All living systems contain chemical elements in various proportions and chemical compounds built from them, both organic and inorganic.

According to the quantitative content in the cell, all chemical elements are divided into 3 groups: macro-, micro- and ultramicroelements.

Macronutrients make up to 99% of the cell mass, of which up to 98% is accounted for by 4 elements: oxygen, nitrogen, hydrogen and carbon. In smaller quantities, cells contain potassium, sodium, magnesium, calcium, sulfur, phosphorus, and iron.

Trace elements are predominantly metal ions (cobalt, copper, zinc, etc.) and halogens (iodine, bromine, etc.). They are present in amounts from 0.001% to 0.000001%.

Ultramicroelements. Their concentration is below 0.000001%. These include gold, mercury, selenium, etc.

A chemical compound is a substance in which the atoms of one or more chemical elements are connected to each other through chemical bonds. Chemical compounds are inorganic and organic. Inorganic include water and mineral salts. Organic compounds are compounds of carbon with other elements.

The main organic compounds of the cell are proteins, fats, carbohydrates and nucleic acids.

Chemical elements and inorganic substances of the cell

The difference between animate and inanimate nature is clearly manifested in their chemical composition. So, the earth's crust is 90% oxygen, silicon, aluminum and sodium (O, Si, Al, Na), and in living organisms about 95% are carbon, hydrogen, oxygen and nitrogen (C, H, O, N) . In addition, eight more chemical elements belong to this group of macronutrients: Na - sodium, Cl - chlorine, S - sulfur, Fe - iron, Mg - magnesium, P - phosphorus, Ca - calcium, K - potassium, the content of which is calculated in tenths and hundredths of a percent. In much smaller quantities, microelements that are equally necessary for life are found: Cu - copper, Mn - manganese, Zn - zinc, Mo - molybdenum, Co - cobalt, F - fluorine, J - iodine, etc.

Only 27 elements (out of 105 known today) perform specific functions in organisms. And as we have already noted, only four - C, H, O, N - serve as the basis of living organisms. It is from them that organic substances (proteins, nucleic acids, carbohydrates, fats, etc.) mainly consist.

The first place among macronutrients belongs to carbon. It is characterized by the ability to form almost all types of chemical bonds. Carbon, to a greater extent than other elements, is capable of forming large molecules. Its atoms can connect with each other, forming rings and chains. As a result, complex molecules of large sizes arise, characterized by a huge variety (today more than 10 million organic substances have been described). In addition, carbon atoms in the same chemical compound exhibit both oxidizing and reducing properties.

Carbon is the basis of all organic compounds. The high content of oxygen and hydrogen is associated with their pronounced oxidizing and reducing properties. Thanks to only three elements - C, H, O - there is a whole set of carbohydrates (sugars), the generalized formula of which looks like CnH2nOn (where n is the number of atoms). To these three elements in the composition of proteins are added N and S atoms, and in the composition of nucleic acids - N and P.

An essential role in living organisms belongs to all the other elements mentioned above. So, Mg atoms are part of chlorophyll, and Fe - hemoglobin. Iodine is contained in the thyroxine molecule (thyroid hormone), and Zn is contained in the insulin molecule (pancreatic hormone). The presence of Na and K ions is necessary for the conduction of a nerve impulse, for transport through the cell membrane. P and Ca salts are found in large quantities in bones and mollusk shells, which ensures the high strength of these formations.

It should be noted that the largest part (up to 85%) of the chemical composition of living organisms is water. Since it is a universal solvent for many inorganic and organic substances, it turns out to be an ideal medium for various chemical reactions. Water is involved in various biochemical reactions (for example, in photosynthesis). With it, excess salts, waste products are excreted from the body. The high heat capacity and relatively high thermal conductivity inherent in water are essential for the thermoregulation of organisms (when sweat evaporates, for example, the skin cools).

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

Macronutrients.

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

The table below shows the main macronutrients in the body:

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

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

Microelements.

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

Examples of trace elements are presented in the table below:

Ultramicroelements.

