>> Chemistry: Chemical elements in the cells of living organisms
More than 70 elements have been found in the composition of substances that form the cells of all living organisms (humans, animals, plants). These elements are usually divided into two groups: macroelements and microelements.
Macronutrients are found in cells in large quantities. First of all, these are carbon, oxygen, nitrogen and hydrogen. In total, they make up almost 98% of the total contents of the cell. In addition to these elements, macronutrients also include magnesium, potassium, calcium, sodium, phosphorus, sulfur and chlorine. Their total content is 1.9%. Thus, for the rest chemical elements accounts for about 0.1%. These are micronutrients. These include iron, zinc, manganese, boron, copper, iodine, cobalt, bromine, fluorine, aluminum, etc.
23 trace elements were found in the milk of mammals: lithium, rubidium, copper, silver, barium, strontium, titanium, arsenic, vanadium, chromium, molybdenum, iodine, fluorine, manganese, iron, cobalt, nickel, etc.
The composition of the blood of mammals includes 24 microelements, and the composition of the human brain - 18 microelements.
As you can see, there are no special elements in the cell that are characteristic only of living nature, that is, at the atomic level there are no differences between living and inanimate nature. These differences are found only at the level of complex substances - at the molecular level. So, along with inorganic substances (water and mineral salts), the cells of living organisms contain substances that are characteristic only for them - organic substances (proteins, fats, carbohydrates, nucleic acids, vitamins, hormones, etc.). These substances are built mainly from carbon, hydrogen, oxygen and nitrogen, i.e. from macroelements. Trace elements are contained in these substances in small quantities, however, their role in the normal life of organisms is enormous. For example, compounds of boron, manganese, zinc, cobalt dramatically increase the yield of individual agricultural plants and increase their resistance to various diseases.
Man and animals receive the trace elements they need for normal life through the plants they feed on. If there is not enough manganese in the food, then growth retardation, a slowdown in the onset of puberty, and metabolic disorders during the formation of the skeleton are possible. The addition of fractions of a milligram of manganese salts to the daily diet of animals eliminates these diseases.
Cobalt is part of vitamin B12, which is responsible for the work of hematopoietic organs. The lack of cobalt in food often causes a serious illness that leads to depletion of the body and even death.
The importance of trace elements for humans was first revealed in the study of such a disease as endemic goiter, which was caused by a lack of iodine in food and water. The intake of salt containing iodine leads to recovery, and its addition to food in small quantities prevents the disease. For this purpose, iodized table salt is carried out, to which 0.001-0.01% potassium iodide is added.
The composition of most biological enzyme catalysts includes zinc, molybdenum and some other metals. These elements, contained in the cells of living organisms in very small quantities, ensure the normal operation of the finest biochemical mechanisms, and are true regulators of vital processes.
Many trace elements are contained in vitamins - organic substances of various chemical nature, which enter the body with food in small doses and have a great influence on the metabolism and overall vital activity of the body. In their biological action, they are close to enzymes, but enzymes are formed by the cells of the body, and vitamins usually come from food. Plants serve as sources of vitamins: citrus fruits, rose hips, parsley, onions, garlic and many others. Some vitamins - A, B1, B2, K - are obtained synthetically. Vitamins got their name from two words: vita - life and amine - containing nitrogen.
Trace elements are also part of hormones - biologically active substances that regulate the functioning of organs and systems of human and animal organs. They take their name from the Greek word harmao - I win. Hormones are produced by the endocrine glands and enter the blood, which carries them throughout the body. Some hormones are obtained synthetically.
1. Macroelements and microelements.
2. The role of trace elements in the life of plants, animals and humans.
3. Organic substances: proteins, fats, carbohydrates.
4. Enzymes.
5. Vitamins.
6. Hormones.
At what level of forms of existence of a chemical element does the difference between animate and inanimate nature begin?
Why are individual macronutrients also called biogenic? List them.
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The chemical composition of the cells of different organisms can differ markedly, but they consist of the same elements. About 70 elements of the periodic table of D.I. Mendeleev, but only 24 of them have importance and are constantly found in living organisms.
Macronutrients - oxygen, hydrocarbon, hydrogen, nitrogen - are part of the molecules of organic substances. Macroelements recently include potassium, sodium, calcium, sulfur, phosphorus, magnesium, iron, chlorine. Their content in the cell is tenths and hundredths of a percent.
