Chemical elements in the cells of living organisms - Knowledge Hypermarket. The chemical composition of the cell - what is it?

In modern conditions, one of the most pressing problems in teaching chemistry is ensuring the practical orientation of subject knowledge. This means the need to clarify the close relationship between the theoretical principles being studied and the practice of life, to demonstrate the applied nature of chemical knowledge. Students begin to study chemistry with interest. In order to maintain the cognitive interest of students, it is necessary to convince them of the effectiveness of chemical knowledge and to form a personal need to master the educational material.

The purpose of this lesson: broaden students' horizons and increase cognitive interest in studying the subject, form ideological concepts about the knowability of nature. This lesson is proposed to be taught in 8th grade after studying the chemical elements of the Periodic Table, when the children already have an idea of ​​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 uniform elements.
Like a formula, like a work schedule,
The structure of the Mendeleev system is strict.
The living world is happening around you,
Enter it, inhale it, touch it with your hands.

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

Teacher: The human body contains 81 chemical elements out of 92 found in nature. The human body is a complex chemical laboratory. It’s 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 is impossible.

On the students’ desks are tables “Biological role of chemical elements” (see. Appendix 2). Time is given to get to know her. The teacher and students analyze the table by asking questions.

Teacher: The basis of life is made up of 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 table make up no more than 2%).
Three main characteristics of nutrients (H, C, N, O, P, S):

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

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

Teacher: Analogue elements in the natural environment enter into competition and can be interchanged in living organisms, negatively affecting them.
Replacing sodium and potassium in animals and humans with lithium causes disorders of the nervous system, since in this case the cells do not conduct nerve impulses. Such disorders lead to schizophrenia.
Thallium, a biological competitor of potassium, replaces it in cell walls and affects the central and peripheral nervous system, gastrointestinal tract and kidneys.
Selenium can replace sulfur in proteins. This is the only element that, when present in high levels in plants, can cause sudden death in animals and humans who eat them.
When calcium is deficient in the soil, the body replaces it with strontium, which gradually disrupts the normal structure of the skeleton. Particularly dangerous is the replacement of calcium with strontium-90, which accumulates in huge quantities at sites of nuclear explosions (during nuclear weapons testing) or during accidents at nuclear power plants. This radionuclide destroys bone marrow.
Cadmium competes with zinc. This element reduces the activity of digestive enzymes, disrupts the process of glycogen formation in the liver, causes skeletal deformation, inhibits bone growth, and also causes severe pain in the lower back and leg muscles, and bone fragility (for example, fractured ribs when coughing). Other negative consequences are lung and rectal cancer, pancreatic dysfunction. Kidney damage, decreased levels of iron, calcium, and phosphorus in the blood. 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. Excess fluorine in the environment (fluoridated water, soil contamination with fluorine compounds around an aluminum production plant and other reasons) prevents the entry of iodine into the human body. In this regard, diseases of the thyroid gland and the endocrine system as a whole occur.

Student messages prepared in advance.

1st student:

Medieval alchemists considered gold to be perfection, and other metals to be an error in the act of creation, and, as is known, they made great efforts to eliminate this error. The idea of ​​​​introducing gold into medical practice is attributed to Paracelsus, who declared 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 used to treat leprosy, lupus, and tuberculosis. In people sensitive to gold, it could cause a disturbance in the composition of the blood, a reaction in the kidneys, liver, affect mood, the growth of teeth and 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:

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

3rd student:

ALUMINUM

Aluminum cookware is called the poor man's cookware, as this metal contributes to the development of senile atherosclerosis. When cooking food in such containers, aluminum partially passes into the body, where it accumulates.

4th student:

• What element is contained 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 content leads to headaches and 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 sulfate and observe the formation of a purple precipitate. They conclude that the protein is destroyed.

5th student:

Man is also nature.
He is also a sunset and a sunrise.
And there are four seasons in it.
And there is a special way of music in it.

