According to cell theory, the cells of all organisms are similar. Cell theory. Further development of cytological knowledge

Cell theory- the most important biological generalization, according to which all living organisms are composed of cells. The study of cells became possible after the invention of the microscope. For the first time, the cellular structure of plants (a cut of a cork) was discovered by the English scientist, physicist R. Hooke, who also proposed the term “cell” (1665). The Dutch scientist Antonie van Leeuwenhoek was the first to describe vertebrate red blood cells, spermatozoa, various microstructures of plant and animal cells, various single-celled organisms, including bacteria, etc.

In 1831, the Englishman R. Brown discovered a nucleus in cells. In 1838, the German botanist M. Schleiden came to the conclusion that plant tissues consist of cells. The German zoologist T. Schwann showed that animal tissues also consist of cells. In 1839, T. Schwann’s book “Microscopic Studies on the Correspondence in the Structure and Growth of Animals and Plants” was published, in which he proves that cells containing nuclei represent the structural and functional basis of all living beings. The main provisions of T. Schwann's cell theory can be formulated as follows.

1. The cell is the basic structural unit of all living beings.
2. Cells of plants and animals are independent, homologous to each other in origin and structure.

M. Schdeiden and T. Schwann mistakenly believed that the main role in the cell belongs to the membrane and new cells are formed from intercellular structureless substance. Subsequently, clarifications and additions were made to the cell theory by other scientists.

Back in 1827, Academician of the Russian Academy of Sciences K.M. Baer, ​​having discovered the eggs of mammals, established that all organisms begin their development from one cell, which is a fertilized egg. This discovery showed that the cell is not only a unit of structure, but also a unit of development of all living organisms.

In 1855, the German physician R. Virchow came to the conclusion that a cell can only arise from a previous cell by dividing it.

At the current level of development of biology basic principles of cell theory can be represented as follows.

1. A cell is an elementary living system, a unit of structure, life activity, reproduction and individual development of organisms.
2. The cells of all living organisms are similar in structure and chemical composition.
3. New cells arise only by dividing pre-existing cells.
4. The cellular structure of organisms is proof of the unity of origin of all living things.

Types of Cellular Organization

There are two types of cellular organization: 1) prokaryotic, 2) eukaryotic. What is common to both types of cells is that the cells are limited by the membrane, the internal contents are represented by the cytoplasm. The cytoplasm contains organelles and inclusions. Organoids- permanent, necessarily present, components of the cell that perform specific functions. Organelles may be bounded by one or two membranes (membrane organelles) or not bounded by membranes (non-membrane organelles). Inclusions- non-permanent components of the cell, which are deposits of substances temporarily removed from metabolism or its final products.

The table lists the main differences between prokaryotic and eukaryotic cells.

Prokaryotes include bacteria, eukaryotes include plants, fungi, and animals. Organisms can consist of one cell (prokaryotes and unicellular eukaryotes) or of many cells (multicellular eukaryotes). In multicellular organisms, specialization and differentiation of cells occurs, as well as the formation of tissues and organs.

