The importance of the most important chemical elements and compounds for the cell and organism. Chemical elements in the cells of living organisms - Knowledge Hypermarket

Elemental composition of the body

By chemical composition The cells of different organisms may differ markedly, but they consist of the same elements. About 70 elements of the periodic table of D.I. Mendeleev, but only 24 of them are of great importance and are constantly found in living organisms.

Macronutrients - oxygen, hydrocarbon, hydrogen, nitrogen - are part of the molecules of organic substances. Macroelements recently include potassium, sodium, calcium, sulfur, phosphorus, magnesium, iron, chlorine. Their content in the cell is tenths and hundredths of a percent.

Magnesium is part of chlorophyll; iron - hemoglobin; phosphorus - bone tissue, nucleic acids; calcium - bones, shellfish turtles, sulfur - in the composition of proteins; potassium, sodium and chloride ions take part in changing the potential of the cell membrane.

trace elements are presented in a cell with hundredths and thousandths of a percent. These are zinc, copper, iodine, fluorine, molybdenum, boron, etc.

Trace elements are part of enzymes, hormones, pigments.

Ultramicroelements - elements, the content of which in the cell does not exceed 0.000001%. These are uranium, gold, mercury, cesium, etc.

Water and its biological significance

Water quantitatively ranks among chemical compounds first place in all cells. Depending on the type of cells, their functional state, the type of organism and the conditions of its presence, its content in cells varies significantly.

Bone tissue cells contain no more than 20% water, adipose tissue - about 40%, muscle cells - 76%, and embryonic cells - more than 90%.

Remark 1

In the cells of any organism, the amount of water decreases markedly with age.

Hence the conclusion that the higher the functional activity of the organism as a whole and of each cell separately, the greater their water content, and vice versa.

Remark 2

A prerequisite for the vital activity of cells is the presence of water. It is the main part of the cytoplasm, supports its structure and the stability of the colloids that make up the cytoplasm.

The role of water in a cell is determined by its chemical and structural properties. First of all, this is due to the small size of the molecules, their polarity and the ability to combine using hydrogen bonds.

Hydrogen bonds are formed with the participation of hydrogen atoms connected to an electronegative atom (usually oxygen or nitrogen). In this case, the Hydrogen atom acquires such a large positive charge that it can form a new bond with another electronegative atom (oxygen or nitrogen). Water molecules also bind to each other, in which one end has a positive charge, and the other is negative. Such a molecule is called dipole. The more electronegative oxygen atom of one water molecule is attracted to the positively charged hydrogen atom of another molecule to form a hydrogen bond.

Due to the fact that water molecules are polar and capable of forming hydrogen bonds, water is a perfect solvent for polar substances, which are called hydrophilic. These are compounds of an ionic nature, in which charged particles (ions) dissociate (separate) in water when a substance (salt) is dissolved. Some non-ionic compounds have the same ability, in the molecule of which there are charged (polar) groups (in sugars, amino acids, simple alcohols, these are OH groups). Substances consisting of non-polar molecules (lipids) are practically insoluble in water, that is, they hydrophobes.

When a substance passes into a solution, its structural particles (molecules or ions) acquire the ability to move more freely, and, accordingly, the reactivity of the substance increases. Due to this, water is the main medium where most chemical reactions take place. In addition, all redox reactions and hydrolysis reactions take place with the direct participation of water.

Water has the highest specific heat capacity of all known substances. This means that with a significant increase in thermal energy, the water temperature rises relatively slightly. This is due to the use of a significant amount of this energy to break hydrogen bonds, which limit the mobility of water molecules.

Due to its high heat capacity, water serves as a protection for plant and animal tissues from a strong and rapid increase in temperature, and the high heat of vaporization is the basis for reliable stabilization of body temperature. The need for a significant amount of energy to evaporate water is due to the fact that hydrogen bonds exist between its molecules. This energy comes from the environment, so evaporation is accompanied by cooling. This process can be observed during sweating, in the case of heat panting in dogs, it is also important in the process of cooling the transpiring organs of plants, especially in desert conditions and in conditions of dry steppes and periods of drought in other regions.