And the special mystery of color,
Sometimes with cruel, sometimes with kind fire.
The man is winter. Or summer.
Or autumn. With thunder and rain.

It contained everything – miles and time.
And he became blind from atomic storms.
Man is both soil and seed.
And a weed in the middle of the field. And bread.

And what is the weather like there?
How much loneliness is there in him? Meetings?
Man is also nature...
So let's save nature!

(S. Ostrovoy)

To consolidate the knowledge acquired in the lesson, the “Smile” test is carried out (see. Appendix 4).
Next, you are asked to fill out the crossword puzzle “Chemical Kaleidoscope” (see. Appendix 5).
The teacher sums up the lesson, noting the most active students.

6th student:

Change, change!
The call is ringing.
It's finally finished
Annoying lesson!

Pulling sulfur by the pigtail,
Magnesium ran past.
The iodine from the class has evaporated,
It was as if I had never been there at all.

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

Potassium and bromine are fighting in the corner:
They won't share the electron.
Oxygen is a naughty boy in the woods
He galloped past on horseback.

Used Books:

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

All living organisms, with the exception of viruses, are composed of cells. Let's figure out what it is and what its structure is.

What is a cell?

It is the basic structural unit of living beings. She has her own metabolism. A cell can also exist as an independent organism: examples of this are ciliates, amoebas, chlamydomonas, etc. This structure consists of a variety of substances, both organic and inorganic. All chemical substances of a cell play a certain function in its structure and metabolism.

Chemical elements

There are about 70 different chemical elements in the cell, but the main ones are oxygen, carbon, hydrogen, potassium, phosphorus, nitrogen, sulfur, chlorine, sodium, magnesium, calcium, iron, zinc, copper. The first three represent the basis of all organic compounds. All chemical elements of the cell play a certain role.

Oxygen

The amount of this element is 65-75 percent of the mass of the entire cell. It is part of almost all organic compounds, as well as water, which is why its content is so high. This element performs a very important function in the cells of organisms: oxygen serves as an oxidizing agent in the process of cellular respiration, as a result of which energy is synthesized.

Carbon

This element, like hydrogen, is found in all organic substances. The chemical composition of the cell contains about 15-18 percent of it. Carbon in the form of CO takes part in the processes of regulation of cellular functions, and it also participates in photosynthesis in the form of CO 2.

Hydrogen

The cell contains approximately 8-10 percent of this element. Its largest amount is found in water molecules. The cells of some bacteria oxidize molecular hydrogen to synthesize energy.

Potassium

The chemical composition of the cell includes about 0.15-0.4% of this chemical element. It plays a very important role, participating in the processes of generating a nerve impulse. That is why it is recommended to use drugs containing potassium to strengthen the nervous system. This element also helps maintain the membrane potential of the cell.

Phosphorus

The amount of this element in the cell is 0.2-1% of its total weight. It is part of ATP molecules, as well as some lipids. Phosphorus is present in the intercellular substance and in the cytoplasm in the form of ions. Its high concentration is observed in muscle and bone tissue cells. In addition, inorganic compounds that include this element are used by the cell to synthesize organic substances.

Nitrogen

This element is included in the chemical composition of the cell in an amount of 2-3%. It is found in proteins, nucleic acids, amino acids and nucleotides.

Sulfur

It is part of many proteins, as it is found in sulfur-containing amino acids. It is present in low concentrations in the cytoplasm and intercellular substance in the form of ions.

Chlorine

Contains in an amount of 0.05-0.1%. Maintains electrical neutrality of the cell.

Sodium

This element is present in the cell in an amount of 0.02-0.03%. It performs the same functions as potassium, and also takes part in osmoregulation processes.

Calcium

The amount of this chemical element is 0.04-2%. Calcium is involved in the process of maintaining the membrane potential of the cell and exocytosis, that is, the release of certain substances (hormones, proteins, etc.) from it.