1) New cells are formed only from bacterial cells.
2) New cells are formed only as a result of the division of original cells.
3) New cells are formed from an old cell
4) New cells are formed by simple division in half.
A2. The ribosome contains
1) DNA 2) mRNA 3) r-RNA 4) t-RNA
A3. Lysosomes in cells are formed in
1) endoplasmic reticulum 2) mitochondria 3) cell center 4) Golgi complex
A4. Unlike chloroplasts, mitochondria
1) have a double membrane 2) have their own DNA 3) have grana 4) have cristae
A5. What function does the cell center perform in a cell?
1) takes part in cell division 2) is the custodian of hereditary information
3) is responsible for protein biosynthesis 4) is the center of template synthesis of ribosomal RNA
A6. What function do lysosomes perform in a cell?
1) break down biopolymers into monomers 2) oxidize glucose to carbon dioxide and water
3) carry out the synthesis of organic substances 4) carry out the synthesis of polysaccharides from glucose
A7. Prokaryotes are organisms that lack
1) cytoplasm 2) nucleus 3) membrane 4) DNA
A8. Organisms that do not need oxygen to live are called:
1) anaerobes 2) eukaryotes 3) aerobes 4) prokaryotes
A9. Complete oxygen breakdown of substances (3rd stage of energy metabolism) occurs in:
1) mitochondria 2) lysosomes 3) cytoplasm 4) chloroplasts
A10. A set of reactions for the biological synthesis of substances in a cell is
1) Dissimilation 2) Assimilation 3) Glycolysis 4) Metabolism
A11. Organisms, organic substances from the external environment, are called:
1) Heterotrophs 2) Saprophytes 3) Phototrophs 4) Autotrophs
A12. Photolysis of water occurs in the cell in
1) mitochondria 2) lysosomes 3) chloroplasts 4) endoplasmic reticulum
A13. During photosynthesis, oxygen is produced as a result of
1) photolysis of water 2) decomposition of carbon dioxide 3) decomposition of glucose 4) synthesis of ATP
A14. The primary structure of a protein molecule, determined by the nucleotide sequence of mRNA,
formed in the process
1) translation 2) transcription 3) reduplication 4) denaturation
A15. A section of DNA that encodes information about the sequence of amino acids in the primary
protein structure is called:
1) gene 2) triplet 3) nucleotide 4) chromosome
A16. The process of division of somatic cells with preservation of the diploid set of chromosomes is
1) Transcription 2) Translation 3) Reproduction 4) MitosisA17. Which triplet on DNA corresponds to the UGC codon on mRNA?
1) TGC 2) AGC 3) TCG 4) ACG
A18. The destruction of the nuclear envelope and the formation of the fission spindle occurs in
1) Anaphase 2) Telophase 3) Prophase 4) Prometaphase
A19. The duplication of all organelles occurs in
1) Anaphase 2) Telophase 3) Interphase 4) Metaphase
In tasks B1-B2, choose three correct answers from the six proposed. Write the answer in the form
sequences of numbers. 2 points for a correctly completed task
IN 1. From the proposed characteristics, select those that relate to mitochondria
1) Contains DNA 4) Regulates all processes of protein synthesis, metabolism and energy
2) Participate in protein synthesis 5) Synthesize organic substances from inorganic
3) Covered with two membranes 6) The inner membrane has projections - cristae
AT 2. Autotrophs versus heterotrophs
1) Synthesize organic substances 4) Use solar energy
2) Absorb organic substances from outside 5) Contain chloroplasts
3) Feed on dead organisms 6) Exist on living organisms

Answer

Cells were discovered in 1665 by R. Hooke. Cell theory, one of the greatest discoveries of the 19th century, was formulated in 1838 by German scientists M. Schleiden and T. Schwann, and later developed and supplemented by R. Virchow. Cell theory includes the following provisions:

1. A cell is the smallest unit of living things.

2. Cells of different organisms have a similar structure, which indicates the unity of living nature.

3. Cell reproduction occurs by dividing the original, mother cell (postulate: each cell is from a cell).

4. Multicellular organisms consist of complex ensembles of cells and their derivatives, united into systems of tissues and organs, and the latter into a whole organism with the help of nervous, humoral and immune regulatory mechanisms.

Cell theory united the concept of the cell as the smallest structural, genetic and functional unit of animal and plant organisms. She armed biology and medicine with an understanding of the general laws of the structure of living things.

Length measures used in cytology

1 µm (micrometer) – 10 –3 mm (10 –6 m)

1 nm (nanometer) – 10 –3 η (10 –9 m)

1 A (amstrom) – 0.1 nm (10 –10 m)

General organization of animal cells

All cells of the human and animal body have a common structural plan. They consist of cytoplasm And kernels and are separated from the environment by a cell membrane.

The human body consists of approximately 10 13 cells, divided into more than 200 types. Depending on their functional specialization, different cells of the body can differ significantly in their shape, size and internal structure. In the human body there are round (blood cells), flat, cubic, prismatic (epithelial), spindle-shaped (muscle), process (nerve) cells. Their sizes range from 4-5 microns (cerebellar granule cells and small lymphocytes) to 250 microns (ovum). The processes of some nerve cells are more than 1 meter long (in neurons of the spinal cord, the processes of which extend to the tips of the fingers of the limbs). Moreover, the shape, size and internal structure of cells always best correspond to the functions they perform.

Structural components of a cell

Cytoplasm- part of the cell separated from the environment cell membrane and including hyaloplasm, organelles And inclusion.

