QUESTIONS AND TASKS FOR REVIEW

Question 1. What chemical elements are included in the cell?

The cell contains about 70 elements. periodic system D. I. Mendeleev. Of these, the main part (98 "%) falls on macroelements - carbon, hydrogen, oxygen, nitrogen, which, together with sulfur and phosphorus, form a group of bioelements.

The share of such elements as sulfur, phosphorus, potassium, sodium, iron, calcium and magnesium accounts for only 1.8% of the substances that make up the Cell.

In addition, the composition of the cell includes microelements iodine (I), fluorine (F), zinc (Zn), copper (Cu), which make up 0.18% of the total mass, and ultramicroelements - gold (Au), silver (An), platinum (P) included in the cells in an amount up to 0.02%.

Question 2. Give examples of the biological role chemical elements.

Bioelements - oxygen, hydrogen, carbon, nitrogen, phosphorus and sulfur - are essential components of the molecules of biological polymers - proteins, polysaccharides and nucleic acids.

Sodium, potassium and chlorine ensure the permeability of cell membranes, the operation of the potassium-sodium (K / Na-) pump, and the conduction of a nerve impulse.

Calcium and phosphorus are structural components of the intercellular substance bone tissue. In addition, calcium is one of the blood clotting factors.

Iron is part of the erythrocyte protein - hemoglobin, and copper is part of a protein similar to it, which is also an oxygen carrier - hemocyanin (for example, in the erythrocytes of mollusks).

Magnesium is an essential part of plant cell chlorophyll. And mod and zinc are part of the hormones of the thyroid and pancreas, respectively.

Question 3. What are trace elements? Give examples and describe them biological significance.

Trace elements - substances that make up the cell in small quantities (from 0.18 to 0.02%). Trace elements include zinc, copper, iodine, fluorine, cobalt.

Being in the composition of the cell in the form of ions and other compounds, they are actively involved in the construction and functioning of a living organism. So, zinc is part of the insulin molecule - the hormone of the pancreas. Iodine is an essential component of thyroxine, a hormone thyroid gland. Fluorine is involved in the formation of bones and tooth enamel. Copper is part of the molecules of some proteins, such as hemocyanin. Cobalt is a component of the vitamin B12 molecule, necessary for the body for hematopoiesis.

Question 4. What inorganic substances are part of the cell?

From not organic matter, which are part of the cell, the most common is water. On average, in a multicellular organism, water makes up to 80% of body weight. In addition, the cell contains various inorganic salts dissociated into ions. These are mainly sodium, potassium, calcium salts, phosphates, carbonates, chlorides.

Question 5. What is biological role water; mineral salts?

Water is the most common inorganic compound in living organisms. Its functions are largely determined by the dipole nature of the structure of its molecules.

1. Water is a universal polar solvent: many chemical substances in the presence of water, they dissociate into ions - cations and anions.

2. Water is a medium where various chemical reactions take place between substances in the cell.

3. Water performs transport function. Most substances are able to penetrate the cell membrane only in dissolved and water form.

4. Water is an important reactant of hydration reactions and the end product of many bio chemical reactions, including oxidation.

5. Water acts as a temperature regulator, which is ensured by its good thermal conductivity and heat capacity, and allows you to maintain the temperature inside the cell with fluctuations in temperature and the environment.

6. Water is the medium for the life of many living organisms.

Life without water is impossible.

Minerals are also important for the processes occurring in living organisms. Its buffering properties depend on the concentration of salts in the cell - the ability of the cell to maintain a slightly alkaline reaction of its contents at a constant level.

Question 6. What substances determine the buffer properties of the cell?

Inside the cell, buffering is provided mainly by the anions H2PO, HPO4-. In the extracellular fluid and blood, the carbonate ion CO and bicarbonate ion HCO play the role of a buffer. Anions of weak acids and alkalis bind hydrogen ions H and hydroxide ions OH due to which the reaction of the medium almost does not change, despite the intake from outside or the formation in the process of metabolism of acidic and alkaline products.

QUESTIONS AND TASKS FOR DISCUSSION

Question 1. What are the differences in the contribution of various elements to the organization of animate and inanimate nature?

