Structure and chemical composition of bacterial
cells

The general structure of a bacterial cell is shown in Figure 2. The internal organization of a bacterial cell is complex. Each systematic group of microorganisms has its own specific structural features.
Cell wall. The bacterial cell is covered with a dense membrane. This surface layer, located outside the cytoplasmic membrane, is called the cell wall (Fig. 2, 14). The wall performs protective and supporting functions, and also gives the cell a permanent, characteristic shape (for example, the shape of a rod or coccus) and represents the external skeleton of the cell. This dense shell makes bacteria similar to plant cells, which distinguishes them from animal cells, which have soft shells.
Inside the bacterial cell, the osmotic pressure is several times, and sometimes tens of times, higher than in the external environment. Therefore, the cell would quickly rupture if it were not protected by such a dense, rigid structure as the cell wall.
The thickness of the cell wall is 0.01-0.04 microns. It makes up from 10 to 50% of the dry mass of bacteria. The amount of material that makes up the cell wall changes during bacterial growth and usually increases with age.
The main structural component of the walls, the basis of their rigid structure in almost all bacteria studied so far is murein (a glycopeptide

mucopeptide). This is an organic compound of a complex structure, which includes nitrogen-carrying sugars - amino sugars and 4-5 amino acids. Moreover, cell wall amino acids have an unusual shape (D-stereoisomers), which is rarely found in nature.

The constituent parts of the cell wall, its components, form a complex, strong structure (Fig. 3, 4 and 5).
Using a staining method first proposed in 1884 by Christian Gram, bacteria can be divided into two groups: gram-positive And
gram-negative. Gram-positive organisms are able to bind some aniline dyes, such as crystal violet, and after treatment with iodine and then alcohol (or acetone) retain the iodine-dye complex. The same bacteria in which this complex is destroyed under the influence of ethyl alcohol (the cells become discolored) are classified as gram-negative.
The chemical composition of the cell walls of gram-positive and gram-negative bacteria is different.
In gram-positive bacteria, the composition of the cell walls includes, in addition to mucopeptides, polysaccharides (complex, high-molecular sugars), teichoic acids
(compounds complex in composition and structure, consisting of sugars, alcohols, amino acids and phosphoric acid). Polysaccharides and teichoic acids are associated with the wall framework - murein. We do not yet know what structure these components of the cell wall of gram-positive bacteria form. Using electronic photographs of thin sections (layering), no gram-positive bacteria were detected in the walls.
Probably all these substances are very tightly interconnected.
The walls of gram-negative bacteria are more complex in chemical composition; they contain a significant amount of lipids (fats) associated with proteins and sugars into complex complexes - lipoproteins and lipopolysaccharides. There is generally less murein in the cell walls of gram-negative bacteria than in gram-positive bacteria.
The wall structure of gram-negative bacteria is also more complex. Using an electron microscope, it was found that the walls of these bacteria are multilayered (Fig.
6).

The inner layer consists of murein. Above this is a wider layer of loosely packed protein molecules. This layer is in turn covered with a layer of lipopolysaccharide. The topmost layer consists of lipoproteins.
The cell wall is permeable: through it, nutrients freely pass into the cell, and metabolic products exit into the environment. Large molecules with high molecular weight do not pass through the shell.
Capsule. The cell wall of many bacteria is surrounded on top by a layer of mucous material - a capsule (Fig. 7). The thickness of the capsule can be many times greater than the diameter of the cell itself, and sometimes it is so thin that it can only be seen through an electron microscope - a microcapsule.
The capsule is not an essential part of the cell; it is formed depending on the conditions in which the bacteria find themselves. It serves as a protective cover for the cell and participates in water metabolism, protecting the cell from drying out.
The chemical composition of capsules is most often polysaccharides.
Sometimes they consist of glycoproteins (complex complexes of sugars and proteins) and polypeptides (genus Bacillus), in rare cases - of fiber (genus Acetobacter).
Mucous substances secreted into the substrate by some bacteria cause, for example, the mucous-stringy consistency of spoiled milk and beer.
Cytoplasm. The entire contents of a cell, with the exception of the nucleus and cell wall, are called cytoplasm. The liquid, structureless phase of the cytoplasm (matrix) contains ribosomes, membrane systems, mitochondria, plastids and other structures, as well as reserve nutrients. The cytoplasm has an extremely complex, fine structure (layered, granular). With the help of an electron microscope, many interesting details of the cell structure have been revealed.

The outer lipoprotein layer of the bacterial protoplast, which has special physical and chemical properties, is called the cytoplasmic membrane (Fig.
2, 15).
Inside the cytoplasm are all vital structures and organelles.
The cytoplasmic membrane plays a very important role - it regulates the entry of substances into the cell and the release of metabolic products to the outside.
Through the membrane, nutrients can enter the cell as a result of an active biochemical process involving enzymes. In addition, the synthesis of some cell components occurs in the membrane, mainly components of the cell wall and capsule.
Finally, the most important enzymes (biological catalysts) are located in the cytoplasmic membrane. The ordered arrangement of enzymes on membranes makes it possible to regulate their activity and prevent the destruction of some enzymes by others. Associated with the membrane are ribosomes - structural particles on which protein is synthesized.
The membrane consists of lipoproteins. It is strong enough and can ensure the temporary existence of a cell without a shell. The cytoplasmic membrane makes up up to 20% of the dry mass of the cell.
In electronic photographs of thin sections of bacteria, the cytoplasmic membrane appears as a continuous strand about 75A thick, consisting of a light layer
(lipids) sandwiched between two darker ones (proteins). Each layer has a width
20-30A. Such a membrane is called elementary (Table 30, Fig. 8).

There is a connection between the plasma membrane and the cell wall in the form of desmoses
- bridges. The cytoplasmic membrane often gives rise to invaginations - invaginations into the cell. These invaginations form special membrane structures in the cytoplasm called
mesosomes. Some types of mesosomes are bodies separated from the cytoplasm by their own membrane. Numerous vesicles and tubules are packed inside these membrane sacs (Fig. 2). These structures perform a variety of functions in bacteria. Some of these structures are analogues of mitochondria. Others perform the functions of the endoplasmic reticulum or Golgi apparatus. By invagination of the cytoplasmic membrane, the photosynthetic apparatus of bacteria is also formed.
After invagination of the cytoplasm, the membrane continues to grow and forms stacks (Table 30), which, by analogy with plant chloroplast granules, are called thylakoid stacks. Pigments (bacteriochlorophyll, carotenoids) and enzymes are localized in these membranes, which often fill most of the cytoplasm of the bacterial cell.
(cytochromes) that carry out the process of photosynthesis.

