Features of the structure of cells of different kingdoms. Structural features of eukaryotic cells. What will we do with the received material?

Overkingdom of prokaryotes

Features of prokaryotic cells

Features of plant cells.

Inclusions

In the cytoplasm of cells there are inclusions - unstable components that act as a reserve of nutrients (drops of fat, lumps of glycogen), various secretions prepared for removal from the cell. Inclusions include some pigments (hemoglobin, lipofucin) and others.
Inclusions are synthesized in the cell and used in the process of metabolism.

There are major differences between animal and plant cells. These differences are associated with the lifestyle and nutrition of these groups of living beings.

There are two groups of organisms on Earth. The first is represented by viruses and phages that do not have a cellular structure. The second group, the most numerous, has a cellular structure. Among these organisms, there are two types of cell organization: prokaryotic (bacteria and blue-green algae) and eukaryotic (all others).

Prokaryotic (or prenuclear) organisms include bacteria and blue-green algae. The genetic apparatus is represented by the DNA of a single circular chromosome, is located in the cytoplasm and is not delimited from it by a membrane. This analogue of the nucleus is called a nucleoid.

Prokaryotic cells are protected by a cell wall (shell), the outer part of which is formed by a glycopeptide - murein. The inner part of the cell wall is represented by the plasma membrane, the protrusions of which into the cytoplasm form mesosomes, which are involved in the construction of cell walls, reproduction, and are the site of DNA attachment. There are few organelles in the cytoplasm, but numerous small ribosomes are present.

There are no microtubules, and there is no movement of the cytoplasm.

Many bacteria have flagella of a simpler structure than those of eukaryotes.

Respiration in bacteria occurs in mesosomes, and in blue-green algae in cytoplasmic membranes. There are no chloroplasts or other cell organelles surrounded by a membrane

The cytoplasm of prokaryotes, compared to the cytoplasm of eukaryotic cells, is much poorer in structural composition. There are numerous smaller ribosomes than in eukaryotic cells. The functional role of mitochondria and chloroplasts in prokaryotic cells is performed by special, rather simply organized membrane folds.

The structure of various eukaryotic cells is similar. But along with the similarities between the cells of organisms of different kingdoms of living nature, there are noticeable differences. They relate to both structural and biochemical features.

A plant cell is characterized by the presence of various plastids, a large central vacuole, which sometimes pushes the nucleus to the periphery, as well as a cell wall located outside the plasma membrane, consisting of cellulose. In the cells of higher plants, the cell center lacks a centriole, which is found only in algae. The reserve nutrient carbohydrate in plant cells is starch.

In the cells of representatives of the fungal kingdom, the cell wall usually consists of chitin, the substance from which the exoskeleton of arthropods is built. There is a central vacuole, no plastids. Only some fungi have a centriole in the cell center. The storage carbohydrate in fungal cells is glycogen.

Animal cells have no dense cell wall and no plastids. There is no central vacuole in an animal cell. The centriole is characteristic of the cellular center of animal cells. Glycogen is also a reserve carbohydrate in animal cells.

These structures, despite the unity of origin, have significant differences.

General plan of cell structure

When considering cells, it is necessary first of all to remember the basic patterns of their development and structure. They have common structural features and consist of surface structures, cytoplasm and permanent structures - organelles. As a result of vital activity, organic substances called inclusions are deposited in them. New cells arise as a result of the division of maternal cells. During this process, two or more young structures can be formed from one original one, which are an exact genetic copy of the original ones. Cells, uniform in their structural features and functions, are combined into tissues. It is from these structures that the formation of organs and their systems occurs.

Comparison of plant and animal cells: table

On the table you can easily see all the similarities and differences in the cells of both categories.

Features for comparison	plant cell	animal cell
Features of the cell wall	Consists of cellulose polysaccharide.	It is a glycocalyx, a thin layer consisting of compounds of proteins with carbohydrates and lipids.
Presence of a cell center	Found only in the cells of lower algal plants.	Found in all cells.
Presence and location of the core	The core is located in the near-wall zone.	The nucleus is located in the center of the cell.
Presence of plastids	The presence of three types of plastids: chloro-, chromo- and leucoplasts.	None.
The ability to photosynthesis	Occurs on the inner surface of chloroplasts.	Not capable.
Nutrition method	Autotrophic.	Heterotrophic.
Vacuoles	Are large	Digestive and
Storage carbohydrate	Starch.	Glycogen.

Main differences

A comparison of plant and animal cells indicates a number of differences in the features of their structure, and therefore their life processes. Thus, despite the unity of the general plan, their surface apparatus differs in chemical composition. Cellulose, which is part of the cell wall of plants, gives them their permanent shape. Animal glycocalyx, on the contrary, is a thin elastic layer. However, the most important fundamental difference between these cells and the organisms they form is the way they feed. Plants have green plastids called chloroplasts in their cytoplasm. On their inner surface, a complex chemical reaction occurs, converting water and carbon dioxide into monosaccharides. This process is possible only in the presence of sunlight and is called photosynthesis. The byproduct of the reaction is oxygen.

conclusions

So, we have compared plant and animal cells, their similarities and differences. The common features are the structure plan, chemical processes and composition, division and genetic code. At the same time, plant and animal cells are fundamentally different in the way they feed the organisms they form.

