Do bacteria have cytoplasm? The Earth's core and the cell nucleus - what do they have in common? Bacterial cell shapes

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.

The cytoplasm of any 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 – not of great importance for operation; 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.

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).

%D0%92%D1%8B%D1%81%D0%BE%D0%BA%D0%B0%D1%8F%20%D1%81%D0%BA%D0%BE%D1%80%D0%BE %D1%81%D1%82%D1%8C%20%D1%80%D0%B0%D0%B7%D0%BC%D0%BD%D0%BE%D0%B6%D0%B5%D0%BD %D0%B8%D1%8F%20(%D0%B7%D0%B0%20%D1%81%D1%83%D1%82%D0%BA%D0%B8%20%D0%BF%D1% 80%D0%BE%D0%B8%D1%81%D1%85%D0%BE%D0%B4%D0%B8%D1%82%20%D1%81%D0%BC%D0%B5%D0% BD%D0%B0%20%D0%B4%D0%B5%D1%81%D1%8F%D1%82%D0%BA%D0%BE%D0%B2%20%D0%BF%D0%BE% D0%BA%D0%BE%D0%BB%D0%B5%D0%BD%D0%B8%D0%B9)%20%D0%BF%D0%BE%D0%B7%D0%B2%D0%BE %D0%BB%D1%8F%D0%B5%D1%82%20%D0%B8%D0%B7%D1%83%D1%87%D0%B0%D1%82%D1%8C%20%D0 %B8%20%D0%B2%D1%8B%D1%8F%D0%B2%D0%BB%D1%8F%D1%82%D1%8C%20%D0%BC%D1%83%D1%82 %D0%B0%D1%86%D0%B8%D0%BE%D0%BD%D0%BD%D1%8B%D0%B5%20%D0%BF%D1%80%D0%BE%D1%86 %D0%B5%D1%81%D1%81%D1%8B%20%D0%B8%20%D0%B8%D0%B7%D0%BC%D0%B5%D0%BD%D0%B5%D0 %BD%D0%B8%D1%8F%20%D0%B2%20%D0%B2%D0%B8%D0%B4%D0%B0%D1%85.

%D0%91%D0%B0%D0%BA%D1%82%D0%B5%D1%80%D0%B8%D0%B8%20%D0%BD%D0%B5%20%D0%B8%D0 %BC%D0%B5%D1%8E%D1%82%20%D0%BF%D1%80%D0%BE%D0%B8%D0%B7%D0%B2%D0%BE%D0%B4%D0 %BD%D0%BE%D0%B9%20%D1%85%D1%80%D0%BE%D0%BC%D0%BE%D1%81%D0%BE%D0%BC%20%E2%94 %80%20%D1%8F%D0%B4%D1%80%D1%8B%D1%88%D0%B5%D0%BA,%20%D0%BA%D0%BE%D1%82%D0% BE%D1%80%D1%8B%D0%B5%20%D0%B5%D1%81%D1%82%D1%8C%20%D1%83%20%D0%B6%D0%B8%D0% B2%D0%BE%D1%82%D0%BD%D1%8B%D1%85,%20%D1%80%D0%B0%D1%81%D1%82%D0%B5%D0%BD%D0 %B8%D0%B9,%20%D0%BF%D1%80%D0%BE%D1%81%D1%82%D0%B5%D0%B9%D1%88%D0%B8%D1%85% 20%D0%B8%20%D0%B3%D1%80%D0%B8%D0%B1%D0%BE%D0%B2.%20%D0%92%20%D0%BD%D0%B8%D1 %85%20%D0%BE%D0%B1%D1%80%D0%B0%D0%B7%D1%83%D1%8E%D1%82%D1%81%D1%8F%20%D1%80 %D0%B8%D0%B1%D0%BE%D1%81%D0%BE%D0%BC%D1%8B%20%D0%B8%20%D0%A0%D0%9D%D0%9A.% 20%D0%A7%D0%B8%D1%81%D0%BB%D0%BE%20%D1%8F%D0%B4%D1%80%D1%8B%D1%88%D0%B5%D0% BA%20%D0%B7%D0%B0%D0%B2%D0%B8%D1%81%D0%B8%D1%82%20%D0%BE%D1%82%20%D0%B1%D0% B0%D0%BB%D0%B0%D0%BD%D1%81%D0%B0%20%D0%B3%D0%B5%D0%BD%D0%BE%D0%B2.

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.

%D0%9A%D0%BB%D0%B5%D1%82%D0%BE%D1%87%D0%BD%D1%8B%D0%B9%20%D0%BE%D1%80%D0%B3 %D0%B0%D0%BD%D0%BE%D0%B8%D0%B4,%20%D0%BA%D0%BE%D1%82%D0%BE%D1%80%D1%8B%D0% B9%20%D1%81%D0%BE%D0%B4%D0%B5%D1%80%D0%B6%D0%B8%D1%82%20%D1%84%D0%B5%D1%80% D0%BC%D0%B5%D0%BD%D1%82%D1%8B,%20%D1%81%D0%BF%D0%BE%D1%81%D0%BE%D0%B1%D1%81 %D1%82%D0%B2%D1%83%D1%8E%D1%89%D0%B8%D0%B5%20%D1%80%D0%B0%D1%81%D1%89%D0%B5 %D0%BF%D0%BB%D0%B5%D0%BD%D0%B8%D1%8E%20%D0%B1%D0%B5%D0%BB%D0%BA%D0%BE%D0%B2 ,%20%D0%BF%D0%BE%D0%BB%D0%B8%D1%81%D0%B0%D1%85%D0%B0%D1%80%D0%B8%D0%B4%D0% BE%D0%B2%20%D0%B8%20%D0%BD%D1%83%D0%BA%D0%BB%D0%B5%D0%B8%D0%BD%D0%BE%D0%B2% D1%8B%D1%85%20%D0%BA%D0%B8%D1%81%D0%BB%D0%BE%D1%82.%20%D0%9E%D1%81%D0%BD%D0 %BE%D0%B2%D0%BD%D0%B0%D1%8F%20%D0%B8%D1%85%20%D1%84%D1%83%D0%BD%D0%BA%D1%86 %D0%B8%D1%8F%20%D0%B7%D0%B0%D0%BA%D0%BB%D1%8E%D1%87%D0%B0%D0%B5%D1%82%D1%81 %D1%8F%20%D0%B2%20%D1%82%D0%BE%D0%BC,%20%D1%87%D1%82%D0%BE%20%D0%BE%D0%BD% D0%B8%20%D1%83%D1%87%D0%B0%D1%81%D1%82%D0%B2%D1%83%D1%8E%D1%82%20%D0%B2%D0% BE%20%D0%B2%D0%BD%D1%83%D1%82%D1%80%D0%B8%D0%BA%D0%BB%D0%B5%D1%82%D0%BE%D1% 87%D0%BD%D0%BE%D0%BC%20%D1%80%D0%B0%D1%81%D1%89%D0%B5%D0%BF%D0%BB%D0%B5%D0% BD%D0%B8%D0%B8.