,
The cytoplasm of bacteria contains ribosomes, protein-synthesizing particles with a diameter of 200A. There are more than a thousand of them in a cage. Ribosomes consist of RNA and protein. In bacteria, many ribosomes are freely located in the cytoplasm, some of them may be associated with membranes.
Ribosomes are centers of protein synthesis in the cell. At the same time, they often connect with each other, forming aggregates called polyribosomes or polysomes.

The cytoplasm of bacterial cells often contains granules of various shapes and sizes.
However, their presence cannot be considered as some kind of permanent sign of a microorganism; it is usually largely related to the physical and chemical conditions of the environment. Many cytoplasmic inclusions are composed of compounds that serve as a source of energy and carbon. These reserve substances are formed when the body is supplied with sufficient nutrients, and, conversely, are used when the body finds itself in conditions that are less favorable in terms of nutrition.
In many bacteria, granules consist of starch or other polysaccharides - glycogen and granulosa. Some bacteria, when grown in a sugar-rich medium, have droplets of fat inside the cell. Another widespread type of granular inclusions is volutin (metachromatin granules). These granules consist of polymetaphosphate (a reserve substance containing phosphoric acid residues).
Polymetaphosphate serves as a source of phosphate groups and energy for the body. Bacteria are more likely to accumulate volutin under unusual nutritional conditions, such as sulfur-free media. In the cytoplasm of some sulfur bacteria there are droplets of sulfur.
In addition to various structural components, the cytoplasm consists of a liquid part - the soluble fraction. It contains proteins, various enzymes, t-RNA, some pigments and low molecular weight compounds - sugars, amino acids.
As a result of the presence of low molecular weight compounds in the cytoplasm, a difference arises in the osmotic pressure of the cellular contents and the external environment, and this pressure may be different for different microorganisms. The highest osmotic pressure is observed in gram-positive bacteria - 30 atm; in gram-negative bacteria it is much lower - 4-8 atm.
Nuclear apparatus. The nuclear substance, deoxyribonucleic acid (DNA), is localized in the central part of the cell.

,
Bacteria do not have such a nucleus as higher organisms (eukaryotes), but have its analogue -
"nuclear equivalent" - nucleoid(see Fig. 2, 8), which is an evolutionarily more primitive form of organization of nuclear matter. Microorganisms that do not have a real nucleus, but have an analogue of it, are classified as prokaryotes. All bacteria are prokaryotes. In the cells of most bacteria, the bulk of DNA is concentrated in one or several places. In eukaryotic cells, DNA is located in a specific structure - the nucleus. The core is surrounded by a shell membrane.

In bacteria, DNA is packed less tightly, unlike true nuclei; A nucleoid does not have a membrane, a nucleolus, or a set of chromosomes. Bacterial DNA is not associated with the main proteins - histones - and is located in the nucleoid in the form of a bundle of fibrils.
Flagella. Some bacteria have appendage structures on the surface; The most widespread of them are flagella - the organs of movement of bacteria.
The flagellum is anchored under the cytoplasmic membrane using two pairs of discs.
Bacteria may have one, two, or many flagella. Their location is different: at one end of the cell, at two, over the entire surface, etc. (Fig. 9). Bacterial flagella have a diameter
0.01-0.03 microns, their length can be many times greater than the length of the cell. Bacterial flagella consist of a protein - flagellin - and are twisted helical filaments.

On the surface of some bacterial cells there are thin villi -
fimbriae.
Life of plants: in 6 volumes. - M.: Enlightenment. Edited by A. L. Takhtadzhyan, chief
editor member-corr. USSR Academy of Sciences, prof. A.A. Fedorov. 1974

• Structure and chemical composition of a bacterial cell

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CYTOPLASMA (CP)

Participate in spore formation.

MESOSOMA

With excessive growth, compared with the growth of the CS, the CPM forms intussusceptions (invaginations) - mesosomes. Mesosomes are the center of energy metabolism of a prokaryotic cell. Mesosomes are analogues of eukaryotic mitochondria, but are simpler in structure.

Well-developed and complexly organized mesosomes are characteristic of Gram+ bacteria.

Bacterial cell wall

In Gram bacteria, mesosomes are less common and are simply organized (loop-shaped). Polymorphism of mesosomes is observed even in the same species of bacteria. Rickettsia does not have mesosomes.

Mesosomes vary in size, shape and location in the cell.

Mesosomes are classified according to their shape:

– – lamellar (lamellar),

- - vesicular (shaped like bubbles),

– – tubular (tubular),

- - mixed.

Mesosomes are classified according to their location in the cell:

– – formed in the zone of cell division and formation of the transverse septum,

- - to which the nucleoid is attached;

– – formed as a result of intussusception of peripheral areas of the CPM.

Functions of mesosomes:

1. Strengthen the energy metabolism of cells, since they increase the total “working” surface of the membranes.

2. Participate in secretory processes(in some Gram+ bacteria).

3. Participate in cell division. During reproduction, the nucleoid moves to the mesosome, receives energy, doubles and divides by amitosis.

Identification of mesosomes:

1. Electron microscopy.

Structure. Cytoplasm (protoplasm) is the contents of the cell, surrounded by the cytoplasm and occupying the main volume of the bacterial cell. The CP is the internal environment of the cell and is a complex colloidal system consisting of water (about 75%) and various organic compounds (proteins, RNA and DNA, lipids, carbohydrates, minerals).

The layer of protoplasm located under the CPM is denser than the rest of the mass in the center of the cell. The fraction of the cytoplasm, which has a homogeneous consistency and contains a set of soluble RNA, enzyme proteins, products and substrates of metabolic reactions, is called cytosol. The other part of the cytoplasm is represented by various structural elements: nucleoid, plasmids, ribosomes and inclusions.

Functions of the cytoplasm:

1. Contains cellular organelles.

Detection of cytoplasm:

1. Electron microscopy.

Structure. Nucleoid - equivalent to the nucleus of eukaryotes, although it differs from it in its structure and chemical composition. The nucleoid is not separated from the CP by the nuclear membrane, does not have nucleoli and histones, contains one chromosome, has a haploid (single) set of genes, and is not capable of mitotic division.

The nucleoid is located in the center of the bacterial cell and contains a double-stranded DNA molecule, a small amount of RNA and proteins. In most bacteria, a double-stranded DNA molecule with a diameter of about 2 nm, a length of about 1 m with a molecular weight of 1–3x109 Da is closed in a ring and tightly packed like a ball. Mycoplasmas have the smallest DNA molecular weight for cellular organisms (0.4–0.8×109 Da).

The DNA of prokaryotes is built in the same way as that of eukaryotes (Fig. 25).

