals, and cellular structure firmly retained in most modern organisms.

  At the same time, dogmatic and methodological incorrect positions cell theory:

  • Cellular structure is the main, but not the only form of existence of life. Viruses can be considered non-cellular life forms. True, they show signs of life (metabolism, ability to reproduce, etc.) only inside cells; outside cells the virus is complex chemical. According to most scientists, in their origin, viruses are associated with the cell, they are part of its genetic material, “wild” genes.
  • It turned out that there are two types of cells - prokaryotic (cells of bacteria and archaebacteria), which do not have a nucleus delimited by membranes, and eukaryotic (cells of plants, animals, fungi and protists), which have a nucleus surrounded by a double membrane with nuclear pores. There are many other differences between prokaryotic and eukaryotic cells. Most prokaryotes do not have internal membrane organelles, and most eukaryotes have mitochondria and chloroplasts. According to the theory of symbiogenesis, these semi-autonomous organelles are descendants bacterial cells. Thus, a eukaryotic cell is a system of more high level organization, it cannot be considered entirely homologous to a bacterial cell (a bacterial cell is homologous to one mitochondria of a human cell). The homology of all cells is thus reduced to the presence in them of a closed outer membrane from a double layer of phospholipids (in archaebacteria it has a different chemical composition than in other groups of organisms), ribosomes and chromosomes - hereditary material in the form of DNA molecules that form a complex with proteins. This, of course, does not negate the common origin of all cells, which is confirmed by their commonality chemical composition.
  • The cellular theory considered the organism as a sum of cells, and the life manifestations of the organism were dissolved in the sum of the life manifestations of its constituent cells. This ignored the integrity of the organism; the laws of the whole were replaced by the sum of the parts.
  • Considering the cell to be a universal structural element, the cell theory considered tissue cells and gametes, protists and blastomeres as completely homologous structures. The applicability of the concept of a cell to protists is a controversial issue in cellular theory in the sense that many complex multinucleated protist cells can be considered as supracellular structures. IN tissue cells, germ cells, protists, a general cellular organization, expressed in the morphological separation of karyoplasm in the form of a nucleus, however, these structures cannot be considered qualitatively equivalent, taking all their specific features beyond the concept of “cell”. In particular, animal or plant gametes are not just cells multicellular organism, and their special haploid generation life cycle, possessing genetic, morphological, and sometimes environmental features and subject to independent action natural selection. At the same time, almost everything eukaryotic cells undoubtedly have common origin and a set of homologous structures - cytoskeletal elements, eukaryotic-type ribosomes, etc.
  • The dogmatic cell theory ignored the specificity of non-cellular structures in the body or even recognized them, as Virchow did, as non-living. In fact, in the body, in addition to cells, there are multinuclear supracellular structures (syncytia, symplasts) and nuclear-free intercellular substance, which has the ability to metabolize and is therefore alive. To establish the specificity of their life manifestations and their significance for the body is the task of modern cytology. At the same time, both multinuclear structures and extracellular substance appear only from cells. Syncytia and symplasts of multicellular organisms are the product of the fusion of parent cells, and the extracellular substance is the product of their secretion, that is, it is formed as a result of cell metabolism.
  • The problem of the part and the whole was resolved metaphysically by the orthodox cell theory: all attention was transferred to the parts of the organism - cells or “elementary organisms”.

  The integrity of the organism is the result of natural, material relationships that are completely accessible to research and discovery. The cells of a multicellular organism are not individuals capable of existing independently (the so-called cell cultures outside the body are artificially created biological systems). As a rule, only those multicellular cells that give rise to new individuals (gametes, zygotes or spores) are capable of independent existence and can be considered as individual organisms. The cell cannot be torn away from environment(as, indeed, any living systems). Focusing all attention on individual cells inevitably leads to unification and a mechanistic understanding of the organism as a sum of parts.

  Cleared of mechanism and supplemented with new data, the cell theory remains one of the most important biological generalizations.

  Cell theory, one of the most important generalizations in biology, was formulated in 1839 by German scientists - zoologist Theodor Schwann and botanist Matthias Schleiden.

  The emergence of the cell theory was preceded by a rather long period of accumulation of data on the structure of living beings. The history of the study of cells is directly related to the invention of the microscope and the improvement of optical technology. One of those who invented this instrument was the great Galileo Galilei (1610). The first microscopes appeared at the turn of the 16th-17th centuries.

  The English scientist Robert Hooke in his book Micrographia (1667) first described cellular structure plant tissues. Examining thin sections of cork, elderberry core, etc. under a microscope, R. Hooke noted the cellular structure of plant tissues and called these cells cells (Fig. 1).

  The most important discoveries were made in the 17th century. and the Dutch self-taught scientist Anton van Leeuwenhoek. He described single-celled organisms(ciliates) and animal cells (erythrocytes, sperm).

  The works of R. Hooke and A. Leeuwenhoek served as an impetus for systematic microscopic studies various living organisms. Already in the 19th century. various intracellular components were identified: nucleus (R. Brown, 1831), protoplasm (J. Purkinje, 1837), chromosomes (W. Flemming, 1880), mitochondria (C. Benoit, 1894) apparatus Golgi (C. Golgi, 1898).

  A new stage in studying thin structure cells began with the invention electron microscope(1938). This tool allows you to study the structure of the smallest intracellular components and, in combination with biochemical and molecular biological methods, determine their functions.
  The main significance of the theory of T. Schwann and M. Schleiden is that they showed the fundamental similarity of plant and animal cells. This position was the most important proof of the unity of living nature. Equally significant is the idea of ​​the independent life activity of each individual cell.

  Modern science confirms the main provisions of the theory of T. Schwann and M. Schleiden. Indeed, all known living organisms consist of cells (we already talked about viruses in Chapter 2), i.e. the cell acts structural unit alive. At the cellular level, we discover the manifestation of such fundamental properties of living things as the ability to reproduce themselves, metabolism, heredity and variability, irritability and movement, and individual development. Therefore, the cell is functional unit alive.

  In the works of R. Virchow (1855-1858), the thesis “every cell is a cell” was formulated, i.e. we are talking about the formation of new cells by dividing the original (mother). Today this is recognized as a biological law (there are no other ways to form cells and increase their number).

  Summarizing all of the above, let us formulate the main provisions of the cellular theory:
  The cell is the basic unit of structure and development of all living organisms and is the smallest structural unit of a living thing.

  The cells of all organisms (both unicellular and multicellular) are similar in chemical composition, structure, basic manifestations of metabolism and vital activity.
  Cells reproduce by dividing them (each new cell is formed by dividing the mother cell);

  The importance of cell theory

  It became clear that the cell is the most important component of living organisms, their main morphophysiological component. The cell is the basis of a multicellular organism, the place where biochemical and physiological processes in organism. All biological processes ultimately occur at the cellular level. Cell theory allowed us to conclude that the chemical composition of all cells is similar, in general terms their structure, which confirms the phylogenetic unity of the entire living world.