The bodies of animate and inanimate nature consist of the same chemical elements, which will explain the unity of their origin. The contribution of chemical elements is the same for both living and inanimate nature.

Question 2. Explain how physicochemical characteristics waters are manifested in providing the vital processes of the cell and the whole organism.

Water is a liquid with a unique combination of a number of important physical and chemical properties.

Water molecules are highly polar and form hydrogen bonds with each other. In liquid water, each molecule is hydrogen bonded to 3 or 4 neighboring molecules. Due to the huge number of hydrogen bonds, water, in comparison with other liquids, has a higher heat capacity and heat of evaporation, a high boiling and melting point, high thermal conductivity. The presence of such qualities allows water to actively participate in thermoregulation.

Water has a low viscosity and is a mobile liquid. The reason for the high mobility of water is the very short lifetime of hydrogen bonds. Therefore, the formation and destruction of a large number of hydrogen bonds constantly occurs in water, which causes given property. Due to its high fluidity, water circulates easily through various cavities organism (circulatory and lymphatic vessels, intercellular spaces, etc.).

Starring water and mineral salts the most important physical and chemical processes taking place in the body. Thus, the concentration of mineral salts dissolved in water determines the magnitude of the osmotic pressure of blood and tissue fluid, the preservation of which at a constant level is a necessary condition for normal life. Inorganic substances are also important in maintaining acid-base balance and in maintaining relative constancy active reaction blood and tissues. Further, mineral salts and water participate in the phenomena of diffusion and osmosis, which play a role in the processes of absorption and excretion.

mineral salts and water, in addition, contribute to the preservation of the colloidal state of living protoplasm. A change in the amount of water in the body and shifts in the salt composition of body fluids and tissue structures entail a violation of the stability of colloids, which may result in irreversible damage and death of individual cells or the body as a whole.

Deprivation of the body of water and mineral salts causes severe impairment and death. In humans, deprivation of water can lead to death in just a few days. This fact should be compared with the fact that with complete starvation and an unlimited supply of water, it is possible to save a person's life even for 40-45 days. With complete starvation, weight loss can reach 40%, while when deprived of water, the loss of even 10% of body weight is accompanied by severe disorders, and the loss of 20-22% of body weight leads to death.

The important role of mineral salts has been established by direct observations. So, with the complete deprivation of animals of mineral salts, that is, with mineral starvation, despite the sufficient intake of all other nutrients and water into the body, loss of appetite, refusal to eat, emaciation and death were observed.
The need for a constant supply of mineral salts and water is explained by the fact that the body constantly loses some of their amounts with urine, sweat and feces.

Physiological role different electrolytes is different and diverse. So, calcium and phosphorus ions are necessary for building bone tissue. Calcium ions are important for the connection of excitation with muscle contraction; sodium and potassium ions are necessary for the emergence of bioelectric potentials. Phosphorus ions as a residue phosphoric acid are part of energy-rich compounds (adenosine triphosphoric, creatine phosphoric acids, etc.), as well as in the composition of phosphatides and phosphoproteins, which are important in the functions nervous tissue and in metabolism.

Some chemical elements that are part of the body in very small quantities (therefore they are called microelements), such as iodine, zinc, iron, cobalt, are involved in the synthesis of complex organic compounds of great functional importance.

Iodine ( general content it in the body of an adult is approximately 0.03 g) is necessary for the synthesis of the thyroid hormone - thyroxine. An extremely important role is played by iron, the amount of which in the body does not exceed 3-5 g. Iron is involved in oxidative processes and oxygen transport by the blood. Zinc is part of the enzyme and plays a role in the formation of the hormone insulin. Cobalt is a part of vitamin B12 necessary for hematopoiesis.

Mineral salts are among the necessary components of the food taken, and their absence can lead to the death of a living organism. They are very actively involved in the activities of all elements of the body, as well as in the normalization of the functioning of its systems. Minerals are necessary for hematopoiesis, the formation of various tissues. For example, calcium and phosphorus are the main structural elements of bone tissue. It is believed that a person needs at least twenty different mineral salts. In our body, they can come with water and food.

For some types of products, high concentration certain minerals, including rare ones. Cereals contain a lot of silicon, and sea ​​plants- iodine.