Rice. 25. Structure of prokaryotic DNA:

A- a fragment of a DNA strand formed by alternating deoxyribose and phosphoric acid residues. The first carbon atom of deoxyribose has a nitrogen base attached to it: 1 - cytosine; 2 - guanine.

B- DNA double helix: D- deoxyribose; F - phosphate; A - adenine; T - thymine; G - guanine; C - cytosine

The DNA molecule carries many negative charges because each phosphate residue contains an ionized hydroxyl group. In eukaryotes, negative charges are neutralized by the formation of a complex of DNA with the main proteins - histones. There are no histones in prokaryotic cells, so charges are neutralized by the interaction of DNA with polyamines and Mg2+ ions.

By analogy with eukaryotic chromosomes, bacterial DNA is often referred to as a chromosome. It is represented in the cell in the singular, since bacteria are haploid. However, before cell division, the number of nucleoids doubles, and during division it increases to 4 or more. Therefore, the terms “nucleoid” and “chromosome” are not always the same. When cells are exposed to certain factors (temperature, pH, ionizing radiation, heavy metal salts, some antibiotics, etc.), multiple copies of the chromosome are formed. When the influence of these factors is eliminated, as well as after the transition to the stationary phase, one copy of the chromosome is found in the cells.

For a long time it was believed that there was no pattern in the distribution of DNA strands on the bacterial chromosome. Special studies have shown that prokaryotic chromosomes are a highly ordered structure. Part of the DNA in this structure is represented by a system of 20–100 independently supercoiled loops. Supercoiled loops correspond to DNA regions that are currently inactive and are located in the center of the nucleoid. Along the periphery of the nucleoid there are despiralized areas where messenger RNA (mRNA) is synthesized. Since transcription and translation processes occur simultaneously in bacteria, the same mRNA molecule can be simultaneously associated with DNA and ribosomes.

In addition to the nucleoid, the cytoplasm of a bacterial cell may contain plasmids - factors of extrachromosomal heredity in the form of additional autonomous circular molecules of double-stranded DNA with a lower molecular weight. Plasmids also encode hereditary information, but it is not vital for the bacterial cell.

Nucleiod functions:

1. Storage and transmission of hereditary information, including the synthesis of pathogenicity factors.

Nucleoid detection:

1. Electron microscopy: in electron diffraction patterns of ultrathin sections, the nucleoid appears as light zones of lower optical density with fibrillar, thread-like DNA structures (Fig. 26). Despite the absence of a nuclear membrane, the nucleoid is quite clearly demarcated from the cytoplasm.

2. Phase contrast microscopy of native preparations.

3. Light microscopy after staining with DNA-specific methods according to Feulgen, according to Pashkov or according to Romanovsky-Giemsa:

– the drug is fixed with methyl alcohol;

– Romanovsky-Giemsa dye (a mixture of equal parts of three dyes - azure, eosin and methylene blue, dissolved in methanol) is poured onto the fixed preparation for 24 hours;

– the paint is drained, the preparation is washed with distilled water, dried and microscoped: the nucleoid is stained purple and is located diffusely in the cytoplasm, colored pale pink.

Read also:

Features of the chemical composition of bacterial cells

Structure of a bacterial cell. The main differences between prokaryotes and eukaryotes. Functions of individual structural elements of a bacterial cell. Features of the chemical composition of the cell walls of gram-positive and gram-negative bacteria.

A bacterial cell consists of a cell wall, a cytoplasmic membrane, cytoplasm with inclusions, and a nucleus called the nucleoid. There are additional structures: capsule, microcapsule, mucus, flagella, pili. Some bacteria are capable of forming spores under unfavorable conditions.
Differences in cell structure
1) Prokaryotes do not have a nucleus, but eukaryotes do.
2) Prokaryotes have only ribosomes (small, 70S) among their organelles, while eukaryotes, in addition to ribosomes (large, 80S), have many other organelles: mitochondria, EPS, cell center, etc.
3) A prokaryotic cell is much smaller than a eukaryotic cell: 10 times in diameter, 1000 times in volume.
1) Prokaryotes have circular DNA, and eukaryotes have linear DNA
2) In prokaryotes, DNA is naked, almost not connected to proteins, and in eukaryotes, DNA is connected to proteins in a 50/50 ratio, forming a chromosome
3) In prokaryotes, DNA lies in a special region of the cytoplasm called the nucleoid, and in eukaryotes, DNA lies in the nucleus.
Permanent components of a bacterial cell.
Nucleoid is the equivalent of a prokaryotic nucleus
The cell wall is different in Gr+ and Gr– bacteria. Determines and maintains a constant shape, provides communication with the external environment, determines the antigenic specificity of bacteria, and has important immunospecific properties; disruption of cell wall synthesis leads to the formation of L-forms of bacteria.
Gr+: this coloring is associated with the content of teichoic and dipoteichoic acids in the CS, which penetrate it through and fix it in the cytoplasm. Peptidoglycan is thick and consists of a plasma membrane bound by beta-glycosidic bonds.
Gr -: a thin layer of peptidoglycans, the outer membrane is represented by lipopolysaccharide glycocoproteins, glycolipids.
CPM - consists of lipoproteins. Perceives all chemical information entering the cell. Is the main barrier. Participates in the process of replication of nucleoid and plasmids; contains a large number of enzymes; Participates in the synthesis of cell wall components.
Mesosomes are analogues of mitochondria in a bacterial cell
70S ribosomes are numerous small granules located in the cytoplasm.
PERMANENT:
Flagella: consist of the protein flagellin, originate from the central nervous system, the main function is motor.
Pili: they are responsible for attachment to the host cell
Plasmids. Capsule, Spores, Inclusions.

Main article: Supramembrane complex

The supramembrane apparatus of bacteria is represented by a cell wall, the specific organization of which serves as the basis for dividing them into two non-taxonomic groups (gram-positive and gram-negative forms) and correlates with a very large number of morphofunctional, metabolic and genetic characteristics. The cell wall of prokaryotes is essentially a multifunctional organelle, extended beyond the protoplast and carrying a significant share of the metabolic load of the cell.

Cell wall of gram-positive bacteria

Cell wall structure

In gram-positive bacteria (Fig. 12, A), the cell wall has a generally simpler structure. The outer layers of the cell wall are formed by protein in complex with lipids. In some species of bacteria, a layer of surface protein globules, the shape, size and arrangement of which are species-specific, has been discovered relatively recently. Inside the cell wall, as well as directly on its surface, enzymes are placed that break down substrates into low molecular weight components, which are subsequently transported through the cytoplasmic membrane into the cell. Enzymes that synthesize extracellular polymers, such as capsular polysaccharides, are also located here.