%D0%AD%D1%82%D0%B8%D1%85%20%D0%BE%D1%80%D0%B3%D0%B0%D0%BD%D0%BE%D0%B8%D0%B4 %D0%BE%D0%B2%20%D0%BD%D0%B5%D1%82%20%D1%83%20%D0%B6%D0%B8%D0%B2%D0%BE%D1%82 %D0%BD%D1%8B%D1%85,%20%D0%B0%20%D0%B8%D1%85%20%D0%BD%D0%B0%D0%BB%D0%B8%D1% 87%D0%B8%D0%B5%20%D1%83%20%D1%80%D0%B0%D1%81%D1%82%D0%B5%D0%BD%D0%B8%D0%B9% 20%D0%BE%D0%B1%D1%83%D1%81%D0%BB%D0%B0%D0%B2%D0%BB%D0%B8%D0%B2%D0%B0%D0%B5% D1%82%20%D0%B8%D1%85%20%D0%BE%D0%BA%D1%80%D0%B0%D1%81%D0%BA%D1%83.%20%D0%9E %D1%81%D0%BD%D0%BE%D0%B2%D0%BD%D0%BE%D0%B5%20%D0%B8%D1%85%20%D0%BF%D1%80%D0 %B5%D0%B4%D0%BD%D0%B0%D0%B7%D0%BD%D0%B0%D1%87%D0%B5%D0%BD%D0%B8%D0%B5%20%E2 %80%93%20%D1%83%D1%87%D0%B0%D1%81%D1%82%D0%B8%D0%B5%20%D0%B2%20%D0%BF%D1%80 %D0%BE%D1%86%D0%B5%D1%81%D1%81%D0%B0%D1%85%20%D1%84%D0%BE%D1%82%D0%BE%D1%81 %D0%B8%D0%BD%D1%82%D0%B5%D0%B7%D0%B0.

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

%D0%AD%D1%82%D0%BE%D1%82%20%D0%BF%D1%80%D0%BE%D1%86%D0%B5%D1%81%D1%81%20%D0 %BD%D0%B0%D0%B7%D1%8B%D0%B2%D0%B0%D0%B5%D1%82%D1%81%D1%8F%20%D1%86%D0%B8%D0 %BA%D0%BB%D0%BE%D0%B7%D0%BE%D0%BC.%20%D0%9E%D0%BD%20%D0%BF%D1%80%D0%B8%D1% 81%D1%83%D1%89%20%D0%B2%D1%81%D0%B5%D0%BC%20%D1%8D%D1%83%D0%BA%D0%B0%D1%80% D0%B8%D0%BE%D1%82%D0%B0%D0%BC.%20%D0%94%D0%B2%D0%B8%D0%B6%D0%B5%D0%BD%D0%B8 %D0%B5%20%D1%86%D0%B8%D1%82%D0%BE%D0%BF%D0%BB%D0%B0%D0%B7%D0%BC%D1%8B%20%D0 %BD%D0%B5%D0%BE%D0%B1%D1%85%D0%BE%D0%B4%D0%B8%D0%BC%D0%BE%20%D0%B4%D0%BB%D1 %8F%20%D1%82%D0%B0%D0%BA%D0%B8%D1%85%20%D0%BF%D1%80%D0%BE%D1%86%D0%B5%D1%81 %D1%81%D0%BE%D0%B2,%20%D0%BA%D0%B0%D0%BA:

%0A
• %D0%BF%D0%BE%D0%BB%D1%83%D1%87%D0%B5%D0%BD%D0%B8%D0%B5%20%D0%BF%D0%B8%D1%82 %D0%B0%D1%82%D0%B5%D0%BB%D1%8C%D0%BD%D1%8B%D1%85%20%D0%B2%D0%B5%D1%89%D0%B5 %D1%81%D1%82%D0%B2;
%0A
• %D0%BC%D0%B5%D1%82%D0%B0%D0%B1%D0%BE%D0%BB%D0%B8%D0%B7%D0%BC;
%0A
• %D0%BF%D0%B5%D1%80%D0%B5%D0%B4%D0%B0%D1%87%D0%B0%20%D0%B3%D0%B5%D0%BD%D0%B5 %D1%82%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D0%B8%D1%85%20%D0%B4%D0%B0%D0%BD%D0%BD %D1%8B%D1%85;
%0A
• %D1%80%D0%B0%D0%B2%D0%BD%D0%BE%D0%BC%D0%B5%D1%80%D0%BD%D0%BE%D0%B5%20%D1%80 %D0%B0%D1%81%D0%BF%D1%80%D0%B5%D0%B4%D0%B5%D0%BB%D0%B5%D0%BD%D0%B8%D0%B5%20 %D0%BF%D0%B8%D1%82%D0%B0%D1%82%D0%B5%D0%BB%D1%8C%D0%BD%D1%8B%D1%85%20%D0%B2 %D0%B5%D1%89%D0%B5%D1%81%D1%82%D0%B2.
%0A