For our body, a certain acid-gap balance is normal. Its maintenance is the basis of effective life activity. Such a balance should be constant, but with some shifts in nutrition, it can fluctuate in one direction or another.

For human nutrition, a shift towards an acidic character is considered characteristic. It is fraught with development various diseases including atherosclerosis.

Acid minerals include chlorine, phosphorus and sulfur. They are found in fish, meat, bread, eggs, cereals, etc. Potassium, sodium, magnesium and calcium are alkaline elements.

They are rich in products such as fruits and vegetables, berries, milk and its derivatives.
The older a person becomes, the more alkaline foods should be present in his diet.

The most essential mineral salts for our body are potassium, calcium, phosphorus, magnesium and iron.

Potassium belongs to the alkali metals. It is needed by our body to build muscles, as well as for the spleen and liver. Potassium contributes to the normalization of digestion processes, and in particular actively stimulates the processing of starches and fats.

This explains the benefits of this element for constipation. In addition, it is indispensable for disorders in blood circulation, inflammatory processes on the skin, weakened work of the heart and flushes of blood.

Shows up quickly muscle mass as well as violations mental activity. This element is contained in sour fruits, raw vegetables, cranberries and barberries, as well as nuts, bran and almonds.

Calcium is equally necessary at any age. Its salts are part of the blood, as well as interstitial and cellular fluid. It is believed that they are necessary to strengthen protective systems body, as well as for the implementation and maintenance of neuromuscular excitability.

The role of calcium salts in their importance for blood clotting, and their lack quickly affects the activity of the heart muscle. This mineral is especially necessary for the bones of the skeleton.

Calcium is present in many foods. But at the same time, it is quite difficult to be absorbed by the body. It is best to consume it with dairy products, for example, half a liter of milk contains its daily rate.

When building a diet, one should take into account the fact that calcium is actively lost by the body during various stressful situations and during illness. This very quickly affects the state of the whole organism. Therefore, if calcium is lost, its intake should be increased.

Phosphorus is essential for stimulating the growth and activity of the body. It affects bone development and is also very important for the brain. A stable intake of this element is necessary for active mental work. But it should be borne in mind that a constant excess of phosphorus can lead to the formation of tumors.

This mineral is found in foods such as fish liver, cheese, yolk, bran, cucumbers, lettuce, radishes, almonds, nuts, lentils.

Magnesium is essential for the hardness of teeth and bones. This element is also present in the muscles, nerves, lungs, brain, giving them density and elasticity. Lack of magnesium in the diet has a very quick effect. nervous tension.

It is magnesium salts that can protect our body from negative impacts various stresses, by supporting the work of cell membranes in the nervous system. Contained in tomatoes, spinach, nuts, celery, wine berries, bran.

Iron is the main element for blood oxidation. Without it, the formation of hemoglobin - red balls - is impossible. With a lack of this microelement, anemia, apathy, reduced vitality and pale infirmity are observed. In the body, iron is deposited in the liver.

Found in lettuce, spinach, asparagus, strawberries, pumpkin, onions, and watermelon.

Mineral salts are inorganic elements. It means that human body cannot synthesize them on its own. The task of a person is a competent approach to building his diet.

In this case, the need for a strict balance in the ratio of mineral salts should be taken into account. Their wrong combination or excess can be harmful and have Negative consequences.

For example, an excessive amount of calcium in the diet can lead to the formation of calcium-containing kidney stones. Also, this element must be correctly combined with phosphorus and potassium. With an excess of table salt, edema and problems with the cardiovascular system may appear. This is because salt retains fluid in the body.

The biological role of mineral salts in the body is great. For their balanced intake, it is necessary to competently approach the preparation of the diet. In this case, it will not be superfluous to consult with nutritionists.

All transformations of substances in the body occur in aquatic environment. Water dissolves nutrients that have entered the body. Together with minerals, it takes part in the construction of cells and in many metabolic reactions.

Water is involved in the regulation of body temperature; evaporating, cools the body, protecting it from overheating; transports dissolved substances.

Water and mineral salts create mainly the internal environment of the body, being the main integral part blood plasma, lymph and tissue fluid. They are involved in maintaining osmotic pressure and the reaction of blood plasma and tissue fluid. Some salts dissolved in the liquid part of the blood are involved in the transport of gases by the blood.