All membranes in cells have a general structural plan, which is summarized in the concept universal biological membrane(Fig. 2-1A).

Universal biological membrane formed by a double layer of phospholipid molecules with a total thickness of 6 microns. In this case, the hydrophobic tails of the phospholipid molecules are turned inward, towards each other, and the polar hydrophilic heads are turned outward of the membrane, towards the water. Lipids provide the basic physicochemical properties of membranes, in particular their fluidity at body temperature. Embedded within this lipid bilayer are proteins. They are divided into integral(permeate the entire lipid bilayer), semi-integral(penetrate up to half of the lipid bilayer), or surface (located on the inner or outer surface of the lipid bilayer).

Rice. 2-1. The structure of the biological membrane (A) and cell membrane (B).

1. Lipid molecule.

2. Lipid bilayer.

3. Integral proteins.

4. Semi-integral proteins.

5. Peripheral proteins.

6. Glycocalyx.

7. Submembrane layer.

8. Microfilaments.

9. Microtubules.

10. Microfibrils.

11. Molecules of glycoproteins and glycolipids.

(According to O.V. Volkova, Yu.K. Eletsky).

In this case, protein molecules are located in a mosaic pattern in the lipid bilayer and can “float” in the “lipid sea” like icebergs, due to the fluidity of the membranes. According to their function, these proteins can be structural(maintain a certain membrane structure), receptor(form receptors for biologically active substances), transport(transport substances across the membrane) and enzymatic(catalyze certain chemical reactions). This is currently the most recognized fluid mosaic model biological membrane was proposed in 1972 by Singer and Nikolson.

Membranes perform a demarcation function in the cell. They divide the cell into compartments, in which processes and chemical reactions can occur independently of each other. For example, the aggressive hydrolytic enzymes of lysosomes, capable of breaking down most organic molecules, are separated from the rest of the cytoplasm by a membrane. If it is destroyed, self-digestion and cell death occurs.

Having a general structural plan, different biological cell membranes differ in their chemical composition, organization and properties, depending on the functions of the structures they form.

Cells are the structural units of organisms. The term was first used by Robert Hooke in 1665. By the 19th century, through the efforts of many scientists (especially Matthias Schleiden and Theodor Schwann), the cell theory had developed. Its main provisions were the following statements:

The cell is the basic unit of structure and development of all living organisms;

The cells of all organisms are similar in their structure, chemical composition, and basic manifestations of life activity;

Each new cell is formed as a result of the division of the original (mother) cell;

In multicellular organisms, cells are specialized in the function they perform and form tissues. Organs are made up of tissues, which are closely interconnected and subject to regulatory systems.

Almost all tissues of multicellular organisms consist of cells. On the other hand, slime molds consist of an unseptated cell mass with many nuclei. The heart muscle of animals is structured in a similar way. A number of structures of the body (shells, pearls, the mineral basis of bones) are formed not by cells, but by the products of their secretion.

Small organisms may consist of only hundreds of cells. The human body includes 10 14 cells. The smallest cell currently known has a size of 0.2 microns, the largest - an unfertilized egg of apyornis - weighs about 3.5 kg. Typical sizes of plant and animal cells range from 5 to 20 microns. Moreover, there is usually no direct relationship between the size of organisms and the size of their cells.

70–80% of the cell mass is water.

In order to maintain the required concentration of substances, the cell must be physically separated from its environment. At the same time, the vital activity of the body involves intensive metabolism between cells. The role of a barrier between cells is played by the plasma membrane.

The internal structure of a cell has long been a mystery to scientists; it was believed that the membrane bounds protoplasm - a kind of liquid in which all biochemical processes occur. Thanks to electron microscopy, the mystery of protoplasm was revealed, and it is now known that inside the cell there is cytoplasm, in which various organelles are present, and genetic material in the form of DNA, collected mainly in the nucleus (in eukaryotes).

Cell structure is one of the important principles of classification of organisms. In the following paragraphs we will first consider the structures common to plant and animal cells, then the characteristic features of plant cells and prenuclear organisms. This section will end with a look at the principles of cell division.

Cytology is the study of cells.

Anthony van Leeuwenhoek discovered that the substance inside the cell is organized in a certain way. He was the first to discover cell nuclei. At this level, the idea of ​​a cell lasted for more than 100 years.