Cell wall: eukaryotes. Found in plants, fungi; absent in animals in animals. Consists of cellulose (in plants) or chitin (in fungi) Prokaryotes: Yes. Consists of polymeric protein-carbohydrate molecules

Cell (plasma) membrane. eukaryotes. Prokaryotes exist.

Nucleus: in eukaryotes. Present and surrounded by a membrane. in prokaryotes. Nuclear region; no nuclear membrane

Pro and eukaryotes have cytoplasm

Chromosomes. eukaryotes. Linear, contain protein. Transcription occurs in the nucleus, translation in the cytoplasm.prokaryotes.Ring; contain virtually no protein. Transcription and translation occur in the cytoplasm

Endoplasmic reticulum (ER) in eukaryotes Yes. in prokaryotes No

Eukaryotes have ribosomes. Prokaryotes have them, but they are smaller in size.

Golgi complex in eukaryotes Yes in prokaryotes No

Lysosomes. in eukaryotes. Yes. in prokaryotes No.

Mitochondria in eukaryotes Yes. In prokaryotes No

Most cells have vacuoles in eukaryotes. No in prokaryotes

Eukaryotes have cilia and flagella. All organisms except higher plants have cilia. Prokaryotes Have some bacteria

Chloroplasts in eukaryotes. Plant cells have them. Prokaryotes have them. No. Photosynthesis of green and purple occurs in bacteriochlorophylls (pigments)

Microtubules, microfilaments in eukaryotes Yes in prokaryotes No

10.Chemical composition of the cell

About 60 elements of the periodic system of Mendeleev were found in cells, which are also found in inanimate nature. This is one of the proofs of the commonality of living and inanimate nature. Hydrogen, oxygen, carbon and nitrogen are the most common in living organisms, which make up about 98% of the mass of cells. This is due to the peculiarities of the chemical properties of hydrogen, oxygen, carbon and nitrogen, as a result of which they turned out to be the most suitable for the formation of molecules that perform biological functions. These four elements are able to form very strong covalent bonds through the pairing of electrons belonging to two atoms. Covalently bonded carbon atoms can form the backbones of countless different organic molecules. Since carbon atoms easily form covalent bonds with oxygen, hydrogen, nitrogen, and also with sulfur, organic molecules achieve exceptional complexity and variety of structure.

In addition to the four main elements in the cell in noticeable quantities (10 s and 100 s fractions of a percent) contains iron, potassium, sodium, calcium, magnesium, chlorine, phosphorus and sulfur. All other elements (zinc, copper, iodine, fluorine, cobalt, manganese, etc.) are found in the cell in very small quantities and are therefore called microelements.

Chemical elements are part of inorganic and organic compounds. Inorganic compounds include water, mineral salts, carbon dioxide, acids and bases. Organic compounds are proteins, nucleic acids, carbohydrates, fats (lipids) and lipoids. In addition to oxygen, hydrogen, carbon and nitrogen, they may contain other elements. Some proteins contain sulfur. Phosphorus is a component of nucleic acids. The hemoglobin molecule includes iron, magnesium is involved in the construction of the chlorophyll molecule. Microelements, despite their extremely low content in living organisms, play an important role in life processes. Iodine is part of the thyroid hormone - thyroxine, cobalt is part of vitamin B 12 . the hormone of the islet part of the pancreas - insulin - contains zinc. In some fish, copper takes the place of iron in the oxygen-carrying pigment molecules.

11,Inorganic substances

N 2 O is the most common compound in living organisms. Its content in different cells varies quite widely: from 10% in tooth enamel to 98% in the body of a jellyfish, but on average it makes up about 80% of body weight. The extremely important role of water in supporting life processes is due to its physicochemical properties. The polarity of molecules and the ability to form hydrogen bonds make water a good solvent for a huge number of substances. Most chemical reactions occurring in a cell can only occur in an aqueous solution. Water is also involved in many chemical transformations.

The total number of hydrogen bonds between water molecules varies depending on t °. At t ° melting ice destroys approximately 15% of hydrogen bonds, at t ° 40 ° C - half. Upon transition to the gaseous state, all hydrogen bonds are destroyed. This explains the high specific heat capacity of water. When the temperature of the external environment changes, water absorbs or releases heat due to the rupture or new formation of hydrogen bonds. In this way, fluctuations in temperature inside the cell turn out to be smaller than in the environment. The high heat of evaporation underlies the efficient mechanism of heat transfer in plants and animals.