%0A

%D0%A6%D0%B8%D0%BA%D0%BB%D0%BE%D0%B7%20%D0%BC%D0%BE%D0%B6%D0%B5%D1%82%20%D0 %B1%D1%8B%D1%82%D1%8C%20%D0%BF%D0%BE%D1%81%D1%82%D0%BE%D1%8F%D0%BD%D0%BD%D1 %8B%D0%BC,%20%D1%81%D0%BF%D0%BE%D0%BD%D1%82%D0%B0%D0%BD%D0%BD%D1%8B%D0%BC% 20%D0%BB%D0%B8%D0%B1%D0%BE%20%D1%81%D0%BF%D1%80%D0%BE%D0%B2%D0%BE%D1%86%D0% B8%D1%80%D0%BE%D0%B2%D0%B0%D0%BD%D0%BD%D1%8B%D0%BC%20%D0%B2%D0%BD%D0%B5%D1% 88%D0%BD%D0%B8%D0%BC%D0%B8%20%D1%84%D0%B0%D0%BA%D1%82%D0%BE%D1%80%D0%B0%D0% BC%D0%B8%20(%D1%82%D0%B5%D0%BC%D0%BF%D0%B5%D1%80%D0%B0%D1%82%D1%83%D1%80%D0 %BE%D0%B9,%20%D1%83%D1%80%D0%BE%D0%B2%D0%BD%D0%B5%D0%BC%20%D0%BE%D1%81%D0% B2%D0%B5%D1%89%D0%B5%D0%BD%D0%B8%D1%8F,%20%D0%BC%D0%B5%D1%85%D0%B0%D0%BD%D0 %B8%D1%87%D0%B5%D1%81%D0%BA%D0%B8%D0%BC%20%D0%B8%D0%BB%D0%B8%20%D1%85%D0%B8 %D0%BC%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D0%B8%D0%BC%20%D0%B2%D0%BE%D0%B7%D0%B4 %D0%B5%D0%B9%D1%81%D1%82%D0%B2%D0%B8%D0%B5%D0%BC).%20%D0%A3%20%D0%B1%D0%B0 %D0%BA%D1%82%D0%B5%D1%80%D0%B8%D0%B9%20%D1%82%D0%B0%D0%BA%D0%BE%D0%B5%20%D0 %BF%D0%BE%D0%BD%D1%8F%D1%82%D0%B8%D0%B5,%20%D0%BA%D0%B0%D0%BA%20%D0%B4%D0% B2%D0%B8%D0%B6%D0%B5%D0%BD%D0%B8%D0%B5%20%D1%86%D0%B8%D1%82%D0%BE%D0%BF%D0% BB%D0%B0%D0%B7%D0%BC%D1%8B,%20%D0%BF%D0%BE%D0%BB%D0%BD%D0%BE%D1%81%D1%82%D1 %8C%D1%8E%20%D0%BE%D1%82%D1%81%D1%83%D1%82%D1%81%D1%82%D0%B2%D1%83%D0%B5%D1 %82.

%D0%91%D0%B0%D0%BA%D1%82%D0%B5%D1%80%D0%B8%D0%B8%20%E2%80%93%20%D1%83%D0%BD %D0%B8%D0%BA%D0%B0%D0%BB%D1%8C%D0%BD%D1%8B%D0%B5%20%D0%BC%D0%B8%D0%BA%D1%80 %D0%BE%D0%BE%D1%80%D0%B3%D0%B0%D0%BD%D0%B8%D0%B7%D0%BC%D1%8B,%20%D1%81%D0% BF%D0%BE%D1%81%D0%BE%D0%B1%D0%BD%D1%8B%D0%B5%20%D1%81%D1%83%D1%89%D0%B5%D1% 81%D1%82%D0%B2%D0%BE%D0%B2%D0%B0%D1%82%D1%8C%20%D0%BA%D0%B0%D0%BA%20%D0%BF% D1%80%D0%B8%20%D0%BD%D0%B0%D0%BB%D0%B8%D1%87%D0%B8%D0%B8%20%D0%BA%D0%B8%D1% 81%D0%BB%D0%BE%D1%80%D0%BE%D0%B4%D0%B0,%20%D1%82%D0%B0%D0%BA%20%D0%B8%20%D0 %B1%D0%B5%D0%B7%20%D0%BD%D0%B5%D0%B3%D0%BE.%20%D0%9C%D0%BD%D0%BE%D0%B3%D0% B8%D0%BC%20%D0%B8%D0%B7%20%D0%BD%D0%B8%D1%85,%20%D1%82%D0%B0%D0%BA%20%D0%B6 %D0%B5%20%D0%BA%D0%B0%D0%BA%20%D1%80%D0%B0%D1%81%D1%82%D0%B5%D0%BD%D0%B8%D1 %8F%D0%BC%20%D0%B8%20%D0%B6%D0%B8%D0%B2%D0%BE%D1%82%D0%BD%D1%8B%D0%BC,%20% D0%B4%D0%BB%D1%8F%20%D0%BC%D0%B5%D1%82%D0%B0%D0%B1%D0%BE%D0%BB%D0%B8%D1%87% D0%B5%D1%81%D0%BA%D0%B8%D1%85%20%D0%BF%D1%80%D0%BE%D1%86%D0%B5%D1%81%D1%81% D0%BE%D0%B2%20%D0%BD%D0%B5%D0%BE%D0%B1%D1%85%D0%BE%D0%B4%D0%B8%D0%BC%20%D0% BA%D0%B8%D1%81%D0%BB%D0%BE%D1%80%D0%BE%D0%B4.%20%D0%A0%D0%B0%D0%B7%D0%BD%D0 %B8%D1%86%D0%B0%20%D0%B2%20%D1%82%D0%BE%D0%BC,%20%D1%87%D1%82%D0%BE%20%D1% 83%20%D1%8D%D1%83%D0%BA%D0%B0%D1%80%D0%B8%D0%BE%D1%82%D0%BE%D0%B2%20%D0%B4% D1%8B%D1%85%D0%B0%D0%BD%D0%B8%D0%B5%20%D0%BF%D1%80%D0%BE%D0%B8%D1%81%D1%85% D0%BE%D0%B4%D0%B8%D1%82%20%D0%B2%20%D0%BC%D0%B8%D1%82%D0%BE%D1%85%D0%BE%D0% BD%D0%B4%D1%80%D0%B8%D1%8F%D1%85,%20%D0%B0%20%D1%83%20%D0%B1%D0%B0%D0%BA%D1 %82%D0%B5%D1%80%D0%B8%D0%B9%20%D0%B7%D0%B0%D0%B4%D0%B5%D0%B9%D1%81%D1%82%D0 %B2%D0%BE%D0%B2%D0%B0%D0%BD%D1%8B%20%D0%BC%D0%B5%D0%B7%D0%BE%D1%81%D0%BE%D0 %BC%D1%8B.%20%D0%A3%20%D1%86%D0%B8%D0%B0%D0%BD%D0%BE%D0%B1%D0%B0%D0%BA%D1% 82%D0%B5%D1%80%D0%B8%D0%B9%20%D0%B4%D1%8B%D1%85%D0%B0%D0%BD%D0%B8%D0%B5%20% D0%BF%D1%80%D0%BE%D0%B8%D1%81%D1%85%D0%BE%D0%B4%D0%B8%D1%82%20%D0%B2%20%D1% 86%D0%B8%D1%82%D0%BE%D0%BF%D0%BB%D0%B0%D0%B7%D0%BC%D0%B0%D1%82%D0%B8%D1%87% D0%B5%D1%81%D0%BA%D0%B8%D1%85%20%D0%BC%D0%B5%D0%BC%D0%B1%D1%80%D0%B0%D0%BD% D0%B0%D1%85.

