Organisms are made up of cells. Cells of different organisms have similar chemical composition. Table 1 presents the main chemical elements found in the cells of living organisms.
Table 1. The content of chemical elements in a cell
According to the content in the cell, three groups of elements can be distinguished. The first group includes oxygen, carbon, hydrogen and nitrogen. They account for almost 98% of the total composition of the cell. The second group includes potassium, sodium, calcium, sulfur, phosphorus, magnesium, iron, chlorine. Their content in the cell is tenths and hundredths of a percent. The elements of these two groups belong to macronutrients(from Greek. macro- big).
The remaining elements, represented in the cell by hundredths and thousandths of a percent, are included in the third group. it trace elements(from Greek. micro- small).
No elements inherent only in living nature were found in the cell. All of these chemical elements are also part of inanimate nature. This indicates the unity of animate and inanimate nature.
The lack of any element can lead to illness, and even death of the body, since each element plays a specific role. Macronutrients of the first group form the basis of biopolymers - proteins, carbohydrates, nucleic acids, and lipids, without which life is impossible. Sulfur is part of some proteins, phosphorus is part of nucleic acids, iron is part of hemoglobin, and magnesium is part of chlorophyll. Calcium plays an important role in metabolism.
Part of the chemical elements contained in the cell is part of inorganic substances - mineral salts and water.
mineral salts are in the cell, as a rule, in the form of cations (K +, Na +, Ca 2+, Mg 2+) and anions (HPO 2-/4, H 2 PO -/4, CI -, HCO 3), the ratio of which determines the acidity of the medium, which is important for the life of cells.
(In many cells, the medium is slightly alkaline and its pH hardly changes, since a certain ratio of cations and anions is constantly maintained in it.)
Of the inorganic substances in wildlife, a huge role is played by water.
Life is impossible without water. It makes up a significant mass of most cells. A lot of water is contained in the cells of the brain and human embryos: more than 80% of water; in adipose tissue cells - only 40%. By old age, the water content in the cells decreases. A person who loses 20% of water dies.
The unique properties of water determine its role in the body. It is involved in thermoregulation, which is due to the high heat capacity of water - consumption a large number energy when heated. What determines the high heat capacity of water?
In a water molecule, an oxygen atom is covalently bonded to two hydrogen atoms. The water molecule is polar because the oxygen atom has a partially negative charge, and each of the two hydrogen atoms has
Partially positive charge. A hydrogen bond is formed between the oxygen atom of one water molecule and the hydrogen atom of another molecule. Hydrogen bonds provide the connection of a large number of water molecules. When water is heated, a significant part of the energy is spent on breaking hydrogen bonds, which determines its high heat capacity.
Water - good solvent . Due to the polarity, its molecules interact with positively and negatively charged ions, thereby contributing to the dissolution of the substance. In relation to water, all substances of the cell are divided into hydrophilic and hydrophobic.
hydrophilic(from Greek. hydro- water and fileo- love) are called substances that dissolve in water. These include ionic compounds (eg salts) and some non-ionic compounds (eg sugars).
hydrophobic(from Greek. hydro- water and phobos- fear) are called substances that are insoluble in water. These include, for example, lipids.
Water plays an important role in the chemical reactions that take place in the cell in aqueous solutions. It dissolves metabolic products that are unnecessary to the body and thereby contributes to their removal from the body. The high water content in the cell gives it elasticity. Water promotes movement various substances within a cell or from cell to cell.
Bodies of animate and inanimate nature consist of the same chemical elements. The composition of living organisms includes inorganic substances - water and mineral salts. The vital numerous functions of water in a cell are due to the peculiarities of its molecules: their polarity, the ability to form hydrogen bonds.
INORGANIC COMPONENTS OF THE CELL
About 90 elements are found in the cells of living organisms, and approximately 25 of them are found in almost all cells. According to the content in the cell, chemical elements are divided into three large groups: macroelements (99%), microelements (1%), ultramicroelements (less than 0.001%).
Macronutrients include oxygen, carbon, hydrogen, phosphorus, potassium, sulfur, chlorine, calcium, magnesium, sodium, and iron.
Microelements include manganese, copper, zinc, iodine, fluorine.