Polysaccharide capsule

The polysaccharide capsule, which externally envelops the cell wall of a number of bacteria, has mainly an adaptive significance, and its presence is not necessary to preserve the vital activity of the cell. Thus, it ensures the attachment of cells to the surface of dense substrates, accumulates some minerals and, in pathogenic forms, prevents their phagocytosis.

Murein

Directly adjacent to the cytoplasmic membrane is a hard murein layer.

Murein, or peptidoglycan, is a copolymer of acetylglucosamine and acetylmuramic acid with oligopeptide cross-links. It is possible that the murein layer is one giant bag molecule that ensures the rigidity of the cell wall and its individual shape.

Teichoic acids

In close contact with the murein layer is the second polymer of the wall of gram-positive bacteria - teichoic acids. They are credited with the role of a cation accumulator and a regulator of ion exchange between the cell and the environment.

Cell wall of gram-negative bacteria

Cell wall structure

Compared to gram-positive forms, the cell wall of gram-negative bacteria is more complex and its physiological significance is incomparably broader. In addition to the murein layer, a second protein-lipid membrane is located closer to the surface (Fig. 12, B, C), which includes lipopolysaccharides. It is covalently linked to murein by crosslinking lipoprotein molecules. The main function of this membrane is the role of a molecular sieve; in addition, enzymes are located on its outer and inner surfaces.

3.Structure of a bacterial cell.

The space bounded by the outer and cytoplasmic membranes is called periplasmic and is a unique property of gram-negative bacteria. A whole set of enzymes are localized in its volume - phosphatases, hydrolases, nucleases, etc. They break down relatively high-molecular nutrient substrates, and also destroy their own cellular material released into the environment from the cytoplasm. To a certain extent, the periplasmic space can be likened to the lysosome of eukaryotes. In the periplasmic zone, it is possible not only for the most efficient occurrence of enzymatic reactions, but also for the isolation from the cytoplasm of compounds that pose a threat to its normal functioning. Material from the site http://wiki-med.com

Functions of the bacterial cell wall

In both gram-positive and gram-negative forms, the cell wall plays the role of a molecular sieve, selectively carrying out passive transport of ions, substrates and metabolites. In bacteria that have the ability to actively move due to flagella, the cell wall is a component of the locomotor mechanism. Finally, certain sections of the cell wall are closely associated with the cytoplasmic membrane in the zone of nucleoid attachment and play an important role in its replication and segregation.

In one species of bacteria, the process of destruction of the old cell wall, which occurs during cell division, is ensured by the work of at least four systems of hydrolytic enzymes present in the cell wall in a latent state. During cell division, a natural and strictly time-sequential activation of these systems occurs, leading to the gradual destruction and exfoliation of the old (“mother”) membrane of the bacterial cell.

Material from the site http://Wiki-Med.com

On this page there is material on the following topics:

• The main component of the cell wall of gram-positive bacteria is

• bacterial cell wall functions

• features of the structure of the bacterial cell wall

• cell wall structure

• characteristics of bacterial cell wall

The cell wall of gram-positive bacteria contains a small amount of polysaccharides, lipids, and proteins. The main component of the cell wall of these bacteria is multilayer peptidoglycan (murein, mucopeptide), accounting for 40-90% of the mass of the cell wall. Teichoic acids (from the Greek teichos - wall) are covalently bound to the peptidoglycan of the cell wall of gram-positive bacteria.
The cell wall of Gram-negative bacteria includes an outer membrane bound by a lipoprotein to an underlying layer of peptidoglycan. On ultrathin sections of bacteria, the outer membrane has the appearance of a wavy three-layer structure, similar to the inner membrane, which is called the cytoplasmic one. The main component of these membranes is a bimolecular (double) layer of lipids. The inner layer of the outer membrane is composed of phospholipids, and the outer layer contains lipopolysaccharide (LPS). The lipopolysaccharide of the outer membrane consists of three fragments: lipid A - a conservative structure, almost the same in gram-negative bacteria; core, or core, core part (lat. core - core), relatively conservative oligosaccharide structure (the most constant part of the LPS core is ketodeoxyoctonic acid); a highly variable O-specific polysaccharide chain formed by repeating identical oligosaccharide sequences (O-antigen). The matrix proteins of the outer membrane permeate it so that protein molecules called porins line hydrophilic pores through which water and small hydrophilic molecules pass.
When the synthesis of the bacterial cell wall is disrupted under the influence of lysozyme,
penicillin, protective factors of the body, cells with a modified (often spherical) shape are formed: protoplasts - bacteria completely devoid of a cell wall; spheroplasts are bacteria with a partially preserved cell wall. Bacteria of the sphero- or protoplast type, which have lost the ability to synthesize peptidoglycan under the influence of antibiotics or other factors and are able to reproduce, are called L-forms.
They are osmotically sensitive, spherical, flask-shaped cells of various sizes, including those passing through bacterial filters. Some L-forms (unstable), when the factor that led to changes in bacteria is removed, can reverse, “returning” to the original bacterial cell.
Between the outer and cytoplasmic membranes there is a periplasmic space, or periplasm, containing enzymes (proteases, lipases, phosphatases, nucleases, beta-lactomases) and components of transport systems.

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).

Cell wall

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 µm 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 mucoid exopolysaccharides, which 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 the form of a helix.
The number of flagella in bacteria of various species 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. Amphitrichus have 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 a method of reproduction, like fungi. Spore-forming bacteria of the genus Bacillus have spores, not exceeding 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). Spores are acid-resistant, therefore they are stained red using the Aujeszky method or the Ziehl-Neelsen method, and the vegetative cell. in 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.

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3. Features of the structure, properties and functions of cell membranes

Diversity of living cells

1.1 General plan of the structure of eukaryotic cells, which also characterizes the structure of an animal cell

A cell is a structural and functional unit of a living thing. All eukaryotic cells are characterized by the presence of the following structures: 1) The cell membrane is an organelle that limits the contents of the cell from the environment...

Diversity of living cells

1.2 Features of the structure of a plant cell

In plant cells there are organelles that are also characteristic of animals, for example, the nucleus, endoplasmic reticulum, ribosomes, mitochondria, Golgi apparatus (see Fig. 2). They lack a cell center, and the function of lysosomes is performed by vacuoles...

Diversity of living cells

1.3 Features of the structure of a mushroom cell

In most fungi, the cell structure and functions it performs are generally similar to plant cells. It consists of a hard shell and internal contents, which is the cytoplasmic system...