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

%D0%A0%D0%B0%D1%81%D1%82%D0%B5%D0%BD%D0%B8%D1%8F%20%D0%B8%20%D0%B3%D1%80%D0 %B8%D0%B1%D1%8B%20%D1%81%D0%BF%D0%BE%D1%81%D0%BE%D0%B1%D0%BD%D1%8B%20%D0%BE %D0%B1%D1%80%D0%B0%D0%B7%D0%BE%D0%B2%D1%8B%D0%B2%D0%B0%D1%82%D1%8C%20%D1%81 %D0%BF%D0%BE%D1%80%D1%8B%20%D0%BA%D0%B0%D0%BA%20%D0%BE%D0%B4%D0%B8%D0%BD%20 %D0%B8%D0%B7%20%D1%81%D0%BF%D0%BE%D1%81%D0%BE%D0%B1%D0%BE%D0%B2%20%D1%80%D0 %B0%D0%B7%D0%BC%D0%BD%D0%BE%D0%B6%D0%B5%D0%BD%D0%B8%D1%8F.%20%D0%91%D0%B0% D0%BA%D1%82%D0%B5%D1%80%D0%B8%D0%B8%20%D0%B6%D0%B5%20%D0%BE%D0%B1%D1%80%D0% B0%D0%B7%D1%83%D1%8E%D1%82%20%D1%81%D0%BF%D0%BE%D1%80%D1%8B,%20%D0%BA%D0%BE %D0%B3%D0%B4%D0%B0%20%D0%B2%D0%BE%D0%B7%D0%BD%D0%B8%D0%BA%D0%B0%D1%8E%D1%82 %20%D0%BD%D0%B5%D0%B1%D0%BB%D0%B0%D0%B3%D0%BE%D0%BF%D1%80%D0%B8%D1%8F%D1%82 %D0%BD%D1%8B%D0%B5%20%D1%83%D1%81%D0%BB%D0%BE%D0%B2%D0%B8%D1%8F%20%D0%B4%D0 %BB%D1%8F%20%D0%B8%D1%85%20%D0%B6%D0%B8%D0%B7%D0%BD%D0%B8%20%D0%B8%20%D1%80 %D0%B0%D0%B7%D0%B2%D0%B8%D1%82%D0%B8%D1%8F.%20%D0%AD%D1%82%D0%B0%20%D0%BE% D1%81%D0%BE%D0%B1%D0%B5%D0%BD%D0%BD%D0%BE%D1%81%D1%82%D1%8C%20%D1%81%D0%B2% D0%BE%D0%B9%D1%81%D1%82%D0%B2%D0%B5%D0%BD%D0%BD%D0%B0%20%D0%BD%D0%B5%20%D0% B2%D1%81%D0%B5%D0%BC%20%D0%B2%D0%B8%D0%B4%D0%B0%D0%BC.%20%D0%92%20%D1%81%D0 %BE%D1%81%D1%82%D0%BE%D1%8F%D0%BD%D0%B8%D0%B8%20%D1%81%D0%BF%D0%BE%D1%80%20 %D0%BC%D0%B8%D0%BA%D1%80%D0%BE%D0%BE%D1%80%D0%B3%D0%B0%D0%BD%D0%B8%D0%B7%D0 %BC%D1%8B%20%D1%81%D0%BF%D0%BE%D1%81%D0%BE%D0%B1%D0%BD%D1%8B%20%D0%BD%D0%B0 %D1%85%D0%BE%D0%B4%D0%B8%D1%82%D1%8C%D1%81%D1%8F%20%D0%B4%D0%BE%D0%BB%D0%B3 %D0%BE%D0%B5%20%D0%B2%D1%80%D0%B5%D0%BC%D1%8F,%20%D0%B2%D1%8B%D0%B4%D0%B5% D1%80%D0%B6%D0%B8%D0%B2%D0%B0%D1%8F%20%D0%BA%D0%B8%D0%BF%D1%8F%D1%87%D0%B5% D0%BD%D0%B8%D0%B5,%20%D0%B7%D0%B0%D0%BC%D0%BE%D1%80%D0%BE%D0%B7%D0%BA%D1%83 %20%D0%B8%20%D0%B4%D1%80%D1%83%D0%B3%D0%B8%D0%B5%20%D0%BD%D0%B5%D0%B3%D0%B0 %D1%82%D0%B8%D0%B2%D0%BD%D1%8B%D0%B5%20%D0%B2%D0%BE%D0%B7%D0%B4%D0%B5%D0%B9 %D1%81%D1%82%D0%B2%D0%B8%D1%8F.

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.

%D0%9A%D0%BB%D0%B5%D1%82%D0%BA%D0%B8%20%D1%8D%D1%83%D0%BA%D0%B0%D1%80%D0%B8 %D0%BE%D1%82%D0%BE%D0%B2,%20%D0%B8%D0%BC%D0%B5%D1%8F%20%D0%B1%D0%BE%D0%BB% D0%B5%D0%B5%20%D1%81%D0%BB%D0%BE%D0%B6%D0%BD%D1%83%D1%8E%20%D0%BE%D1%80%D0% B3%D0%B0%D0%BD%D0%B8%D0%B7%D0%B0%D1%86%D0%B8%D1%8E,%20%D1%81%D0%BF%D0%BE%D1 %81%D0%BE%D0%B1%D0%BD%D1%8B%20%D1%80%D0%B0%D0%B7%D0%BC%D0%BD%D0%BE%D0%B6%D0 %B0%D1%82%D1%8C%D1%81%D1%8F%20%D1%82%D1%80%D0%B5%D0%BC%D1%8F%20%D1%81%D0%BF %D0%BE%D1%81%D0%BE%D0%B1%D0%B0%D0%BC%D0%B8:

%D0%9F%D1%80%D0%BE%D1%81%D1%82%D0%BE%D1%82%D0%B0%20%D1%81%D1%82%D1%80%D0%BE %D0%B5%D0%BD%D0%B8%D1%8F%20%D0%BA%D0%BB%D0%B5%D1%82%D0%BA%D0%B8%20%D0%B1%D0 %B0%D0%BA%D1%82%D0%B5%D1%80%D0%B8%D0%B9%20%D0%BF%D0%BE%D0%B7%D0%B2%D0%BE%D0 %BB%D0%B8%D0%BB%D0%B0%20%D0%B8%D0%BC%20%D0%B1%D1%8B%D1%82%D1%8C%20%D0%BF%D0 %B5%D1%80%D0%B2%D0%BE%D0%BE%D1%82%D0%BA%D1%80%D1%8B%D0%B2%D0%B0%D1%82%D0%B5 %D0%BB%D1%8F%D0%BC%D0%B8%20%D0%BD%D0%B0%20%D0%BD%D0%B0%D1%88%D0%B5%D0%B9%20 %D0%BF%D0%BB%D0%B0%D0%BD%D0%B5%D1%82%D0%B5.%20%D0%98%D1%85%20%D1%81%D0%BF% D0%BE%D1%81%D0%BE%D0%B1%D0%BD%D0%BE%D1%81%D1%82%D1%8C%20%D1%81%D1%83%D1%89% D0%B5%D1%81%D1%82%D0%B2%D0%BE%D0%B2%D0%B0%D1%82%D1%8C%20%D0%B2%20%D0%BB%D1% 8E%D0%B1%D1%8B%D1%85%20%D1%83%D1%81%D0%BB%D0%BE%D0%B2%D0%B8%D1%8F%D1%85%20% D0%B8%20%D0%B2%20%D0%BB%D1%8E%D0%B1%D1%8B%D1%85%20%D1%81%D1%80%D0%B5%D0%B4% D0%B0%D1%85%20%D1%83%D0%BA%D0%B0%D0%B7%D1%8B%D0%B2%D0%B0%D0%B5%D1%82%20%D0% BD%D0%B0%20%D1%82%D0%BE,%20%D1%87%D1%82%D0%BE%20%D0%BE%D0%BD%D0%B8%20%D1%81 %D0%BF%D0%BE%D1%81%D0%BE%D0%B1%D0%BD%D1%8B%20%D0%B2%D1%8B%D0%B6%D0%B8%D1%82 %D1%8C%20%D1%82%D0%B0%D0%BC,%20%D0%B3%D0%B4%D0%B5%20%D0%B4%D0%BB%D1%8F%20% D0%B4%D1%80%D1%83%D0%B3%D0%B8%D1%85%20%D0%BE%D1%80%D0%B3%D0%B0%D0%BD%D0%B8% D0%B7%D0%BC%D0%BE%D0%B2%20%D0%B6%D0%B8%D0%B7%D0%BD%D1%8C%20%D0%B1%D1%83%D0% B4%D0%B5%D1%82%20%D0%BD%D0%B5%D0%B2%D0%BE%D0%B7%D0%BC%D0%BE%D0%B6%D0%BD%D0% B0.

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.

Driver's license of a foreign citizen in Russia: validity, use, exchange The main document of any driver is the license. In Russia, a driver's license (VU) is a standard document in the form of [...]

Increase in pension in August: permanent or one-time Today, when the ruble exchange rate is falling more and more, and food prices in Russia, unfortunately, are not inclined to decrease, any assistance from the state can become a significant help in […]

Psychological problems of minor parents Today, the psychological problems of minor parents are developing more and more. According to statistics, young minor parents abandon their child […]

How to register an application to the prosecutor's office PROSECUTOR GENERAL OFFICE OF THE RUSSIAN FEDERATION ORDER dated December 27, 2007 N 212 ON THE PROCEDURE FOR RECORDING AND CONSIDERATION IN THE PROSECUTOR'S OFFICE OF THE RUSSIAN FEDERATION REPORTS ABOUT […]

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 Gram stained ( 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 the bacterial cell and its size have great importance during 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 streptococcus bacteria (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.

Bacteria are the oldest group of organisms currently existing on Earth. The first bacteria probably appeared more than 3.5 billion years ago and for almost a billion years they were the only living creatures on our planet. Since these were the first representatives of living nature, their body had a primitive structure.

Over time, their structure became more complex, but to this day bacteria are considered the most primitive single-celled organisms. It is interesting that some bacteria still retain the primitive features of their ancient ancestors. This is observed in bacteria living in hot sulfur springs and anoxic mud at the bottom of reservoirs.

Most bacteria are colorless. Only a few are purple or green. But the colonies of many bacteria have a bright color, which is caused by the release of a colored substance into the environment or pigmentation of cells.

The discoverer of the world of bacteria was Antony Leeuwenhoek, a Dutch naturalist of the 17th century, who first created a perfect magnifying microscope that magnifies objects 160-270 times.

Bacteria are classified as prokaryotes and are classified into a separate kingdom - Bacteria.

Body Shape

Bacteria are numerous and diverse organisms. They vary in shape.

Name of the bacterium	Bacteria shape	Bacteria image
Cocci		Ball-shaped
Bacillus		Rod-shaped
Vibrio		Comma-shaped
Spirillum		Spiral
Streptococci		Chain of cocci
Staphylococcus		Clusters of cocci
Diplococcus		Two round bacteria enclosed in one mucous capsule

Methods of transportation

Among bacteria there are mobile and immobile forms. Motiles move due to wave-like contractions or with the help of flagella (twisted helical threads), which consist of a special protein called flagellin. There may be one or more flagella. In some bacteria they are located at one end of the cell, in others - at two or over the entire surface.

But movement is also inherent in many other bacteria that lack flagella. Thus, bacteria covered on the outside with mucus are capable of gliding movement.

Some aquatic and soil bacteria lacking flagella have gas vacuoles in the cytoplasm. There may be 40-60 vacuoles in a cell. Each of them is filled with gas (presumably nitrogen). By regulating the amount of gas in the vacuoles, aquatic bacteria can sink into the water column or rise to its surface, and soil bacteria can move in the soil capillaries.

Habitat

Due to their simplicity of organization and unpretentiousness, bacteria are widespread in nature. Bacteria are found everywhere: in a drop of even the purest spring water, in grains of soil, in the air, on rocks, in polar snow, desert sands, on the ocean floor, in oil extracted from great depths, and even in the water of hot springs with a temperature of about 80ºC. They live on plants, fruits, various animals and in the human intestines, oral cavity, on the limbs, on the surface of the body.

Bacteria are the smallest and most numerous living creatures. Due to their small size, they easily penetrate into any cracks, crevices, or pores. Very hardy and adapted to various living conditions. They tolerate drying, extreme cold, and heating up to 90ºC without losing their viability.