Water also has a high thermal conductivity, which ensures uniform distribution of heat throughout the body. Thus, there is no risk of local “hot spots” that can cause damage to cell elements. This means that the high specific heat capacity and high thermal conductivity for a liquid make water an ideal medium for maintaining the optimal thermal regime of the body.

Water has a high surface tension. This property is very important for adsorption processes, movement of solutions through tissues (blood circulation, upward and downward movement through the plant, etc.).

Water is used as a source of oxygen and hydrogen, which are released during the light phase of photosynthesis.

Important physiological properties of water include its ability to dissolve gases ($O_2$, $CO_2$, etc.). In addition, water as a solvent is involved in the process of osmosis, which plays an important role in the life of cells and the body.

Hydrocarbon properties and its biological role

If we do not take into account water, we can say that most of the cell molecules belong to hydrocarbon, so-called organic compounds.

Remark 3

Hydrocarbon, having unique chemical abilities fundamental to life, is its chemical basis.

Thanks to small size and availability on outer shell four electrons, a hydrocarbon atom can form four strong covalent bonds with other atoms.

Most important is the ability of hydrocarbon atoms to connect with each other, forming chains, rings and, ultimately, the skeleton of large and complex organic molecules.

In addition, the hydrocarbon easily forms covalent bonds with other biogenic elements (usually with $H, Mg, P, O, S$). This explains the existence of an astronomical number of diverse organic compounds that ensure the existence of living organisms in all its manifestations. Their diversity is manifested in the structure and size of molecules, their chemical properties, degree of saturation of the carbon skeleton and different form molecules, which is determined by the angles of intramolecular bonds.

Biopolymers

These are high-molecular (molecular weight 103 - 109) organic compounds, the macromolecules of which consist of a large number of repeating units - monomers.

Biopolymers are proteins, nucleic acids, polysaccharides and their derivatives (starch, glycogen, cellulose, hemicellulose, pectin, chitin, etc.). The monomers for them are, respectively, amino acids, nucleotides and monosaccharides.

Remark 4

About 90% of the dry mass of a cell is made up of biopolymers: polysaccharides predominate in plants, while proteins predominate in animals.

Example 1

In a bacterial cell there are about 3 thousand types of proteins and 1 thousand nucleic acids, and in humans the number of proteins is estimated at 5 million.

Biopolymers not only form the structural basis of living organisms, but also play a conducting role in life processes.

The structural basis of biopolymers are linear (proteins, nucleic acids, cellulose) or branched (glycogen) chains.

And nucleic acids, immune reactions, metabolic reactions - and are carried out due to the formation of biopolymer complexes and other properties of biopolymers.

Today, a lot has been discovered and isolated in its pure form chemical elements periodic tables, and a fifth of them are found in every living organism. They, like bricks, are the main components of organic and inorganic substances.

What chemical elements are part of the cell, the biology of which substances can be used to judge their presence in the body - we will consider all this later in the article.

What is the constancy of the chemical composition

To maintain stability in the body, each cell must maintain the concentration of each of its components at a constant level. This level is determined by species, habitat, environmental factors.

To answer the question of what chemical elements are part of the cell, it is necessary to clearly understand that any substance contains any of the components of the periodic table.

Sometimes in question about hundredths and thousandths of a percent of the content of a certain element in a cell, but at the same time, a change in the named number by at least a thousandth part can already carry serious consequences for the body.

Of the 118 chemical elements in a human cell, there should be at least 24. There are no such components that would be found in a living organism, but were not part of inanimate objects of nature. This fact confirms the close relationship between living and non-living in the ecosystem.

The role of various elements that make up the cell

So what are the chemical elements that make up a cell? Their role in the life of the organism, it should be noted, directly depends on the frequency of occurrence and their concentration in the cytoplasm. However, despite different content elements in the cell, the significance of each of them is equally high. Deficiency of any of them can lead to a detrimental effect on the body, turning off the most important bio chemical reactions.