The study of the cell accelerated in the 1830s with the advent of improved microscopes. In 1838-1839, the botanist Matthias Schleiden and the anatomist Theodor Schwann almost simultaneously put forward the idea of ​​the cellular structure of the body. T. Schwann coined the term “cell theory” and introduced this theory to the scientific community. The emergence of cytology is closely related to the creation of cell theory - the broadest and most fundamental of all biological generalizations. 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.

The most important addition to the cell theory was the statement of the famous German naturalist Rudolf Virchow that each cell is formed as a result of the division of another cell.

In the 1870s, two methods of eukaryotic cell division were discovered, later called mitosis and meiosis. Already 10 years after this, it was possible to establish the main genetic features of these types of division. It was found that before mitosis, chromosomes are doubled and distributed evenly between daughter cells, so that the daughter cells retain the same number of chromosomes. Before meiosis, chromosomes also double, but in the first (reduction) division, bichromatid chromosomes diverge to the poles of the cell, so that cells with a haploid set are formed, the number of chromosomes in them is half that in the mother cell. It was found that the number, shape and size of chromosomes - the karyotype - are the same in all somatic cells of animals of a given species, and the number of chromosomes in gametes is half as much. Subsequently, these cytological discoveries formed the basis of the chromosomal theory of heredity.

Cytologythe science of cells - the structural and functional units of almost all living organisms

In a multicellular organism, all the complex manifestations of life arise from the coordinated activity of its constituent cells. The task of a cytologist is to determine how a living cell is built and how it performs its normal functions. Pathomorphologists also study cells, but they are interested in the changes that occur in cells during illness or after death. Despite the fact that scientists had long ago accumulated a lot of data on the development and structure of animals and plants, it was only in 1839 that the basic concepts of cell theory were formulated and the development of modern cytology began.

Cells are the smallest units of life, as demonstrated by the ability of tissues to break down into cells, which can then continue to live in “tissue” or cell culture and multiply like tiny organisms. According to cell theory, all organisms are made up of one or many cells. There are several exceptions to this rule. For example, in the body of slime molds (myxomycetes) and some very small flatworms, the cells are not separated from each other, but form a more or less fused structure - the so-called. syncytium. However, it can be considered that this structure arose secondarily as a result of the destruction of sections of cell membranes that were present in the evolutionary ancestors of these organisms. Many fungi grow by forming long thread-like tubes, or hyphae. These hyphae, often divided by partitions - septa - into segments, can also be considered as peculiar elongated cells. The bodies of protists and bacteria consist of one cell.

There is one important difference between bacterial cells and the cells of all other organisms: the nuclei and organelles (“little organs”) of bacterial cells are not surrounded by membranes, and therefore these cells are called prokaryotic (“prenuclear”); all other cells are called eukaryotic (with “true nuclei”): their nuclei and organelles are enclosed in membranes. This article covers only eukaryotic cells.

Opening the cell

The study of the smallest structures of living organisms became possible only after the invention of the microscope, i.e. after 1600. The first description and images of cells were given in 1665 by the English botanist R. Hooke: examining thin sections of dried cork, he discovered that they “consist of many boxes.” Hooke called each of these boxes a cell (“chamber”). The Italian researcher M. Malpighi (1674), the Dutch scientist A. van Leeuwenhoek, and the Englishman N. Grew (1682) soon provided a lot of data demonstrating the cellular structure of plants. However, none of these observers realized that the really important substance was the gelatinous material that filled the cells (later called protoplasm), and the “cells” that seemed so important to them were simply lifeless cellulose boxes that contained this substance. Until the middle of the 19th century. In the works of a number of scientists, the beginnings of a certain “cellular theory” as a general structural principle were already visible. 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.

Creation of cell theory. The amount of direct information about the cell and its contents increased enormously after 1830, when improved microscopes became available. Then, in 1838–1839, what is called “the master’s finishing touch” happened. The botanist M. Schleiden and the anatomist T. Schwann almost simultaneously put forward the idea of ​​cellular structure. 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.

Discovery of protoplasm. At first, undeservedly much attention was paid to the cell walls. However, F. Dujardin (1835) described living jelly in unicellular organisms and worms, calling it “sarcoda” (i.e., “resembling meat”).

