Biological role chemical elements in living organisms

1. Macro and microelements in the environment and the human body

The biological role of chemical elements in the human body is extremely diverse.

The main function of macronutrients is to build tissues, maintain a constant osmotic pressure, ionic and acid-base composition.

Trace elements, being part of enzymes, hormones, vitamins, biologically active substances as complexing agents or activators, are involved in metabolism, reproduction processes, tissue respiration, and neutralization of toxic substances. Trace elements actively influence the processes of hematopoiesis, oxidation - recovery, permeability of blood vessels and tissues. Macro- and microelements - calcium, phosphorus, fluorine, iodine, aluminum, silicon determine the formation of bone and dental tissues.

There is evidence that the content of some elements in the human body changes with age. So, the content of cadmium in the kidneys and molybdenum in the liver increases with old age. The maximum content of zinc is observed during puberty, then it decreases and in old age reaches a minimum. The content of other trace elements, such as vanadium and chromium, also decreases with age.

Many diseases associated with a deficiency or excessive accumulation of various trace elements have been identified. Fluorine deficiency causes dental caries, iodine deficiency - endemic goiter, excess molybdenum - endemic gout. Such patterns are connected with the fact that the balance of optimal concentrations of biogenic elements is maintained in the human body - chemical homeostasis. Violation of this balance due to a lack or excess of the element can lead to various diseases.

In addition to the six main macroelements - organogens - carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus, which make up carbohydrates, fats, proteins and nucleic acids, "inorganic" macroelements are necessary for normal human and animal nutrition - calcium, chlorine, magnesium, potassium, sodium - and trace elements - copper, fluorine, iodine, iron, molybdenum, zinc, and also, possibly (proven for animals), selenium, arsenic, chromium, nickel, silicon, tin, vanadium.

The lack of elements such as iron, copper, fluorine, zinc, iodine, calcium, phosphorus, magnesium and some others in the diet leads to serious consequences for human health.

However, it must be remembered that not only a deficiency, but also an excess of biogenic elements is harmful to the body, since this disrupts chemical homeostasis. For example, with the intake of excess manganese with food, the level of copper in the plasma increases (synergism of Mn and Cu), and in the kidneys it decreases (antagonism). Increasing the content of molybdenum in food leads to an increase in the amount of copper in the liver. An excess of zinc in food causes inhibition of the activity of iron-containing enzymes (antagonism of Zn and Fe).

Mineral components, which are vital in negligible amounts, become toxic at higher concentrations.

A number of elements (silver, mercury, lead, cadmium, etc.) are considered toxic, since their entry into the body already in trace amounts leads to severe pathological phenomena. chemical mechanism The toxic effects of certain trace elements will be discussed below.

Biogenic elements are widely used in agriculture. The addition of small amounts of microelements - boron, copper, manganese, zinc, cobalt, molybdenum - to the soil dramatically increases the yield of many crops. It turns out that microelements, by increasing the activity of enzymes in plants, contribute to the synthesis of proteins, vitamins, nucleic acids, sugars and starch. Some of the chemical elements have a positive effect on photosynthesis, accelerate the growth and development of plants, seed maturation. Trace elements are added to animal feed to increase their productivity.

Various elements and their compounds are widely used as medicines.

Thus, the study of the biological role of chemical elements, the elucidation of the relationship between the exchange of these elements and other biologically active substances - enzymes, hormones, vitamins contributes to the creation of new medicines and development optimal modes their dosing for both therapeutic and prophylactic purposes.

The basis for studying the properties of elements and, in particular, their biological role is periodic law DI. Mendeleev. Physiochemical properties, and, consequently, their physiological and pathological role, are determined by the position of these elements in periodic system DI. Mendeleev.

As a rule, with an increase in the charge of the nucleus of atoms, the toxicity of the elements of this group increases and their content in the body decreases. The decrease in content is obviously due to the fact that many elements of long periods are poorly absorbed by living organisms due to large atomic and ionic radii, high nuclear charge, complexity of electronic configurations, and low solubility of compounds. The body contains significant amounts of light elements.

Macroelements include s-elements of the first (hydrogen), third (sodium, magnesium) and fourth (potassium, calcium) periods, as well as p-elements of the second (carbon, nitrogen, oxygen) and third (phosphorus, sulfur, chlorine) periods. All of them are vital. Most of the remaining s- and p-elements of the first three periods (Li, B, Al, F) are physiologically active, s- and p-elements of large periods (n> 4) rarely act as indispensable. The exception is s-elements - potassium, calcium, iodine. Physiologically active include some s- and p-elements of the fourth and fifth periods - strontium, arsenic, selenium, bromine.