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

Contents of chemical cells. The cells of living beings differ significantly from their environment not only in the structure of the chemical compounds that make up their composition, but also in the set and content of chemical elements. Of the currently known chemical elements, about 90 have been found in wildlife. Depending on the content of these elements in the organisms of living beings, they can be divided into three groups:

1) macronutrients, that is, elements contained in cells in significant quantities (from tens of percent to hundredths of a percent). This group includes oxygen, carbon, nitrogen, sodium, calcium, phosphorus, sulfur, potassium, chlorine. In total, these elements make up about 99% of the mass of cells, with 98% being the share of the first four elements (hydrogen, oxygen, carbon and nitrogen).

2) trace elements, which account for less than hundredths of a percent of the mass. These elements include iron, zinc, manganese, cobalt, copper, nickel, iodine, fluorine. In total, they make up about 1% of the mass of cells. Despite the fact that the content of these elements in the cell is small, they are necessary for its life. In the absence or low content of these elements, various diseases occur. Lack of iodine, for example, leads a person to the occurrence of thyroid disease, and a lack of iron can cause anemia.

3) ultramicroelements, the content of which in the cell is extremely small (less than 10 -12%). This group includes bromine, gold, selenium, silver, vanadium and many other elements. Most of these elements are also necessary for the normal functioning of organisms. So, for example, selenium deficiency leads to cancer, and boron deficiency causes disease in plants. Some elements of this group, like trace elements, are part of enzymes.

Unlike living organisms, the most common elements in the earth's crust are oxygen, silicon, aluminum and sodium. Since the content of carbon, hydrogen and nitrogen in living matter is higher than in the earth's crust, it can be concluded that the molecules that contain these elements are necessary for the implementation of processes that ensure vital activity.

The four most common elements in living matter have one thing in common: they easily form covalent bonds by pairing electrons. In order to form stable electronic bonds, the hydrogen atom on the outer electron shell lacks one electron, the oxygen atom - two, nitrogen - three and carbon - four electrons. These elements can easily react with each other, filling the outer electron shells. In addition, three elements: nitrogen, oxygen and carbon - are able to form both single and double bonds, which significantly increases the number of chemical compounds built from these elements.

Carbon, hydrogen and oxygen have proven to be suitable for the formation of living matter also because they are the lightest among the elements that form covalent bonds. Very important from the point of view of biology is also the ability of a carbon atom to form covalent bonds with four other carbon atoms at once. Thus, covalently bonded carbon atoms are able to form the frameworks of a huge number of very different organic molecules.

And other inorganic substances, their role in the life of cells. Most of the chemical compounds that make up a cell are characteristic only of living organisms. However, in the cell there are a number of substances that are also found in inanimate nature. This is primarily water, which on average makes up about 80% of the mass of cells (its content may vary depending on the type of cell and its age), as well as some salts.

Water is an extremely unusual substance in physical and chemical terms, which differs significantly in properties from other solvents. The first cells originated in the primordial ocean, and in the process of further development learned to use these unique properties of water.

Compared to other liquids, water is characterized by an unusually high boiling point, melting point, specific heat capacity, as well as high heat of evaporation, melting, thermal conductivity and surface tension. This is due to the fact that water molecules are more strongly bonded to each other than the molecules of other solvents.

The high heat capacity of water (the ability to absorb heat with a slight change in its own temperature) protects the cell from sudden temperature fluctuations, and such a property of water as a high heat of evaporation is used by living organisms to protect against overheating: the evaporation of liquid by plants and animals is a protective reaction to an increase in temperature . The presence of high thermal conductivity in water ensures the possibility of uniform distribution of heat between the individual parts of the body. Water is practically incompressible, thanks to which the cells maintain their shape and are characterized by elasticity.

