Bacteria core. The Earth's core and the cell nucleus - what do they have in common? What diseases does Klebsiella cause?

The fact that bacteria, together with archaea, were classified by biologists as prokaryotes allows us to draw some conclusions about the structural features of these microorganisms. In particular, it is possible to answer the question of whether bacteria have the same nucleus as many other living organisms.

Their main difference from eukaryotes is that bacteria do not have a nucleus. Bacterial cells generally do not have developed intracellular membrane structures. In a cyanobacterial cell, small membrane-like formations resembling vesicles called thylakoids can be found. They contain systems that carry out photosynthesis - pigments and an enzyme complex. These microorganisms, recognized as the most evolutionarily advanced, carry out the process of photosynthesis similarly to eukaryotes - organisms whose cells have a real, formed nucleus.

Small membrane formations help bacterial cells organize the basic processes that ensure their existence.

If we compare them by function with the organelles of eukaryotic cells, we can find the primitive Golgi apparatus, mitochondria, and EPS (endoplasmic reticulum). However, bacteria do not have a true nucleus surrounded by a membrane. All bacteria have a nucleoid, not a nucleus - a circular DNA molecule freely located in the cytoplasm.

The shape of a bacterium is determined by its cell wall. Its size together with the capsule in some cases may be larger than the cell located inside. The wall has selective permeability and is capable of letting necessary substances in and removing metabolic products from it. Outside it you can often find flagella or villi - protrusions of the membrane that allow the body to move spontaneously.

The presence of a cell wall is characteristic of a group of bacteria called gram-positive. Below the cell wall is a membrane. But there is no DNA around the DNA molecule, which suggests that bacteria do not have a membrane-formed nucleus.

Cytoplasm

Under this complex shell of the bacterium there is cytoplasm - a gel mass of varying density, in the thickness of which there are inclusions:

• protein-producing ribosomes;
• small membrane structures;
• fatty inclusions (glycogen);
• polyphosphate compounds (volutin);
• polysaccharides;
• beta-hydroxybutyric acid.

The composition of the inclusion depends on the bacterium’s need for energy sources and nutrients. Some bacteria have a cytoskeleton - a system of tubes that can orient its main components inside the cell. In particular, they allow the DNA molecule to be positioned correctly during replication, despite the fact that bacteria do not have a true nucleus and histones in the cell.

Nucleoid

Approximately in the center of the cell, a nucleoid is found - the location of hereditary information. The bacterium does not have a formed nucleus that would have its own membrane, basic proteins (histones) and an enzyme complex that takes part in the reproduction of hereditary information and its implementation.

The absence of a formed nucleus determines the simple process of reproducing genetic information - the circular DNA molecule simply doubles before cell division, and one copy ends up in daughter organisms.

However, there is a peculiarity in the transfer of genetic information that makes bacteria unique to geneticists and molecular biologists. The possibility of their functioning is precisely due to the fact that bacteria do not have a nucleus in the cell. Non-chromosomal elements capable of transmitting information bypassing the nucleus have been found inside cells. The most studied among them are:

1. Plasmids.
2. Transposons and IS elements (insertion sequences).
3. Temperate phages.

It is curious that the amount of genetic information found in transposable elements significantly exceeds its number in the main DNA molecule. They are directly related to:

• protective reactions of bacteria,
• their rapid addiction to medications,
• the ability to synthesize antibiotics and sugars unusual for bacteria and to use some sources of nutrition that are unusual for their species.

Eukaryotic organisms have nothing like bacterial plasmids, since they have a structured nucleus that prevents contact of the main genome with non-nuclear elements. They are capable of independent reproduction and have their own set of necessary genes for this.

High variability was the reason that biologists for a long time believed that they had no such thing as a species. Only the emergence of pure cultures made it possible to conclude that this concept is quite applicable to these organisms, and the location of the main genome in them is their primitive nucleus or nucleoid.

Thus, bacteria do not have a nucleus, and this allows them to exchange genetic information “horizontally,” quickly transferring useful genes within the existing cell population and significantly increasing their adaptability to change environment.

Archaeal cells - options for nuclear-free existence

The closest relatives of bacteria, archaea, were until recently called archaebacteria and only recently were identified as a separate taxon. Externally they have a similar structure. The main differences were discovered relatively recently, when it turned out that not only the angular shape of the cell and the tendency to extreme living conditions distinguish these microorganisms, but also the characteristics of the biochemical reactions that provide their nutrition.

Like bacteria, archaea do not have a formed nucleus. Their transcription (synthesis of single-stranded RNA based on DNA, from which proteins are subsequently read) and translation (the reading process itself) are coupled. Their RNA polymerase (an enzyme that reads RNA from DNA) is similar in structure to eukaryotic ones and consists of 9-12 subunits (eubacteria have enzymes with four subunits).

The absence of a nucleus is not the only feature of archaea. Their replication does not have an origin characterized by a specific sequence of nucleotides that are recognized by the enzyme. Typically, whether bacteria or other organisms have a nucleus or not, removing enzyme attachment points will reduce the rate of reproduction. In the case of archaea, everything happens the other way around - in the absence of these points, they begin to multiply even faster.

Such unconventional way is possible due to the presence of enzymes in archaebacteria that allow sections of the genome to exchange fragments with each other. Many bacteria that do not have a nucleus have multiple recombination starting points, and their activity determines whether they are used in this moment or not. Removal of these points activates a mechanism whose efficiency is higher, the lower the activity of the recombination start points.

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All living organisms on Earth are made up of cells. It can be either an independent unit of life or a component of organisms that are more complex in their organization. Much of what the cells of higher organisms have, the cells of bacteria (prokaryotes) do not have.

The main difference is the lack of a formal core

The main difference between bacterial cells and eukaryotic cells (plants, animals and fungi) is that they do not have a clearly defined nucleus. All genetic information in bacteria is contained in a special protein complex called a nucleoid. Despite its primitive structure, the nucleoid is capable of accurately and clearly transmitting genetic data from one generation to another. The DNA of microorganisms is a highly polymeric compound, which consists of a certain number of nucleoids located in exact sequence among themselves. When this sequence is violated, a mutation of the species occurs, which leads either to the formation of a new form, or to the acquisition or loss of any properties.

Features in the transmission of hereditary information

In animals and plants, each species has a clearly defined nucleus and a certain number of chromosomes, which are responsible for the transmission of hereditary information. Bacteria, not having a clearly defined nucleus and having only one chromosome, are devoid of signs of such a phenomenon as dominance. The chromosome looks like a spiral coiled into a ring and is attached to the cytoplasmic membrane at one point. There are species with 2 or 4 chromosomes, but they are the same. In addition to chromosomes, the genotype of microorganisms also includes the following functional units:

• plasmids (contain a small number of genes, their composition is variable);
• IS sequences do not carry genes responsible for information; they are able to move along the chromosome and insert themselves into any part of it;
• transposons (contain a structural gene that is responsible for a particular hereditary trait).

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What organelles do microorganisms lack?

Unlike animal, plant and fungal cells, bacterial cells (prokaryotes) do not have the following organelles:

• lysosomes;
• plastids;
• mitochondria;
• Golgi complex;
• endoplasmic reticulum.