Water as a solvent takes part in the phenomena of osmosis, which plays an important role in the vital activity of the body's cells. Osmosis refers to the penetration of solvent molecules through a semi-permeable membrane into a solution of a substance. Semi-permeable membranes are membranes that allow molecules of the solvent to pass through, but do not pass molecules (or ions) of the solute. Therefore, osmosis is a one-way diffusion of water molecules in the direction of a solution.

Mineral salts.

Most of the inorganic substances in cells are in the form of salts in a dissociated or solid state. The concentration of cations and anions in the cell and in its environment is not the same. The cell contains quite a lot of K and a lot of Na. In the extracellular environment, for example in blood plasma, in sea water, on the contrary, there is a lot of sodium and little potassium. Cell irritability depends on the ratio of concentrations of Na+, K+, Ca2+, Mg2+ ions. In the tissues of multicellular animals, K is part of the multicellular substance that ensures the cohesion of cells and their ordered arrangement. The osmotic pressure in the cell and its buffering properties largely depend on the concentration of salts. Buffering is the ability of a cell to maintain the slightly alkaline reaction of its contents at a constant level. Buffering inside the cell is provided mainly by H2PO4 and HPO42- ions. In extracellular fluids and blood, the role of a buffer is played by H2CO3 and HCO3-. Anions bind H ions and hydroxide ions (OH-), due to which the reaction inside the cell of extracellular fluids remains virtually unchanged. Insoluble mineral salts (for example, Ca phosphate) provide strength to the bone tissue of vertebrates and mollusk shells.

12.Organic substances of the cell

Squirrels.

Among the organic substances of the cell, proteins are in first place both in quantity (10 - 12% of the total mass of the cell) and in importance. Proteins are high-molecular polymers (with a molecular weight from 6000 to 1 million and above), the monomers of which are amino acids. Living organisms use 20 amino acids, although there are many more. Any amino acid contains an amino group (-NH2), which has basic properties, and a carboxyl group (-COOH), which has acidic properties. Two amino acids are combined into one molecule by establishing an HN-CO bond, releasing a water molecule. The bond between the amino group of one amino acid and the carboxyl group of another is called a peptide bond. Proteins are polypeptides containing tens and hundreds of amino acids. Molecules of various proteins differ from each other in molecular weight, number, composition of amino acids and the sequence of their location in the polypeptide chain. It is therefore clear that proteins are extremely diverse; their number in all types of living organisms is estimated at 1010 - 1012.

A chain of amino acid units connected covalently by peptide bonds in a specific sequence is called the primary structure of a protein. In cells, proteins look like spirally twisted fibers or balls (globules). This is explained by the fact that in natural protein the polypeptide chain is laid out in a strictly defined way, depending on the chemical structure of its constituent amino acids.

First, the polypeptide chain folds into a spiral. Attraction occurs between atoms of neighboring turns and hydrogen bonds are formed, in particular, between NH and CO groups located on adjacent turns. A chain of amino acids, twisted in the form of a spiral, forms the secondary structure of the protein. As a result of further folding of the helix, a configuration specific to each protein arises, called the tertiary structure. The tertiary structure is due to the action of cohesive forces between hydrophobic radicals present in some amino acids and covalent bonds between the SH groups of the amino acid cysteine ​​(S-S bonds). The number of amino acids with hydrophobic radicals and cysteine, as well as the order of their arrangement in the polypeptide chain, are specific to each protein. Consequently, the features of the tertiary structure of a protein are determined by its primary structure. The protein exhibits biological activity only in the form of a tertiary structure. Therefore, replacing even one amino acid in a polypeptide chain can lead to a change in the configuration of the protein and to a decrease or loss of its biological activity.

In some cases, protein molecules combine with each other and can only perform their function in the form of complexes. So, hemoglobin is a complex of four molecules and only in this form is it capable of attaching and transporting O. such aggregates represent the quaternary structure of the protein.

Based on their composition, proteins are divided into two main classes - simple and complex. Simple proteins consist only of amino acids nucleic acids (nucleotides), lipids (lipoproteins), Me (metal proteins), P (phosphoproteins).

The functions of proteins in the cell are extremely diverse. One of the most important is the construction function: proteins are involved in the formation of all cell membranes and cell organelles, as well as intracellular structures. The enzymatic (catalytic) role of proteins is extremely important. Enzymes accelerate chemical reactions occurring in the cell by 10 and 100 million times. Motor function is provided by special contractile proteins. These proteins are involved in all types of movements that cells and organisms are capable of: the flickering of cilia and the beating of flagella in protozoa, muscle contraction in animals, the movement of leaves in plants, etc. The transport function of proteins is to attach chemical elements (for example, hemoglobin adds O) or biologically active substances (hormones) and transfer them to the tissues and organs of the body. The protective function is expressed in the form of the production of special proteins, called antibodies, in response to the penetration of foreign proteins or cells into the body. Antibodies bind and neutralize foreign substances. Proteins play an important role as sources of energy. With complete splitting 1g. proteins are released 17.6 kJ (~ 4.2 kcal).