Magnesium

The chemical composition of the cell includes 0.02-0.03% of this element. It takes part in energy metabolism and DNA synthesis, is a component of enzymes, chlorophyll, and is found in ribosomes and mitochondria.

Iron

The amount of this element is 0.01-0.015%. However, there is much more of it in red blood cells, since it is the basis of hemoglobin.

Zinc

Contained in insulin, as well as in many enzymes.

Copper

This element is one of the components of oxidative enzymes that take part in the synthesis of cytochromes.

Squirrels

These are the most complex compounds in the cell, the main substances of which it consists. They consist of amino acids connected in a certain order into a chain, and then twisted into a ball, the shape of which is specific to each type of protein. These substances perform many important functions in cell life. One of the most important is the enzymatic function. Proteins act as natural catalysts, speeding up the chemical reaction process hundreds of thousands of times - the breakdown and synthesis of any substances is impossible without them. Each type of enzyme participates only in one specific reaction and cannot enter into another. Proteins also perform a protective function. Substances of this group that protect the cell from foreign proteins entering it are called antibodies. These substances also protect the entire body from pathogenic viruses and bacteria. In addition, these connections perform a transport function. It lies in the fact that there are transporter proteins in the membranes that carry certain substances outside or inside the cell. The plastic function of these substances is also very important. They are the main building material of which the cell, its membranes and organelles are composed. Sometimes proteins also perform an energy function - with a lack of fats and carbohydrates, the cell breaks down these substances.

Lipids

This group of substances includes fats and phospholipids. The former are the main source of energy. They can also accumulate as reserve substances in case of starvation of the body. The latter serve as the main component of cell membranes.

Carbohydrates

The most common substance in this group is glucose. It and similar simple carbohydrates perform an energy function. Carbohydrates also include polysaccharides, whose molecules consist of thousands of united molecules - monosaccharides. They mainly perform a structural role, being part of membranes. The main polysaccharides of plant cells are starch and cellulose, and those of animals are glycogen.

Nucleic acids

This group of chemical compounds includes DNA, RNA and ATP.

DNA

This substance performs the most important function - it is responsible for the storage and hereditary transmission of genetic information. DNA is found in the chromosomes of the nucleus. The macromolecules of this substance are formed from nucleotides, which, in turn, consist of a nitrogenous base represented by purines and pyrimidines, hydrocarbons and phosphoric acid residues. They come in four types: adenyl, guanyl, thymidyl and cytidyl. The name of the nucleotide depends on which purines are included in its composition; these can be adenine, guanine, thymine and cytosine. The DNA molecule has the shape of two chains twisted into a spiral.

RNA

This compound performs the function of implementing the information that is in DNA through the synthesis of proteins, the composition of which is encrypted. This substance is very similar to the nucleic acid described above. Their main difference is that RNA consists of one chain, not two. RNA nucleotides also contain the nitrogenous base uracil instead of thymine and ribose. Therefore, this substance is formed from nucleotides such as adenyl, guanyl, uridyl and cytidyl.

ATP

Any energy obtained by plant cells during photosynthesis or by animals due to the oxidation of fats and carbohydrates is ultimately stored in ATP, from which the cell receives it when needed.

All organisms on our planet consist of cells that are similar in chemical composition. In this article we will briefly talk about the chemical composition of the cell, its role in the life of the entire organism, and find out what science studies this issue.

Groups of elements of the chemical composition of the cell

The science that studies the components and structure of a living cell is called cytology.

All elements included in the chemical structure of the body can be divided into three groups:

• macroelements;
• microelements;
• ultramicroelements.

Macroelements include hydrogen, carbon, oxygen and nitrogen. They account for almost 98% of all constituent elements.

Microelements are present in tenths and hundredths of a percent. And a very low content of ultramicroelements - hundredths and thousandths of a percent.

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Translated from Greek, “macro” means big, and “micro” means small.

Scientists have found that there are no special elements that are unique to living organisms. Therefore, both living and inanimate nature consists of the same elements. This proves their relationship.