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Mitochondria

The presence of these organelles in plant and animal cells makes it possible to provide the necessary energy through redox processes. They are also capable of transmitting genetic information.

Golgi complex

The function of these organelles is to accumulate, change and subsequently remove substances from plant and animal cells.

Endoplasmic reticulum

It is a cellular organelle consisting of a system of tubules and vesicles. Located in the cytoplasm and bounded by a membrane. It participates in metabolic processes, ensuring the transport of substances from the outside into the cytoplasm.

In microorganisms, many of the functions of these organelles are performed by the mesosome. This structure is formed as a result of being drawn into the cell membrane. It is involved in DNA replication, in the creation of cellular partitions and in a number of other vital processes.

Differences in the life activity of prokaryotic and eukaryotic cells

The cells of microorganisms differ from the cells of animals, plants and fungi not only in their structure, they have their own characteristics in life activity.

Movement of the cytoplasm

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Photosynthesis process

Blue-green microorganisms, like plants, are capable of accumulating solar energy and producing oxygen necessary for the life of other organisms. The difference is that in bacteria the process of photosynthesis occurs on membranes, and in plants in chloroplasts.

Phagocytosis and pinocytosis

Bacteria do not have a dense cell wall, so they completely lack physiological processes such as phagocytosis and pinocytosis. Phagocytosis is the ability to capture solid particles by drawing them inward. Pinocytosis is a similar process, only liquid substances enter the cell.

Sporulation

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Reproduction

The method of bacterial reproduction is quite simple: cell division in two. An adult cell divides into two young cells, which grow, feed, and, reaching maturity, also divide. Under favorable conditions, one bacterial cell is capable of producing 72 generations per day.

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Biology lesson on the topic “Prokaryotic cell. Bacteria"

Presentation for the lesson

Attention! Slide previews are for informational purposes only and may not represent all the features of the presentation. If you are interested in this work, please download the full version.

Goals:

consolidate knowledge about prokaryotes, show the features of the structure and functioning of a prokaryotic cell, the diversity of bacteria;

reveal the role of bacteria in human life and in nature;

continue to develop the skills to compare, analyze, and draw conclusions.

Lesson type: study of material, primary consolidation of knowledge and methods of activity.

Methods: reproductive and partially search.

Equipment: tables, questionnaires, interactive equipment.

1. Organizational moment.

2. Determining the topic of the lesson.

3. Organisms: prokaryotes, eukaryotes.

4. History of discovery.

5. Features of the structure of a bacterial cell, reproduction, sporulation.

6. Application of bacteria.

7. Consolidation of knowledge, assessment.

8. Homework.

1. Organizational moment: greeting, presence of students, preparation for the lesson.

2. Determining the topic of the lesson. (Slide No. 1, 2)

The text of the slide opens one line at a time; students must determine which organisms are being discussed.

3. Work with the information sheet, analyze the contents, compare prokaryotic organisms with eukaryotic organisms.

(Information sheets are distributed in advance to each student)

Know: Bacteria are single-celled organisms, prokaryotes, mostly heterotrophs. Structure, life activity, reproduction and distribution of bacteria. Diversity of bacteria in structure, feeding method, habitat. The place of bacteria in the system of the organic world. Pathogenic bacteria and the fight against them. Use of bacteria by humans. The role of bacteria as destructive organisms in nature. (information sheets are distributed in advance to each student).

Our planet is home to a great variety of very different organisms, and all this stunning diversity can be attributed to either prokaryotes or eukaryotes, the structural features of which need to be known. The German scientist E. Haeckel was the first to draw serious attention to the significant differences between microorganisms and plants, fungi and animals. He proposed to separate them into a separate kingdom.

4. Contribution of A. Leeuwenhoek, R. Koch, L. Pasteur to the history of the discovery of bacteria. (teacher's story).

5. The teacher’s story about the features of the structure and functioning of a prokaryotic cell using the example of a bacterial cell.

(optional – E. coli).

(Working with slides No. 3-7)

Comparing the size of bacteria with the thickness of a human hair.

The structure of a bacterial cell.

6. The role of bacteria in nature.

There are many different bacteria
Harmful and useful.
How can you use them?
This is interesting.

Stories from students, teachers using additional information, presentations (slides 8-13).

The importance of bacteria for humans.

- in humans: plague, cholera, tuberculosis, dysentery, meningitis, typhus, etc.;

- in animals: bacteriosis.

Lead to food spoilage.

The role of bacteria in nature:

• As a result of the activity of putrefactive bacteria, the earth is cleared of dead plants and animals.
• Many bacteria take part in the geochemical processes of the formation of sulfur, phosphorus, oil, and in the nitrogen cycle.

Advances in microbiology make it possible to delegate many operations that were previously performed by technical means to the “fragile shoulders” of bacteria. A new technology for laying roads involves the use of bacterial colonies instead of asphalt pavers. A colony of bacteria slowly but surely eats the nutrient solution, producing a layer of road surface in return.

A method has been proposed to protect teeth from destruction. The teeth are coated with a layer of certain proteins, which is inoculated with special types of bacteria. The authors of the invention believe that this will protect even the roots of teeth from destruction.

Some bacteria feed on soluble calcium salts, releasing calcite, a water-insoluble mineral that is a constituent of marble. By covering the damaged surface of marble monuments with a nutrient solution and adding a culture of appropriate bacteria, it is possible to achieve uniform restoration of the surface of the monument.

“I sharpen damask knives”

Problem from the Center for Eye Microsurgery S. N. Fedorov. After cutting the retina with a scalpel, the latter is covered with a scalpel and makes a sharp radius of 30 microns out of 300... (1 micron is equal to 0.001 millimeters). How to sharpen a scalpel for your next operation? Engineers proposed a special sharpening machine, physicists - a plaza... Biologists proposed theirs - a scalpel with a microlayer of the retina is placed in a culture of bacteria that eat organic matter.

One of the most important pieces of evidence is that fingerprints are taken this way. The surface of the objects is covered with talcum powder, and then it is blown off. Where the talc remains, there is an imprint of the papillary line. If the print is clear, then identifying the villain is quite easy. What if the line - that is, a small fatty imprint of the skin - is unclear and the talc does not linger on it? How to find out the location of all, even the smallest, lines of a fingerprint? Bacteria are used to clearly capture subtle fingerprints. They are applied to the prints along with a special gel - they multiply only where the fingerprint of the papillary line lies. After 24 hours, bacterial colonies exactly follow the skin patterns. They use bacteria that live on the human body.

Recently, many reports have appeared in the press about the use of bacteria for the extraction and/or enrichment of ores. The first place (in terms of the number of publications) is occupied by iron bacteria, which use iron in their metabolism. In the USA, about 10% of the total amount of mined copper is obtained with the help of lithotrophic bacteria (feeding on inorganic matter).

7. Consolidation of knowledge, assessment. Assignments are distributed to students for individual work.

1. A cell that does not have a formed nucleus belongs to:

A. - bacteria B. - fungus

V. – plant G. – animal.

2. The carriers of hereditary information in the cell are:

A. – chromosomes B. – chloroplasts

B. – cytoplasm G. – ribosomes.

3. Organisms whose body consists of one cell that does not have a formed nucleus, feeding mainly on organic substances are:

xn--i1abbnckbmcl9fb.xn--p1ai

Structure of a bacterial cell

Cell membranes

Most bacteria have three shells:

• cell membrane;
• cell wall;
• mucous capsule.