Diversity of living cells

1.4 General plan of the structure of prokaryotic cells, which also characterizes the structure of a bacterial cell

A prokaryotic cell is structured as follows. The main feature of these cells is the absence of a morphologically expressed nucleus, but there is a zone in which DNA is located (nucleoid).

Bacterial cell structure

Ribosomes are located in the cytoplasm...

Fundamentals of Microbiology

1. Describe the structure of a bacterial cell. Sketch the cell organelles

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Features of the visual and auditory sensory systems

13. Simple, complex and super complex cells and their functions

"Simple" and "complex" cells. Neurons that respond to simple linear stimuli (slits, edges, or dark stripes) are called “simple”, and those that respond to complex and moving stimuli are called “complex”...

Features of cell structure

1. The cell as an elementary structural unit of the body. Basic components of a cell

The cell is the basic structural and functional unit of life, bounded by a semipermeable membrane and capable of self-reproduction. In a plant cell, first of all, it is necessary to distinguish between the cell membrane and the contents...

Distribution and dynamics of the wild boar population in the Bryansk region

1.1 Structural features

The wild boar (Sus scrofa L.) is a massive animal with short, relatively thin legs. The body is relatively short, the front part is very massive, the back area of ​​the shoulder blades is strongly raised, the neck is thick, short, almost motionless...

Structure, properties and functions of proteins

2. Functions of cell organelles

Cell organelles and their functions: 1. Cell membrane - consists of 3 layers: 1. rigid cell wall; 2. a thin layer of pectin substances; 3. thin cytoplasmic filament. The cell membrane provides mechanical support and protection...

4.1 Structural features

The thallus is a plasmodium capable of amoeba-like movements on the surface or inside the substrate. During sexual reproduction, plasmodia transform into fruiting bodies called sporocarps...

Taxonomic group of slime molds

5.1 Structural features

The vegetative body is in the form of a multinucleate protoplast, incapable of independent movement and located inside the host plant cell. Special sporulation is not formed. The wintering stage is represented by spores...

Energy system of the cell. Classification of muscle tissue. Structure of sperm

Energy system of the cell. General plan of the structure of mitochondria and plastids, their functions. Hypothesis of the symbiotic origin of mitochondria and chloroplasts

Eukaryotic cells have a unique organelle, the mitochondrion, in which ATP molecules are formed through the process of oxidative phosphorylation. It is often said that mitochondria are the energy stations of the cell (Figure 1)...

Features of the structure of a bacterial cell. Main organelles and their functions

Differences between bacteria and other cells

1. Bacteria are prokaryotes, that is, they do not have a separate nucleus.

2. The cell wall of bacteria contains a special peptidoglycan - murein.

3. The bacterial cell lacks the Golgi apparatus, endoplasmic reticulum, and mitochondria.

4. The role of mitochondria is performed by mesosomes - invaginations of the cytoplasmic membrane.

5. There are many ribosomes in a bacterial cell.

6. Bacteria may have special organelles of movement - flagella.

7. The sizes of bacteria range from 0.3-0.5 to 5-10 microns.

Based on the shape of the cells, bacteria are divided into cocci, rods and convoluted.

In a bacterial cell there are:

1) main organelles:

a) nucleoid;

b) cytoplasm;

c) ribosomes;

d) cytoplasmic membrane;

e) cell wall;

2) additional organelles:

a) disputes;

b) capsules;

c) villi;

d) flagella.

Cytoplasm is a complex colloidal system consisting of water (75%), mineral compounds, proteins, RNA and DNA, which are part of the nucleoid organelles, ribosomes, mesosomes, and inclusions.

Nucleoid is a nuclear substance dispersed in the cytoplasm of the cell. It does not have a nuclear membrane or nucleoli. DNA, represented by a double-stranded helix, is localized in it. Usually closed in a ring and attached to the cytoplasmic membrane. Contains about 60 million base pairs. This is pure DNA and does not contain histone proteins. Their protective function is performed by methylated nitrogenous bases. The nucleoid encodes the basic genetic information, i.e., the genome of the cell.

Along with the nucleoid, the cytoplasm may contain autonomous circular DNA molecules with a lower molecular weight - plasmids. They also encode hereditary information, but it is not vital for the bacterial cell.

Ribosomes are ribonucleoprotein particles 20 nm in size, consisting of two subunits - 30 S and 50 S. Ribosomes are responsible for protein synthesis. Before protein synthesis begins, these subunits are combined into one - 70 S. Unlike eukaryotic cells, bacterial ribosomes are not united into the endoplasmic reticulum.

Mesosomes are derivatives of the cytoplasmic membrane. Mesosomes can be in the form of concentric membranes, vesicles, tubes, or in the form of a loop. Mesosomes are associated with the nucleoid. They are involved in cell division and sporulation.

Inclusions are metabolic products of microorganisms, which are located in their cytoplasm and are used as reserve nutrients. These include inclusions of glycogen, starch, sulfur, polyphosphate (volutin), etc.

Modern science has made fantastic progress over the past centuries. However, some mysteries still excite the minds of outstanding scientists.

Nowadays, the answer to the pressing question has not been found - how many varieties of bacteria exist on our huge planet?

Bacterium- an organism with a unique internal organization, which is characterized by all the processes characteristic of living organisms. The bacterial cell has many amazing features, one of which is its variety of shapes.

A bacterial cell can be spherical, rod-shaped, cubic or star-shaped. In addition, the bacteria are slightly bent or form a variety of curls.

Cell shape plays an important role in the proper functioning of a microorganism, as it can influence the ability of a bacterium to attach to other surfaces, obtain necessary substances, and move around.

The minimum cell size is usually 0.5 µm, but in exceptional cases the size of the bacterium can reach 5.0 µm.

The structure of the cell of any bacterium is strictly ordered. Its structure is significantly different from the structure of other cells, such as plants and animals. Cells of all types of bacteria do not have such elements as: a differentiated nucleus, intracellular membranes, mitochondria, lysosomes.

Bacteria have specific structural components - permanent and non-permanent.

The permanent components include: the cytoplasmic membrane (plasmolemma), cell wall, nucleoid, cytoplasm. Non-permanent structures are: capsule, flagella, plasmids, pili, villi, fimbriae, spores.

Cytoplasmic membrane

Any bacterium is surrounded by a cytoplasmic membrane (plasmolemma), which includes 3 layers. The membrane contains globulins, which are responsible for the selective transport of various substances into the cell.

The plasmalemma also performs the following important functions:

• mechanical– ensures the autonomous functioning of the bacterium and all structural elements;
• receptor– proteins located in the plasmalemma act as receptors, that is, they help the cell perceive various signals;
• energy– some proteins are responsible for the energy transfer function.