Water and mineral salts are part of the digestive juices, which largely determines their importance for the digestive process. And although neither water nor mineral salts are sources of energy in the body, their entry into the body and removal from there are prerequisite his normal activities.

Loss of body water leads to very serious violations. For example, in case of indigestion in infants, the most dangerous is dehydration of the body, which leads to convulsions, loss of consciousness, etc. It is the sharp dehydration of the body due to fluid loss that causes such severe course such infectious disease like cholera. Deprivation of water for several days is fatal to humans.

Water exchange

Replenishment of the body with water occurs constantly due to its absorption from digestive tract. A person needs 2-2.5 liters of water per day with a normal diet and normal temperature environment. This amount of water comes from the following sources: a) drinking water (about 1 liter); b) water contained in food (about 1 liter); c) water, which is formed in the body during the metabolism of proteins, fats and carbohydrates (300-350 ml).

The main organs that remove water from the body are the kidneys, sweat glands, lungs and intestines. The kidneys remove 1.2-1.5 liters of water from the body per day as part of the urine. Sweat glands remove 500-700 ml of water per day through the skin in the form of sweat. At normal temperature and air humidity per 1 cm2 skin about 1 mg of water is released every 10 minutes. In the deserts of the Arabian Peninsula, however, a person daily loses about 10 liters of water through sweat. During intensive work, a lot of fluid is also released in the form of sweat: for example, in two halves of a tense football match, a football player loses about 4 liters of water.

The lungs in the form of water vapor remove 350 ml of water. This amount increases sharply with deepening and quickening of breathing, and then 700-800 ml of water can be released per day.

Through the intestines with feces, 100-150 ml of water is excreted per day. With a disorder of the activity of the intestine with feces, it can be excreted a large number of water (with diarrhea), which can lead to depletion of the body of water. For the normal functioning of the body, it is important that the intake of water completely covers its consumption.

The ratio of the amount of water consumed to the amount allocated is water balance.

If more water is excreted from the body than it enters, then there is a feeling thirst. As a result of thirst, a person drinks water until normal water balance is restored.

Salt exchange

When excluded from diet animal minerals lead to severe disorders in the body and even death. The presence of minerals is associated with the phenomenon of excitability - one of the main properties of living things. The growth and development of bones, nerve elements, muscles depend on the content of minerals; they determine the reaction of the blood (pH), contribute to the normal functioning of the heart and nervous system, are used to form hemoglobin (iron), of hydrochloric acid gastric juice(chlorine).

Mineral salts create a certain osmotic pressure, which is so necessary for the life of cells.

At mixed diet an adult gets everything he needs minerals in sufficient quantity. Only table salt added to human food cooking. Growing children's body particularly in need of additional intake of many minerals.

The body constantly loses a certain amount of mineral salts in urine, sweat and feces. Therefore, mineral salts, like water, must constantly enter the body. Content individual elements in the human body is not the same (Table 13).

Regulation of water-salt metabolism

The constancy of the osmotic pressure of the internal environment of the body, determined by the content of water and salts, is regulated by the body.

With a lack of water in the body, the osmotic pressure of the tissue fluid increases. This leads to irritation of special receptors located in the tissues - osmoreceptors. Impulses from them are sent along special nerves to the brain to the center of regulation of water-salt metabolism. From there, the excitation is sent to the endocrine gland - the pituitary gland, which releases a special hormone into the bloodstream that causes urinary retention. Reducing the excretion of water in the urine restores the disturbed balance.

This example clearly shows the interaction of nervous and humoral mechanisms of regulation physiological functions. Reflex starts nervously from osmoreceptors, and then the humoral mechanism is activated - the entry of a special hormone into the blood.

The center of regulation of water-salt metabolism controls all ways of transporting water in the body: its excretion with urine, sweat and through the lungs, redistribution between body organs, absorption from the digestive tract, secretion, and water consumption. Particularly important in this regard are certain parts of the diencephalon. If an animal is introduced into these areas with electrodes, and then through them begin to irritate the brain electric shock, then the animals begin to eagerly drink water. In this case, the amount of water drunk can exceed 40% of body weight. As a result, there are signs of water poisoning associated with a decrease in the osmotic pressure of blood plasma and tissue fluid. V vivo these centers of the diencephalon are under the controlling influence of the cortex hemispheres brain.