There is practically no place on Earth where bacteria are not found, but in varying quantities. The living conditions of bacteria are varied. Some of them require atmospheric oxygen, others do not need it and are able to live in an oxygen-free environment.

In the air: bacteria rise to the upper atmosphere up to 30 km. and more.

There are especially many of them in the soil. 1 g of soil can contain hundreds of millions of bacteria.

In water: in the surface layers of water in open reservoirs. Beneficial aquatic bacteria mineralize organic residues.

In living organisms: pathogenic bacteria enter the body from the external environment, but only under favorable conditions cause diseases. Symbiotic live in the digestive organs, helping to break down and absorb food, and synthesize vitamins.

External structure

The bacterial cell is covered with a special dense shell - a cell wall, which performs protective and supporting functions, and also gives the bacterium a permanent, characteristic shape. The cell wall of a bacterium resembles the wall of a plant cell. It is permeable: through it, nutrients freely pass into the cell, and metabolic products exit into the environment. Often, bacteria produce an additional protective layer of mucus on top of the cell wall - a capsule. The thickness of the capsule can be many times greater than the diameter of the cell itself, but it can also be very small. The capsule is not an essential part of the cell; it is formed depending on the conditions in which the bacteria find themselves. It protects the bacteria from drying out.

On the surface of some bacteria there are long flagella (one, two or many) or short thin villi. The length of the flagella can be many times greater than the size of the body of the bacterium. Bacteria move with the help of flagella and villi.

Internal structure

Inside the bacterial cell there is dense, immobile cytoplasm. It has a layered structure, there are no vacuoles, therefore various proteins (enzymes) and reserve nutrients are located in the substance of the cytoplasm itself. Bacterial cells do not have a nucleus. A substance carrying hereditary information is concentrated in the central part of their cell. Bacteria, - nucleic acid - DNA. But this substance is not formed into a nucleus.

The internal organization of a bacterial cell is complex and has its own specific characteristics. The cytoplasm is separated from the cell wall by the cytoplasmic membrane. In the cytoplasm there is a main substance, or matrix, ribosomes and a small number of membrane structures that perform a variety of functions (analogues of mitochondria, endoplasmic reticulum, Golgi apparatus). The cytoplasm of bacterial cells often contains granules of various shapes and sizes. The granules may be composed of compounds that serve as a source of energy and carbon. Droplets of fat are also found in the bacterial cell.

In the central part of the cell, the nuclear substance is localized - DNA, which is not delimited from the cytoplasm by a membrane. This is an analogue of the nucleus - a nucleoid. The nucleoid does not have a membrane, a nucleolus, or a set of chromosomes.

Eating methods

Bacteria have different feeding methods. Among them there are autotrophs and heterotrophs. Autotrophs are organisms that are capable of independently producing organic substances for their nutrition.

Plants need nitrogen, but cannot absorb nitrogen from the air themselves. Some bacteria combine nitrogen molecules in the air with other molecules, resulting in substances that are available to plants.

These bacteria settle in the cells of young roots, which leads to the formation of thickenings on the roots, called nodules. Such nodules form on the roots of plants of the legume family and some other plants.

The roots provide carbohydrates to the bacteria, and the bacteria to the roots provide nitrogen-containing substances that can be absorbed by the plant. Their cohabitation is mutually beneficial.

Plant roots secrete a lot of organic substances (sugars, amino acids and others) that bacteria feed on. Therefore, especially many bacteria settle in the soil layer surrounding the roots. These bacteria convert dead plant debris into plant-available substances. This layer of soil is called the rhizosphere.

There are several hypotheses about the penetration of nodule bacteria into root tissue:

• through damage to epidermal and cortex tissue;
• through root hairs;
• only through the young cell membrane;
• thanks to companion bacteria producing pectinolytic enzymes;
• due to stimulation of the synthesis of B-indoleacetic acid from tryptophan, always present in plant root secretions.

The process of introduction of nodule bacteria into root tissue consists of two phases:

• infection of root hairs;
• process of nodule formation.

In most cases, the invading cell actively multiplies, forms so-called infection threads and, in the form of such threads, moves into the plant tissue. Nodule bacteria emerging from the infection thread continue to multiply in the host tissue.

Plant cells filled with rapidly multiplying cells of nodule bacteria begin to rapidly divide. The connection of a young nodule with the root of a legume plant is carried out thanks to vascular-fibrous bundles. During the period of functioning, the nodules are usually dense. By the time optimal activity occurs, the nodules acquire a pink color (thanks to the leghemoglobin pigment). Only those bacteria that contain leghemoglobin are capable of fixing nitrogen.

Nodule bacteria create tens and hundreds of kilograms of nitrogen fertilizer per hectare of soil.

Metabolism

Bacteria differ from each other in their metabolism. In some it occurs with the participation of oxygen, in others - without it.

Most bacteria feed on ready-made organic substances. Only a few of them (blue-green, or cyanobacteria) are capable of creating organic substances from inorganic ones. They played an important role in the accumulation of oxygen in the Earth's atmosphere.

Bacteria absorb substances from the outside, tear their molecules into pieces, assemble their shell from these parts and replenish their contents (this is how they grow), and throw unnecessary molecules out. The shell and membrane of the bacterium allows it to absorb only the necessary substances.

If the shell and membrane of a bacterium were completely impermeable, no substances would enter the cell. If they were permeable to all substances, the contents of the cell would mix with the medium - the solution in which the bacterium lives. To survive, bacteria need a shell that allows necessary substances to pass through, but not unnecessary substances.

The bacterium absorbs nutrients located near it. What happens next? If it can move independently (by moving a flagellum or pushing mucus back), then it moves until it finds the necessary substances.

If it cannot move, then it waits until diffusion (the ability of molecules of one substance to penetrate into the thicket of molecules of another substance) brings the necessary molecules to it.

Bacteria, together with other groups of microorganisms, perform enormous chemical work. By converting various compounds, they receive the energy and nutrients necessary for their life. Metabolic processes, methods of obtaining energy and the need for materials for building the substances of their bodies are diverse in bacteria.