This viscous substance was, in his opinion, endowed with all the properties of living things. Schleiden also discovered a fine-grained substance in plant cells and called it “plant mucilage” (1838). Eight years later, G. von Mohl used the term “protoplasm” (used in 1840 by J. Purkinje to designate the substance from which animal embryos are formed in the early stages of development) and replaced the term “plant mucus” with it. In 1861, M. Schultze discovered that sarcoda is also found in the tissues of higher animals and that this substance is identical both structurally and functionally to the so-called. plant protoplasm. For this “physical basis of life,” as T. Huxley later defined it, the general term “protoplasm” was adopted. The concept of protoplasm played an important role in its time; however, it has long been clear that protoplasm is not homogeneous either in its chemical composition or in structure, and this term gradually fell out of use. Currently, the main components of a cell are usually considered to be the nucleus, cytoplasm and cellular organelles. The combination of cytoplasm and organelles practically corresponds to what the first cytologists had in mind when speaking of protoplasm.

Basic properties of living cells

The study of living cells has shed light on their vital functions. It was found that the latter can be divided into four categories: mobility, irritability, metabolism and reproduction.

Motility manifests itself in various forms: 1) intracellular circulation of cell contents; 2) flow, which ensures the movement of cells (for example, blood cells); 3) beating of tiny protoplasmic processes - cilia and flagella; 4) contractility, most developed in muscle cells.

Irritability is expressed in the ability of cells to perceive a stimulus and respond to it with an impulse, or a wave of excitation. This activity is expressed to the highest degree in nerve cells.

Metabolism includes all transformations of matter and energy that occur in cells.

Reproduction is ensured by the cell's ability to divide and form daughter cells. It is the ability to reproduce themselves that allows cells to be considered the smallest units of life. However, many highly differentiated cells have lost this ability.

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 as the most important units providing the physical basis of heredity and the development process.

Development of new methods. 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 microscope itself was also improved. Important advances in its design include: an illuminator located under the table to focus the light beam; apochromatic lens to correct coloring imperfections that distort the image; immersion lens, providing a clearer image and magnification of 1000 times or more.

It has also been found that basic dyes, such as hematoxylin, have an affinity for the nuclear contents, while acidic dyes, such as eosin, stain the cytoplasm; this observation served as the basis for the development of a variety of contrast or differential staining methods. Thanks to these methods and improved microscopes, the most important information about the structure of the cell, its specialized “organs” and various non-living inclusions that the cell itself either synthesizes or absorbs from the outside and accumulates gradually accumulated.

Law of genetic continuity. The concept of genetic continuity of cells was of fundamental importance for the further development of cell theory. At one time, Schleiden believed that cells were formed as a result of a kind of crystallization from cellular fluid, and Schwann went even further in this erroneous direction: in his opinion, cells arose from a certain “blastema” fluid located outside the 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” (“Every 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 in it of intensely stained threads called chromatin. Subsequent studies showed that when a cell divides, these threads 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 a number typical for a given species chromosomes. Consequently, Virchow’s aphorism can be extended to chromosomes (carriers of hereditary characteristics), since each of them comes from a pre-existing one.

In 1865 it was established that the male reproductive cell (spermatozoon, or sperm) is a full-fledged, albeit highly specialized cell, and 10 years later O. Hertwig traced the path of the sperm in the process of fertilization of the egg. And finally, in 1884, E. van Beneden showed that during the formation of both the sperm and the egg, modified cell division (meiosis) occurs, as a result of which they receive one set of chromosomes instead of two. Thus, each mature sperm and each mature egg contains only half the number of chromosomes compared to the rest of the cells of a given organism, and during fertilization, the normal number of chromosomes is simply restored. As a result, the fertilized egg contains one set of chromosomes from each of the parents, which is the basis for the inheritance of characteristics on both the paternal and maternal lines. In addition, fertilization stimulates the onset of egg fragmentation and the development of a new individual.

The idea that chromosomes retain their identity and maintain genetic continuity from one generation of cells to the next was finally formed in 1885 (Rabel). It was soon established that chromosomes differ qualitatively from each other in their influence on development (T. Boveri, 1888). Experimental data also began to appear in favor of the previously stated hypothesis of V.Ru (1883), according to which even individual parts of chromosomes influence the development, structure and functioning of the organism.