Ultramicroelements include silver, gold, bromine, selenium.
| ELEMENTS | CONTENT IN THE BODY (%) | BIOLOGICAL SIGNIFICANCE |
| Macronutrients: | ||
| O.C.H.N | 62-3 | They are part of all organic substances of the cell, water |
| Phosphorus R | 1,0 | They are part of nucleic acids, ATP (forms macroergic bonds), enzymes, bone tissue and tooth enamel |
| Calcium Ca +2 | 2,5 | In plants it is part of the cell membrane, in animals it is part of the bones and teeth, it activates blood clotting |
| Trace elements: | 1-0,01 | |
| Sulfur S | 0,25 | Contains proteins, vitamins and enzymes |
| Potassium K+ | 0,25 | Causes the conduction of nerve impulses; activator of protein synthesis enzymes, photosynthesis processes, plant growth |
| Chlorine CI - | 0,2 | Is a component of gastric juice in the form of hydrochloric acid, activates enzymes |
| Sodium Na+ | 0,1 | Provides conduction of nerve impulses, maintains osmotic pressure in the cell, stimulates the synthesis of hormones |
| Magnesium Mg +2 | 0,07 | Included in the chlorophyll molecule, found in bones and teeth, activates DNA synthesis, energy metabolism |
| Iodine I - | 0,1 | It is part of the thyroid hormone - thyroxine, affects metabolism |
| Iron Fe+3 | 0,01 | It is part of hemoglobin, myoglobin, the lens and cornea of the eye, an enzyme activator, and is involved in the synthesis of chlorophyll. Provides oxygen transport to tissues and organs |
| Ultramicroelements: | less than 0.01, trace amounts | |
| Copper Si +2 | Participates in the processes of hematopoiesis, photosynthesis, catalyzes intracellular oxidative processes | |
| Manganese Mn | Increases the yield of plants, activates the process of photosynthesis, affects the processes of hematopoiesis | |
| Bor V | Influences the growth processes of plants | |
| Fluorine F | It is part of the enamel of the teeth, with a deficiency, caries develops, with an excess - fluorosis | |
| Substances: | ||
| H 2 0 | 60-98 | It makes up the internal environment of the body, participates in the processes of hydrolysis, structures the cell. Universal solvent, catalyst, contributor chemical reactions |
ORGANIC COMPONENTS OF A CELL
| SUBSTANCES | STRUCTURE AND PROPERTIES | FUNCTIONS |
| Lipids | ||
| Esters of higher fatty acids and glycerol. Phospholipids also contain an H 3 PO4 residue. They have hydrophobic or hydrophilic-hydrophobic properties, high energy intensity | Construction- forms a bilipid layer of all membranes. Energy. Thermoregulatory. Protective. Hormonal(corticosteroids, sex hormones). Components vitamins D, E. Source of water in the body. Spare nutrient |
|
| Carbohydrates | ||
| Monosaccharides: glucose, fructose, ribose, deoxyribose |
Well soluble in water | Energy |
| Disaccharides: sucrose, maltose (malt sugar) |
Soluble in water | Components of DNA, RNA, ATP |
| Polysaccharides: starch, glycogen, cellulose |
Poorly soluble or insoluble in water | Reserve nutrient. Construction - the shell of a plant cell |
| Squirrels | Polymers. Monomers - 20 amino acids. | Enzymes are biocatalysts. |
| I structure - the sequence of amino acids in the polypeptide chain. Communication - peptide - CO- NH- | Construction - are part of the membrane structures, ribosomes. | |
| II structure - a-helix, bond - hydrogen | Motor (contractile muscle proteins). | |
| III structure - spatial configuration a- spirals (globule). Bonds - ionic, covalent, hydrophobic, hydrogen | Transport (hemoglobin). Protective (antibodies). Regulatory (hormones, insulin) | |
| Structure IV is not characteristic of all proteins. The connection of several polypeptide chains into a single superstructure. They are poorly soluble in water. Action high temperatures, concentrated acids and alkalis, salts of heavy metals causes denaturation | ||
| Nucleic acids: | Biopolymers. Made up of nucleotides | |
| DNA - deoxy-ribonucleic acid. | Nucleotide composition: deoxyribose, nitrogenous bases - adenine, guanine, cytosine, thymine, H 3 PO 4 residue. Complementarity of nitrogenous bases A \u003d T, G \u003d C. Double helix. Capable of self-doubling | They form chromosomes. Storage and transmission of hereditary information, genetic code. Biosynthesis of RNA, proteins. Encodes the primary structure of a protein. Contained in the nucleus, mitochondria, plastids |
| RNA - ribonucleic acid. | Nucleotide composition: ribose, nitrogenous bases - adenine, guanine, cytosine, uracil, H 3 PO 4 residue Complementarity of nitrogenous bases A \u003d U, G \u003d C. One chain | |
| Messenger RNA | Transfer of information about the primary structure of the protein, involved in protein biosynthesis | |
| Ribosomal RNA | Builds the body of the ribosome | |
| Transfer RNA | Encodes and transports amino acids to the site of protein synthesis - the ribosome | |
| Viral RNA and DNA | The genetic apparatus of viruses | |
Enzymes.