Carbohydrates.

Carbohydrates, or saccharides, are organic substances with the general formula (CH2O)n. Most carbohydrates have twice the number of H atoms as the number of O atoms, as in water molecules. Therefore, these substances were called carbohydrates.

In a living cell, carbohydrates are found in quantities not exceeding 1-2, sometimes 5% (in the liver, in the muscles). Plant cells are the richest in carbohydrates, where their content in some cases reaches 90% of the dry matter mass (seeds, potato tubers, etc.).

Carbohydrates are simple and complex. Simple carbohydrates are called monosaccharides. Depending on the number of carbohydrate atoms in the molecule, monosaccharides are called trioses, tetroses, pentoses or hexoses. Of the six carbon monosaccharides - hexoses - the most important are glucose, fructose and galactose. Glucose is contained in the blood (0.1-0.12%). The pentoses ribose and deoxyribose are part of nucleic acids and ATP. If two monosaccharides are combined in one molecule, the compound is called a disaccharide. Table sugar, obtained from cane or sugar beets, consists of one molecule of glucose and one molecule of fructose, milk sugar - of glucose and galactose.

Complex carbohydrates formed by many monosaccharides are called polysaccharides. The monomer of polysaccharides such as starch, glycogen, cellulose is glucose.

Carbohydrates perform two main functions: construction and energy. Cellulose forms the walls of plant cells. The complex polysaccharide chitin serves as the main structural component of the exoskeleton of arthropods. Chitin also performs a construction function in fungi. Carbohydrates play the role of the main source of energy in the cell. During the oxidation process 1g. 17.6 kJ (~4.2 kcal) of carbohydrates are released. Starch in plants and glycogen in animals are deposited in cells and serve as an energy reserve.

Nucleic acids.

The importance of nucleic acids in a cell is very great. The peculiarities of their chemical structure provide the possibility of storing, transferring and inheriting to daughter cells information about the structure of protein molecules that are synthesized in each tissue at a certain stage of individual development. Since most of the properties and characteristics of cells are determined by proteins, it is clear that the stability of nucleic acids is the most important condition for the normal functioning of cells and entire organisms. Any changes in the structure of cells or the activity of physiological processes in them, thus affecting vital activity. The study of the structure of nucleic acids is extremely important for understanding the inheritance of traits in organisms and the patterns of functioning of both individual cells and cellular systems - tissues and organs.

There are 2 types of nucleic acids - DNA and RNA.

DNA is a polymer consisting of two nucleotide helices arranged to form a double helix. Monomers of DNA molecules are nucleotides consisting of a nitrogenous base (adenine, thymine, guanine or cytosine), a carbohydrate (deoxyribose) and a phosphoric acid residue. The nitrogenous bases in the DNA molecule are connected to each other by an unequal number of H-bonds and are arranged in pairs: adenine (A) is always against thymine (T), guanine (G) against cytosine (C). Schematically, the arrangement of nucleotides in a DNA molecule can be depicted as follows:

The diagram shows that the nucleotides are connected to each other not randomly, but selectively. The ability for selective interaction of adenine with thymine and guanine with cytosine is called complementarity. The complementary interaction of certain nucleotides is explained by the peculiarities of the spatial arrangement of atoms in their molecules, which allow them to come closer and form H-bonds. In a polynucleotide chain, neighboring nucleotides are linked to each other through a sugar (deoxyribose) and a phosphoric acid residue.

RNA, like DNA, is a polymer whose monomers are nucleotides. The nitrogenous bases of three nucleotides are the same as those that make up DNA (A, G, C); the fourth - uracil (U) - is present in the RNA molecule instead of thymine. RNA nucleotides differ from DNA nucleotides in the structure of the carbohydrate they contain (ribose instead of deoxyribose).

In a chain of RNA, nucleotides are joined by forming covalent bonds between the ribose of one nucleotide and the phosphoric acid residue of another.

The structure differs between two-stranded RNA. Double-stranded RNAs are the custodians of genetic information in a number of viruses, i.e. They perform the functions of chromosomes. Single-stranded RNA transfers information about the structure of proteins from the chromosome to the place of their synthesis and participates in protein synthesis.

There are several types of single-stranded RNA. Their names are determined by their function or location in the cell. Most of the RNA in the cytoplasm (up to 80-90%) is ribosomal RNA (rRNA), contained in ribosomes. rRNA molecules are relatively small and consist of an average of 10 nucleotides. Another type of RNA (mRNA) that carries information about the sequence of amino acids in proteins that must be synthesized to ribosomes. The size of these RNAs depends on the length of the DNA region from which they were synthesized. Transfer RNAs perform several functions. They deliver amino acids to the site of protein synthesis, “recognize” (by the principle of complementarity) the triplet and RNA corresponding to the transferred amino acid, and carry out the precise orientation of the amino acid on the ribosome.

Fats and lipoids.