Listing what chemical elements are part of the human cell, we need to mention three main types, which we will consider below:

The main biogenic elements of the cell

It is not surprising that the elements O, C, H, N are biogenic, because they form all organic and many inorganic substances. It is impossible to imagine proteins, fats, carbohydrates or nucleic acids without these essential components for the body.

The function of these elements determined their high content in the body. Together they account for 98% of the total dry body weight. How else can the activity of these enzymes be manifested?

Oxygen. Its content in the cell is about 62% of the total dry mass. Functions: construction of organic and inorganic substances, participation in the respiratory chain;
Carbon. Its content reaches 20%. Main function: included in all;
Hydrogen. Its concentration takes a value of 10%. In addition to being a component of organic matter and water, this element also participates in energy transformations;
Nitrogen. The amount does not exceed 3-5%. Its main role is the formation of amino acids, nucleic acids, ATP, many vitamins, hemoglobin, hemocyanin, chlorophyll.

These are the chemical elements that make up the cell and form most of the substances necessary for normal life.

Importance of macronutrients

Macronutrients will also help to suggest which chemical elements are part of the cell. From the biology course, it becomes clear that, in addition to the main ones, 2% of the dry mass is made up of other components of the periodic table. And macronutrients include those whose content is not lower than 0.01%. Their main functions are presented in the form of a table.


Calcium (Ca)		Responsible for the contraction of muscle fibers, is part of pectin, bones and teeth. Enhances blood clotting.
Phosphorus (P)		It is part of the most important source of energy - ATP.
		Participates in the formation of disulfide bridges during protein folding into a tertiary structure. Included in the composition of cysteine and methionine, some vitamins.
		Potassium ions are involved in cells and also affect the membrane potential.
		Major anion in the body
Sodium (Na)		Analogue of potassium involved in the same processes.
Magnesium (Mg)		Magnesium ions are the regulators of the process In the center of the chlorophyll molecule, there is also a magnesium atom.
		Participates in the transport of electrons through the ETC of respiration and photosynthesis, is a structural link of myoglobin, hemoglobin and many enzymes.

We hope that from the above it is easy to determine which chemical elements are part of the cell and are macroelements.

trace elements

There are also such components of the cell, without which the body cannot function normally, but their content is always less than 0.01%. Let's determine which chemical elements are part of the cell and belong to the group of microelements.


		It is part of the enzymes of DNA and RNA polymerases, as well as many hormones (for example, insulin).
		Participates in the processes of photosynthesis, synthesis of hemocyanin and some enzymes.
		It is a structural component of the hormones T3 and T4 of the thyroid gland
Manganese (Mn)	less than 0.001	Included in enzymes, bones. Participates in nitrogen fixation in bacteria
	less than 0.001	Influences the process of plant growth.
		It is part of the bones and tooth enamel.

Organic and inorganic substances

In addition to these, what other chemical elements are included in the composition of the cell? The answers can be found simply by studying the structure of most substances in the body. Among them, molecules of organic and inorganic origin are distinguished, and each of these groups has a fixed set of elements in its composition.

The main classes of organic substances are proteins, nucleic acids, fats and carbohydrates. They are built entirely from the main biogenic elements: the skeleton of the molecule is always formed by carbon, and hydrogen, oxygen and nitrogen are part of the radicals. In animals, proteins are the dominant class, and in plants, polysaccharides.

Inorganic substances are all mineral salts and, of course, water. Among all the inorganics in the cell, the most is H 2 O, in which the rest of the substances are dissolved.

All of the above will help you determine which chemical elements are part of the cell, and their functions in the body will no longer be a mystery to you.

About 70 elements have been found in the cells of different organisms periodic system elements of D. I. Mendeleev, but only 24 of them have a well-established value and are found constantly in all types of cells.

largest specific gravity in the elemental composition of the cell falls on oxygen, carbon, hydrogen and nitrogen. These are the so-called main or nutrients. These elements account for more than 95% of the mass of cells, and their relative content in living matter is much higher than in earth's crust. Also vital are calcium, phosphorus, sulfur, potassium, chlorine, sodium, magnesium, iodine and iron. Their content in the cell is calculated in tenths and hundredths of a percent. The listed elements form a group macronutrients.