The most important function of proteins is catalytic. Protein molecules that increase the rate of chemical reactions in a cell by several orders of magnitude are called enzymes. Not a single biochemical process in the body occurs without the participation of enzymes.
Over 2000 enzymes have been discovered so far. Their efficiency is many times higher than the efficiency of inorganic catalysts used in production. So, 1 mg of iron in the composition of the catalase enzyme replaces 10 tons of inorganic iron. Catalase increases the rate of decomposition of hydrogen peroxide (H 2 O 2) by 10 11 times. The enzyme catalyzing the formation of carbonic acid (CO 2 + H 2 O \u003d H 2 CO 3) accelerates the reaction by 10 7 times.
An important property of enzymes is the specificity of their action; each enzyme catalyzes only one or a small group of similar reactions.
The substance that an enzyme acts on is called substrate. The structures of the enzyme molecule and the substrate must exactly match each other. This explains the specificity of the action of enzymes. When a substrate is combined with an enzyme, the spatial structure of the enzyme changes.
The sequence of interaction between the enzyme and the substrate can be depicted schematically:
Substrate+Enzyme - Enzyme-substrate complex - Enzyme+Product.
It can be seen from the diagram that the substrate combines with the enzyme to form an enzyme-substrate complex. In this case, the substrate is transformed into a new substance - the product. At the final stage, the enzyme is released from the product and again interacts with the next substrate molecule.
Enzymes function only at a certain temperature, concentration of substances, acidity of the environment. A change in conditions leads to a change in the tertiary and quaternary structure of the protein molecule, and, consequently, to the suppression of the activity of the enzyme. How does this happen? Only a certain part of the enzyme molecule has catalytic activity, called active center. The active center contains from 3 to 12 amino acid residues and is formed as a result of the bending of the polypeptide chain.
Under the influence of various factors, the structure of the enzyme molecule changes. In this case, the spatial configuration of the active center is disturbed, and the enzyme loses its activity.
Enzymes are proteins that act as biological catalysts. Thanks to enzymes, the rate of chemical reactions in cells increases by several orders of magnitude. An important property of enzymes is the specificity of action under certain conditions.
Nucleic acids.
Nucleic acids were discovered in the second half of the 19th century. Swiss biochemist F. Miescher, who isolated a substance with a high content of nitrogen and phosphorus from the nuclei of cells and called it "nuclein" (from lat. nucleus- nucleus).
Nucleic acids store hereditary information about the structure and functioning of every cell and all living beings on Earth. There are two types of nucleic acids - DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Nucleic acids, like proteins, are species-specific, that is, organisms of each species have their own type of DNA. To find out the reasons for species specificity, consider the structure of nucleic acids.
Nucleic acid molecules are very long chains consisting of many hundreds and even millions of nucleotides. Any nucleic acid contains only four types of nucleotides. The functions of nucleic acid molecules depend on their structure, their constituent nucleotides, their number in the chain, and the sequence of the compound in the molecule.