Among the d-elements, it is mainly the elements of the fourth period that are vital: manganese, iron, zinc, copper, cobalt. Recently, it has been established that the physiological role of some other d-elements of this period is also undoubted: titanium, chromium, vanadium.

d-Elements of the fifth and sixth periods, with the exception of molybdenum, do not show pronounced positive physiological activity. Molybdenum is also part of a number of redox enzymes (for example, xanthine oxide, aldehyde oxidase) and plays an important role in the course of biochemical processes.

2. General aspects of the toxicity of heavy metals to living organisms

A comprehensive study of the problems associated with assessing the state of the natural environment shows that it is very difficult to draw a clear line between natural and anthropogenic factors changes in ecological systems. The last decades have convinced us of this. that human impact on nature causes not only direct, easily identifiable damage, but also causes a number of new, often hidden processes that transform or destroy the environment. Natural and anthropogenic processes in the biosphere are in a complex relationship and interdependence. So, the course of chemical transformations leading to the formation of toxic substances is influenced by climate, the state of the soil cover, water, air, the level of radioactivity, etc. Under the current conditions, when studying the processes of chemical pollution of ecosystems, the problem arises of finding natural, mainly due to natural factors, levels of the content of certain chemical elements or compounds. The solution to this problem is possible only on the basis of long-term systematic observations of the state of the components of the biosphere, the content of various substances, that is, on the basis of environmental monitoring.

Pollution environment heavy metals is directly related to the ecological and analytical monitoring of supertoxicants, since many of them exhibit high toxicity already in trace amounts and are able to concentrate in living organisms.

The main sources of environmental pollution with heavy metals can be divided into natural (natural) and artificial (anthropogenic). Natural include volcanic eruption, dust storms, forest and steppe fires, sea ​​salts blown up by the wind, vegetation, etc. Natural sources of pollution are either systematic, uniform, or short-term spontaneous and, as a rule, have little effect on general level pollution. The main and most dangerous sources of pollution of nature with heavy metals are anthropogenic.

In the process of studying the chemistry of metals and their biochemical cycles in the biosphere, the dual role that they play in physiology is revealed: on the one hand, most metals are necessary for the normal course of life; on the other hand, at elevated concentrations, they exhibit high toxicity, that is, they have bad influence on the state and activity of living organisms. The boundary between the necessary and toxic concentrations of elements is very vague, which complicates the reliable assessment of their impact on the environment. The amount at which some metals become truly dangerous depends not only on the degree of contamination of ecosystems by them, but also on the chemical characteristics of their biochemical cycle. In table. 1 shows the series of molar toxicity of metals for different types living organisms.

Table 1. Representative sequence of molar toxicity of metals

Organisms Toxicity series Algae Hg>Cu>Cd>Fe>Cr>Zn>Co>MnFungiAg>Hg>Cu>Cd>Cr>Ni>Pb>Co>Zn>Fe >Zn > Pb> CdFishAg>Hg>Cu> Pb>Cd>Al> Zn> Ni> Cr>Co>Mn>>SrMammalsAg, Hg, Cd> Cu, Pb, Sn, Be>> Mn, Zn, Ni, Fe , Cr >> Sr >Сs, Li, Al

For each type of organism, the order of the metals in the rows of the table from left to right reflects the increase in the molar amount of the metal required for the manifestation of the toxicity effect. The minimum molar value refers to the metal with the highest toxicity.

V.V. Kovalsky, based on their importance for life, divided the chemical elements into three groups:

Vital (irreplaceable) elements that are constantly contained in the body (are part of enzymes, hormones and vitamins): H, O, Ca, N, K, P, Na, S, Mg, Cl, C, I, Mn, Cu, Co, Fe, Mo, V. Their deficiency leads to disruption of the normal life of humans and animals.