Magnesium is part of chlorophyll; iron - hemoglobin; phosphorus - bone tissue, nucleic acids; calcium - bones, shellfish turtles, sulfur - in the composition of proteins; potassium, sodium and chloride ions take part in changing the potential of the cell membrane.
trace elements are presented in a cell with hundredths and thousandths of a percent. These are zinc, copper, iodine, fluorine, molybdenum, boron, etc.
Trace elements are part of enzymes, hormones, pigments.
Ultramicroelements - elements, the content of which in the cell does not exceed 0.000001%. These are uranium, gold, mercury, cesium, etc.
Water and its biological significance
Water quantitatively occupies the first place among chemical compounds in all cells. Depending on the type of cells, their functional state, the type of organism and the conditions of its presence, its content in cells varies significantly.
Bone tissue cells contain no more than 20% water, adipose tissue - about 40%, muscle cells - 76%, and embryonic cells - more than 90%.
Remark 1
In the cells of any organism, the amount of water decreases markedly with age.
Hence the conclusion that the higher the functional activity of the organism as a whole and of each cell separately, the greater their water content, and vice versa.
Remark 2
A prerequisite for the vital activity of cells is the presence of water. It is the main part of the cytoplasm, supports its structure and the stability of the colloids that make up the cytoplasm.
The role of water in a cell is determined by its chemical and structural properties. First of all, this is due to the small size of the molecules, their polarity and the ability to combine using hydrogen bonds.
Hydrogen bonds are formed with the participation of hydrogen atoms connected to an electronegative atom (usually oxygen or nitrogen). In this case, the Hydrogen atom acquires such a large positive charge that it can form a new bond with another electronegative atom (oxygen or nitrogen). Water molecules also bind to each other, in which one end has a positive charge, and the other is negative. Such a molecule is called dipole. The more electronegative oxygen atom of one water molecule is attracted to the positively charged hydrogen atom of another molecule to form a hydrogen bond.
Due to the fact that water molecules are polar and capable of forming hydrogen bonds, water is a perfect solvent for polar substances, which are called hydrophilic. These are compounds of an ionic nature, in which charged particles (ions) dissociate (separate) in water when a substance (salt) is dissolved. Some non-ionic compounds have the same ability, in the molecule of which there are charged (polar) groups (in sugars, amino acids, simple alcohols, these are OH groups). Substances consisting of non-polar molecules (lipids) are practically insoluble in water, that is, they hydrophobes.
When a substance passes into a solution, its structural particles (molecules or ions) acquire the ability to move more freely, and, accordingly, the reactivity of the substance increases. Due to this, water is the main medium where most of the chemical reactions. In addition, all redox reactions and hydrolysis reactions take place with the direct participation of water.
Water has the highest specific heat capacity of all known substances. This means that with a significant increase in thermal energy, the water temperature rises relatively slightly. This is due to the use of a significant amount of this energy to break hydrogen bonds, which limit the mobility of water molecules.
Due to its high heat capacity, water serves as a protection for plant and animal tissues from a strong and rapid increase in temperature, and the high heat of vaporization is the basis for reliable stabilization of body temperature. The need for a significant amount of energy to evaporate water is due to the fact that hydrogen bonds exist between its molecules. This energy comes from environment Therefore, evaporation is accompanied by cooling. This process can be observed during sweating, in the case of heat panting in dogs, and it is also important in the process of cooling the transpiring organs of plants, especially in desert conditions and in conditions of dry steppes and periods of drought in other regions.
Water also has a high thermal conductivity, which ensures uniform distribution of heat throughout the body. Thus, there is no risk of local “hot spots” that can cause damage to cell elements. So high specific heat and high liquid thermal conductivity make water an ideal medium for maintaining optimal thermal regime organism.
Water has a high surface tension. This property is very important for adsorption processes, the movement of solutions through tissues (blood circulation, ascending and descending movement through the plant, etc.).
Water is used as a source of oxygen and hydrogen, which are released during the light phase of photosynthesis.
Important physiological properties of water include its ability to dissolve gases ($O_2$, $CO_2$, etc.). In addition, water as a solvent is involved in the process of osmosis, which plays an important role in the life of cells and the body.