Fats are compounds of high-molecular fatty acids and trihydric alcohol glycerol. Fats do not dissolve in water - they are hydrophobic. There are always other complex hydrophobic fat-like substances called lipoids in the cell.

One of the main functions of fats is energy. During the splitting 1g. fats to CO2 and H2O, a large amount of energy is released - 38.9 kJ (~9.3 kcal). The fat content in the cell ranges from 5-15% of the dry matter weight. In living tissue cells, the amount of fat increases to 90%. Accumulating in the cells of adipose tissue of animals, in the seeds and fruits of plants, fat serves as a reserve source of energy.

Fats and lipids also perform a construction function; they are part of cell membranes. Due to poor thermal conductivity, fat is capable of a protective function. In some animals (seals, whales) it is deposited in the subcutaneous adipose tissue, forming a layer up to 1 m thick. The formation of some lipoids precedes the synthesis of a number of hormones. Consequently, these substances also have the function of regulating metabolic processes.

18. Stages of energy metabolism : The unified process of energy metabolism can be divided into three successive stages:

The first one is preparatory. At this stage, high-molecular organic substances in the cytoplasm, under the action of appropriate enzymes, are broken down into small molecules: proteins - into amino acids, polysaccharides (starch, glycogen) - into monosaccharides (glucose), fats - into glycerol and fatty acids, nucleic acids - into nucleotides, etc. .d. During this stage, a small amount of energy is released and dissipated as heat.

The second stage is anoxic, or incomplete. The substances formed at the preparatory stage - glucose, amino acids, etc. - undergo further enzymatic breakdown without access to oxygen. An example is the enzymatic oxidation of glucose (glycolysis), which is one of the main sources of energy for all living cells. Glycolysis is a multi-stage process of breakdown of glucose under anaerobic (oxygen-free) conditions to pyruvic acid (PVA), and then to lactic, acetic, butyric acids or ethyl alcohol, occurring in the cytoplasm of the cell. The carrier of electrons and protons in these redox reactions is nicotinamide adenine dinucleotide (NAD) and its reduced form NAD *H. The products of glycolysis are pyruvic acid, hydrogen in the form of NADH and energy in the form of ATP.
With different types of fermentation, the further fate of glycolysis products is different. In animal cells and numerous bacteria, PVK is reduced to lactic acid. The well-known lactic acid fermentation (during the disposal of milk, the formation of sour cream, kefir, etc.) is caused by lactic acid fungi and bacteria.
During alcoholic fermentation, the products of glycolysis are ethyl alcohol and CO2. For other microorganisms, fermentation products may be butyl alcohol, acetone, acetic acid, etc.
During oxygen-free fission, part of the released energy is dissipated in the form of heat, and part is accumulated in ATP molecules.

The third stage of energy metabolism - the stage of oxygen breakdown, or aerobic respiration, occurs in mitochondria. At this stage, electron-transfer enzymes play an important role in the oxidation process. The structures that ensure the passage of the third stage are called the electron transport chain. The electron transport chain receives energy carrier molecules that received an energy charge at the second stage of glucose oxidation. Electrons from molecules - energy carriers, move in steps along the links of a chain from a higher energy level to a lower one. The released energy is spent on charging ATP molecules. The electrons of molecules - energy carriers, which gave up energy to “charge” ATP, ultimately combine with oxygen. As a result, water is formed. In the electron transport chain, oxygen is the final receiver of electrons. Thus, all living things need oxygen as the final sink for electrons. Oxygen provides a potential difference in the electron transport chain and, as it were, attracts electrons from high energy levels of energy carrier molecules to its low energy level. Along the way, energy-rich ATP molecules are synthesized.

15. Triplety - a meaningful unit of code is a combination of three nucleotides (triplet, or codon).

Continuity - There are no punctuation marks between triplets, that is, the information is read continuously.

Non-overlapping - the same nucleotide cannot simultaneously be part of two or more triplets (not observed for some overlapping gene viruses, mitochondria and bacteria that encode several frameshift proteins).

Unambiguity (specificity)- a specific codon corresponds to only one amino acid (however, the UGA codon in Euplotes crassus encodes two amino acids - cysteine ​​and selenocysteine)

Degeneracy (redundancy)- several codons can correspond to the same amino acid.

Versatility- the genetic code works the same in organisms of different levels of complexity - from viruses to humans (genetic engineering methods are based on this; there are a number of exceptions, shown in the table in the section “Variations of the standard genetic code” below).

Noise immunity- mutations of nucleotide substitutions that do not lead to a change in the class of the encoded amino acid are called conservative; nucleotide substitution mutations that lead to a change in the class of the encoded amino acid are called radical. The genetic code is a method of encoding the amino acid sequence of proteins using a sequence of nucleotides, characteristic of all living organisms.