Other chemical elements: copper, manganese, molybdenum, cobalt, zinc, boron, fluorine, chromium, selenium, aluminum, iodine, iron, silicon - are found in extremely small quantities (less than 0.01% of cell mass). They belong to the group trace elements.

The percentage of one or another element in the body in no way characterizes the degree of its importance and necessity in the body. So, for example, many trace elements are part of various biologically active substances - enzymes, vitamins (cobalt is part of vitamin B 12), hormones (iodine is part of thyroxin); affect the growth and development of organisms (zinc, manganese, copper) , hematopoiesis (iron, copper), cellular respiration processes (copper, zinc), etc. The content and significance for the life of cells and the body as a whole of various chemical elements are given in the table:

The most important chemical elements of the cell

Element	Symbol	Approximate content, %	Significance for the cell and organism
Oxygen	O	62	Included in water and organic matter; involved in cellular respiration
Carbon	C	20	Included in all organic substances
Hydrogen	H	10	Included in water and organic matter; participates in energy conversion processes
Nitrogen	N	3	Included in amino acids, proteins, nucleic acids, ATP, chlorophyll, vitamins
Calcium	Ca	2,5	It is part of the cell wall in plants, bones and teeth, increases blood clotting and contractility of muscle fibers
Phosphorus	P	1,0	Included in bone tissue and tooth enamel, nucleic acids, ATP, some enzymes
Sulfur	S	0,25	Included in amino acids (cysteine, cystine and methionine), some vitamins, participates in the formation of disulfide bonds in the formation of the tertiary structure of proteins
Potassium	K	0,25	It is contained in the cell only in the form of ions, activates the enzymes of protein synthesis, causes a normal rhythm of cardiac activity, participates in the processes of photosynthesis, generation of bioelectric potentials
Chlorine	Cl	0,2	The negative ion predominates in the body of animals. Hydrochloric acid component in gastric juice
Sodium	Na	0,10	Contained in the cell only in the form of ions, causes a normal rhythm of cardiac activity, affects the synthesis of hormones
Magnesium	mg	0,07	Included in chlorophyll molecules, as well as bones and teeth, activates energy metabolism and DNA synthesis
Iodine	I	0,01	Included in thyroid hormones
Iron	Fe	0,01	It is a part of many enzymes, hemoglobin and myoglobin, participates in the biosynthesis of chlorophyll, in electron transport, in the processes of respiration and photosynthesis
Copper	Cu	Traces	Included in the composition of hemocyanins in invertebrates, in the composition of some enzymes, participates in the processes of hematopoiesis, photosynthesis, hemoglobin synthesis
Manganese	Mn	Traces	It is part of or increases the activity of certain enzymes, participates in the development of bones, nitrogen assimilation and the process of photosynthesis
Molybdenum	Mo	Traces	It is part of some enzymes (nitrate reductase), participates in the processes of binding atmospheric nitrogen by nodule bacteria
Cobalt	co	Traces	Included in vitamin B 12, participates in the fixation of atmospheric nitrogen by nodule bacteria
Bor	B	Traces	Influences the growth processes of plants, activates the restorative enzymes of respiration
Zinc	Zn	Traces	It is part of some enzymes that break down polypeptides, is involved in the synthesis of plant hormones (auxins) and glycolysis
Fluorine	F	Traces	Part of the enamel of teeth and bones

The cell is the basic unit of life on Earth. It has all the characteristics of a living organism: it grows, reproduces, exchanges substances and energy with the environment, and reacts to external stimuli. The beginning of biological evolution is associated with the appearance of cellular life forms on Earth. Unicellular organisms are cells that exist separately from each other. The body of all multicellular organisms - animals and plants - is built from more or less cells, which are a kind of building blocks that make up a complex organism. Regardless of whether the cell is an integral living system - a separate organism or is only a part of it, it is endowed with a set of features and properties common to all cells.