Each nucleotide is made up of three components: a nitrogenous base, a carbohydrate, and phosphoric acid. Each DNA nucleotide contains one of the four types of nitrogenous bases (adenine - A, thymine - T, guanine - G or cytosine - C), as well as a deoxyribose carbohydrate and a phosphoric acid residue.
Thus, DNA nucleotides differ only in the type of nitrogenous base.
The DNA molecule consists of a huge number of nucleotides connected in a chain in a certain sequence. Each type of DNA molecule has its own number and sequence of nucleotides.
DNA molecules are very long. For example, a literal record of the nucleotide sequence in DNA molecules from one human cell (46 chromosomes) would require a book of about 820,000 pages. The alternation of four types of nucleotides can form an infinite number of variants of DNA molecules. These features of the structure of DNA molecules allow them to store a huge amount of information about all the signs of organisms.
In 1953, the American biologist J. Watson and the English physicist F. Crick created a model for the structure of the DNA molecule. Scientists have found that each DNA molecule consists of two strands interconnected and spirally twisted. It looks like a double helix. In each chain, four types of nucleotides alternate in a specific sequence.
The nucleotide composition of DNA is different different types bacteria, fungi, plants, animals. But it does not change with age, it depends little on changes. environment. Nucleotides are paired, that is, the number of adenine nucleotides in any DNA molecule is equal to the number of thymidine nucleotides (A-T), and the number of cytosine nucleotides is equal to the number of guanine nucleotides (C-G). This is due to the fact that the connection of two chains to each other in a DNA molecule obeys a certain rule, namely: adenine of one chain is always connected by two hydrogen bonds only with Thymine of the other chain, and guanine by three hydrogen bonds with cytosine, that is, the nucleotide chains of one molecule DNA is complementary, complement each other.
Nucleic acid molecules - DNA and RNA are made up of nucleotides. The composition of DNA nucleotides includes a nitrogenous base (A, T, G, C), a deoxyribose carbohydrate and a residue of a phosphoric acid molecule. The DNA molecule is a double helix, consisting of two strands connected by hydrogen bonds according to the principle of complementarity. The function of DNA is to store hereditary information.
In the cells of all organisms there are molecules of ATP - adenosine triphosphoric acid. ATP is a universal cell substance, the molecule of which has energy-rich bonds. The ATP molecule is one kind of nucleotide, which, like other nucleotides, consists of three components: a nitrogenous base - adenine, a carbohydrate - ribose, but instead of one it contains three residues of phosphoric acid molecules (Fig. 12). The bonds indicated by the icon in the figure are rich in energy and are called macroergic. Each ATP molecule contains two macroergic bonds.
When the high-energy bond is broken and one molecule of phosphoric acid is cleaved off with the help of enzymes, 40 kJ / mol of energy is released, and ATP is converted into ADP - adenosine diphosphoric acid. With the elimination of one more phosphoric acid molecule, another 40 kJ / mol is released; AMP is formed - adenosine monophosphoric acid. These reactions are reversible, that is, AMP can turn into ADP, ADP - into ATP.
ATP molecules are not only broken down, but also synthesized, so their content in the cell is relatively constant. The importance of ATP in the life of the cell is enormous. These molecules play a leading role in the energy metabolism necessary to ensure the vital activity of the cell and the organism as a whole.
Rice. 12. Scheme of the structure of ATP.| adenine - |
An RNA molecule, as a rule, is a single chain consisting of four types of nucleotides - A, U, G, C. Three main types of RNA are known: mRNA, rRNA, tRNA. The content of RNA molecules in the cell is not constant, they are involved in protein biosynthesis. ATP is the universal energy substance of the cell, in which there are energy-rich bonds. ATP plays a central role in the exchange of energy in the cell. RNA and ATP are found both in the nucleus and in the cytoplasm of the cell.
Tasks and tests on the topic "Topic 4. "Chemical composition of the cell.""
- polymer, monomer;
- carbohydrate, monosaccharide, disaccharide, polysaccharide;
- lipid, fatty acid, glycerol;
- amino acid, peptide bond, protein;
- catalyst, enzyme, active site;
- nucleic acid, nucleotide.
Algorithm for solving problems.
Type 1. DNA self-copying.
One of the DNA chains has the following nucleotide sequence:
AGTACCGATACCGATTTCG...