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.

Laws of Heredity

The second stage in the development of cytology as a science covers 1900–1935. It came after the basic laws of heredity, formulated by G. Mendel in 1865, were rediscovered in 1900, but did not attract attention and were consigned to oblivion for a long time. Cytologists, although they continued to study the physiology of the cell and its organelles such as the centrosome, mitochondria and Golgi apparatus, focused their main attention on the structure of chromosomes and their behavior. Crossbreeding experiments carried out at the same time rapidly increased the amount of knowledge about modes of inheritance, which led to the emergence of modern genetics as a science. As a result, a “hybrid” branch of genetics emerged—cytogenetics.

Achievements of modern cytology

New techniques, especially electron microscopy, the use of radioactive isotopes and high-speed centrifugation, developed after the 1940s, have made enormous strides in the study of cell structure. In developing a unified concept of the physicochemical aspects of life, cytology is increasingly moving closer to other biological disciplines. At the same time, its classical methods, based on fixation, staining and studying cells under a microscope, still retain practical importance.

Cytological methods are used, in particular, in plant breeding to determine the chromosomal composition of plant cells. Such studies are of great assistance in planning experimental crosses and evaluating the results obtained. A similar cytological analysis is carried out on human cells: it allows us to identify some hereditary diseases associated with changes in the number and shape of chromosomes. Such an analysis in combination with biochemical tests is used, for example, in amniocentesis to diagnose hereditary defects in the fetus.

However, the most important application of cytological methods in medicine is the diagnosis of malignant neoplasms. In cancer cells, especially in their nuclei, specific changes occur that are recognized by experienced pathologists.

Cytology is a fairly simple and highly informative method for screening diagnostics of various manifestations of papillomavirus. This study is conducted in both men and women. However, to a greater extent this type of diagnosis is performed in women with various diseases of the cervix.

The result of the study directly depends on the technique of collecting material for the study. In women, it is recommended to collect material from the surface of the vulva, vagina, and cervix using a spatula, a Volkmann spoon, or a universal plastic probe. To obtain a scraping of the epithelium from the cervical canal, there are many cervical brushes available. There are also probes with which you can simultaneously obtain scrapings from both the endocervix and exocervix. It would not be superfluous to say that the study should be carried out after excluding any inflammatory processes. First, mucus and vaginal discharge are removed with a gauze swab, after which the material is collected. The study can be performed on any day of the cycle with the exception of the periovulatory period and menstruation. In addition, a cytological examination should be carried out no earlier than 2 days after the last sexual intercourse, during the treatment of infectious and inflammatory diseases (especially if various antiseptics, vaginal suppositories and creams, spermicides are used), and also no earlier than 48 hours after colposcopy, during which bite and Lugol solutions were used.

The material is applied to the glass slide in an even layer, after which they are fixed, for example, with Nikiforov’s mixture. Staining is performed using Papanicolaou staining. The study of cytological smears stained in this way is considered a reference and is called the Pap-smear test.

Correctly performed sampling of the material leads to the fact that the test sample should contain at least 8,000 – 15,000 cells.

Diagnosis of various cervical conditions assessed during cytological examination is based on the Papanicolaou classification. It distinguishes:

1. 1st class - these are normal epithelial cells.

2. Class 2 represents epithelial cells with an almost normal structure, but there is a slight increase in nuclei and the appearance of metaplastic epithelium.

3. Class 3 is characterized by pronounced changes in cells in the form of enlarged nuclei. This condition is called dyskaryosis.

4. 4th class – visualization of cells that can be assigned the value of atypia.

5. 5th class - these are typical cancer cells.

However, the Papanicolaou classification does not have absolutely accurate criteria for diagnosing papillomavirus, so recently the interpretation of the results is based on the Bethesda classification. Based on the cytological data, the doctor’s tactics for managing women are largely determined.

At the present stage, so-called liquid cytology is being introduced, which is the collection of material into a liquid preservative. Next, HPV typing using PCR and cytology is performed from one sample.

A specific sign of the presence of human papillomavirus infection during a cytological examination is the determination of koilocytes. Koilocytes are dying epithelial cells that have characteristic changes caused by the presence of the human papillomavirus in them. Cytologically, it is a cell with oxyphilic staining. There is a clearing zone around the nucleus, and in the cytoplasm there are many vacuoles containing viral particles. There may be cytoplasmic fibrils along the periphery of koilocytes.