Disruption of the functioning of the plasmalemma leads to the fact that the bacterium is destroyed and dies.

Cell wall

A structural component unique to bacterial cells is the cell wall. This is a rigid, permeable membrane that acts as an important component of the structural skeleton of the cell. It is located on the outside of the cytoplasmic membrane.

The cell wall provides protection and also gives the cell a permanent shape. Its surface is covered with numerous spores, which allow necessary substances to enter and remove decay products from the microorganism.

Protecting internal components from osmotic and mechanical stress is another function of the wall. It plays an indispensable role in controlling cell division and the distribution of hereditary characteristics within it. It contains peptidoglycan, which is what gives the cell valuable immunobiological characteristics.

The thickness of the cell wall ranges from 0.01 to 0.04 µm. With age, bacteria grow and the amount of material from which it is built increases accordingly.

Nucleoid

Nucleoid is a prokaryote in which all the hereditary information of a bacterial cell is stored. The nucleoid is located in the central part of the bacterium. Its properties are equivalent to the core.

A nucleoid is one DNA molecule closed in a ring. The length of the molecule is 1 mm, and the volume of information is about 1000 features.

The nucleoid is the main carrier of material about the properties of the bacterium and the main factor in the transmission of these properties to the offspring. The nucleoid in bacterial cells does not have a nucleolus, membrane or basic proteins.

Cytoplasm

Cytoplasm– an aqueous solution containing the following components: mineral compounds, nutrients, proteins, carbohydrates and lipids. The ratio of these substances depends on the age and type of bacteria.

The cytoplasm contains various structural components: ribosomes, granules and mesosomes.

• Ribosomes are responsible for protein synthesis. Their chemical composition includes RNA molecules and protein.
• Mesosomes are involved in the formation of spores and cell reproduction. They can take the form of a bubble, loop, or tube.
• The granules serve as an additional energy resource for bacterial cells. These elements come in a variety of forms. They contain polysaccharides, starch, and droplets of fat.

Capsule

Capsule is a mucous structure tightly bound to the cell wall. Examining it under a light microscope, you can see that the capsule envelops the cell and its outer boundaries have a clearly defined contour. In a bacterial cell, the capsule serves as a protective barrier against phages (viruses).

Bacteria form a capsule when environmental conditions become aggressive. The capsule includes mainly polysaccharides, and in certain cases it may contain fiber, glycoproteins, and polypeptides.

Main functions of the capsule:

• • adhesion to cells in the human body. For example, streptococci adhere to tooth enamel and, in alliance with other microbes, provoke the appearance of caries;
  • protection from negative environmental conditions: toxic substances, mechanical damage, increased oxygen levels;
  • participation in water metabolism (protecting the cell from drying out);
  • creation of an additional osmotic barrier.

The capsule forms 2 layers:

• internal – part of the cytoplasm layer;
• external - the result of the excretory function of the bacterium.

The classification is based on the structural features of the capsules. They are:

• normal;
• complex capsules;
• with striated fibrils;
• intermittent capsules.

Some bacteria also form a microcapsule, which is a mucous formation. A microcapsule can only be identified under an electron microscope, since the thickness of this element is only 0.2 microns or even less.

Flagella

Most bacteria have cell surface structures that ensure its motility and movement - flagella. These are long processes in the shape of a left-handed spiral, built from flagellin (a contractile protein).

The main function of flagella is that they allow bacteria to move through a liquid environment in search of more favorable conditions. The number of flagella in one cell can vary: from one to several flagella, flagella on the entire surface of the cell or only on one of its poles.

There are several types of bacteria depending on the number of flagella they contain:

• Monotrichs- they have only one flagellum.
• Lophotrichs– have a certain number of flagella at one end of the bacterium.
• Amphitrichy– characterized by the presence of flagella at polar opposite poles.
• Peritrichous– flagella are located over the entire surface of the bacterium; they are characterized by slow and smooth movement.
• Atriches– flagella are absent.

Flagella perform motor activity by performing rotational movements. If bacteria do not have flagella, they are still able to move, or rather slide, using mucus on the surface of the cell.

Plasmids

Plasmids are small, mobile DNA molecules that are separate from chromosomal factors of heredity. These components usually contain genetic material that makes the bacteria more resistant to antibiotics.

They can transfer their properties from one microorganism to another. Despite all their features, plasmids do not act as important elements for the life of a bacterial cell.

Pili, villi, fimbriae

These structures are localized on the surfaces of bacteria. There are from two units to several thousand per cell. Both the bacterial motile cell and the immobile one have these structural elements, since they do not have any effect on the ability to move.

In quantitative terms, pili reach several hundred per bacterium. There are pili that are responsible for nutrition, water-salt metabolism, as well as conjugative (sexual) pili.

The villi are characterized by a hollow cylindrical shape. It is through these structures that viruses penetrate the bacterium.

Villi are not considered essential components of bacteria, since the process of division and growth can be successfully completed without them.

Fimbriae are located, as a rule, at one end of the cell. These structures allow the microorganism to fixate in the tissues of the body. Some fimbriae have special proteins that contact the receptor ends of cells.

Fimbriae differ from flagella in that they are thicker and shorter, and also do not implement the function of movement.

Controversy

Spores are formed in the event of negative physical or chemical manipulation of the bacterium (as a result of drying out or lack of nutrients). They vary in spore size, since they can be completely different in different cells. The shape of the spores also differs - they are oval or spherical.

Based on their location in the cell, spores are divided into:

• central - their position in the very center, such as in the anthrax bacillus;
• subterminal - located at the end of the stick, giving the shape of a club (for the causative agent of gas gangrene).

In a favorable environment, the spore life cycle includes the following stages:

• preparatory stage;
• activation stage;
• initiation stage;
• germination stage.

The spores are distinguished by their special vitality, which is achieved thanks to their shell. It is multilayered and consists mainly of protein. The increased immunity of spores to negative conditions and external influences is ensured precisely thanks to proteins.

Structure of a bacterial cell

The cytoplasm of most bacteria is surrounded by membranes: a cell wall, a cytoplasmic membrane and a capsular (mucous) layer. These structures take part in metabolism; food products enter through the cell membranes and metabolic products are removed. They protect the cell from the action of harmful environmental factors and largely determine the surface properties of the cell (surface tension, electrical charge, osmotic state, etc.). These structures in a living bacterial cell are in constant functional interaction.

Cell wall. A bacterial cell is separated from the external environment by a cell wall. Its thickness is 10-20 nm, its mass reaches 20-50% of the cell mass. This is a complex multifunctional system that determines the constancy of the cell’s shape, its surface charge, anatomical integrity, the ability to adsorb phages, participation in immune reactions, contact with the external environment and protection from adverse external influences. The cell wall has elasticity and sufficient strength and can withstand intracellular pressure of 1-2 MPa.