What sequence of nucleotides does the second chain of the same molecule have?
To write the nucleotide sequence of the second strand of a DNA molecule, when the sequence of the first strand is known, it is enough to replace thymine with adenine, adenine with thymine, guanine with cytosine, and cytosine with guanine. Making this substitution, we get the sequence:
TACTGGCTATGAGCTAAATG...
Type 2. Protein coding.
The amino acid chain of the ribonuclease protein has the following beginning: lysine-glutamine-threonine-alanine-alanine-alanine-lysine ...
What sequence of nucleotides starts the gene corresponding to this protein?
To do this, use the table of the genetic code. For each amino acid, we find its code designation in the form of the corresponding trio of nucleotides and write it out. Arranging these triplets one after another in the same order as the corresponding amino acids go, we obtain the formula for the structure of the messenger RNA section. As a rule, there are several such triples, the choice is made according to your decision (but only one of the triples is taken). There may be several solutions, respectively.
AAACAAAATSUGTSGGTSUGTSGAAG
What amino acid sequence does a protein begin with if it is encoded by such a sequence of nucleotides:
ACGCCATGGCCGGT...
According to the principle of complementarity, we find the structure of the informational RNA section formed on a given segment of the DNA molecule:
UGCGGGUACCCGCCCA...
Then we turn to the table of the genetic code and for each trio of nucleotides, starting from the first, we find and write out the amino acid corresponding to it:
Cysteine-glycine-tyrosine-arginine-proline-...
Ivanova T.V., Kalinova G.S., Myagkova A.N. "General Biology". Moscow, "Enlightenment", 2000
- Topic 4. " Chemical composition cells." §2-§7 pp. 7-21
- Topic 5. "Photosynthesis." §16-17 pp. 44-48
- Topic 6. "Cellular respiration." §12-13 pp. 34-38
- Topic 7. " genetic information." §14-15 pp. 39-44
A2. Which scientist discovered the cell? 1) A. Leeuwenhoek 2) T. Schwann 3) R. Hooke 4) R. Virkhov
A3. The content of what chemical element prevails in the dry matter of the cell? 1) nitrogen 2) carbon 3) hydrogen 4) oxygen
A4. What phase of meiosis is shown in the figure? 1) Anaphase I 2) Metaphase I 3) Metaphase II 4) Anaphase II
A5. What organisms are chemotrophs? 1) animals 2) plants 3) nitrifying bacteria 4) fungi A6. The formation of a two-layer embryo occurs during the period 1) crushing 2) gastrulation 3) organogenesis 4) postembryonic period
A7. The totality of all the genes of an organism is called 1) genetics 2) gene pool 3) genocide 4) A8 genotype. In the second generation, with monohybrid crossing and with complete dominance, splitting of characters is observed in the ratio 1) 3:1 2) 1:2:1 3) 9:3:3:1 4) 1:1
A9. Physical mutagenic factors include 1) ultraviolet radiation 2) nitrous acid 3) viruses 4) benzpyrene
A10. Where in a eukaryotic cell is ribosomal RNA synthesized? 1) ribosome 2) rough ER 3) nucleolus of the nucleus 4) Golgi apparatus
A11. What is the term for a section of DNA that codes for one protein? 1) codon 2) anticodon 3) triplet 4) gene
A12. Name the autotrophic organism 1) boletus mushroom 2) amoeba 3) tubercle bacillus 4) pine
A13. What is nuclear chromatin? 1) karyoplasm 2) RNA strands 3) fibrous proteins 4) DNA and proteins
A14. At what stage of meiosis does crossing over occur? 1) prophase I 2) interphase 3) prophase II 4) anaphase I
A15. What is formed during organogenesis from the ectoderm? 1) chord 2) neural tube 3) mesoderm 4) endoderm
A16. A non-cellular form of life is 1) euglena 2) bacteriophage 3) streptococcus 4) ciliate
A17. The synthesis of a protein on i-RNA is called 1) translation 2) transcription 3) reduplication 4) dissimilation
A18. In the light phase of photosynthesis, 1) synthesis of carbohydrates 2) synthesis of chlorophyll 3) absorption of carbon dioxide 4) photolysis of water occurs
A19. Cell division with the preservation of the chromosome set is called 1) amitosis 2) meiosis 3) gametogenesis 4) mitosis
A20. Plastic metabolism includes 1) glycolysis 2) aerobic respiration 3) assembly of the mRNA chain on DNA 4) breakdown of starch to glucose