The unique properties of water are determined by the structural features of its molecule, which arise as a result of the specific arrangement of electrons in the oxygen and hydrogen atoms that make up the molecule. The oxygen atom, in the outer electron orbit of which there are two electrons, combines them with two electrons of hydrogen atoms (each hydrogen atom has one electron in the outer electron orbit). As a result, two covalent bonds are formed between an oxygen atom and two hydrogen atoms. However, the more negative oxygen atom tends to attract electrons to itself. As a result, each of the hydrogen atoms acquires a small positive charge, and the oxygen atom carries a negative charge. The negatively charged oxygen atom of one water molecule is attracted to the positively charged hydrogen atom of another molecule, which leads to the formation of a hydrogen bond. Thus, the water molecules are bound to each other.

An important property of a hydrogen bond is its lower strength compared to (it is about 20 times weaker than a covalent bond). Therefore, hydrogen bonds are relatively easy to form and easy to break. However, even at 100° there is still a fairly strong interaction between the water molecules. The presence of hydrogen bonds between water molecules provides it with some structure, which explains its unusual properties such as high boiling, melting and high heat capacity.

Another characteristic property of the water molecule is its dipole nature. As mentioned above, the hydrogen atoms in the water molecule carry a small positive charge, and the oxygen atoms carry a negative charge. However, the H-O-H bond angle is 104.5°, so in a water molecule the negative charge is concentrated on one side and the positive charge on the other. The dipole nature of a water molecule characterizes its ability to orient itself in an electric field. It is this property of water that determines its uniqueness as a solvent: if the molecules of substances contain charged groups of atoms, they enter into electrostatic interactions with water molecules, and these substances dissolve in it. Such substances are called hydrophilic. There are a large number of hydrophilic compounds in cells: these are salts, low molecular weight organic compounds, carbohydrates, nucleic acids. However, there are a number of substances that contain almost no charged atoms and do not dissolve in water. These compounds include, in particular, lipids (fats). Such substances are called hydrophobic. Hydrophobic substances do not interact with water, but interact well with each other. Lipids, which are hydrophobic compounds, form two-dimensional structures (membranes) that are almost impermeable to water.

Due to its polarity, water dissolves more chemicals than any other solvent. It is in the aquatic environment of the cell, where various chemicals are dissolved, that numerous chemical reactions take place, without which life is impossible. Water also dissolves reaction products and removes them from cells and from multicellular organisms. Due to the movement of water in the organisms of animals and plants, various substances are exchanged between tissues.

One of the important properties of water as a chemical compound is that it enters into many chemical reactions occurring in the cell. These reactions are called hydrolysis reactions. In turn, water molecules are formed as a result of many reactions occurring in living organisms.

The mass of the hydrogen atom is very small, its only electron in the water molecule is held by the oxygen atom. As a result, the nucleus of the hydrogen atom (proton) is able to break away from the water molecule, resulting in the formation of a hydroxyl ion (OH -) and a proton (H +).

H 2 O<=>H + + OH -

This process is called water dissociation. Hydroxyl and hydrogen ions formed during the dissociation of water are also participants in many important reactions that occur in the body.

In addition to water, an important role in the life of cells is played by those dissolved in it, which are represented by cations of potassium, sodium, magnesium, calcium and others, as well as anions of hydrochloric, sulfuric, carbonic and phosphoric acids.

Many cations are characterized by an uneven distribution between the cell and its environment: for example, in the cytoplasm of the cell, the concentration of K + is higher, and the concentration of Na + and Ca 2+ is lower than in the environment of the cell. Both the natural environment (for example, the ocean) and body fluids (blood), which are similar in ionic composition to sea water, can be external to the cell. The uneven distribution of cations between the cell and the environment is maintained in the process of life, for which the cell expends a significant part of the energy generated in it. The uneven distribution of ions between the cell and the environment is necessary for the implementation of many important processes for life, in particular for the conduction of excitation through nerve and muscle cells, the implementation of muscle contraction. After the death of a cell, the concentration of cations outside the cell and inside it quickly equalizes.