The cell membrane is in direct contact with the contents of the cell - the cytoplasm. It is thin and soft.

The cell wall is a dense, thicker membrane. Its function is to protect and support the cell. The cell wall and membrane have pores through which the substances it needs enter the cell.

Many bacteria have a mucous capsule that performs a protective function and ensures adhesion to different surfaces.

It is thanks to the mucous membrane that streptococci (a type of bacteria) stick to the teeth and cause caries.

Cytoplasm

Cytoplasm is the internal contents of a cell. 75% consists of water. In the cytoplasm there are inclusions - drops of fat and glycogen. They are the cell's reserve nutrients.

Rice. 1. Diagram of the structure of a bacterial cell.

Nucleoid means “like a nucleus.” Bacteria do not have a real, or, as they also say, formed nucleus. This means that they do not have a nuclear envelope and nuclear space, like the cells of fungi, plants and animals. DNA is found directly in the cytoplasm.

• stores hereditary information;
• implements this information by controlling the synthesis of protein molecules characteristic of a given type of bacteria.

The absence of a true nucleus is the most important feature of a bacterial cell.

Unlike plant and animal cells, bacteria do not have organelles built from membranes.

But the bacterial cell membrane in some places penetrates the cytoplasm, forming folds called mesosomes. The mesosome is involved in cell reproduction and energy exchange and, as it were, replaces membrane organelles.

The only organelles present in bacteria are ribosomes. These are small bodies that are located in the cytoplasm and synthesize proteins.

Many bacteria have a flagellum, with which they move in a liquid environment.

Bacterial cell shapes

The shape of bacterial cells is different. Bacteria in the shape of a ball are called cocci. In the form of a comma - vibrios. Rod-shaped bacteria are bacilli. Spirilla have the appearance of a wavy line.

Rice. 2. Shapes of bacterial cells.

Bacteria can only be seen under a microscope. The average cell size is 1-10 microns. Bacteria up to 100 microns in length are found. (1 µm = 0.001 mm).

Sporulation

When unfavorable conditions occur, the bacterial cell enters a dormant state called a spore. The causes of sporulation may be:

• low and high temperatures;
• drought;
• lack of nutrition;
• life-threatening substances.

The transition occurs quickly, within 18-20 hours, and the cell can remain in a state of spores for hundreds of years. When normal conditions are restored, the bacterium germinates from the spore within 4-5 hours and returns to its normal mode of life.

Rice. 3. Scheme of spore formation.

Reproduction

Bacteria reproduce by division. The period from the birth of a cell to its division is 20-30 minutes. Therefore, bacteria are widespread on Earth.

What have we learned?

We learned that, in general terms, bacterial cells are similar to plant and animal cells, they have a membrane, cytoplasm, and DNA. The main difference between bacterial cells is the absence of a formed nucleus. Therefore, bacteria are called prenuclear organisms (prokaryotes).

Autouristi.ru

• Bacterial cells do not have a formed nucleus

Bacterial cells do not have a formed nucleus

Choose one, the most correct option. In what environment does the AIDS virus usually die?
1) in the lymph
2) in breast milk
3) in saliva
4) in the air

Choose one, the most correct option. Viruses have such signs of living things as
1) food
2) growth
3) metabolism
4) heredity

The AIDS virus is very unstable and is easily destroyed in air. You can become infected with it only through sexual intercourse without a condom and through a transfusion of contaminated blood.

Choose one, the most correct option. The AIDS virus infects human blood
1) red blood cells
2) platelets
3) lymphocytes
4) blood platelets

Bacterial cell structure

In the cytoplasm of bacteria, various types of inclusions have been identified, which can be solid, liquid and gaseous. They are reserve nutrients (polysaccharides, lipids, sulfur deposits, etc.) and metabolic products.

Capsule is a mucous structure, more than 0.2 microns thick, associated with the cell wall and clearly demarcated from the environment. It is detected by light microscopy in the case of staining bacteria using special methods (according to Olt, Mikhin, Burri-Gins). Many bacteria form a microcapsule - a mucous formation less than 0.2 microns, identified only by electron microscopy or by chemical and immunochemical methods. The capsule is not an essential structure of the cell; its loss does not cause the death of the bacterium. It is necessary to distinguish mucus from the capsule - mucoid exopolysaccharides. Mucous substances are deposited on the surface of the cell, often exceeding its diameter and have no clear boundaries.

The structure and composition of gram-negative microorganisms is characterized by some features. The cell wall of gram-negative bacteria is thinner than that of gram-positive bacteria and is 14-17 nm. It consists of two layers: external and internal. The inner layer is represented by peptidoglycan, which encircles the cell in the form of a thin (2 nm) continuous network. Peptidoglycan in gram-negative bacteria is 1-10%, its microfibrils are cross-linked less tightly than those of gram-positive bacteria, the pores are wider and therefore the complex of gentian violet and iodine is washed out of the wall with ethanol, the microorganisms are painted red (the color of an additional dye - fuchsin). The outer layer contains phospholipids, monopolysaccharides, lipoprotein and proteins. Lipopolysaccharide (LPS) from the cell walls of gram-negative bacteria, toxic to animals, is called endotoxin. Teichoic acids have not been found in gram-negative bacteria. The gap between the cell wall and the cytoplasmic membrane is called the periplasmic space, which contains enzymes.

Cytoplasm forms the internal environment of the cell, which unites all intracellular structures and ensures their interaction with each other.

The substance of prokaryotic capsules consists mainly of homo- or heteropolysaccharides. Some bacteria (for example, Leuconostoc) have several microbial cells enclosed in a capsule. Bacteria enclosed in one capsule form clusters called zoogels.

This Gram staining of prokaryotes is explained by the specific chemical composition and structure of their cell wall. The cell wall of gram-positive bacteria is massive, thick (20-100 nm), tightly adjacent to the cytoplasmic membrane, most of its chemical composition is represented by peptidoglycan (40-90%), which is associated with teichoic acids. The wall of gram-positive microorganisms contains small amounts of polysaccharides, lipids, and proteins. The structural microfibrils of peptidoglycan are cross-linked tightly, compactly, the pores in it are narrow and therefore the violet complex is not washed out, the bacteria are painted blue-violet.

The cytoplasm of the cell is a semi-liquid mass that occupies the main volume of the bacterium, containing up to 90% water. It consists of a homogeneous fraction called cytosol, which includes structural elements - ribosomes, intracytoplasmic membranes, various types of formation, nucleoid. In addition, the cytoplasm contains soluble RNA components, substrate substances, enzymes, and metabolic products.

Bookshelf

Glycolysis- the process of breakdown of glucose without the participation of oxygen (anaerobic). A molecule containing 6 carbon atoms is split into 2 three-carbon molecules of pyruvic acid - PVK, 2 molecules of ATP, water, 2 molecules of NAD-H.
Respiration is an aerobic process, the process of complete oxidation of glucose. There is a sequential oxidation of PVC molecules to CO2 with the formation of another ATP molecule and four electron acceptors.
Electron transport chain - hydrogen atoms are transferred to NAD+ to form NAD-H. The NAD-H molecule delivers hydrogen atoms to the respiratory chain, turning back into NAD+. The electrons of hydrogen atoms are transported along the chain, enter into redox reactions, and release energy for the synthesis of ATP. At the end of the chain a water molecule is formed.
55% of the energy is stored in the form of high-energy bonds of ATP molecules. 45% is dissipated as heat.