A21. Choose the wrong statement In prokaryotes, the DNA molecule 1) is closed in a ring 2) is not associated with proteins 3) contains uracil instead of thymine 4) is present in singular
A22. Where does the third stage of catabolism take place - complete oxidation or respiration? 1) in the stomach 2) in mitochondria 3) in lysosomes 4) in cytoplasm
A23. Asexual reproduction includes 1) parthenocarpic fruit formation in cucumber 2) parthenogenesis in bees 3) reproduction of tulip bulbs 4) self-pollination in flowering plants
A24. What organism in the postembryonic period develops without metamorphosis? 1) lizard 2) frog 3) Colorado beetle 4) fly
A25. The human immunodeficiency virus infects 1) gonads 2) T-lymphocytes 3) erythrocytes 4) skin and lungs
A26. Cell differentiation begins at the stage of 1) blastula 2) neurula 3) zygote 4) gastrula
A27. What are protein monomers? 1) monosaccharides 2) nucleotides 3) amino acids 4) enzymes
A28. In what organelle does the accumulation of substances and the formation of secretory vesicles take place? 1) Golgi apparatus 2) rough ER 3) plastid 4) lysosome
A29. What disease is sex-linked? 1) deafness 2) diabetes 3) hemophilia 4) hypertension
A30. Indicate the incorrect statement The biological significance of meiosis is as follows: 1) the genetic diversity of organisms increases 2) the stability of the species increases when environmental conditions change 3) it becomes possible to recombine traits as a result of crossing over 4) the probability of combinative variability of organisms decreases.
b) oxygenc) carbon d) hydrogen 2. Which of the chemical elements is simultaneously part of bone tissue and nucleic acids? a) potassium b) phosphorus c) calcium d) zinc 3. When water freezes, the distance between molecules: a) decreases b) increases c) does not change 4. Children develop rickets with a lack of: a) manganese and iron b) calcium and phosphorus c) copper and zinc d) sulfur and nitrogen 5. Which of the elements is included in the chlorophyll molecule? a) sodium b) potassium c) magnesium d) chlorine 6. Write out from a number of chemical elements: O, C, H, N, Fe, K, S, Zn, Cu contained in the cell, those that are: a) the basis organic compounds b) macroelements c) trace elements 7. Write out from the proposed series of elements: O, Si, Fe, H, C, N, Al, Mg those that prevail: a) in wildlife b) in inanimate nature 8. What is the value water for the life of the cell: a) a medium for chemical elements b) a solvent c) a source of oxygen during photosynthesis The chemical composition of the cell. organic matter. 1. Which of the named chemical compounds is not a biopolymer? a) protein b) glucose c) DNA d) cellulose 2. From which compounds are hydrocarbons synthesized during photosynthesis? a) from O2 and H2O b) from CO2 and H2 c) from CO2 and H2O d) from CO2 and H2CO3 3. Which of the products is more appropriate to give to a tired marathon runner at a distance to maintain strength? a) a piece of sugar b) a little butter c) a piece of meat d) a little mineral water 4. The ability of camels to tolerate thirst well is explained by the fact that fats: a) retain water in the body b) release water during oxidation c) create a heat-insulating layer that reduces evaporation 5. The greatest amount of energy is released during splitting one gram: a) C5H12O5 b) C6H10O6 c) C6H12O6 d) C6H12O5 6. In which case is the formula of the glucose molecule correctly written? a) ether b) alcohol c) water) hydrochloric acid
Message about the chemical element Cu (copper)1.The value of chemical
element for the human body
2. What does the lack of this element lead to?
3. What does an excess of this element lead to?
4. What foods contain
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. The disruption of this balance
The effect of a deficiency or excess of an 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 - calcium, chlorine, magnesium, potassium are necessary for normal human and animal nutrition. , 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, when an excess of manganese is taken 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 2n and Re).