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.

Provisions of the Schleiden-Schwann cell theory

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

Basic provisions of modern cell theory

1. The cell is the elementary unit of life; outside the cell there is no life.
2. A cell is a single system; it includes many naturally interconnected elements, representing an integral formation consisting of conjugated functional units - organelles.
3. The cells of all organisms are homologous.
4. A cell comes into being only by dividing the mother cell, after doubling its genetic material.
5. A multicellular organism is a complex system of many cells united and integrated into systems of tissues and organs connected to each other.
6. The cells of multicellular organisms are totipotent.

Additional provisions of the cell theory

To bring the cell theory into more complete compliance with the data of modern cell biology, the list of its provisions is often supplemented and expanded. In many sources, these additional provisions differ; their set is quite arbitrary.

1. Prokaryotic and eukaryotic cells are systems of different levels of complexity and are not completely homologous to each other (see below).
2. The basis of cell division and reproduction of organisms is the copying of hereditary information - nucleic acid molecules (“each molecule of a molecule”). The concept of genetic continuity applies not only to the cell as a whole, but also to some of its smaller components - mitochondria, chloroplasts, genes and chromosomes.
3. A multicellular organism is a new system, a complex ensemble of many cells, united and integrated in a system of tissues and organs, connected to each other through chemical factors, humoral and nervous (molecular regulation).
4. Multicellular cells are totipotent, that is, they have the genetic potential of all cells of a given organism, are equivalent in genetic information, but differ from each other in the different expression (function) of various genes, which leads to their morphological and functional diversity - to differentiation.

Story

17th century

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, Mole proved that even seemingly non-cellular plant structures, such as water-bearing tubes, develop from cells.

Meyen in “Phytotomy” (1830) describes plant cells that “are either solitary, so that each cell is 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.

In 1831, Robert Brown describes the nucleus and suggests that it is a permanent component of the 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.

Purkinje and his students (especially G. Valentin should be highlighted) revealed in the first and most general form the microscopic structure of the 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 1837, Purkinje gave a series of talks in Prague. In them, he reported on his observations on the structure of the gastric glands, nervous system, etc. The table attached to his report gave clear images of some cells of animal tissues. Nevertheless, Purkinje was unable to establish the homology of plant cells and animal cells:

• 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, not homology of these structures (understanding the terms “analogy” and “homology” in the modern sense).

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 on the intestinal epithelium, in which he described its various types and their cellular structure.

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 the correct principle for comparing 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.

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.

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. Schwann's main mistake was the opinion he expressed, following Schleiden, about the possibility of the emergence of cells from structureless non-cellular matter.

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.

For the further development of cell theory, its extension to protists (protozoa), which were recognized as free-living cells, was essential (Siebold, 1848).

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

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

In 1861, Brücko put forward a theory about the complex structure of the cell, which he defines as an “elementary organism,” and further elucidated 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

Since the second half of the 19th century, cell theory has acquired an increasingly metaphysical character, reinforced by Verworn’s “Cellular Physiology,” which considered any physiological process occurring in the body as a simple sum of the 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 laid down by O. B. Lepeshinskaya and her adherents as the basis for the theory she put forward did not confirm the data on the development of 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. The improvement of cellular structure was the main direction of evolutionary development in both plants and animals, and the cellular structure is firmly retained in most modern organisms.

At the same time, the dogmatic and methodologically incorrect provisions of the cell theory must be re-evaluated:

• 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 a complex chemical substance. 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 of bacterial cells. Thus, a eukaryotic cell is a system of a higher level of 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, thus, has been reduced to the presence of a closed outer membrane made of 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 forming a complex with proteins . This, of course, does not negate the common origin of all cells, which is confirmed by the commonality of their 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, and protists, a general cellular organization is manifested, 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, gametes of animals or plants are not just cells of a multicellular organism, but a special haploid generation of their life cycle, possessing genetic, morphological, and sometimes environmental characteristics and subject to the independent action of natural selection. At the same time, almost all eukaryotic cells undoubtedly have a 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) and can be considered as separate organisms are capable of independent existence. A cell cannot be separated from its 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.