The main components of the cell wall are peptidoglycans(glycopeptides, mucopeptides, mureins, glycosaminopeptides), which are found only in prokaryotes. A specific heteropolymer of peptidoglycan consists of alternating residues of N-acetylglucosamine and N-acetylmuramic acid, interconnected through β-1-4-glycosidic bonds, diaminopimelic acid (DAP), D-glutamic acid, L- and D-alanine in the ratio 1:1:1:1:2. The glycosidic and peptide bonds that link peptidoglycan subunits together give them a molecular network or sac structure. The murein network of the prokaryotic cell wall also includes teichoic acids, polypeptides, lipopolysaccharides, lipoproteins, etc. The cell wall has rigidity; it is this property that determines the shape of the bacterial wall. The cell wall has tiny pores through which metabolic products are transported.

Gram stain. Most bacteria are divided into two groups depending on their chemical composition. This property was first noticed in 1884 by the Danish physicist H. Gram. The essence is that when staining bacteria with gentian violet (crystal violet, methyl violet, etc.), in some bacteria the paint with iodine forms a compound that is retained by the cells when they are treated with alcohol. Such bacteria are colored blue-violet and are called gram-positive (Gr +). Discolored bacteria are gram-negative (Gr -), they are stained with contrasting paint (magenta). Gram staining is diagnostic, but only for prokaryotes that have a cell wall.

In structure and chemical composition, gram-positive bacteria differ significantly from gram-negative ones. In gram-positive bacteria, the cell wall is thicker, homogeneous, amorphous, and contains a lot of murein, which is associated with teichoic acids. In gram-negative bacteria, the cell wall is thinner, layered, contains little murein (5-10%), and there are no teichoic acids.

Table 1.1 Chemical composition of Gr+ and Gr- bacteria

The bacterial organism is represented by one single cell. The forms of bacteria are varied. The structure of bacteria differs from the structure of animal and plant cells.

The cell lacks a nucleus, mitochondria and plastids. The carrier of hereditary information DNA is located in the center of the cell in a folded form. Microorganisms that do not have a true nucleus are classified as prokaryotes. All bacteria are prokaryotes.

It is estimated that there are over a million species of these amazing organisms on earth. To date, about 10 thousand species have been described.

A bacterial cell has a wall, a cytoplasmic membrane, cytoplasm with inclusions and a nucleotide. Of the additional structures, some cells have flagella, pili (a mechanism for adhesion and retention on the surface) and a capsule. Under unfavorable conditions, some bacterial cells are capable of forming spores. The average size of bacteria is 0.5-5 microns.

External structure of bacteria

Rice. 1. The structure of a bacterial cell.

Cell wall

• The cell wall of a bacterial cell is its protection and support. It gives the microorganism its own specific shape.
• The cell wall is permeable. Nutrients pass inward and metabolic products pass through it.
• Some types of bacteria produce special mucus that resembles a capsule that protects them from drying out.
• Some cells have flagella (one or more) or villi that help them move.
• Bacterial cells that appear pink when stained with Gram stain ( gram-negative), the cell wall is thinner and multilayered. Enzymes that help break down nutrients are released.
• Bacteria that appear violet on Gram staining ( gram-positive), the cell wall is thick. Nutrients that enter the cell are broken down in the periplasmic space (the space between the cell wall and the cytoplasmic membrane) by hydrolytic enzymes.
• There are numerous receptors on the surface of the cell wall. Cell killers - phages, colicins and chemical compounds - are attached to them.
• Wall lipoproteins in some types of bacteria are antigens called toxins.
• With long-term treatment with antibiotics and for a number of other reasons, some cells lose their membranes, but retain the ability to reproduce. They acquire a rounded shape - L-shape and can persist in the human body for a long time (cocci or tuberculosis bacilli). Unstable L-forms have the ability to return to their original form (reversion).

Rice. 2. The photo shows the structure of the bacterial wall of gram-negative bacteria (left) and gram-positive bacteria (right).

Capsule

Under unfavorable environmental conditions, bacteria form a capsule. The microcapsule adheres tightly to the wall. It can only be seen in an electron microscope. The macrocapsule is often formed by pathogenic microbes (pneumococci). In Klebsiella pneumoniae, the macrocapsule is always found.

Rice. 3. In the photo is pneumococcus. Arrows indicate the capsule (electronogram of an ultrathin section).

Capsule-like shell

The capsule-like shell is a formation loosely associated with the cell wall. Thanks to bacterial enzymes, the capsule-like shell is covered with carbohydrates (exopolysaccharides) from the external environment, which ensures the adhesion of bacteria to different surfaces, even completely smooth ones.

For example, streptococci, when entering the human body, are able to stick to teeth and heart valves.

The functions of the capsule are varied:

• protection from aggressive environmental conditions,
• ensuring adhesion (sticking) to human cells,
• Possessing antigenic properties, the capsule has a toxic effect when introduced into a living organism.

Rice. 4. Streptococci are capable of sticking to tooth enamel and, together with other microbes, cause caries.

Rice. 5. The photo shows damage to the mitral valve due to rheumatism. The cause is streptococci.

Flagella

• Some bacterial cells have flagella (one or more) or villi that help them move. The flagella contain the contractile protein flagellin.
• The number of flagella can be different - one, a bundle of flagella, flagella at different ends of the cell or over the entire surface.
• Movement (random or rotational) is carried out as a result of the rotational movement of the flagella.
• The antigenic properties of flagella have a toxic effect in disease.
• Bacteria that do not have flagella, when covered with mucus, are able to glide. Aquatic bacteria contain 40-60 vacuoles filled with nitrogen.

They provide diving and ascent. In the soil, the bacterial cell moves through soil channels.

Rice. 6. Scheme of attachment and operation of the flagellum.

Rice. 7. The photo shows different types of flagellated microbes.

Rice. 8. The photo shows different types of flagellated microbes.

Drank

• Pili (villi, fimbriae) cover the surface of bacterial cells. The villus is a helically twisted thin hollow thread of protein nature.
• General type drank provide adhesion (sticking) to host cells. Their number is huge and ranges from several hundred to several thousand. From the moment of attachment, any .
• Sex drank facilitate the transfer of genetic material from the donor to the recipient. Their number is from 1 to 4 per cell.

Rice. 9. The photo shows E. coli. Flagella and pili are visible. The photo was taken using a tunneling microscope (STM).

Rice. 10. The photo shows numerous pili (fimbriae) of cocci.