View- a set of individuals that have morphological and physiological similarities, freely interbreed with each other and produce fertile offspring, occupy a certain area and live in similar environmental conditions.
Type criteria: morphological, physiological, biochemical, genetic, geographical, environmental.
Population- a group of morphologically similar individuals of the same species, freely interbreeding and occupying a specific habitat in the species’ range.
Heredity- the property of preserving and transmitting signs of structure and function from parents to offspring. The characteristics recorded in the genotype are inherited.
Variability- the ability to change and acquire new characteristics within a species.
Natural selection- the main factor determining the direction of evolution. Environmental conditions play the role of a selecting factor.
As a result of driving natural selection, individuals with changes are predominantly preserved, and stabilizing selection - with stable characteristics corresponding to the environment.

Gregor Mendel- founder of genetics.
Genetics- the science of heredity and variability. Research methods used in genetics: genetic, cytogenetic, biochemical, genealogical, twin.
Genotype- the totality of all the genes of an organism.
Phenotype- the totality of all external and internal characteristics.
Different genotypes can determine the same phenotype.
Hybrid- an individual obtained from parents that differ in certain characteristics.
Different forms of the same gene that determine different manifestations of the same trait are called alleles. They are designated by letters, for example: A - gene for dark hair, and - light hair.
A trait that appears in the offspring and suppresses the manifestation of another trait is called dominant.
A trait that does not appear externally in the offspring is called recessive.
Hybrid organisms are organisms obtained by crossing genetically dissimilar parental forms.
Variability- non-hereditary (modification) and hereditary (genotypic).
The limits of modification variability of a trait are called reaction norm. The phenotype of an organism is determined by the interaction of the genotype with environmental factors.
Hereditary variability is combinative and mutational.
Mutations- sudden changes in genes or chromosomes. This changes the amount or structure of the DNA of a given organism.
There are gene (point) and chromosomal mutations. Gene mutations are associated with changes in individual genes, while chromosomal mutations are caused by changes in the number or structure of chromosomes.
Genetics is the scientific basis of selection. Selection- a science that deals with improving existing and creating new varieties of plants and animal breeds.
Basic selection methods - hybridization And selection. New methods: receiving heterosis, polyploids, experimental mutagenesis. There are spontaneous and methodical, mass and individual artificial selection, closely related and unrelated crossing, intraspecific and distant hybridization.
Biotechnology- purposeful modification and use of biological objects in the food industry, medicine, nature conservation, etc. Directions: microbiological production, cell engineering, genetic engineering.

Mitosis phases:
Prophase- spiralization of chromosomes, dissolution of the nuclear membrane, a division spindle begins to form from one centriole to another.
Metaphase- chromosomes in the equatorial plane of the cell.
Anaphase- Chromosome chromatids diverge to the poles of the cell, becoming new chromosomes.
Telophase- despiralization of chromosomes, formation of the nuclear membrane, cell septum, formation of 2 daughter cells.
During the process of mitosis, chromatids are evenly distributed between daughter cells, so that each of them receives the same set of chromosomes as in the mother cell.

Energy exchange
3 stages:
1) Preparatory (in lysosomes): molecules of substances break down with the release of energy (heat).
2) Oxygen-free (in the cytoplasm): organic substances are broken down into even simpler ones, part of the released energy goes to the synthesis of ATP.
3) Oxygen (in mitochondria): PVA molecules are oxidized to CO2 and H2O, the released energy is stored in 36 ATP molecules.
In the cells of anaerobes - microorganisms that live in an oxygen-free environment - only 2 stages of energy metabolism occur: preparatory and oxygen-free.

Plastic exchange
Plastic metabolism is characterized by reactions of the synthesis of organic substances, which involve the expenditure of energy. Both the nucleus and the cytoplasm are involved in protein biosynthesis. The nuclear chromosomes store information about the sequence of amino acids in the protein molecule. This information is encrypted using genetic code.
Genetic code is a sequence of nucleotides in a DNA molecule that determines the sequence of amino acids in a protein molecule.
The genetic code is triplet (each amino acid corresponds to a sequence of three nucleotides), non-overlapping (the same nucleotide cannot be part of two neighboring code triplets), universal (in all organisms the same amino acids are encoded by the same triplets).
Protein biosynthesis is a complex process that results in the implementation of genetic information.
Transcription- information about the structure of the protein is copied from DNA to mRNA.
Broadcast- Amino acids are joined in a specific sequence by pegtidic bonds to form a polypeptide chain.

3 main parts: plasma membrane, cytoplasm, core.
The plasma membrane separates the cell and its contents from the environment. Consists of lipids and protein molecules (external, submerged, penetrating). Ensures the flow of nutrients into the cell and the removal of metabolic products from it: diffusion, through pores, phagocytosis (proteins and polysaccharides enter), pinocytosis (liquid). Has selective permeability.
In the cells of plants, fungi, and most bacteria, there is a cell membrane above the plasma membrane that performs a protective function and plays the role of a skeleton. In plants, it consists of cellulose and is covered with polysaccharides, which ensure contact between cells of the same tissue. In mushrooms - from a chitin-like substance.
The composition of the cytoplasm includes water, amino acids, proteins, carbohydrates, ATP (adenosine triphosphoric acid), and inorganic substances. The cytoplasm contains the nucleus and organelles of the cell. The cytoplasm is permeated with protein microtubules that form the cell's cytoskeleton, thanks to which the cell maintains a constant shape.
Lysosomes- “digestive stations” of the cell, break down complex organic substances into simpler molecules.
Mitochondria- “power stations” of the cell, ATP synthesis, source of energy.
Organic substances are synthesized in plastids (plant cells). Leukoplasts- colorless plastids, accumulate starch. Chromoplasts- synthesis of carotenoids (yellow, orange, red coloring of fruits and flowers). Chloroplasts are green plastids that contain chlorophyll. Chromo- and chloroplasts are involved in photosynthesis.
Vacuoles accumulate nutrients and breakdown products in vacuolar sap. Permanent vacuoles - in a plant cell, up to 90% of the volume. Temporary vacuoles - in an animal cell, no more than 5% of the cell volume.
EPS ( endoplasmic reticulum) - synthesis of lipids and carbohydrates. ER - smooth and rough (there are ribosomes, they are involved in protein synthesis).
Cell center(2 centrioles) participates in cell division, forms a division spindle. Golgi complex- transport-storage function, formation of lysosomes, cell membrane.

Bacterial cells do not have a formed nucleus

The science of microbiology studies the structure and functioning of microorganisms.

Predatory bacteria are known to eat representatives of other types of prokaryotes.

Thus, a new spore cell appears inside the cell, surrounded by two membranes. Then, between the membranes, a cortical layer or cortex is formed, consisting of special peptidoglycan molecules.