The anions of weak acids contained in the cell (HC0 3 -, HPO 4 2-) play an important role in maintaining a constant concentration of hydrogen ions (pH) inside the cell. Despite the fact that both alkalis and acids are formed in the process of life in the cell, normally the reaction in the cell is almost neutral. This is due to the fact that weak acid anions can bind acid protons and alkali hydroxyl ions, thus neutralizing the intracellular environment. In addition, anions of weak acids enter into chemical reactions carried out in the cell: in particular, anions of phosphoric acid are necessary for the synthesis of such an important compound for the cell as ATP.

Inorganic substances are found in living organisms not only in a dissolved state, but also in a solid state. For example, bones are formed mainly from calcium phosphate (magnesium phosphate is also present in smaller amounts), and shells are formed from calcium carbonate.

Organic matter of the cell. Biopolymers

In living organisms there is a huge number of various compounds that are practically not found in inanimate nature and which are called organic compounds. The molecular frameworks of these compounds are built from carbon atoms. Among organic compounds, low molecular weight substances (organic acids, their esters, amino acids, free fatty acids, nitrogenous bases, etc.) can be distinguished. However, the bulk of the dry matter of the cell is represented by high-molecular compounds, which are polymers. Polymers are compounds formed from low molecular weight repeating units (monomers) successively linked to each other by a covalent bond and forming a long chain, which can be either straight or branched. Among polymers, homopolymers are distinguished, consisting of identical monomers. If we denote the monomer by some symbol, for example, by the letter X, then the structure of the homopolymer can be conditionally represented as follows: -X-X-…-X-X. The composition of heteropolymers includes monomers of various structures. If the monomers that make up the heteropolymer are denoted as X and Y, then the structure of the heteropolymer can be represented, for example, in the form XXYYXY…XXYYXY. Biopolymers (that is, polymers found in nature) include proteins, nucleic acids, and carbohydrates.

Squirrels

Structure of proteins. Among the organic compounds present in the cell, proteins are the main ones: they account for at least 50% of the dry matter. All proteins are made up of carbon, hydrogen, oxygen, and nitrogen. In addition, almost all of them contain sulfur. Some proteins also contain phosphorus, iron, magnesium, zinc, copper, manganese. So, iron is part of the hemoglobin protein found in the erythrocytes of many animals, and magnesium is found in the pigment chlorophyll, which is necessary for photosynthesis.

A characteristic feature of proteins is their large molecular weight: it ranges from several thousand to hundreds of thousands and even millions of kilodaltons. The monomer, that is, the structural unit of any protein, are amino acids, which are characterized by a similar, but not quite the same structure.

As can be seen from the presented formula, the amino acid molecule consists of two parts. The boxed portion is the same for all amino acids. It contains an amino group (-NH 2) attached to a carbon atom and a further carboxyl group (-COOH). The second part of the amino acid molecule, shown in the formula in the form of the Latin letter R, is called the side chain, or radical. It has a different structure for different amino acids. Proteins contain 20 different amino acids as structural elements (monomers), thus, 20 side chains of different structure can be found in proteins. Side radicals can be negatively or positively charged, contain aromatic rings and heterocyclic structures, hydrophobic groups, hydroxyl (-OH) groups or sulfur atoms.

In protein molecules, consecutively located amino acid molecules are covalently connected to each other, forming long unbranched polymer chains. The amino acids in the chain are arranged in such a way that the amino group of one amino acid interacts with the carboxyl group of another. When these two groups interact, a water molecule is released and a peptide bond is formed. The resulting compound is called a peptide. If a peptide consists of two amino acids, it is called a dipeptide, of three - a tripeptide. Protein molecules can contain hundreds or even thousands of amino acid residues. Thus, proteins are polypeptides. It should be noted that protein molecules are not randomly built polymers of various lengths - each protein molecule is characterized by a certain sequence of amino acids, which is determined by the structure of the gene encoding this protein.