Hydrocarbon properties and its biological role
If we do not take into account water, we can say that most of the cell molecules belong to hydrocarbon, so-called organic compounds.
Remark 3
Hydrocarbon, having unique chemical abilities fundamental to life, is its chemical basis.
Thanks to small size and the presence of four electrons on the outer shell, a hydrocarbon atom can form four strong covalent bonds with other atoms.
Most important is the ability of hydrocarbon atoms to join with each other, forming chains, rings and, finally, the skeleton of large and complex organic molecules.
In addition, the hydrocarbon easily forms covalent bonds with other biogenic elements (usually with $H, Mg, P, O, S$). This explains the existence of an astronomical amount of various organic compounds that ensure the existence of living organisms in all its manifestations. Their diversity is manifested in the structure and size of molecules, their chemical properties, degree of saturation of the carbon skeleton and different form molecules, which is determined by the angles of intramolecular bonds.
Biopolymers
These are high-molecular (molecular weight 103 - 109) organic compounds, the macromolecules of which consist of a large number links that repeat - monomers.
Biopolymers include proteins, nucleic acids, polysaccharides and their derivatives (starch, glycogen, cellulose, hemicellulose, pectins, chitin, etc.). The monomers for them are, respectively, amino acids, nucleotides and monosaccharides.
Remark 4
About 90% of the dry mass of a cell is made up of biopolymers: polysaccharides predominate in plants, while proteins predominate in animals.
Example 1
In a bacterial cell there are about 3 thousand types of proteins and 1 thousand nucleic acids, and in humans the number of proteins is estimated at 5 million.
Biopolymers not only form the structural basis of living organisms, but also play a conducting role in life processes.
The structural basis of biopolymers are linear (proteins, nucleic acids, cellulose) or branched (glycogen) chains.
And nucleic acids, immune reactions, metabolic reactions - and are carried out due to the formation of biopolymer complexes and other properties of biopolymers.
Today, many chemical elements of the periodic table have been discovered and isolated in their pure form, and a fifth of them are found in every living organism. They, like bricks, are the main components of organic and inorganic substances.
What chemical elements are part of the cell, the biology of which substances can be used to judge their presence in the body - we will consider all this later in the article.
What is the constancy of the chemical composition
To maintain stability in the body, each cell must maintain the concentration of each of its components at a constant level. This level is determined by species, habitat, environmental factors.
To answer the question of what chemical elements are part of the cell, it is necessary to clearly understand that any substance contains any of the components of the periodic table.
Sometimes we are talking about hundredths and thousandths of a percent of the content of a certain element in a cell, but at the same time, a change in the named number by at least a thousandth part can already have serious consequences for the body.
Of the 118 chemical elements in a human cell, there should be at least 24. There are no such components that would be found in a living organism, but were not part of inanimate objects of nature. This fact confirms the close relationship between living and non-living in the ecosystem.
The role of various elements that make up the cell
So what are the chemical elements that make up a cell? Their role in the life of the organism, it should be noted, directly depends on the frequency of occurrence and their concentration in the cytoplasm. However, despite the different content of elements in the cell, the significance of each of them is equally high. A deficiency of any of them can lead to a detrimental effect on the body, turning off the most important biochemical reactions from metabolism.
Listing what chemical elements are part of the human cell, we need to mention three main types, which we will consider below:
The main biogenic elements of the cell
It is not surprising that the elements O, C, H, N are biogenic, because they form all organic and many inorganic substances. It is impossible to imagine proteins, fats, carbohydrates or nucleic acids without these essential components for the body.
The function of these elements determined their high content in the body. Together they account for 98% of the total dry body weight. How else can the activity of these enzymes be manifested?
- Oxygen. Its content in the cell is about 62% of the total dry mass. Functions: construction of organic and inorganic substances, participation in the respiratory chain;
- Carbon. Its content reaches 20%. Main function: included in all;
- Hydrogen. Its concentration takes a value of 10%. In addition to being a component of organic matter and water, this element also participates in energy transformations;
- Nitrogen. The amount does not exceed 3-5%. Its main role is the formation of amino acids, nucleic acids, ATP, many vitamins, hemoglobin, hemocyanin, chlorophyll.