The mechanism of water balance regulation is very important in practical life. In cases where water has to be saved, in no case should it be drunk in one gulp, but always in very small sips. You will feel that you are drunk, although you have drunk a little water. Knowledge of the features of the regulation of water-salt metabolism is important in one more case. In hot weather, you are usually very thirsty, and no matter how much water you drink, you are still thirsty. But it is worth consciously enduring a little, despite the feeling of thirst, and it passes. That is why you should not drink a lot in the heat, on a hike, etc. The Right Tactic here is this: knowing that there is a difficult hike or a long stay in the sun, it is better to drink water "in reserve" in advance, at a time when you still do not want to drink. In this case, then there is no such strong feeling of thirst as if you started drinking in the heat.

Two more practical advice. Before setting off on a hike, you should drink mineral or salted water or eat some moderately salty food - feta cheese, salted cheese, etc. - and drink it well with water. The fact is that a lot of salts are lost with sweat, and this leads to an increase in fatigue, muscle weakness etc. You also need to know that in the heat often there is a "false thirst": you want to drink not because there is little fluid in the body, but because of the drying of the oral mucosa. In this case, simply rinse your mouth with water.

The chemical composition of plant and animal cells is very similar, which indicates the unity of their origin. More than 80 chemical elements have been found in cells, but only 27 of them have a known physiological role.

All elements are divided into three groups:

• macronutrients, the content of which in the cell is up to 10 - 3%. These are oxygen, carbon, hydrogen, nitrogen, phosphorus, sulfur, calcium, sodium and magnesium, which together make up over 99% of the mass of cells;
• trace elements, the content of which ranges from 10 - 3% to 10 - 12%. These are manganese, copper, zinc, cobalt, nickel, iodine, bromine, fluorine; they account for less than 1.0% of the mass of cells;
• multimicroelements, making up less than 10 - 12%. These are gold, silver, uranium, selenium and others - in total less than 0.01% of the cell mass. The physiological role of most of these elements has not been established.

All of these elements are part of the inorganic and organic substances of living organisms or are contained in the form of ions.

Inorganic compounds of cells are represented by water and mineral salts.

The most common inorganic compound in the cells of living organisms is water. Its content in different cells ranges from 10% in tooth enamel to 85% in nerve cells and up to 97% in the cells of the developing embryo. The amount of water in the cells depends on the nature metabolic processes: the more intense they are, the higher the water content. On average, the body of multicellular organisms contains about 80% water. Such high content water speaks of important role due to its chemical nature.

The dipole nature of the water molecule allows it to form an aqueous (solvate) shell around proteins, which prevents them from sticking to each other. This bound water, constituting 4 - 5% of its total content. The rest of the water (about 95%) is called free. Free water is a universal solvent for many organic and inorganic compounds. Most chemical reactions take place only in solutions. The penetration of substances into the cell and the removal of dissimilation products from it in most cases is possible only in dissolved form. Water is also directly involved in biochemical reactions occurring in the cell (hydrolysis reactions). The regulation of the thermal regime of cells is also associated with water, since it has good thermal conductivity and heat capacity.

Water is actively involved in the regulation of osmotic pressure in cells. The penetration of solvent molecules through a semipermeable membrane into a solution of a substance is called osmosis, and the pressure with which the solvent (water) penetrates through the membrane is called osmotic pressure. The value of osmotic pressure increases with increasing concentration of the solution. The osmotic pressure of body fluids in humans and most mammals is equal to the pressure of 0.85% sodium chloride solution. Solutions with this osmotic pressure are called isotonic, more concentrated - hypertonic, and less concentrated - hypotonic. The phenomenon of osmosis underlies wall stress plant cells(turgor).

In relation to water, all substances are divided into hydrophilic (water-soluble) - mineral salts, acids, alkalis, monosaccharides, proteins, etc. and hydrophobic (water-insoluble) - fats, polysaccharides, some salts and vitamins, etc. In addition to water, solvents can be fats and alcohols.