Table 2. Characteristics of some metalloenzymes - bioinorganic complexes

Metal-enzyme Central atom Ligand environment Object of concentration Enzyme action Carboanhydrase Zn (II) Amino acid residues Erythrocytes Catalyzes reversible hydration of carbon dioxide: CO 2+H 2O↔N 2SO 3↔N ++NSO 3Zn (II) carboxypeptidase Amino acid residues Pancreas, liver, intestine Catalyzes protein digestion, participates in peptide bond hydrolysis: R 1CO-NH-R 2+H 2O↔R 1-COOH+R 2NH 2Catalase Fe (III) Amino acid residues, histidine, tyrosine Blood Catalyzes the decomposition reaction of hydrogen peroxide: 2H 2ABOUT 2= 2N 2O + O 2Fe(III) peroxidaseProteinsTissue, bloodOxidation of substrates (RH 2) hydrogen peroxide: RH 2+ H 2O 2=R+2H 2Cu(II) oxidoreductase Amino acid residues Heart, liver, kidneys Catalyzes oxidation with molecular oxygen: 2H 2R+O 2= 2R + 2H 2O Pyruvate carboxylase Mn (II) Tissue proteins Liver, thyroid gland Enhances the action of hormones. Catalyzes the process of carboxylation with pyruvic acid Aldehyde oxidase Mo (VI) Tissue proteins Liver Participates in the oxidation of aldehydes Ribonucleotide reductase Co (II) Tissue proteins Liver Participates in the biosynthesis of ribonucleic acids

• impurity elements permanently contained in the body: Ga, Sb, Sr, Br, F, B, Be, Li, Si, An, Cs, Al, Ba, Ge, As, Rb, Pb, Ra, Bi, Cd, Cr, Ni, Ti, Ag, Th, Hg, U, Se. Their biological role is little understood or unknown.
• impurity elements found in the body Sc, Tl, In, La, Pr, Sm, W, Re, Tb, etc. Data on the amount and biological role are not clear.
• The table shows the characteristics of a number of metalloenzymes, which include such vital metals as Zn, Fe, Cu, Mn, Mo.
• Depending on the behavior in living systems, metals can be divided into 5 types:
• - necessary elements, with a lack of which functional disorders occur in the body;
• - stimulants (metals necessary and not necessary for the body can act as stimulants);
• inert elements that are harmless at certain concentrations and do not have any effect on the body (for example, inert metals used as surgical implants):
• therapeutic agents used in medicine;
• toxic elements, at high concentrations leading to irreversible functional disorders, death of the body.
• Depending on the concentration and time of contact, the metal can act according to one of the indicated types.
• Figure 1 shows a diagram of the dependence of the state of the organism on the concentration of metal ions. The solid curve in the diagram describes the immediate positive response, the optimal level, and the transition of the positive effect to the negative one after the concentration values ​​of the desired element pass through the maximum. At high concentrations, the required metal becomes toxic.
• The dotted curve shows the biological response to a metal toxic to the body without the effect of an essential or stimulating element. This curve comes with some delay, which indicates the ability of a living organism to “not react” to small amounts of a toxic substance (threshold concentration).
• From the diagram it follows that the necessary elements become toxic in excess quantities. The organism of animals and humans maintains the concentration of elements in the optimal range through a complex of physiological processes called homeostasis. The concentration of all, without exception, the necessary metals is under strict control of homeostasis.

• Fig.1 Biological response depending on the concentration of the metal. ( Mutual arrangement two curves relative to the concentration scale conditionally)
• metal toxicity ion poisoning
• Of particular interest is the content of chemical elements in the human body. Human organs differently concentrate various chemical elements in themselves, that is, macro- and microelements are unevenly distributed between different organs and tissues. Most trace elements (the content in the body is within 10 -3-10-5%) accumulates in the liver, bone and muscle tissues. These fabrics are the main depot for many metals.
• Elements may show a specific affinity for certain organs and be contained in them in high concentrations. It is known that zinc is concentrated in the pancreas, iodine in the thyroid gland, vanadium, along with aluminum and arsenic, accumulates in hair and nails, cadmium, mercury, molybdenum - in the kidneys, tin in the intestinal tissues, strontium - in the prostate gland, bone tissue, manganese in the pituitary gland, etc. In the body, trace elements can be found in bound state, and in the form of free ionic forms. It has been established that aluminum, copper and titanium in the brain tissues are in the form of complexes with proteins, while manganese is in ionic form.
• In response to the intake of excessive concentrations of elements into the body, a living organism is able to limit or even eliminate the resulting toxic effect due to the presence of certain detoxification mechanisms. The specific mechanisms of detoxification in relation to metal ions are currently not well understood. Many metals in the body can be converted into less harmful forms in the following ways:
• formation of insoluble complexes in intestinal tract;
• transport of metal with blood to other tissues where it can be immobilized (as, for example, Pb + 2 in the bones);

The cells of living organisms chemical composition significantly differ from the inanimate environment surrounding them and in structure chemical compounds, and by 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 , trace elements And ultramicroelements .