These are the chemical elements that make up the cell and form most of the substances necessary for normal life.
Importance of macronutrients
Macronutrients will also help to suggest which chemical elements are part of the cell. From the biology course, it becomes clear that, in addition to the main ones, 2% of the dry mass is made up of other components of the periodic table. And macronutrients include those whose content is not lower than 0.01%. Their main functions are presented in the form of a table.
Calcium (Ca) | Responsible for the contraction of muscle fibers, is part of pectin, bones and teeth. Enhances blood clotting. |
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Phosphorus (P) | It is part of the most important source of energy - ATP. |
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Participates in the formation of disulfide bridges during protein folding into a tertiary structure. Included in the composition of cysteine and methionine, some vitamins. |
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Potassium ions are involved in cells and also affect the membrane potential. |
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Major anion in the body |
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Sodium (Na) | Analogue of potassium involved in the same processes. |
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Magnesium (Mg) | Magnesium ions are the regulators of the process In the center of the chlorophyll molecule, there is also a magnesium atom. |
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Participates in the transport of electrons through the ETC of respiration and photosynthesis, is a structural link of myoglobin, hemoglobin and many enzymes. |
We hope that from the above it is easy to determine which chemical elements are part of the cell and are macroelements.
trace elements
There are also such components of the cell, without which the body cannot function normally, but their content is always less than 0.01%. Let's determine which chemical elements are part of the cell and belong to the group of microelements.
It is part of the enzymes of DNA and RNA polymerases, as well as many hormones (for example, insulin). |
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Participates in the processes of photosynthesis, synthesis of hemocyanin and some enzymes. |
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It is a structural component of the hormones T3 and T4 of the thyroid gland |
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Manganese (Mn) | less than 0.001 | Included in enzymes, bones. Participates in nitrogen fixation in bacteria |
less than 0.001 | Influences the process of plant growth. |
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It is part of the bones and tooth enamel. |
Organic and inorganic substances
In addition to these, what other chemical elements are included in the composition of the cell? The answers can be found simply by studying the structure of most substances in the body. Among them, molecules of organic and inorganic origin are distinguished, and each of these groups has a fixed set of elements in its composition.
The main classes of organic substances are proteins, nucleic acids, fats and carbohydrates. They are built entirely from the main biogenic elements: the skeleton of the molecule is always formed by carbon, and hydrogen, oxygen and nitrogen are part of the radicals. In animals, proteins are the dominant class, and in plants, polysaccharides.
Inorganic substances are all mineral salts and, of course, water. Among all the inorganics in the cell, the most is H 2 O, in which the rest of the substances are dissolved.
All of the above will help you determine which chemical elements are part of the cell, and their functions in the body will no longer be a mystery to you.
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 - the consumption of a large amount of 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, participant in 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 |
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| 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 in the 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
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.
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 medicines and the development of optimal regimens for their dosing, both for 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. Physico-chemical 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. But the most common route for toxic metals to enter the body is ingestion through food and water. Bibliographic list 1. Karapetyants M.Kh., Drakin S.I. General and inorganic chemistry. - M.: Chemistry, 1993. - 590 p. Akhmetov N.S. General and inorganic chemistry. Textbook for high schools. - M.: Higher. school, 2001. - 679 p. Drozdov D.A., Zlomanov V.P., Mazo G.N., Spiridonov F.M. Inorganic chemistry. In 3 volumes. T. Chemistry of intransitive elements. / Ed. Yu.D. Tretyakova - M.: Ed. "Academy", 2004, 368s. 5. Tamm I.E., Tretyakov Yu.D. Inorganic chemistry: In 3 volumes, V.1. Physico-chemical foundations of inorganic chemistry. Textbook for university students / Ed. Yu.D. Tretyakov. - M.: Ed. "Academy", 2004, 240s. Korzhukov N.G. General and inorganic chemistry. Proc. Benefit. / Under the editorship of V.I. Delyan-M.: Ed. MISIS: INFRA-M, 2004, 512s. Ershov Yu.A., Popkov V.A., Berlyand A.S., Knizhnik A.Z. General chemistry. Biophysical chemistry. Chemistry of biogenic elements. 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- transformation by the liver and kidneys into a less toxic form.