Rice. 11. The photo shows a bacterial cell with fimbriae.

Cytoplasmic membrane

• The cytoplasmic membrane is located under the cell wall and is a lipoprotein (up to 30% lipids and up to 70% proteins).
• Different bacterial cells have different membrane lipid compositions.
• Membrane proteins perform many functions. Functional proteins are enzymes due to which the synthesis of its various components, etc. occurs on the cytoplasmic membrane.
• The cytoplasmic membrane consists of 3 layers. The phospholipid double layer is permeated with globulins, which ensure the transport of substances into the bacterial cell. If its function is disrupted, the cell dies.
• The cytoplasmic membrane takes part in sporulation.

Rice. 12. The photo clearly shows a thin cell wall (CW), a cytoplasmic membrane (CPM) and a nucleotide in the center (the bacterium Neisseria catarrhalis).

Internal structure of bacteria

Rice. 13. The photo shows the structure of a bacterial cell. The structure of a bacterial cell differs from the structure of animal and plant cells - the cell lacks a nucleus, mitochondria and plastids.

Cytoplasm

The cytoplasm is 75% water, the remaining 25% is mineral compounds, proteins, RNA and DNA. The cytoplasm is always dense and motionless. It contains enzymes, some pigments, sugars, amino acids, a supply of nutrients, ribosomes, mesosomes, granules and all sorts of other inclusions. In the center of the cell, a substance is concentrated that carries hereditary information - the nucleoid.

Granules

The granules are made up of compounds that are a source of energy and carbon.

Mesosomes

Mesosomes are cell derivatives. They have different shapes - concentric membranes, vesicles, tubes, loops, etc. Mesosomes have a connection with the nucleoid. Participation in cell division and sporulation is their main purpose.

Nucleoid

A nucleoid is an analogue of a nucleus. It is located in the center of the cell. It contains DNA, the carrier of hereditary information in a folded form. Unwound DNA reaches a length of 1 mm. The nuclear substance of a bacterial cell does not have a membrane, a nucleolus or a set of chromosomes, and does not divide by mitosis. Before dividing, the nucleotide is doubled. During division, the number of nucleotides increases to 4.

Rice. 14. The photo shows a section of a bacterial cell. A nucleotide is visible in the central part.

Plasmids

Plasmids are autonomous molecules coiled into a ring of double-stranded DNA. Their mass is significantly less than the mass of a nucleotide. Despite the fact that hereditary information is encoded in the DNA of plasmids, they are not vital and necessary for the bacterial cell.

Rice. 15. The photo shows a bacterial plasmid. The photo was taken using an electron microscope.

Ribosomes

Ribosomes of a bacterial cell are involved in the synthesis of protein from amino acids. The ribosomes of bacterial cells are not united into the endoplasmic reticulum, like those of cells with a nucleus. It is ribosomes that often become the “target” for many antibacterial drugs.

Inclusions

Inclusions are metabolic products of nuclear and non-nuclear cells. They represent a supply of nutrients: glycogen, starch, sulfur, polyphosphate (valutin), etc. Inclusions often, when painted, take on a different appearance than the color of the dye. You can diagnose by currency.

Shapes of bacteria

The shape of a bacterial cell and its size are of great importance in their identification (recognition). The most common shapes are spherical, rod-shaped and convoluted.

Table 1. Main forms of bacteria.

Globular bacteria

The spherical bacteria are called cocci (from the Greek coccus - grain). They are arranged one by one, two by two (diplococci), in packets, in chains, and like bunches of grapes. This location depends on the method of cell division. The most harmful microbes are staphylococci and streptococci.

Rice. 16. In the photo there are micrococci. The bacteria are round, smooth, and white, yellow and red in color. In nature, micrococci are ubiquitous. They live in different cavities of the human body.

Rice. 17. The photo shows diplococcus bacteria - Streptococcus pneumoniae.

Rice. 18. The photo shows Sarcina bacteria. Coccoid bacteria cluster together in packets.

Rice. 19. The photo shows the bacteria streptococci (from the Greek “streptos” - chain).

Arranged in chains. They are causative agents of a number of diseases.

Rice. 20. In the photo, the bacteria are “golden” staphylococci. Arranged like “bunches of grapes”. The clusters are golden in color. They are causative agents of a number of diseases.

Rod-shaped bacteria

Rod-shaped bacteria that form spores are called bacilli. They have a cylindrical shape. The most prominent representative of this group is the bacillus. The bacilli include plague and hemophilus influenzae. The ends of rod-shaped bacteria may be pointed, rounded, chopped off, flared, or split. The shape of the sticks themselves can be regular or irregular. They can be arranged one at a time, two at a time, or form chains. Some bacilli are called coccobacilli because they have a round shape. But, nevertheless, their length exceeds their width.

Diplobacillus are double rods. Anthrax bacilli form long threads (chains).

The formation of spores changes the shape of the bacilli. In the center of the bacilli, spores form in butyric acid bacteria, giving them the appearance of a spindle. In tetanus bacilli - at the ends of the bacilli, giving them the appearance of drumsticks.

Rice. 21. The photo shows a rod-shaped bacterial cell. Multiple flagella are visible. The photo was taken using an electron microscope. Negative.

Rice. 24. In butyric acid bacilli, spores are formed in the center, giving them the appearance of a spindle. In tetanus sticks - at the ends, giving them the appearance of drumsticks.

Twisted bacteria

No more than one whorl has a cell bend. Several (two, three or more) are campylobacters. Spirochetes have a peculiar appearance, which is reflected in their name - “spira” - bend and “hate” - mane. Leptospira (“leptos” - narrow and “spera” - gyrus) are long filaments with closely spaced curls. Bacteria resemble a twisted spiral.

Rice. 27. In the photo, a spiral-shaped bacterial cell is the causative agent of “rat bite disease.”

Rice. 28. In the photo, Leptospira bacteria are the causative agents of many diseases.

Rice. 29. In the photo, Leptospira bacteria are the causative agents of many diseases.

Club-shaped

Corynebacteria, the causative agents of diphtheria and listeriosis, have a club-shaped form. This shape of the bacterium is given by the arrangement of metachromatic grains at its poles.

Rice. 30. The photo shows corynebacteria.

Read more about bacteria in the articles:

Bacteria have lived on planet Earth for more than 3.5 billion years. During this time they learned a lot and adapted to a lot. The total mass of bacteria is enormous. It is about 500 billion tons. Bacteria have mastered almost all known biochemical processes. The forms of bacteria are varied. The structure of bacteria has become quite complex over millions of years, but even today they are considered the most simply structured single-celled organisms.