The 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 animate 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 reach an exceptional complexity and variety of structure.

In addition to the four main elements, the cell contains iron, potassium, sodium, calcium, magnesium, chlorine, phosphorus and sulfur in noticeable amounts (10th and 100th parts of a percent). 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, other elements can be included in their composition. Some proteins contain sulfur. Phosphorus is a constituent of nucleic acids. The hemoglobin molecule includes iron, magnesium is involved in the construction of the chlorophyll molecule. Trace elements, despite their extremely low content in living organisms, play an important role in life processes. Iodine is part of the thyroid hormone - thyroxine, cobalt - in the composition of vitamin B 12 hormone of the islet of the pancreas - insulin - contains zinc. In some fish, the place of iron in the molecules of oxygen-carrying pigments is occupied by copper.

inorganic substances

Water. H 2 O is the most common compound in living organisms. Its content in different cells varies over a fairly wide range: from 10% in tooth enamel to 98% in the body of a jellyfish, but on average it is about 80% of body weight. The extremely important role of water in ensuring life processes is due to its physical and chemical properties. The polarity of the molecules and the ability to form hydrogen bonds make water a good solvent for a huge number of substances. Most of the chemical reactions that take place 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 water. When the t ° 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 t ° inside the cell are smaller than in 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 the one-way diffusion of water molecules in the direction of the solution.

mineral salts. Most of the inorganic 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 + , Ca 2+ , Mg 2+ ions. In the tissues of multicellular animals, K is part of a multicellular substance that ensures the cohesion of cells and their orderly arrangement. The osmotic pressure in the cell and its buffer properties largely depend on the concentration of salts. Buffering is the ability of a cell to maintain a slightly alkaline reaction of its contents at a constant level. Buffering inside the cell is provided mainly by H 2 PO 4 and HPO 4 2- ions. In extracellular fluids and in the blood, H 2 CO 3 and HCO 3 - play the role of a buffer. Anions bind H ions and hydroxide ions (OH -), due to which the reaction inside the cell of extracellular fluids practically does not change. Insoluble mineral salts (for example, Ca phosphate) provide strength to the bone tissue of vertebrates and mollusk shells.

The organic matter of the cell

Squirrels. Among the organic substances of the cell, proteins are in first place both in quantity (10 - 12% of the total cell mass) and in value. Proteins are high molecular weight polymers (with a molecular weight of 6,000 to 1 million or more) whose monomers are amino acids. Living organisms use 20 amino acids, although there are many more. The composition of any amino acid includes an amino group (-NH 2), 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 with the release of a water molecule. The bond between the amino group of one amino acid and the carboxyl of another is called a peptide bond. Proteins are polypeptides containing tens or hundreds of amino acids. Molecules of various proteins differ from each other in molecular weight, number, composition of amino acids and their sequence in the polypeptide chain. It is clear, therefore, that proteins are of great diversity, their number in all types of living organisms is estimated at 10 10 - 10 12.

A chain of amino acid units connected by covalent peptide bonds in a certain sequence is called the primary structure of a protein. In cells, proteins have the form of helically twisted fibers or balls (globules). This is due to the fact that in a natural protein, the polypeptide chain is folded in a strictly defined way, depending on chemical structure its constituent amino acids.

First, the polypeptide chain coils into a helix. Attraction arises between the 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 a 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 the hydrophobic radicals present in some amino acids and covalent bonds between the SH groups of the amino acid cysteine ( S-S connections). The number of amino acids hydrophobic radicals and cysteine, as well as the order of their arrangement in the polypeptide chain, is specific for 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, the replacement of even one amino acid in the 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 oxygen. Such aggregates represent the quaternary structure of the protein. According to 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 building function: proteins are involved in the formation of all cell membranes and cell organelles, as well as intracellular structures. Of exceptional importance is the enzymatic (catalytic) role of proteins. Enzymes speed up the chemical reactions that take place in the cell by 10 ki 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: flickering of cilia and beating of flagella in protozoa, muscle contraction in animals, movement of leaves in plants, etc. The transport function of proteins is to attach chemical elements (for example, hemoglobin attaches 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 of 1g. proteins are released 17.6 kJ (~ 4.2 kcal).