Other bacteria satisfy all their needs for carbon necessary for the synthesis of organic substances in the body at the expense of inorganic compounds. They are called autotrophs. Autotrophic bacteria are capable of synthesizing organic substances from inorganic ones. Among them are:

Chemosynthesis

The use of radiant energy is the most important, but not the only way to create organic matter from carbon dioxide and water. Bacteria are known that use not sunlight as an energy source for such synthesis, but the energy of chemical bonds occurring in the cells of organisms during the oxidation of certain inorganic compounds - hydrogen sulfide, sulfur, ammonia, hydrogen, nitric acid, ferrous compounds of iron and manganese. They use the organic matter formed using this chemical energy to build the cells of their body. Therefore, this process is called chemosynthesis.

The most important group of chemosynthetic microorganisms are nitrifying bacteria. These bacteria live in the soil and oxidize ammonia formed during the decay of organic residues to nitric acid. The latter reacts with mineral compounds of the soil, turning into salts of nitric acid. This process takes place in two phases.

Iron bacteria convert ferrous iron into oxide iron. The resulting iron hydroxide settles and forms the so-called bog iron ore.

Some microorganisms exist due to the oxidation of molecular hydrogen, thereby providing an autotrophic method of nutrition.

A characteristic feature of hydrogen bacteria is the ability to switch to a heterotrophic lifestyle when provided with organic compounds and the absence of hydrogen.

Thus, chemoautotrophs are typical autotrophs, since they independently synthesize the necessary organic compounds from inorganic substances, and do not take them ready-made from other organisms, like heterotrophs. Chemoautotrophic bacteria differ from phototrophic plants in their complete independence from light as an energy source.

Bacterial photosynthesis

Some pigment-containing sulfur bacteria (purple, green), containing specific pigments - bacteriochlorophylls, are able to absorb solar energy, with the help of which hydrogen sulfide in their bodies is broken down and releases hydrogen atoms to restore the corresponding compounds. This process has much in common with photosynthesis and differs only in that in purple and green bacteria the hydrogen donor is hydrogen sulfide (occasionally carboxylic acids), and in green plants it is water. In both of them, the separation and transfer of hydrogen is carried out due to the energy of absorbed solar rays.

This bacterial photosynthesis, which occurs without the release of oxygen, is called photoreduction. Photoreduction of carbon dioxide is associated with the transfer of hydrogen not from water, but from hydrogen sulfide:

6СО 2 +12Н 2 S+hv → С6Н 12 О 6 +12S=6Н 2 О

The biological significance of chemosynthesis and bacterial photosynthesis on a planetary scale is relatively small. Only chemosynthetic bacteria play a significant role in the process of sulfur cycling in nature. Absorbed by green plants in the form of sulfuric acid salts, sulfur is reduced and becomes part of protein molecules. Further, when dead plant and animal remains are destroyed by putrefactive bacteria, sulfur is released in the form of hydrogen sulfide, which is oxidized by sulfur bacteria to free sulfur (or sulfuric acid), forming sulfites in the soil that are accessible to plants. Chemo- and photoautotrophic bacteria are essential in the nitrogen and sulfur cycle.

Sporulation

Spores form inside the bacterial cell. During the process of sporulation, the bacterial cell undergoes a number of biochemical processes. The amount of free water in it decreases and enzymatic activity decreases. This ensures the resistance of the spores to unfavorable environmental conditions ( high temperature, high salt concentration, drying, etc.). Sporulation is characteristic of only a small group of bacteria.

Spores are an optional stage in the life cycle of bacteria. Sporulation begins only with a lack of nutrients or accumulation of metabolic products. Bacteria in the form of spores can remain dormant for a long time. Bacterial spores can withstand prolonged boiling and very long freezing. When favorable conditions occur, the spore germinates and becomes viable. Bacterial spores are an adaptation to survive in unfavorable conditions.

Reproduction

Bacteria reproduce by dividing one cell into two. Having reached a certain size, the bacterium divides into two identical bacteria. Then each of them begins to feed, grows, divides, and so on.

After cell elongation, a transverse septum gradually forms, and then the daughter cells separate; In many bacteria, under certain conditions, after dividing, cells remain connected in characteristic groups. In this case, depending on the direction of the division plane and the number of divisions, different shapes. Reproduction by budding occurs as an exception in bacteria.

Under favorable conditions, cell division in many bacteria occurs every 20-30 minutes. With such rapid reproduction, the offspring of one bacterium in 5 days can form a mass that can fill all seas and oceans. A simple calculation shows that 72 generations (720,000,000,000,000,000,000 cells) can be formed per day. If converted into weight - 4720 tons. However, this does not happen in nature, since most bacteria quickly die under the influence of sunlight, drying, lack of food, heating to 65-100ºC, as a result of struggle between species, etc.

The bacterium (1), having absorbed enough food, increases in size (2) and begins to prepare for reproduction (cell division). Its DNA (in a bacterium the DNA molecule is closed in a ring) doubles (the bacterium produces a copy of this molecule). Both DNA molecules (3,4) find themselves attached to the wall of the bacterium and, as the bacterium elongates, move apart (5,6). First the nucleotide divides, then the cytoplasm.

After the divergence of two DNA molecules, a constriction appears on the bacterium, which gradually divides the body of the bacterium into two parts, each of which contains a DNA molecule (7).

It happens (in Bacillus subtilis) that two bacteria stick together and a bridge is formed between them (1,2).

The jumper transports DNA from one bacterium to another (3). Once in one bacterium, DNA molecules intertwine, stick together in some places (4), and then exchange sections (5).

The role of bacteria in nature

Gyre

Bacteria are the most important link in the general cycle of substances in nature. Plants create complex organic substances from carbon dioxide, water and mineral salts in the soil. These substances return to the soil with dead fungi, plants and animal corpses. Bacteria break down complex substances into simple ones, which are then used by plants.

Bacteria destroy complex organic substances of dead plants and animal corpses, excretions of living organisms and various wastes. Feeding on these organic substances, saprophytic bacteria of decay turn them into humus. These are a kind of orderlies of our planet. Thus, bacteria actively participate in the cycle of substances in nature.

Soil formation

Since bacteria are distributed almost everywhere and occur in huge numbers, they largely determine various processes occurring in nature. In autumn, the leaves of trees and shrubs fall, above-ground shoots of grasses die, old branches fall off, and from time to time the trunks of old trees fall. All this gradually turns into humus. In 1 cm3. The surface layer of forest soil contains hundreds of millions of saprophytic soil bacteria of several species. These bacteria convert humus into various minerals that can be absorbed from the soil by plant roots.

Some soil bacteria are able to absorb nitrogen from the air, using it in vital processes. These nitrogen-fixing bacteria live independently or settle in the roots of legume plants. Having penetrated the roots of legumes, these bacteria cause the growth of root cells and the formation of nodules on them.