Bacterial spores can exist in a dormant state for a long time (tens, hundreds and even thousands of years).

A number of mutants have been obtained in E. Coli, in which a cell septum is formed either in an unusual place, or, along with a septum with normal localization, an additional septum is formed close to the cell pole, and small cells (mini-cells) measuring 0.3-0. 5µm. Mini-cells, as a rule, are deprived of DNA, since during the division of the parent cell the Nucleoid does not enter them. Due to the lack of DNA, minicells are used in bacterial genetics to study the expression of gene function in extrachromosomal factors of heredity and other issues. After the cells are inoculated into a fresh nutrient medium, the bacteria do not multiply for some time - this phase is called the initial stationary or lag phase. The lag phase turns into a phase of positive acceleration. In this phase, the division of the bacterium begins. When the cell growth rate of the entire population reaches a constant value, the logarithmic phase of reproduction begins. The logarithmic phase is replaced by a phase of negative acceleration, then the stationary phase begins. The number of viable cells in this phase is constant. This is followed by a phase of population decline. They are influenced by: the type of bacterial culture, the age composition of the culture, the composition of the nutrient medium, growing temperature, aeration, etc.

Heterotrophic bacteria assimilate carbon, assimilate carbon from organic compounds of various chemical natures, and easily assimilate substances containing unsaturated bonds or carbon atoms with partially oxidized valences. In this regard, the most accessible sources of carbon are sugars, polyhydric alcohols, and others. Some heterotrophs, along with the assimilation of organic carbon, can also assimilate inorganic carbon.

The cytoplasmic membrane of the bacterium adheres to the inner surface of the cell wall, separates it from the cytoplasm, and is a functionally very important component of the cell. Redox enzymes are localized in the membrane, and such important cell functions as cell division, biosynthesis of a number of components, chemo and photosynthesis, etc. are associated with the membrane system. The thickness of the membrane in most cells is 7-10 nm. Electromicroscopic method revealed that it consists of three layers: two electron-dense and intermediate electron-transparent. The membrane contains proteins, phospholipids, microproteins, a small amount of carbohydrates and some other compounds. Many cell membrane proteins are enzymes involved in respiration processes, as well as in the biosynthesis of components of the cell wall and capsule. The membrane also contains permeases that ensure the transfer of soluble substances into the cell. The membrane serves as an astronomical barrier; it has selective semi-permeability and is responsible for the entry of nutrients and metabolic waste products into the cell.

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The concept of “cytoplasm” is complex, and when translated from Greek it means “cell contents”. Modern science understands cytoplasm as a complex dynamic physicochemical system contained within the plasma membrane. That is, all the intracellular contents of prokaryotes, excluding the chromosome, are considered the cytoplasm of the bacterial cell.

The cytoplasm of a prokaryotic cell has 2 layers of restriction:

• cytoplasmic membrane (CPM);
• cell wall.

The layers that limit the cytoplasm in bacteria have different functions and properties.

Bacterial cell wall

The outer covering layer of prokaryotes, the cell wall, is a dense shell and performs a number of functions:

• protection from external influences;
• giving the microorganism a characteristic shape.

In fact, the cell wall of microorganisms is a kind of exoskeleton. This structure is justified - after all, the intracellular osmotic pressure can be tens of times higher than the external pressure, and without the protection of a dense cell wall, the bacterium will simply burst.

A dense cell wall is characteristic only of bacterial and plant cells - an animal cell has a soft shell.

The bacterial cell wall, which limits the contents of the cell, has a thickness of 0.01 to 0.04 microns, and the thickness of the wall increases during the life of the microorganism. Despite the density of the cell membrane, it is permeable. Nutrients pass inside without hindrance, and waste products are removed from it.

Cytoplasmic membrane

Between the cytoplasm and the cell wall is the CPM - the cytoplasmic membrane. In a bacterial cell it performs a number of functions:

• regulates the intake of nutrients and the removal of waste products;
• synthesizes compounds for the cell wall;
• controls the activity of a number of enzymes located on it.

The cytoplasmic membrane is so strong that a bacterial cell can exist for some time even without a cell wall.

Intracellular composition of the microorganism

Studies using an electron microscope have revealed a very complex structure of the intracellular substance.

Any cytoplasm bacterial cell contains a large amount of water, it contains various organic and inorganic compounds - vital structures and organelles. Thus, in the cytosol (cytoplasmic matrix), the intracellular fluid, ribosomes, plastids and a supply of nutrients are located.

All intracellular contents are divided into three groups:

• hyaloplasm (cytosol or matrix of the cytoplasm);
• organelles are essential parts of a bacterial cell;
• inclusions are optional parts.

The cytoplasmic matrix is ​​not an aqueous solution, but a gel with varying viscosity. The aggregate state of hyaloplasm - gel-sol (higher or lower degree of viscosity) is in dynamic equilibrium and depends on external conditions.

The hyaloplasm of a bacterial organism includes the following structures:

• inorganic substances;
• metabolites of organic origin;
• biopolymers (proteins, polysaccharides).

The main purpose of hyaloplasm is to unite all existing inclusions and ensure stable chemical interaction between them.

Intracellular organelles of prokaryotes are microstructural plasmatic compounds responsible for life-support functions and are present in almost all bacterial cells. Organelles are divided into two large groups:

• mandatory - are vital for the functioning of the body;
• optional - do not have of great importance for functioning; microorganisms of even the same strain can differ in the set of these organelles.

Obligatory organelles

The organelles necessary for cell functioning include:

• nucleoid (bacterial chromosome) – is a circular double-stranded DNA molecule;
• ribosomes (responsible for protein synthesis) - similar to the ribosomes of cells that have a nucleus; can move freely in the cytoplasm or be associated with the CPM;
• cytoplasmic membrane (CPM);
• mesosomes are responsible for energy metabolism and participate in the process of cell division; are the result of invagination of the cytoplasmic membrane.

In the central part of the bacterial space there is an analogue of the eukaryotic nucleus - the nucleoid (DNA of the microorganism). In the case of eukaryotes, DNA is located only in the nucleus, but in bacteria, DNA can be concentrated in one place or dispersed in several places (plasmids).

Other differences between the bacterial chromosome and eukaryotic nuclei are:

• more loose packaging;
• absence of organelles characteristic of the nucleus - nucleoli, membranes and others;
• have no connection with histones - the main proteins.

As an analogue of the eukaryotic nucleus, the bacterial chromosome is a primitive form in terms of the organization of nuclear matter.

Optional organelles of prokaryotes

Optional bacterial organelles do not have a significant effect on the functional abilities of the bacterial organism. A characteristic feature of prokaryotes is the manifestation of dissociation, as a result of which morphotypes (morphovars) are formed - strains of microorganisms of the same species that have morphological differences.

As a result, the bacterial colony exhibits differences not only in morphological characteristics, but also physiological, biochemical, genetic. The main differences between morphovars and each other are precisely in the composition of optional organelles.

Optional organelles include:

• plasmids - carriers of genetic information, similar to the bacterial chromosome, but much smaller in size and with the possibility of the presence of several copies in the body;
• inclusions containing nutrients (for example, volutin); may be characteristic feature specific type of microorganism.