Carbohydrates. Carbohydrates or saccharides are organic compounds general formula(CH 2 O) n. Most carbohydrates have twice the number of H atoms more number 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 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, glucose, fructose and galactose are the most important. 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 combine in one molecule, such a compound is called a disaccharide. Dietary sugar, obtained from cane or sugar beets, consists of one molecule of glucose and one molecule of fructose, milk sugar - from glucose and galactose.

Complex carbohydrates formed by many monosaccharides are called polysaccharides. The monomer of such polysaccharides 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 is the main structural component of the exoskeleton of arthropods. Chitin also performs a building function in fungi. Carbohydrates play the role of the main source of energy in the cell. In the process of oxidation of 1 g of carbohydrates, 17.6 kJ (~ 4.2 kcal) are released. Starch in plants and glycogen in animals are stored in cells and serve as an energy reserve.

Nucleic acids. The value of nucleic acids in the cell is very high. The peculiarities of their chemical structure provide the possibility of storing, transferring and transmitting by inheritance to daughter cells information about the structure of protein molecules that are synthesized in each tissue at a certain stage. individual development. Since most of the properties and features of cells are due to proteins, it is clear that the stability of nucleic acids is essential condition normal functioning of cells and whole organisms. Any changes in the structure of cells or the activity of physiological processes in them, thus affecting life. 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, enclosed so that a double helix is formed. 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 interconnected 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:

Fig. 1. Arrangement of nucleotides in a DNA molecule

From Fig.1. It can be seen 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 approach each other and form H-bonds. In a polynucleotide chain, adjacent nucleotides are linked together through a sugar (deoxyribose) and a phosphoric acid residue. RNA, like DNA, is a polymer whose monomers are nucleotides. The nitrogenous bases of the 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 their carbohydrate (ribose instead of deoxyribose).

In an RNA chain, nucleotides are connected by forming covalent bonds between the ribose of one nucleotide and the phosphoric acid residue of another. Two-stranded RNAs differ in structure. Double-stranded RNAs are the keepers of genetic information in a number of viruses, i.e. perform the functions of chromosomes. Single-stranded RNAs carry out the transfer of information about the structure of proteins from the chromosome to the site of their synthesis and participate in protein synthesis.

There are several types of single-stranded RNA. Their names are due to their function or location in the cell. Most of the cytoplasmic RNA (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 to be synthesized to ribosomes. The size of these RNAs depends on the length of the DNA segment from which they were synthesized. Transfer RNAs perform several functions. They deliver amino acids to the site of protein synthesis, "recognize" (according to the principle of complementarity) the triplet and RNA corresponding to the transferred amino acid, and carry out the exact orientation of the amino acid on the ribosome.

Fats and lipoids. Fats are compounds of fatty macromolecular acids and the trihydric alcohol glycerol. Fats do not dissolve in water - they are hydrophobic. There are always other complex hydrophobic fat-like substances in the cell, called lipoids. One of the main functions of fats is energy. During the breakdown of 1 g of fat to CO 2 and H 2 O, it is released a large number of energy - 38.9 kJ (~ 9.3 kcal). The fat content in the cell ranges from 5-15% of the dry matter mass. In the cells of living tissue, the amount of fat increases to 90%. The main function of fats in the animal (and partly plant) world is storage.