Mineral salts in certain concentrations are necessary for the normal functioning of cells. So, nitrogen and sulfur are part of proteins, phosphorus is part of DNA, RNA and ATP, magnesium is part of many enzymes and chlorophyll, iron is part of hemoglobin, zinc is part of the pancreatic hormone, iodine is part of thyroid hormones etc. Insoluble salts of calcium and phosphorus provide strength to bone tissue, sodium, potassium and calcium cations - irritability of cells. Calcium ions take part in blood coagulation.

Anions of weak acids and weak alkalis bind hydrogen (H+) and hydroxyl (OH-) ions, as a result of which a slightly alkaline reaction is maintained at a constant level in cells and interstitial fluid. This phenomenon is called buffering.

Organic compounds make up about 20 - 30% of the mass of living cells. These include biological polymers - proteins, nucleic acids and polysaccharides, as well as fats, hormones, pigments, ATP, etc.

Squirrels

Proteins make up 10 - 18% of the total cell mass (50 - 80% of the dry mass). The molecular weight of proteins ranges from tens of thousands to many millions of units. Proteins are biopolymers whose monomers are amino acids. All proteins of living organisms are built from 20 amino acids. Despite this, the diversity of protein molecules is enormous. They differ in size, structure and functions, which are determined by the number and order of amino acids. Apart from simple proteins(albumins, globulins, histones) there are also complex ones, which are compounds of proteins with carbohydrates (glycoproteins), fats (lipoproteins) and nucleic acids (nucleoproteins).

Each amino acid consists of a hydrocarbon radical linked to an acidic carboxyl group (-COOH) and a basic amino group (-NH2). Amino acids differ from each other only by radicals. Amino acids are amphoteric compounds that have properties of both acids and bases. This phenomenon makes it possible for acids to form long chains. In this case, strong covalent (peptide) bonds are established between the acidic carbon and the nitrogen of the main groups (-CO-NH-) with the release of a water molecule. Compounds consisting of two amino acid residues are called dipeptides, three - tripeptides, many - polypeptides.

The proteins of living organisms consist of hundreds and thousands of amino acids, that is, they are macromolecules. Various properties and the functions of protein molecules are determined by the sequence of amino acids that are encoded in DNA. This sequence is called the primary structure of the protein molecule, which, in turn, determines the subsequent levels of spatial organization and biological properties proteins. The primary structure of a protein molecule is due to peptide bonds.

The secondary structure of a protein molecule is achieved by its spiralization due to the establishment of hydrogen bonds between the atoms of adjacent turns of the helix. They are weaker than covalent, but, repeated many times, create a fairly strong connection. Functioning in the form of a twisted spiral is characteristic of some fibrillar proteins (collagen, fibrinogen, myosin, actin, etc.).

Many protein molecules become functionally active only after acquiring a globular (tertiary) structure. It is formed by repeatedly folding the spiral into a three-dimensional formation - a globule. This structure is crosslinked, as a rule, by even weaker disulfide bonds. Most proteins (albumins, globulins, etc.) have a globular structure.

Some functions require the participation of proteins with more high level organization, in which there is an association of several globular protein molecules into a single system - a quaternary structure (chemical bonds may be different). For example, a hemoglobin molecule consists of four different globules and a heme group containing an iron ion.

The loss of a protein molecule structural organization called denaturation. It can be caused by various chemical (acids, alkalis, alcohol, salts heavy metals etc.) and physical ( high temperature and pressure ionizing radiation etc.) factors. First, a very weak - Quaternary, then tertiary, secondary, and under more severe conditions, the primary structure is destroyed. If under the influence of the denaturing factor the primary structure is not affected, then when the protein molecules return to normal conditions environment, their structure is completely restored, i.e., renaturation occurs. This property of protein molecules is widely used in medicine for the preparation of vaccines and sera and in Food Industry for food concentrates. With irreversible denaturation (destruction of the primary structure), proteins lose their properties.

Proteins perform the following functions: building, catalytic, transport, motor, protective, signaling, regulatory and energy.

How construction material proteins are part of all cell membranes, hyaloplasm, organelles, nuclear juice, chromosomes and nucleoli.