Despite the quantitative content of a chemical element, the absence or reduction of at least one of them leads to the death of the entire organism. After all, each of them has its own meaning.

The role of the chemical composition of the cell

Macroelements are the basis of biopolymers, namely proteins, carbohydrates, nucleic acids and lipids.

Microelements are part of vital organic substances and participate in metabolic processes. They are constituent components of mineral salts, which are in the form of cations and anions, their ratio determines the alkaline environment. Most often it is slightly alkaline, because the ratio of mineral salts does not change.

Hemoglobin contains iron, chlorophyll - magnesium, proteins - sulfur, nucleic acids - phosphorus, metabolism occurs with a sufficient amount of calcium.

Rice. 2. Cell composition

Some chemical elements are components of inorganic substances, such as water. It plays an important role in the life of both plant and animal cells. Water is a good solvent, because of this all substances inside the body are divided into:

• Hydrophilic - dissolves in water;
• Hydrophobic - do not dissolve in water.

Thanks to the presence of water, the cell becomes elastic, it promotes the movement of organic substances in the cytoplasm.

Rice. 3. Cell substances.

Table “Properties of the chemical composition of the cell”

To clearly understand what chemical elements are part of the cell, we included them in the following table:

What have we learned?

Each cell of living nature has its own set of chemical elements. In terms of their composition, objects of living and inanimate nature have similarities, this proves their close relationship. Each cell consists of macroelements, microelements and ultramicroelements, each of which has its own role. The absence of at least one of them leads to illness and even death of the entire organism.

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Cells of living organisms according to their chemical composition differ significantly from the surrounding inanimate environment both in the structure of chemical compounds and in the set and content of chemical elements. In total, about 90 chemical elements are present (discovered to date) in living organisms, which, depending on their content, are divided into 3 main groups: macronutrients , microelements And ultramicroelements .

Macroelements.

Macronutrients are present in significant quantities in living organisms, ranging from hundredths of a percent to tens of percent. If the content of any chemical substance in the body exceeds 0.005% of body weight, such a substance is classified as a macronutrient. They are part of the main tissues: blood, bones and muscles. These include, for example, the following chemical elements: hydrogen, oxygen, carbon, nitrogen, phosphorus, sulfur, sodium, calcium, potassium, chlorine. Macroelements in total make up about 99% of the mass of living cells, with the majority (98%) being hydrogen, oxygen, carbon and nitrogen.

The table below shows the main macronutrients in the body:

All four of the most common elements in living organisms (hydrogen, oxygen, carbon, nitrogen, as mentioned earlier) are characterized by one common property. These elements lack one or more electrons in the outer orbit to form stable electronic bonds. Thus, the hydrogen atom lacks one electron in its outer orbit to form a stable electronic bond; the oxygen, nitrogen and carbon atoms need two, three and four electrons, respectively. In this regard, these chemical elements easily form covalent bonds due to electron pairing, and can easily interact with each other, filling their outer electron shells. In addition, oxygen, carbon and nitrogen can form not only single but also double bonds. As a result, the number of chemical compounds that can be formed from these elements significantly increases.

In addition, carbon, hydrogen and oxygen are the lightest among the elements that can form covalent bonds. Therefore, they turned out to be most suitable for the formation of compounds that make up living matter. It is necessary to separately note another important property of carbon atoms - the ability to form covalent bonds with four other carbon atoms at once. Thanks to this ability, frameworks are created from a huge number of different organic molecules.

Microelements.

Although the content microelements does not exceed 0.005% for each individual element, and in total they constitute only about 1% of the cell mass; microelements are necessary for the life of organisms. In their absence or insufficient content, various diseases can occur. Many microelements are part of the non-protein groups of enzymes and are necessary for their catalytic function.
For example, iron is a component of heme, which is part of cytochromes, which are components of the electron transport chain, and hemoglobin, a protein that transports oxygen from the lungs to the tissues. Iron deficiency in the human body causes the development of anemia. And the lack of iodine, which is part of the thyroid hormone - thyroxine, leads to diseases associated with deficiency of this hormone, such as endemic goiter or cretinism.