These bacteria produce nitrogen compounds that plants use. Bacteria obtain carbohydrates and mineral salts from plants. Thus, there is a close relationship between the legume plant and the nodule bacteria, which is beneficial to both one and the other organism. This phenomenon is called symbiosis.

Thanks to symbiosis with nodule bacteria, leguminous plants enrich the soil with nitrogen, helping to increase yield.

Distribution in nature

Microorganisms are ubiquitous. The only exceptions are the craters of active volcanoes and small areas at the epicenters of exploded atomic bombs. Neither the low temperatures of Antarctica, nor the boiling streams of geysers, nor saturated salt solutions in salt pools, nor the strong insolation of mountain peaks, nor the harsh irradiation of nuclear reactors interfere with the existence and development of microflora. All living beings constantly interact with microorganisms, often being not only their repositories, but also their distributors. Microorganisms are natives of our planet, actively exploring the most incredible natural substrates.

Soil microflora

The number of bacteria in the soil is extremely large - hundreds of millions and billions of individuals per gram. There are much more of them in soil than in water and air. The total number of bacteria in soils changes. The number of bacteria depends on the type of soil, their condition, and the depth of the layers.

On the surface of soil particles, microorganisms are located in small microcolonies (20-100 cells each). They often develop in the thickness of clots of organic matter, on living and dying plant roots, in thin capillaries and inside lumps.

The soil microflora is very diverse. Here there are different physiological groups of bacteria: putrefaction bacteria, nitrifying bacteria, nitrogen-fixing bacteria, sulfur bacteria, etc. among them there are aerobes and anaerobes, spore and non-spore forms. Microflora is one of the factors in soil formation.

The area of ​​development of microorganisms in the soil is the zone adjacent to the roots of living plants. It is called the rhizosphere, and the totality of microorganisms contained in it is called the rhizosphere microflora.

Microflora of reservoirs

Water is a natural environment where microorganisms develop in large numbers. The bulk of them enters the water from the soil. A factor that determines the number of bacteria in water and the presence of nutrients in it. The cleanest waters are from artesian wells and springs. Open reservoirs and rivers are very rich in bacteria. The largest number of bacteria is found in the surface layers of water, closer to the shore. As you move away from the shore and increase in depth, the number of bacteria decreases.

Clean water contains 100-200 bacteria per ml, and polluted water contains 100-300 thousand or more. There are many bacteria in the bottom sludge, especially in the surface layer, where the bacteria form a film. This film contains a lot of sulfur and iron bacteria, which oxidize hydrogen sulfide to sulfuric acid and thereby prevent fish from dying. There are more spore-bearing forms in silt, while non-spore-bearing forms predominate in water.

In terms of species composition, the microflora of water is similar to the microflora of soil, but there are also specific forms. By destroying various waste that gets into the water, microorganisms gradually carry out the so-called biological purification of water.

Air microflora

The microflora of the air is less numerous than the microflora of soil and water. Bacteria rise into the air with dust, can remain there for some time, and then settle on the surface of the earth and die from lack of nutrition or under the influence of ultraviolet rays. The number of microorganisms in the air depends on the geographical zone, terrain, time of year, dust pollution, etc. each speck of dust is a carrier of microorganisms. Most bacteria are in the air above industrial enterprises. The air in rural areas is cleaner. The cleanest air is over forests, mountains, and snowy areas. The upper layers of air contain fewer microbes. The air microflora contains many pigmented and spore-bearing bacteria, which are more resistant than others to ultraviolet rays.

Microflora of the human body

The human body, even a completely healthy one, is always a carrier of microflora. When the human body comes into contact with air and soil, various microorganisms, including pathogenic ones (tetanus bacilli, gas gangrene, etc.), settle on clothing and skin. The most frequently exposed parts of the human body are contaminated. E. coli and staphylococci are found on the hands. There are over 100 types of microbes in the oral cavity. The mouth, with its temperature, humidity, and nutrient residues, is an excellent environment for the development of microorganisms.

The stomach has an acidic reaction, so the majority of microorganisms in it die. Starting from the small intestine, the reaction becomes alkaline, i.e. favorable for microbes. The microflora in the large intestines is very diverse. Each adult excretes about 18 billion bacteria daily in excrement, i.e. more individuals than people on the globe.

Internal organs that are not connected to the external environment (brain, heart, liver, bladder, etc.) are usually free of microbes. Microbes enter these organs only during illness.

Bacteria in the cycle of substances

Microorganisms in general and bacteria in particular play a large role in the biologically important cycles of substances on Earth, carrying out chemical transformations that are completely inaccessible to either plants or animals. Various stages of the cycle of elements are carried out by organisms different types. The existence of each individual group of organisms depends on the chemical transformation of elements carried out by other groups.

Nitrogen cycle

The cyclic transformation of nitrogenous compounds plays a primary role in supplying the necessary forms of nitrogen to organisms of the biosphere with different nutritional needs. Over 90% of total nitrogen fixation is due to the metabolic activity of certain bacteria.

Carbon cycle

The biological transformation of organic carbon into carbon dioxide, accompanied by the reduction of molecular oxygen, requires the joint metabolic activity of various microorganisms. Many aerobic bacteria carry out complete oxidation of organic substances. Under aerobic conditions, organic compounds are initially broken down by fermentation, and the organic end products of fermentation are further oxidized by anaerobic respiration if inorganic hydrogen acceptors (nitrate, sulfate, or CO 2 ) are present.

Sulfur cycle

Sulfur is available to living organisms mainly in the form of soluble sulfates or reduced organic sulfur compounds.

Iron cycle

Some freshwater bodies contain high concentrations of reduced iron salts. In such places, a specific bacterial microflora develops - iron bacteria, which oxidize reduced iron. They participate in the formation of bog iron ores and water sources rich in iron salts.

Bacteria are the most ancient organisms, appearing about 3.5 billion years ago in the Archean. For about 2.5 billion years they dominated the Earth, forming the biosphere, and participated in the formation of the oxygen atmosphere.

Bacteria are one of the most simply structured living organisms (except viruses). They are believed to be the first organisms to appear on Earth.

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 conditions environment- 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 is in these “gaps” and “holes” ancient world and in that ancient era the first organisms with a fundamentally different structure were born - 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 to establish in a “calm atmosphere” effective system 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, better ways to adapt 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. Indeed, from the point of view of chemistry, photosynthesis and oxygen respiration are 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"