The catalytic (enzymatic) function is performed by enzyme proteins, which accelerate the course of biochemical reactions in cells by tens and hundreds of thousands of times. normal pressure and a temperature of about 37 °C. Each enzyme can catalyze only one reaction, i.e., the action of enzymes is strictly specific. The specificity of enzymes is due to the presence of one or more active centers in which there is close contact between the molecules of the enzyme and a specific substance (substrate). Some enzymes are used in medical practice and food industry.

The transport function of proteins is to transport substances, such as oxygen (hemoglobin) and some biologically active substances(hormones).

The motor function of proteins is that all types of motor reactions of cells and organisms are provided by special contractile proteins - actin and myosin. They are found in all muscles, cilia and flagella. Their threads are able to contract using the energy of ATP.

The protective function of proteins is associated with the production of special protein substances by leukocytes - antibodies in response to the penetration of foreign proteins or microorganisms into the body. Antibodies bind, neutralize and destroy compounds that are not characteristic of the body. An example of the protective function of proteins is the conversion of fibrinogen into fibrin during blood clotting.

The signal (receptor) function is carried out by proteins due to the ability of their molecules to change their structure under the influence of many chemical and physical factors, as a result of which the cell or organism perceives these changes.

The regulatory function is carried out by hormones of a protein nature (for example, insulin).

The energy function of proteins lies in their ability to be a source of energy in the cell (as a rule, in the absence of others). With complete enzymatic cleavage of 1 g of protein, 17.6 kJ of energy is released.

Carbohydrates

Carbohydrates are an essential component of both animal and plant cells. In plant cells, their content reaches 90% of dry weight (in potato tubers), and in animals - 5% (in liver cells). The composition of carbohydrate molecules includes carbon, hydrogen and oxygen, and the number of hydrogen atoms in most cases is twice the number of oxygen atoms.

All carbohydrates are divided into mono-, di- and polysaccharides. Monosaccharides often contain five (pentoses) or six (hexoses) carbon atoms, the same amount of oxygen and twice as much hydrogen (for example, C6H12OH - glucose). Pentoses (ribose and deoxyribose) are part of nucleic acids and ATP. Hexoses (glucose and fructose) are constantly present in the cells of plant fruits, giving them a sweet taste. Glucose is found in the blood and serves as a source of energy for animal cells and tissues. Disaccharides combine two monosaccharides in one molecule. Dietary sugar (sucrose) consists of glucose and fructose molecules, milk sugar (lactose) includes glucose and galactose. All mono- and disaccharides are highly soluble in water and have a sweet taste. Polysaccharide molecules are formed as a result of the polymerization of monosaccharides. The monomer of polysaccharides - starch, glycogen, cellulose (fiber) is glucose. Polysaccharides are practically insoluble in water and do not have a sweet taste. The main polysaccharides - starch (in plant cells) and glycogen (in animal cells) are deposited in the form of inclusions and serve as reserve energy substances.

Carbohydrates are formed in green plants during photosynthesis and can be used later for the biosynthesis of amino acids, fatty acids and other connections.

Carbohydrates perform three main functions: building (structural), energy and storage. Cellulose forms the walls of plant cells; complex polysaccharide - chitin - the outer skeleton of arthropods. Carbohydrates in combination with proteins (glycoproteins) are part of bones, cartilage, tendons and ligaments. Carbohydrates act as the main source of energy in the cell: when 1 g of carbohydrates are oxidized, 17.6 kJ of energy is released. Glycogen is stored in the muscles and liver cells as a reserve nutrient.

Lipids

Lipids (fats) and lipoids are mandatory components all cells. Fats are esters of high molecular weight fatty acids and the trihydric alcohol glycerol, and lipoids are esters of fatty acids with other alcohols. These compounds are insoluble in water (hydrophobic). Lipids can form complex complexes with proteins (lipoproteins), carbohydrates (glycolipids), phosphoric acid residues (phospholipids), etc. The fat content in a cell ranges from 5 to 15% of the dry matter mass, and in the cells of the subcutaneous adipose tissue - up to 90%.