With the complete oxidation of 1 g of fat (to carbon dioxide and water), about 9 kcal of energy is released. (1 kcal \u003d 1000 cal; calorie (cal, cal) is an off-system unit of the amount of work and energy, equal to the amount of heat required to heat 1 ml of water by 1 ° C at a standard atmospheric pressure of 101.325 kPa; 1 kcal \u003d 4.19 kJ) . When oxidized (in the body) 1 g of proteins or carbohydrates, only about 4 kcal / g is released. In a wide variety of aquatic organisms - from unicellular diatoms to giant sharks - fat will "float", reducing the average body density. The density of animal fats is about 0.91-0.95 g/cm³. The bone density of vertebrates is close to 1.7-1.8 g/cm³, and the average density of most other tissues is close to 1 g/cm³. It is clear that quite a lot of fat is needed to "balance" a heavy skeleton.

Fats and lipoids perform and building 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.

AT modern conditions one of the most urgent problems of teaching chemistry is to ensure the practical orientation of subject knowledge. This means the need to clarify the close relationship between the studied theoretical positions and the practice of life, to demonstrate the applied nature of chemical knowledge. Students are excited to learn chemistry. In order to maintain the cognitive interest of students, it is necessary to convince them of the effectiveness of chemical knowledge, to form a personal need for mastering educational material.

Purpose of this lesson: to broaden the horizons of students and increase cognitive interest in the study of the subject, to form worldview concepts about the cognizability of nature. This lesson is proposed to be held in the 8th grade after studying the chemical elements of the Periodic Table, when the children already have an idea about their diversity.

DURING THE CLASSES

Teacher:

There is nothing else in nature
Neither here nor there, in the depths of space:
Everything - from small grains of sand to planets -
It consists of single elements.
Like a formula, like a labor schedule,
The structure of the Mendeleev system is strict.
The world around you is alive
Enter it, breathe in, touch it with your hands.

The lesson begins with a theatrical scene “Who is the most important in the table?” (cm. Appendix 1).

Teacher: The human body contains 81 chemical elements out of 92 found in nature. The human body is a complex chemical laboratory. It is hard to imagine that our daily well-being, mood and even appetite can depend on minerals. Without them, vitamins are useless, the synthesis and breakdown of proteins, fats and carbohydrates are impossible.

On the tables of the students there are tables “The biological role of chemical elements” (see. Appendix 2). Take time to get to know her. The teacher, together with the students, analyzes the table by asking questions.

Teacher: The basis of life is the six elements of the first three periods (H, C, N, O, P, S), which account for 98% of the mass of living matter (the remaining elements of the periodic system are no more than 2%).
Three main attributes of biogenic elements (H, C, N, O, P, S):

small size of atoms
small relative atomic mass,
the ability to form strong covalent bonds.

Students are given texts (see. Appendix 3). Task: read the text carefully; highlight the elements necessary for life and the elements dangerous to living organisms; find them in the Periodic system and explain their role.
After completing the task, several students analyze different texts.

Teacher: Elements-analogues in the natural environment enter into competition and can be interchanged in living organisms, negatively affecting them.
Replacing sodium and potassium in the organisms of animals and humans with lithium causes disorders of the nervous system, since in this case the cells do not conduct a nerve impulse. Such disorders lead to schizophrenia.
Thallium, a biological competitor of potassium, replaces it in cell walls, affects the central and peripheral nervous system, gastrointestinal tract and kidneys.
Selenium can replace sulfur in proteins. This is the only element that, at high levels in plants, can cause sudden death of animals and humans who eat them.
Calcium, when it is deficient in the soil, is replaced in the body by strontium, which gradually disrupts the normal structure of the skeleton. Especially dangerous is the replacement of calcium with strontium-90, which accumulates in huge quantities in places of nuclear explosions (when testing nuclear weapons) or during accidents at nuclear power plants. This radionuclide destroys the bone marrow.
Cadmium competes with zinc. This element reduces the activity of digestive enzymes, disrupts the formation of glycogen in the liver, causes skeletal deformity, inhibits bone growth, and also causes severe pain in the lower back and leg muscles, bone fragility (for example, broken ribs when coughing). Other negative consequences are lung and rectal cancer, pancreatic dysfunction. Kidney damage, decreased blood levels of iron, calcium, phosphorus. This element inhibits self-purification processes in aquatic and terrestrial plants (for example, a 20-30-fold increase in cadmium in tobacco leaves is noted).
Halogens can be very easily interchanged in the body. An excess of fluorine in the environment (fluorinated water, soil contamination with fluorine compounds around an aluminum production plant, and other reasons) prevents iodine from entering the human body. As a result, thyroid disease endocrine system generally.