DNA uses four nitrogenous bases - adenine (A), guanine (G), cytosine (C), thymine (T), which in Russian literature are designated by the letters A, G, C and T. These letters make up the alphabet of the genetic code. RNA uses the same nucleotides, with the exception of thymine, which is replaced by a similar nucleotide - uracil, which is designated by the letter U (U in Russian-language literature). In DNA and RNA molecules, nucleotides are arranged in chains and, thus, sequences of genetic letters are obtained.

Genetic code

The proteins of almost all living organisms are built from only 20 types of amino acids. These amino acids are called canonical. Each protein is a chain or several chains of amino acids connected in a strictly defined sequence. This sequence determines the structure of the protein, and therefore all its biological properties.

The implementation of genetic information in living cells (that is, the synthesis of a protein encoded by a gene) is carried out using two matrix processes: transcription (that is, the synthesis of mRNA on a DNA matrix) and translation of the genetic code into an amino acid sequence (synthesis of a polypeptide chain on mRNA). Three consecutive nucleotides are sufficient to encode 20 amino acids, as well as the stop signal indicating the end of the protein sequence. A set of three nucleotides is called a triplet. Accepted abbreviations corresponding to amino acids and codons are shown in the figure.

Properties of DNA molecules

The genetic information in all cells is encoded as a sequence of nucleotides in deoxyribonucleic acid. The first stage of implementing this information is the formation of a DNA-related molecule - ribonucleic acid, which in turn participates in the synthesis of specific proteins. The phenotypic characteristics of any organism are ultimately manifested in the variety and number of proteins encoded by DNA. Information connection between the molecules of the genetic apparatus - DNA, RNA and proteins.

In order for genetic information to be passed from one generation of cells to the next, DNA replication must occur, a process in which parent DNA molecules are duplicated and then distributed among offspring. This process must be carried out with great precision, and damage or random errors that occur in the DNA during or between replication cycles must be corrected before they end up in the genomes of descendants. In addition, genetic information must be expressed to form a phenotype. In all cellular organisms, gene expression involves the copying of DNA to form RNA and the subsequent translation of the RNA into proteins. Transcription produces several types of RNA. Some of them, messenger RNAs, encode proteins, others are involved in various processes necessary for the assembly of a complete protein. DNA not only encodes the cell's enzymatic apparatus; it participates in repair processes, and under certain conditions rearrangements can occur in it. DNA replication, repair, and rearrangements are key processes by which organisms maintain and modify their characteristic phenotype.

Many viruses also have genetic information encoded in their DNA. The mechanisms of replication, repair, rearrangement and expression of viral DNA are similar to the mechanisms used by the cells of other organisms. The genome of some viruses is not DNA, but RNA. The genomic RNA of such viruses is either directly translated into proteins or has the genetic information necessary for the synthesis of RNA molecules, which in turn are translated into proteins. Those viruses whose genome is represented by RNA throughout their life cycle must themselves replicate the parental RNA to produce progeny viral particles. There is a class of retroviruses whose reproductive cycle begins with the fact that their genetic information is translated into DNA language during the so-called reverse transcription. The resulting copies of DNA, or proviruses, are capable of replication and expression only after integration into the chromosomal DNA of the cell. In this integrated form, viral genomes replicate along with the host cell's DNA, and they use the cell's transcriptional machinery to produce a new generation of viral genomes and the mRNA needed to synthesize viral proteins.

The key to the transfer of genetic information between nucleic acids, whether by replication, transcription or reverse transcription, is that the nucleic acid molecule is used as a template in the directed assembly of identical or related structures. As far as is known, the information stored in proteins is not used to assemble the corresponding nucleic acids, i.e. no reverse translation detected. However, proteins play a key role in the processes of information transfer both between nucleic acids and from nucleic acids to proteins.

Structure and behavior of DNA Components of the DNA molecule and the chemical bonds connecting them Using chemical and physical methods, it has been established that DNA is a polymer consisting of four different but related monomers. Each monomer - nucleotide - contains one of four heterocyclic nitrogenous bases: adenine, guanine, cytosine or thymine, linked to deoxyribose phosphate. Long polynucleotide chains are formed by connecting deoxyribose residues of neighboring nucleotides using phosphodiester bonds. Each phosphate connects a hydroxyl group at the 3-carbon deoxyribose atom of one nucleotide to an OH group at the 5-carbon deoxyribose atom of an adjacent nucleotide.

The frequency of occurrence of any two bases in the DNA of bacteria, bacteriophages and yeast in a certain neighborhood depends on the quantitative content of these bases in the DNA. The frequency of occurrence of 5"-CG-3" and 5"-GC-3" in prokaryotic DNA is almost the same and close to random; the same can be said about the dinucleotides 5"-GA-3" and 5"-AG-3". However, in the DNA of animals, animal and plant viruses, the frequencies of occurrence of 5"-CG-3" are from 1/2 to 1/5 of the frequencies of 5"-GC-3". Thus, the 5"-CG-3" sequence is quite rare in the DNA of higher eukaryotes; this is due to the ability of this dinucleotide to serve as a target for methylation and its role in the regulation of gene expression.