Fats perform building, energy, storage and protective functions. The bimolecular layer of lipids (mainly phospholipids) forms the basis of all biological cell membranes. Lipids are part of the sheaths of nerve fibers. Fats are a source of energy: with the complete breakdown of 1 g of fat, 38.9 kJ of energy is released. They serve as a source of water released during their oxidation. Fats are a reserve source of energy, accumulating in the adipose tissue of animals and in the fruits and seeds of plants. They protect organs from mechanical damage(for example, the kidneys are wrapped in a soft fatty "case"). Accumulating in the subcutaneous fatty tissue of some animals (whales, seals), fats perform a heat-insulating function.

Nucleic acids Nucleic acids are of paramount biological importance and are complex high-molecular biopolymers, the monomers of which are nucleotides. They were first discovered in the nuclei of cells, hence their name.

There are two types of nucleic acids: deoxyribonucleic (DNA) and ribonucleic (RNA). DNA enters mainly into the chromatin of the nucleus, although a small amount of it is also contained in some organelles (mitochondria, plastids). RNA is found in the nucleoli, ribosomes, and in the cytoplasm of the cell.

The structure of the DNA molecule was first deciphered by J. Watson and F. Crick in 1953. It consists of two polynucleotide chains connected to each other. DNA monomers are nucleotides, which include: a five-carbon sugar - deoxyribose, a phosphoric acid residue and a nitrogenous base. Nucleotides differ from one another only in their nitrogenous bases. The composition of DNA nucleotides includes the following nitrogenous bases: adenine, guanine, cytosine and thymine. Nucleotides are connected in a chain by the formation of covalent bonds between the deoxyribose of one and the phosphoric acid residue of the adjacent nucleotide. Both chains are combined into one molecule by hydrogen bonds that arise between the nitrogenous bases of different chains, and due to a certain spatial configuration, two bonds are established between adenine and thymine, and three between guanine and cytosine. As a result, the nucleotides of the two chains form pairs: A-T, G-C. The strict correspondence of nucleotides to each other in paired DNA chains is called complementary. This property underlies the replication (self-doubling) of the DNA molecule, i.e., the formation of a new molecule based on the original one.

replication

Replication happens in the following way. Under the action of a special enzyme (DNA polymerase), hydrogen bonds between the nucleotides of two chains are broken, and the corresponding DNA nucleotides (A-T, G-C) are attached to the released bonds according to the principle of complementarity. Consequently, the order of nucleotides in the "old" DNA strand determines the order of nucleotides in the "new", i.e., the "old" DNA strand is a template for the synthesis of the "new". Such reactions are called matrix synthesis reactions, they are characteristic only for living things. DNA molecules can contain from 200 to 2 x 108 nucleotides. A huge variety of DNA molecules is achieved by their different sizes and different nucleotide sequences.

The role of DNA in a cell is to store, reproduce and transmit genetic information. Thanks to matrix synthesis, the hereditary information of daughter cells exactly matches the mother's.

RNA

RNA, like DNA, is a polymer built from monomers - nucleotides. The structure of RNA nucleotides is similar to that of DNA, but there are the following differences: instead of deoxyribose, RNA nucleotides contain a five-carbon sugar - ribose, and instead of the nitrogenous base of thymine - uracil. The other three nitrogenous bases are the same: adenine, guanine, and cytosine. Compared to DNA, RNA contains fewer nucleotides and, therefore, its molecular weight is smaller.

Double- and single-stranded RNAs are known. Double-stranded RNA is contained in some viruses, performing (like DNA) the role of the keeper and transmitter of hereditary information. In the cells of other organisms, single-stranded RNAs are found, which are copies of the corresponding sections of DNA.

There are three types of RNA in cells: messenger, transport, and ribosomal.

Messenger RNA (i-RNA) consists of 300-30,000 nucleotides and makes up approximately 5% of all RNA contained in the cell. It is a copy of a specific piece of DNA (gene). i-RNA molecules act as carriers of genetic information from DNA to the site of protein synthesis (into ribosomes) and are directly involved in the assembly of its molecules.

Transfer RNA (t-RNA) makes up to 10% of all cell RNA and consists of 75-85 nucleotides. tRNA molecules transport amino acids from the cytoplasm to the ribosomes.

The main part of the cytoplasmic RNA (about 85%) is ribosomal RNA (r-RNA). It is part of the ribosome. rRNA molecules include 3 - 5 thousand nucleotides. It is believed that r-RNA provides a certain spatial relationship between i-RNA and t-RNA.