Optional bacterial organelles are not a permanent feature of a given species—many inclusions are sources of carbon or energy. Under favorable conditions, the microorganism forms a similar reserve in the intracellular space, which is consumed when unfavorable conditions occur.

Inclusions containing nutrients belong to the granular type of compounds. According to their composition they can be divided into:

• polysaccharides – granulosa (starch), glycogen;
• volutin (metachromatin granules) – contains polymetaphosphate;
• fat drops;
• drops of sulfur.

It is the inclusion of low molecular weight formations that leads to the emergence of different values ​​of osmotic pressure of the bacterial cytoplasm and the external environment.

The substance of the intracellular space of a living bacterium is in constant motion (this is called cyclosis), thereby moving the substances and organelles contained in it.

The fate of life on Earth was decided approximately 2.6 billion years ago. The greatest ecological crisis coincided with the greatest evolutionary leap. If the disaster had been a little stronger, the planet could have remained lifeless forever. If it were weaker, perhaps bacteria would still be the only inhabitants of the Earth...

The appearance of eukaryotes - living cells with a nucleus - is the second most significant (after the origin of life itself) event in biological evolution. We will talk about when, how and why the cell nucleus appeared.

Life on Earth has come a long way from the first living cell to mammals and humans. Along this path there were many epoch-making events, many great discoveries and ingenious inventions were made. Which one was the most important? Maybe the formation of the human brain or the emergence of animals on land? Or maybe the emergence of multicellular organisms? Scientists here are almost unanimous: the greatest achievement of evolution was the appearance of cells of the modern type - with a nucleus, chromosomes, vacuoles and other organs, the unpronounceable names of which we vaguely remember from school. The very cells that make up our body.

And in the beginning the cells were completely different. They had no nuclei, no vacuoles, no other “organs”, and there was only one chromosome, and it had the shape of a ring. This is how the cells of bacteria, the first inhabitants of the Earth, are structured to this day. Between these primary cells and modern, improved ones there is a much larger gap than between a jellyfish and a person. How did nature manage to overcome it?

Bacterial world

For a billion years or more, the Earth was the kingdom of bacteria. Already in the oldest sedimentary rocks of the earth's crust (their age is 3.5 billion years), remains of blue-green algae, or cyanobacteria, have been discovered. These microscopic organisms still thrive today. Over billions of years they have hardly changed. It is they who color the water in lakes and ponds a bright bluish-green color, and then they say that “the water is blooming.” Blue-green algae are by no means the most primitive of bacteria. From the origin of life to the appearance of cyanobacteria, many millions of years of evolution most likely passed. Unfortunately, no traces of those ancient eras were preserved in the earth's crust: merciless time and geological disasters destroyed, melting in the hot depths, all sedimentary rocks that arose in the first hundreds of millions of years of the Earth's existence.

Cyanobacteria are organisms that are not only ancient, but also honored. They were the ones who “invented” chlorophyll and photosynthesis. Their unnoticed work over many millions of years gradually enriched the ocean and atmosphere with oxygen, which made possible appearance real plants and animals. At first, all the oxygen was spent on the oxidation of iron dissolved in the ocean. Oxidized iron precipitated: this is how the largest deposits of iron ore were formed. Only when the iron was “finished” did oxygen begin to accumulate in the water and enter the atmosphere.

For at least a billion years, cyanobacteria were the undivided masters of the Earth and almost its only inhabitants. The bottom of the World Ocean was covered with bluish-green carpets. In these carpets, cyanobacterial mats, other bacteria lived along with the blue-green ones. All of them were perfectly adapted to each other and to the harsh conditions of the primitive ocean. At that time - the Archean era (Archaean) - it was very hot on Earth. The carbon dioxide-rich atmosphere created a powerful greenhouse effect. Because of this, by the end of the Archean, the World Ocean warmed up to 50–60°C. Dissolving in water, carbon dioxide turned into acid; hot acidic waters were irradiated with hard ultraviolet light (after all, the Earth did not yet have a modern atmosphere with a saving ozone shield). In addition, a huge amount of toxic salts of heavy metals were dissolved in the water. Constant volcanic eruptions, emissions of ash and gases, sharp fluctuations in environmental conditions - all this did not make life easier for the first inhabitants of the planet.

The bacterial communities that evolved in such an inhospitable environment were incredibly resilient and resilient. Because of this, their evolution was very slow. They were already adapted to almost everything, and there was no need for them to improve. For life on Earth to begin to develop and become more complex, a catastrophe was required. It was necessary to destroy this ultra-resistant bacterial world, which seemed eternal and indestructible, in order to free up living space for something new.

Planetary catastrophe - formation of the earth's core

The long-awaited revolution, which put an end to the protracted stagnation and brought life out of the bacterial “dead end,” occurred 2.7–2.5 billion years ago, at the very end of the Archean era. Russian geologists O. G. Sorokhtin and S. A. Ushakov, authors of the newest physical theory of the development of the Earth, calculated that at this time our planet underwent the largest and most catastrophic transformation in its entire history.

According to their hypothesis, the cause of the disaster was the emergence of an iron core on our planet. From the formation of the Earth until the end of the Archean, a molten mixture of iron and its divalent oxide (FeO) accumulated in the upper layers of the mantle. Approximately 2.7 billion years ago, the mass of this melt exceeded a certain threshold, after which the heavy, viscous, hot liquid literally “failed” to the center of the Earth, displacing its primary, lighter core. These enormous movements of huge masses of matter in the bowels of the planet tore and crushed its thin surface shell - the earth's crust. Volcanoes were erupting everywhere. The ancient continents came closer, collided and merged into a single supercontinent Monogea - just above the place where liquid iron flowed into the interior of the planet. The deep rocks that came to the surface entered into a chemical reaction with atmospheric carbon dioxide, and very soon there was almost no carbon dioxide left in the atmosphere. The greenhouse effect became much weaker, which led to severe cooling: the ocean temperature dropped from +60°C to +6. Just as suddenly and sharply, the acidity of sea water decreased.

It was the greatest of disasters. But even she could not destroy the cyanobacteria. They survived, although they had a really hard time. The disappearance of the carbon dioxide atmosphere meant severe famine for them, because cyanobacteria, like higher plants, use carbon dioxide as a raw material for the synthesis of organic substances. There are fewer bacterial mats. There are fragments left of the solid blue carpets that lined the seabed. The bacterial world did not die, but was greatly damaged, “holes” and “gaps” appeared in it. It was in these “gaps” and “holes” of the ancient world that the first organisms with a fundamentally different structure were born in that ancient era - more complex and perfect single-celled creatures that were destined to become the new masters of the planet.

Appearance of the cell nucleus

A bacterial cell is a complex living structure. But the cells of higher organisms - plants, animals, fungi and even the so-called protozoa (amoebas, ciliates) - are much more complex. A bacterial cell has neither a nucleus nor any other internal “organs” surrounded by a membrane. Therefore, bacteria are called “prokaryotes” (which means “pre-nuclear” in Greek). In higher organisms, the cell has a nucleus surrounded by a double membrane (hence the name “eukaryotes,” i.e., having a pronounced nucleus), as well as “ internal organs", the most important of which are mitochondria (a kind of energy stations). Mitochondria break down organic matter into carbon dioxide and water, using oxygen as an oxidizing agent. We breathe solely to provide oxygen to the mitochondria of our cells. In addition to mitochondria, the most important organs of a eukaryotic cell are plastids (chloroplasts), used for photosynthesis, which are found only in plants.