Student messages prepared in advance.

1st student:

Medieval alchemists considered gold to be perfection, and other metals to be a mistake in the act of creation, and, as you know, they made great efforts to eliminate this error. The idea of introducing gold into medical practice is attributed to Paracelsus, who proclaimed that the goal of chemistry should not be the transformation of all metals into gold, but the preparation of medicines. Medicines made from gold and its compounds have been tried to treat many diseases. They were treated for leprosy, lupus, and tuberculosis. In people sensitive to gold, it could cause a violation of the composition of the blood, a reaction from the kidneys, liver, affect mood, growth of teeth, hair. Gold ensures the functioning of the nervous system. It is found in corn. And the strength of blood vessels depends on germanium. The only food product containing germanium is garlic.

2nd student:

AT human body the largest amount of copper is found in the brain and liver, and this circumstance alone indicates its importance in life. It was found that with pain, the concentration of copper in the blood and cerebrospinal fluid increases. In Syria and Egypt, newborns wear copper bracelets to prevent rickets and epilepsy.

3rd student:

ALUMINUM

Aluminum utensils are called the utensils of the poor, as this metal contributes to the development of senile atherosclerosis. When cooking in such dishes, aluminum partially passes into the body, where it accumulates.

4th student:

What element is found in apples? (Iron.)
What is its biological role? (The body contains 3 g of iron, of which 2 g is in the blood. Iron is part of hemoglobin. Insufficient iron leads to headache, rapid fatigue.)

Then students conduct a laboratory experiment, the purpose of which is to experimentally prove the effect of salts of certain metals on protein. They mix the protein with solutions of alkali and copper sulphate and observe the precipitation of a purple precipitate. Make a conclusion about the destruction of the protein.

5th student:

Man is also nature.
He is also a sunset and a sunrise.
And it has four seasons.
And a special move in music.

And a special sacrament of color,
Now with cruel, now with good fire.
Man is winter. Or summer.
Or autumn. With thunder and rain.

All contained in itself - miles and time.
And from atomic storms he was blind.
Man is both soil and seed.
And weeds in the middle of the field. And bread.

And what is the weather like in it?
How much loneliness is there? Meetings?
Man is nature too...
So let's take care of nature!

(S. Ostrovoy)

To consolidate the knowledge gained in the lesson, the “Smile” test is carried out (see. Appendix 4).
Next, it is proposed to fill in the crossword “Chemical Kaleidoscope” (see. Annex 5).
The teacher sums up the lesson, noting the most active students.

6th student:

Change, change!
The call is pouring.
Finally it's finished
Boring lesson!

Pulling sulfur by the pigtail,
Magnesium ran past.
Iodine evaporated from the classroom
It's like it never happened at all.

Fluorine accidentally set fire to water,
Chlorine ate someone else's book.
Carbon suddenly with hydrogen
I managed to become invisible.

Potassium, bromine are fighting in the corner:
They don't share an electron.
Oxygen - naughty on boron
Past galloped on horseback.

Used Books:

O.V. Baidalina On the applied aspect of chemical knowledge. “Chemistry at school” No. 5, 2005
Chemistry and ecology in the school course. “First of September” No. 14, 2005
I. N. Pimenova, A. V. Pimenov“Lectures on general biology”, tutorial, Saratov, JSC Publishing house "Lyceum", 2003
About chemistry in verse, Who is the most important in the table? “First of September”, No. 15, 2005
Metals in the human body. “Chemistry at school”, No. 6, 2005
Crossword "Chemical kaleidoscope". “First of September”, No. 1 4, 2005
"I'm going to chemistry class." The book for the teacher. M. “First of September”, 2002, p. 12.