After the end of the DNA synthesis cycle, some purine and pyrimidine bases may undergo chemical modification. As a result, some DNA contains 5-methylcytosine, 5-hydroxymethylcytosine, 5-hydroxymethyluracil and N-methyladenine. In the DNA of some bacteriophages, mono- or disaccharides are attached to the hydroxymethyl group of hydroxymethylcytosine using a glycosidic bond. The DNA of most lower eukaryotes and invertebrates contains relatively little 5-methylcytosine and N"-methyladenine. However, in vertebrates, base methylation is a common occurrence, with 5-methylcytosine being the most common. It has been shown that more than 95% of the methyl groups in vertebrate DNA are rarely found in cytosine residues of CG dinucleotides occurring and more than 50% of such dinucleotides are methylated.There are clear indications that the degree of methylation of some CG-containing sequences is an important factor in the regulation of the expression of certain genes.In plants, 5-methylcytosine can be found in CG dinucleotides and CNG trinucleotides.

Animation script O 9 9 – L-7

"Comparison of eukaryotic and prokaryotic cells".

Screen 1.

Laboratory work: “Comparison of eukaryotic and prokaryotic cells.”

(Fig. 1) (Fig. 2)

Screen 2

Equipment: table, on the table:

Microscope tissue napkin ready-made microscopic preparations of bacteria and eukaryotic cells

Tables of the cell structure of eukaryotes and prokaryotes

Screen 3.

(Top line of the screen) Laboratory work: “Comparison of eukaryotic and prokaryotic cells.”

Goal: To get acquainted with two levels of cells, study the structure of a bacterial cell, compare the structure of bacterial cells and simple organisms.

Screen 4. (Top line of screen) Eukaryotes.

Demonstration of text + voiceover

(Fig. 3) (Fig. 4) (Fig. 5)

Eukaryotes or nuclear (from the Greek eu - good and carion - core) are organisms containing a clearly defined nucleus in their cells. Eukaryotes include unicellular and multicellular plants, fungi and animals, that is, all organisms except bacteria. Eukaryotic cells of different kingdoms differ in a number of characteristics. But in many ways their structure is similar. What are the features of eukaryotic cells? From previous lessons, you know that animal cells do not have a cell wall, which plants and fungi have, and there are no plastids, which plants and some bacteria have. Vacuoles in animal cells are very small and unstable. Centrioles have not been found in higher plants.

Screen 5. (Top line of screen) Prokaryotes.

Demonstration of text + voiceover

(Fig. 6)

Prokaryotic or prenuclear cells (from the Latin pro - instead, in front and carion) do not have a formed nucleus. Their nuclear substance is located in the cytoplasm and is not delimited from it by a membrane. Prokaryotes are the most ancient primitive single-celled organisms. These include bacteria and cyanobacteria. They reproduce by simple division. In prokaryotes, a single circular DNA molecule is located in the cytoplasm, which is called a nucleoid or bacterial chromosome, in which all the hereditary information of the bacterial cell is recorded. Ribosomes are located directly in the cytoplasm. Prokaryotic cells are haploid. They do not contain mitochondria, the Golgi complex, or the ER. ATP synthesis occurs in them at the plasma membrane. Prokaryotic cells, like eukaryotic cells, are covered by a plasma membrane. On top of which is a cell wall and a mucous capsule. Despite their relative simplicity, prokaryotes are typical independent cells.

Screen 6 (

Demonstration of the text + voiceover: “Before carrying out practical work, you must read the instructions.”

The sentences appear sequentially above the picture.

1. Examine prepared micropreparations of eukaryotic cells under a microscope: amoeba vulgaris, Chlamydomonas and Mucor.

2. Examine the finished microslide of a prokaryotic cell under a microscope.

3. Consider tables with the structure of eukaryotic and prokaryotic cells.

4. Fill out the table, noting the presence of an organoid “+” and the absence of “-”. Write which organisms are prokaryotes and eukaryotes.

Comparative characteristics of prokaryotes and eukaryotes

Signs	Prokaryotes	eukaryotes
Availability of a designed kernel
Cytoplasm
Cell membrane
Mitochondria
Ribosomes
Which organisms are

Screen 7 ( Top line) Laboratory work: “Comparison of eukaryotic and prokaryotic cells.”