Examples of microelements are presented in the table below:

Ultramicroelements.

To the group ultramicroelements includes elements whose content in the body is extremely low (less than 10-12%). These include bromine, gold, selenium, silver, vanadium and many other elements. Most of them are also necessary for the normal functioning of living organisms. For example, a lack of selenium can lead to cancer, and a lack of boron is the cause of some diseases in plants. Many elements of this group, as well as microelements, are part of enzymes.

The cell is the elementary 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 a greater or lesser number of cells, which are a kind of blocks that make up a complex organism. Regardless of whether a cell is an integral living system - a separate organism or constitutes only a part of it, it is endowed with a set of characteristics and properties common to all cells.

Chemical composition of the cell

About 60 elements of Mendeleev's periodic table, which are also found in inanimate nature, were found in cells. This is one of the proofs of the commonality of living and inanimate nature. In living organisms, the most abundant are hydrogen, oxygen, carbon and nitrogen, which make up about 98% of the mass of cells. This is due to the peculiar chemical properties of hydrogen, oxygen, carbon and nitrogen, as a result of which they turned out to be most suitable for the formation of molecules that perform biological functions. These four elements are capable of forming very strong covalent bonds by pairing electrons belonging to two atoms. Covalently bonded carbon atoms can form the frameworks of countless different organic molecules. Since carbon atoms easily form covalent bonds with oxygen, hydrogen, nitrogen, and sulfur, organic molecules achieve exceptional complexity and structural diversity.

In addition to the four main elements, the cell contains noticeable quantities (10th and 100th fractions of a percent) of 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 trace elements.

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.

Inorganic substances

Water. H 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 ° When ice melts, approximately 15% of hydrogen bonds are destroyed, 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 life of the body’s cells. Osmosis is the penetration of solvent molecules through a semi-permeable membrane into a solution of a substance. Semi-permeable membranes are those that allow solvent molecules to pass through, but do not allow solute molecules (or ions) to pass through. Therefore, osmosis is the one-way diffusion of water molecules in the direction of the 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 +, Ca 2+, Mg 2+ 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 H 2 PO 4 and HPO 4 2- ions. In extracellular fluids and blood, the role of a buffer is played by H 2 CO 3 and HCO 3 -. 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.

Organic cell matter

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. 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, 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 10 10 - 10 12.

A chain of amino acid units connected covalently by peptide bonds in a specific sequence is called the primary structure of the 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. Thus, 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. 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 (metalloproteins), P (phosphoproteins).

The functions of proteins in a 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. 17.6 kJ (~4.2 kcal) of proteins are released.

Carbohydrates. Carbohydrates, or saccharides, are organic substances with the general formula (CH 2 O) n. Most carbohydrates have twice the number of H atoms as the number of O atoms, as in water molecules. That's why 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 found in 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 from 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 of 1 g of carbohydrates, 17.6 kJ (~4.2 kcal) is 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:

Fig. 1. Location of nucleotides in a DNA molecule

From Fig.1. it is clear 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 breakdown of 1 g of fats into CO 2 and H 2 O, 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%. The main function of fats in the animal (and partly plant) world is storage.

When 1 g of fat is completely oxidized (to carbon dioxide and water), about 9 kcal of energy is released. (1 kcal = 1000 cal; calorie (cal) is an extra-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 standard atmospheric pressure 101.325 kPa; 1 kcal = 4.19 kJ) . When 1 g of proteins or carbohydrates is oxidized (in the body), only about 4 kcal/g is released. In a variety of aquatic organisms - from single-celled diatoms to basking sharks - fat will "float", reducing average body density. The density of animal fats is about 0.91-0.95 g/cm³. The density of vertebrate bone tissue 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 you need quite a lot of fat to “balance” a heavy skeleton.

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.