Macronutrients.

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 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. Macronutrients in total make up about 99% of the mass of living cells, with most (98%) falling on 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 (these are hydrogen, oxygen, carbon, nitrogen, as mentioned earlier) are characterized by one common property. These elements lack one or more electrons in their outer orbit to form stable electronic bonds. So, the hydrogen atom lacks one electron in the outer orbit to form a stable electronic bond, the atoms of oxygen, nitrogen and carbon lack two, three and four electrons, respectively. In this regard, these chemical elements easily form covalent bonds due to pairing of electrons, and can easily interact with each other, filling their external 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 increases significantly.

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

Microelements.

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

Examples of trace elements are presented in the table below:

Ultramicroelements.

Into the group ultramicroelements includes elements whose content in the body is extremely small (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 trace elements, are part of enzymes.

Cell

From the point of view of the concept of living systems according to A. Lehninger.

A living cell is an isothermal system of organic molecules capable of self-regulation and self-reproduction, extracting energy and resources from the environment.

flows in the cell a large number of sequential reactions, the rate of which is regulated by the cell itself.

The cell maintains itself in a stationary dynamic state far from equilibrium with the environment.

Cells operate on the principle of minimal consumption of components and processes.

That. a cell is an elementary living open system capable of independent existence, reproduction and development. It is an elementary structural and functional unit of all living organisms.

The chemical composition of cells.

Of the 110 elements of the periodic system of Mendeleev, 86 were found to be permanently present in the human body. 25 of them are necessary for normal life, and 18 of them are absolutely necessary, and 7 are useful. In accordance with the percentage in the cell, chemical elements are divided into three groups:

Macronutrients The main elements (organogens) are hydrogen, carbon, oxygen, nitrogen. Their concentration: 98 - 99.9%. They are universal components of the organic compounds of the cell.

Trace elements - sodium, magnesium, phosphorus, sulfur, chlorine, potassium, calcium, iron. Their concentration is 0.1%.

Ultramicroelements - boron, silicon, vanadium, manganese, cobalt, copper, zinc, molybdenum, selenium, iodine, bromine, fluorine. They affect metabolism. Their absence is the cause of diseases (zinc - diabetes, iodine - endemic goiter, iron - pernicious anemia, etc.).

Modern medicine knows the facts of the negative interaction of vitamins and minerals:

Zinc reduces the absorption of copper and competes for absorption with iron and calcium; (and zinc deficiency causes weakening immune system, a number of pathological conditions from the endocrine glands).

Calcium and iron reduce the absorption of manganese;

Vitamin E does not combine well with iron, and vitamin C does not combine well with B vitamins.

Positive interaction:

Vitamin E and selenium, as well as calcium and vitamin K, act synergistically;

Vitamin D is essential for the absorption of calcium;

Copper promotes absorption and increases the efficiency of using iron in the body.

inorganic components of the cell.

Water- the most important component cells, the universal dispersion medium of living matter. Active cells of terrestrial organisms consist of 60 - 95% water. In resting cells and tissues (seeds, spores) water is 10-20%. Water in the cell is in two forms - free and associated with cellular colloids. Free water is the solvent and dispersion medium of the colloidal system of protoplasm. Her 95%. Bound water (4-5%) of all cell water forms fragile hydrogen and hydroxyl bonds with proteins.

Water properties:

Water is a natural solvent for mineral ions and other substances.

Water is the dispersed phase of the colloidal system of protoplasm.

Water is the medium for the reactions of cell metabolism, because. physiological processes occur in an exclusively aquatic environment. Provides reactions of hydrolysis, hydration, swelling.

Participates in many enzymatic reactions of the cell and is formed in the process of metabolism.

Water is the source of hydrogen ions during photosynthesis in plants.

Biological value of water:

Most biochemical reactions take place only in an aqueous solution; many substances enter and exit cells in a dissolved form. This characterizes the transport function of water.

Water provides hydrolysis reactions - the breakdown of proteins, fats, carbohydrates under the action of water.

Due to the high heat of evaporation, the body is cooled. For example, perspiration in humans or transpiration in plants.

The high heat capacity and thermal conductivity of water contributes to the uniform distribution of heat in the cell.

Due to the forces of adhesion (water - soil) and cohesion (water - water), water has the property of capillarity.

The incompressibility of water determines the stress state of the cell walls (turgor), the hydrostatic skeleton in roundworms.