Demonstration

Voice acting

A microscope and ready-made micropreparations of plant tissues appear. The hand wipes the mirror with a napkin, then an eye appears, looking into the eyepiece. Hands place the specimen of amoeba vulgaris on the stage, then rotate the revolving table, the lens stops, the image of the lens and the numbers on it are enlarged (x8), the lens returns to its original size. Hands rotate the mirror. Increasing the drug. Zoom in and show microscopic specimen of amoeba A ready-made chlamydomonas preparation appears. Hands place the specimen on the stage. The eye is directed towards the eyepiece. Zoom in and show the structure of the cell. The preparation is removed and the microscope is removed. The finished drug Mukora appears. Hands place the specimen on the stage. The eye is directed towards the eyepiece. Zoom in and show the structure of the cell. The preparation is removed and the microscope is removed. A ready-made preparation of a bacterial cell appears. Hands place the specimen on the stage. The eye is directed towards the eyepiece. Zoom in and show the structure of the cell. Tables appear with the structure of eukaryotic cells (Figure 12) (Fig. 13) And prokaryotes (Fig. 14) A notebook and pen appear. One hand takes the notebook, opens it and fills out the table. Signs Prokaryotes eukaryotes Availability of a designed kernel Cytoplasm Cell membrane Mitochondria Ribosomes Which organisms are bacteria Mushrooms, plants, animals (Table 1) Output text: Inside a prokaryotic cell there are no organelles surrounded by membranes, i.e. it has no endoplasmic reticulum, no mitochondria, no plastids, no Golgi complex, no nucleus. Prokaryotes often have organelles of movement - flagella and cilia. Eukaryotes have a nucleus and organelles, a more complex structure that indicates the process of evolution.

Prepare the microscope for use. Examine prepared micropreparations of eukaryotic cells under a microscope. Consider tables with the structure of eukaryotic and prokaryotic cells. Fill out the table, noting the presence of the organoid “+” and the absence of “-”. Write which organisms are prokaryotes and eukaryotes. Draw a conclusion: Are there fundamental differences between prokaryotes and eukaryotes? What does this mean?

The science that studies the structure and function of cells - cytology .

Cells can differ from each other in shape, structure and function, although the basic structural elements of most cells are similar. Systematic groups of cells – prokaryotic And eukaryotic (superkingdoms prokaryotes and eukaryotes) .

Prokaryotic cells do not contain a true nucleus and a number of organelles (the kingdom of the crushed cell).
Eukaryotic cells contain a nucleus in which the hereditary apparatus of the organism is located (superkingdoms fungi, plants, animals).

Any organism develops from a cell.
This applies to organisms that were born as a result of both asexual and sexual methods of reproduction. That is why the cell is considered the unit of growth and development of the organism.

According to the method of nutrition and cell structure, they are divided into kingdoms :

• Drobyanki;
• Mushrooms;
• Plants;
• Animals.

Bacterial cells (kingdom Drobyanka) have: a dense cell wall, one circular DNA molecule (nucleoid), ribosomes. These cells lack many organelles characteristic of eukaryotic plant, animal and fungal cells. Based on their feeding method, bacteria are divided into phototrophs, chemotrophs, and heterotrophs.

Fungal cells covered with a cell wall that differs in chemical composition from the cell walls of plants. It contains chitin, polysaccharides, proteins and fats as its main components. The reserve substance of fungal and animal cells is glycogen.

Plant cells contain: chloroplasts, leucoplasts and chromoplasts; they are surrounded by a dense cell wall of cellulose and also have vacuoles with cell sap. All green plants are autotrophic organisms.

U animal cells no dense cell walls. They are surrounded by a cell membrane through which the exchange of substances with the environment occurs.

THEMATIC TASKS

Part A

A1. Which of the following is consistent with the cell theory?
1) the cell is an elementary unit of heredity
2) the cell is a unit of reproduction
3) the cells of all organisms are different in their structure
4) the cells of all organisms have different chemical compositions

A2. Precellular life forms include:
1) yeast
2) penicillium
3) bacteria
4) viruses

A3. A plant cell differs from a fungal cell in structure:
1) kernels
2) mitochondria
3) cell wall
4) ribosome

A4. One cell consists of:
1) influenza virus and amoeba
2) mucor mushroom and cuckoo flax
3) planaria and volvox
4) green euglena and slipper ciliates

A5. Prokaryotic cells have:
1) core
2) mitochondria
3) Golgi apparatus
4) ribosomes

A6. The species of the cell is indicated by:
1) the shape of the nucleus
2) number of chromosomes
3) membrane structure
4) primary protein structure

A7. The role of cell theory in science is
1) opening of the cell nucleus
2) opening the cell
3) generalization of knowledge about the structure of organisms
4) discovery of metabolic mechanisms

Part B

IN 1. Select features characteristic only of plant cells
1) there are mitochondria and ribosomes
2) cell wall made of cellulose
3) there are chloroplasts
4) storage substance - glycogen
5) reserve substance – starch
6) the nucleus is surrounded by a double membrane

AT 2. Select the characteristics that distinguish the kingdom of Bacteria from the rest of the kingdoms of the organic world.
1) heterotrophic mode of nutrition
2) autotrophic method of nutrition
3) the presence of a nucleoid
4) absence of mitochondria
5) absence of a core
6) presence of ribosomes

VZ. Find a correspondence between the structural features of the cell and the kingdoms to which these cells belong

Part C

C1. Give examples of eukaryotic cells that do not have a nucleus.
C2. Prove that cell theory generalized a number of biological discoveries and predicted new discoveries.