But the main thing in a eukaryotic cell is, of course, its nucleus. The nucleus stores hereditary information written in the four-letter language of the genetic code in DNA molecules. Bacteria, of course, also have DNA - a single ring-shaped molecule containing all the genes of a given species of bacteria. But bacterial DNA lies directly in the internal environment of the cell - in its cytoplasm, where active metabolism takes place. This means that the immediate environment of a precious molecule resembles a chemical plant or an alchemist’s laboratory, where hundreds of thousands of a wide variety of substances appear and disappear every second. Each of them can potentially affect hereditary information, as well as those molecular mechanisms that read this information and “bring it to life.” In such “unsanitary” conditions, it is not easy to create an effective and reliable “maintenance system” - storing, reading, reproducing and repairing DNA. It is even more difficult to create a molecular mechanism that could “meaningfully” (in accordance with the situation) control the operation of such a system.

This is precisely the great meaning of the isolation of the cell nucleus. The genes were reliably isolated from the cytoplasm with its seething chemistry. Now it was possible in a “calm environment” to establish an effective system for their regulation. And then it turned out that with the same set of genes, a cell can behave completely differently under different conditions.

As is well known, the same book can be read in different ways (especially if the book is good). Depending on preparation, mood and life situation, the reader will find one thing in the book for the first time, and after re-reading it a year later, something completely different. The same is true for the eukaryotic genome. Depending on the conditions, it is “read” differently, and the cells that develop as a result of this “reading” also turn out to be different. This is how the mechanism of non-hereditary adaptive variability appeared - an “invention” that greatly increased the stability and viability of organisms.

Without this system of gene regulation, multicellular animals and plants would never have appeared. After all, the whole essence of a multicellular organism is that genetically identical cells, depending on conditions, become different - they take on different functions, form different tissues and organs. Prokaryotes (bacteria) are fundamentally incapable of this.

How do bacteria adapt to changing conditions? They quickly mutate and exchange genes with each other. The vast majority of them die, but since there are a lot of bacteria, there is always a chance that one of the mutants will be viable in new conditions. The method is reliable, but monstrously wasteful. And most importantly - a dead end. With such a strategy, there is no reason to become more complex or improve. Bacteria are not capable of progress. That is why modern bacteria are almost no different from archean ones.

The oldest traces of the presence of eukaryotes are found in sedimentary rocks about 2.7 billion years old. This is exactly the time when the Earth's iron core formed. Apparently, the catastrophe that almost destroyed the bacterial world forced earthly life to seriously “think” about finding new, the best ways adaptation to a changing environment. Life cannot stand still; it is doomed to eternal improvement. So the appearance of the earth's core may have caused the appearance of the cellular nucleus.

Miracles of integration, or Can a team become a single organism?

At the beginning of the 20th century, scientists noticed that plastids and mitochondria are surprisingly reminiscent of bacteria in their structure. It took almost a century to collect facts and evidence, but now it can be considered firmly established that the eukaryotic cell arose as a result of the cohabitation (symbiosis) of several different bacterial cells.

In truth, everything was clear with plastids and mitochondria for a long time. These “organs” of the eukaryotic cell have their own circular DNA - exactly the same as that of bacteria. They reproduce independently inside the host cell, simply dividing in half, as is common among prokaryotes. They are never formed anew, “out of nothing.” By all indications, they are real bacteria. Moreover, we can even say exactly which ones: mitochondria resemble the so-called alpha-proteobacteria, and plastids resemble the cyanobacteria already familiar to us. These famous “inventors” of chlorophyll and photosynthesis never “shared” their “discovery” with anyone: to this day, having become an important internal part of plant cells, they keep under their “control” almost all photosynthesis on the planet (and therefore, and almost all production of organic matter and oxygen!).

But where did the host cell itself come from? What microbe was its “ancestor”? Among living bacteria, a candidate for this role could not be found for a long time. The fact is that the genes of eukaryotes, contained in the cell nucleus, differ sharply in their structure from the genes of most bacteria: they consist of many separate “sense” pieces, separated by long “nonsense” sections of DNA. To “read” such a gene, all its pieces need to be carefully “cut out” and “glued together.” Nothing like this is observed in ordinary bacteria.

To the surprise of scientists, the “eukaryotic” genome structure, as well as many other unique features of eukaryotes, were found in the strangest and most mysterious group of prokaryotic organisms - archaebacteria. These creatures are incredibly resilient: they can even live in boiling water from geothermal springs. For some archaebacteria, the optimal temperature for life lies in the range of +90–110°C, and at +80°C they already begin to freeze.

Most scientists now believe that the eukaryotic cell arose as a result of some archaebacterium (possibly adapted to life in acidic and hot water) acquired intracellular symbiont cohabitants from among ordinary bacteria.

The acquisition of intracellular cohabitants led to the presence of several different genomes in one cell. They had to be managed somehow. The creation of such a guiding center of the cell - the cell nucleus - has become a vital necessity. According to one hypothesis, the nuclear membrane could have arisen as a random result of the uncoordinated work of several groups of genes responsible for the formation of cell walls in newly united bacteria.

The various microbes that gave rise to the eukaryotic cell did not immediately merge into a single organism. At first they simply lived together in the same bacterial community, gradually adapting to each other and learning to benefit from such cohabitation. The oxygen released by cyanobacteria was toxic to them. In the course of evolution, they “invented” a lot different ways fight against this by-product of your life. One of these methods was... breathing. Recent studies have shown that the protein-enzyme complex responsible for oxygen respiration of mitochondria arose as a result of a slight change in photosynthetic enzymes. After all, from the point of view of chemistry, photosynthesis and oxygen respiration are one and the same chemical reaction, only going in opposite directions:

CO 2 + H 2 O + energy ↔ organic matter.

The third member of the community is archaebacteria. They could take excess organic matter from cyanobacteria, ferment it and thereby convert it into a form more “digestible” for respiring bacteria.

Similar microbial communities can still be found today. The life of bacteria in such communities proceeds surprisingly amicably and harmoniously. Microbes have even “learned” to exchange special chemical signals in order to better coordinate their actions. In addition, they actively exchange genes. By the way, it is precisely this ability that hinders the fight against infectious diseases: as soon as one bacteria, as a result of a random mutation, acquires a gene for resistance to a new antibiotic, very soon other types of bacteria can acquire this gene through exchange. All this makes the bacterial community look like a single organism.

Apparently, catastrophic events at the end of the Archean era forced microbial communities to go even further along the path of integration. Cells different types bacteria, which had long been “ground in” and adapted to each other, began to unite under a common shell. This was necessary for the most coherent, centralized regulation life processes in times of crisis.

The community has become an organism. Individuals merged together, giving up their independence in order to create a new individuality of a higher order.

Bricks

A favorite argument of opponents of the theory of evolution is the impossibility of creating a new complex structure (for example, a new gene) by enumerating random variants (mutations). Anti-evolutionists argue that it is just as likely that a tornado sweeping over a city dump can assemble a spaceship from garbage and debris. And they are absolutely right!