Mineral components, which are vital in negligible amounts, become toxic at higher concentrations.
Vital necessity, deficiency, toxicity of a chemical element are presented in the form of a dependence curve "The concentration of an element in food products - the reaction of the body" (Fig. 5.5). The approximately horizontal section of the curve (plateau) describes the area of concentrations corresponding to optimal growth, health, reproduction. The large extent of the plateau indicates not only the low toxicity of the element, but also the great ability of the body to adapt to significant changes in the content of this element. On the contrary, a narrow plateau indicates a significant toxicity of the element and a sharp transition from the amounts necessary for the body to life-threatening. When leaving the plateau (increase in the concentration of the trace element), all elements become toxic. Ultimately, a significant increase in the concentration of trace elements can be fatal.
A number of elements (silver, mercury, lead, cadmium, etc.)
are toxic, since their entry into the body already in microquantities leads to severe pathological phenomena. The chemical mechanism of the toxic effects of some 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.
widely used various elements and their compounds 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 drugs and the development of optimal dosage regimens for both therapeutic and prophylactic purposes.
The biological role of 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. The chemical mechanism of the toxic effects of some 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 the periodic law of D.I. Mendeleev. Physiochemical properties, and, consequently, their physiological and pathological role, are determined by the position of these elements in the periodic system of D.I. 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
Comprehensive study of the problems associated with the assessment of the condition natural environment shows that it is very difficult to draw a clear line between natural and anthropogenic factors in changing 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 in them, that is, on the basis of environmental monitoring.
Environmental pollution with 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 wind-blown, vegetation, etc. Natural sources of pollution are either systematic uniform or short-term spontaneous and, as a rule, have little effect on the overall level of 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 a harmful effect 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 of 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, intestines 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 2O 2= 2N 2O + O 2Fe(III) peroxidaseProteinsTissue, bloodOxidation of substrates (RH 2) hydrogen peroxide: RH 2+ H 2O 2=R+2H 2Oxireductase Cu (II) Amino acid residues Heart, liver, kidneys Catalyzes oxidation with the help of 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 So, in response to the action of toxic ions of lead, mercury, cadmium, etc., the human liver and kidneys increase the synthesis of metallothiones - proteins of low molecular weight, in which approximately 1/3 of the amino acid residues is cysteine. A high content and a certain arrangement of sulfhydryl SH-groups provide the possibility of strong binding of metal ions. The mechanisms of metal toxicity are generally well known, but it is very difficult to find them for any particular metal. One of these mechanisms is the concentration between essential and toxic metals for possessing binding sites in proteins, since metal ions stabilize and activate many proteins, being part of many enzyme systems. In addition, many protein macromolecules have free sulfhydryl groups that can interact with toxic metal ions such as cadmium, lead, and mercury, resulting in toxic effects. However, it is not exactly established which macromolecules harm a living organism in this case. The manifestation of toxicity of metal ions in different organs and tissues is not always associated with the level of their accumulation - there is no guarantee that the greatest damage occurs in that part of the body where the concentration of this metal is higher. So lead(II) ions, being more than 90% of total in the body immobilized in the bones, exhibit toxicity due to 10% distributed in other tissues of the body. The immobilization of lead ions in the bones can be considered as a detoxification process. The toxicity of a metal ion is usually not associated with its need for the body. However, toxicity and necessity have one thing in common: as a rule, there is a relationship between metal ions from each other, exactly, as well as between metal and non-metal ions, in the overall contribution to the effectiveness of their action. For example, cadmium toxicity is more pronounced in a system with zinc deficiency, while lead toxicity is exacerbated by calcium deficiency. Similarly, the adsorption of iron from vegetable food is inhibited by the complexing ligands present in it, and an excess of zinc ions can inhibit the adsorption of copper, etc. Determination of the mechanisms of toxicity of metal ions is often complicated by the existence of various ways of their penetration into a living organism. Metals can be ingested with food, water, absorbed through the skin, penetrated by inhalation, etc. Absorption with dust is the main route of penetration in industrial pollution. As a result of inhalation, most metals settle in the lungs and only then spread to other organs. 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- transformation by the liver and kidneys into a less toxic form.