But large evolutionary transformations, apparently, do not occur at all by sorting through countless small, random mutations. Using the example of the origin of the eukaryotic cell - and this, as already noted, is the largest evolutionary event since the appearance of life - one can clearly see how Nature, creating something fundamentally new, complex, progressive, skillfully uses ready-made, tested “bricks”, assembling from them, like from a designer, a new organism. Apparently, this “block” principle of assembling new living systems permeates the entire biological evolution and largely determines its pace and features. Based on this principle (from large, pre-prepared and tested blocks), new genes, proteins, and new groups of organisms are built. (By the way, the genes of archaebacteria and eukaryotes were divided into separate pieces, most likely, precisely for this purpose: such blocks are very convenient to recombine.)

Science is steadily approaching a new vision of Nature. Gradually we begin to understand that all living things around us are not at all a random set of species and forms, but a complex and unified organism, developing according to its own immutable laws. Any living organism, any living cell, and we ourselves are bricks in the great “constructor” of Nature. And each of these bricks may turn out to be irreplaceable.

Based on an article for the magazine "Paradox"

In electron microscopy of ultrathin sections, the cytoplasmic membrane is a three-layer membrane (2 dark layers 2.5 nm thick are separated by a light intermediate layer). In structure, it is similar to the plasmalemma of animal cells and consists of a double layer of phospholipids with embedded surface and integral proteins, as if penetrating through the structure of the membrane. With excessive growth (compared to the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complex twisted membrane structures, called mesosomes. Less complexly twisted structures are called intracytoplasmic membranes.

Cytoplasm

The cytoplasm consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes, responsible for the synthesis (translation) of proteins. Bacterial ribosomes have a size of about 20 nm and a sedimentation coefficient of 70S, in contrast to the 80S ribosomes characteristic of eukaryotic cells. Ribosomal RNAs (rRNAs) are conserved elements of bacteria (the “molecular clock” of evolution). 16S rRNA is part of the small ribosomal subunit, and 23S rRNA is part of the large ribosomal subunit. The study of 16S rRNA is the basis of gene systematics, allowing one to assess the degree of relatedness of organisms.
The cytoplasm contains various inclusions in the form of glycogen granules, polysaccharides, beta-hydroxybutyric acid and polyphosphates (volutin). They are reserve substances for the nutrition and energy needs of bacteria. Volutin has an affinity for basic dyes and is easily detected using special staining methods (for example, Neisser) in the form of metachromatic granules. The characteristic arrangement of volutin granules is revealed in the diphtheria bacillus in the form of intensely stained cell poles.

Nucleoid

Nucleoid is the equivalent of a nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, closed in a ring and tightly packed like a ball. The nucleus of bacteria, unlike eukaryotes, does not have a nuclear envelope, nucleolus and basic proteins (histones). Typically, a bacterial cell contains one chromosome, represented by a DNA molecule closed in a ring.
In addition to the nucleoid, represented by one chromosome, the bacterial cell contains extrachromosomal factors of heredity - plasmids, which are covalently closed rings of DNA.

Capsule, microcapsule, mucus

The capsule is a mucous structure more than 0.2 microns thick, firmly associated with the bacterial cell wall and having clearly defined external boundaries. The capsule is visible in imprint smears from pathological material. In pure bacterial cultures, the capsule is formed less frequently. It is detected by special methods of staining a smear (for example, according to Burri-Gins), which create a negative contrast of the substances of the capsule: ink creates a dark background around the capsule. The capsule consists of polysaccharides (exopolysaccharides), sometimes of polypeptides, for example, in the anthrax bacillus it consists of polymers of D-glutamic acid. The capsule is hydrophilic and prevents phagocytosis of bacteria. The capsule is antigenic: antibodies against the capsule cause its enlargement (capsule swelling reaction).
Many bacteria form a microcapsule - a mucous formation less than 0.2 microns thick, detectable only by electron microscopy. It is necessary to distinguish from the capsule slie - mucoid exopolysaccharides that do not have clear boundaries. Mucus is soluble in water.
Bacterial exopolysaccharides are involved in adhesion (sticking to substrates); they are also called glycocalyx. Besides synthesis
exopolysaccharides by bacteria, there is another mechanism for their formation: through the action of extracellular enzymes of bacteria on disaccharides. As a result, dextrans and levans are formed.

Flagella

Bacterial flagella determine the motility of the bacterial cell. Flagella are thin filaments originating from the cytoplasmic membrane and are longer than the cell itself. The thickness of the flagella is 12-20 nm, length 3-15 µm. They consist of 3 parts: a spiral filament, a hook and a basal body containing a rod with special disks (1 pair of disks in gram-positive bacteria and 2 pairs of disks in gram-negative bacteria). Flagella are attached to the cytoplasmic membrane and cell wall by discs. This creates the effect of an electric motor with a motor rod that rotates the flagellum. Flagella consist of a protein - flagellin (from flagellum - flagellum); is an H antigen. Flagellin subunits are twisted in a spiral.
Number of flagella in bacteria various types varies from one (monotrich) in Vibrio cholerae to tens and hundreds of flagella extending along the perimeter of the bacterium (peritrich) in Escherichia coli, Proteus, etc. Lophotrichs have a bundle of flagella at one end of the cell. Amphitrichy has one flagellum or a bundle of flagella at opposite ends of the cell.

Drank

Pili (fimbriae, villi) are thread-like formations, thinner and shorter (3-10 nm x 0.3-10 µm) than flagella. Pili extend from the cell surface and consist of the protein pilin, which has antigenic activity. There are pili responsible for adhesion, that is, for attaching bacteria to the affected cell, as well as pili responsible for nutrition, water-salt metabolism and sexual (F-pili), or conjugation pili. Pili are numerous - several hundred per cell. However, there are usually 1-3 sex pili per cell: they are formed by so-called “male” donor cells containing transmissible plasmids (F-, R-, Col-plasmids). A distinctive feature of the sex pili is the interaction with special “male” spherical bacteriophages, which are intensively adsorbed on the sex pili.

Controversy

Spores are a peculiar form of resting firmicute bacteria, i.e. bacteria
with a gram-positive type of cell wall structure. Spores are formed under unfavorable conditions for the existence of bacteria (drying, nutrient deficiency, etc.. One spore (endospore) is formed inside the bacterial cell. The formation of spores contributes to the preservation of the species and is not method of reproduction like mushrooms. Spore-forming bacteria of the genus Bacillus have spores that do not exceed the diameter of the cell. Bacteria in which the size of the spore exceeds the diameter of the cell are called clostridia, for example, bacteria of the genus Clostridium (lat. Clostridium - spindle). The spores are acid-resistant, therefore they are stained red using the Aujeszky method or the Ziehl-Neelsen method, and the vegetative cell is stained blue.

The shape of the spores can be oval, spherical; location in the cell is terminal, i.e. at the end of the stick (in the causative agent of tetanus), subterminal - closer to the end of the stick (in the causative agents of botulinum, gas gangrene) and central (in the anthrax bacillus). The spore persists for a long time due to the presence of a multilayer shell, calcium dipicolinate, low water content and sluggish metabolic processes. Under favorable conditions, spores germinate, going through three successive stages: activation, initiation, germination.