The sequence of amino acid residues in a protein molecule determines its primary structure, that is, its formula. Just as an alphabet of 33 letters can create a huge number of words, with 20 amino acids you can create an almost unlimited number of proteins, differing both in the number of amino acids they contain and in their sequence. The total number of different proteins found in all types of living organisms is about 10 10 -10 12 . The most important task of modern biology is to determine the primary structure of proteins, as well as to establish the relationship between the primary structure and the functional activity of proteins. Since the amino acid sequence is determined by the structure of the gene, the primary structure of proteins is currently determined by finding out the nucleotide sequence in the corresponding gene, using genetic engineering methods for this.

A protein molecule in its native (intact) state has its characteristic spatial structure, or conformation. It is determined by how the polypeptide chain of the protein folds in solution. Most often, individual sections of the polypeptide chain are folded into a spiral (α-helix) or form zigzag structures that are located antiparallel, the so-called folded layer, or β-structure. The formation of the α-helix and β-structure leads to the formation of the secondary structure of the protein. In this case, the side chains of amino acids are located on the outside of the helix or zigzag structure. The helical structure is stabilized by hydrogen bonds that form between the NH groups located on one turn and the CO groups located on the other turn of the helix. These hydrogen bonds are parallel to the axis of the helix.

The folded layer structure is also stabilized by the hydrogen bonds that form between parallel layers. Although hydrogen bonds are weaker than covalent bonds, their presence in a significant amount makes the structures of the α-helix or β-folded layer type sufficiently strong.

Helical regions and structures such as folded layer are further packaged, resulting in the formation of the tertiary structure of the protein. At this stage, soluble proteins usually form a globular coil-like structure with charged amino acid residues on the surface and hydrophobic amino acid residues inside the coil. In this case, amino acid residues that are located far from each other in the polypeptide chain often approach each other. Each protein has its own way of packaging, which is already set at the level of the primary structure of this protein, that is, it depends on the order of amino acids in the polypeptide chain.

Many proteins are composed of several polypeptide chains of the same or different structure. When such chains are combined, a complex protein is formed, which is characterized by a quaternary structure. Such proteins are called oligomers, and the individual polypeptide chains that make up the oligomer are called monomers.

Most of the protein molecules are able to maintain their biological activity, that is, the ability to perform their characteristic function only in a narrow range of temperatures and acidity of the environment. With an increase in temperature or a change in acidity to extreme values, changes occur in the structure of proteins, which are called denaturation. An example of denaturation is the coagulation of the protein of an egg, which is observed when it is boiled. During denaturation, covalent bonds are not broken, but the quaternary, tertiary and secondary structure characteristic of a given protein is destroyed, as a result of which, in the denatured state, the polypeptide chains of proteins form random and random coils and loops.

Functions of proteins. Proteins are characterized by a significant variety of functions. The largest and most biologically important group of proteins are enzyme proteins, which are catalysts that accelerate the course of various chemical reactions.

The second largest group of proteins is represented by proteins that are structural elements of the cell. These, for example, include the fibrillar protein collagen, the main structural protein that is part of the connective and bone. Other types of proteins are components of the contractile and motor systems. Such, for example, are actin and myosin, the two main elements of the contractile system of muscles. Structural proteins form the cell cytoskeleton, which is a bundle of fibrillar proteins that connect various cell organelles with each other and with the plasma membrane of the cell.

Some proteins perform a transport function, they are able to bind and carry various substances with the blood stream. The best known of these proteins is hemoglobin, which is found in the erythrocytes of vertebrates and, by binding to oxygen, transports it from the lungs to tissues. Serum lipoproteins carry complex lipids with the bloodstream, and serum albumin carries free fatty acids.

Transport proteins also include proteins that are built into biological membranes and carry out the transfer of various substances through these membranes. Under normal conditions, the cell membrane is poorly permeable to substances such as K + , Na + , Ca 2+ , since the pores formed by channel proteins are closed. However, some influences, such as electrical impulses or biologically active substances that bind to the channels, open the pore, as a result of which the ion that can penetrate this channel moves from one side of the membrane to the other in the direction of decreasing concentration. The movement of ions in the opposite direction is carried out with the expenditure of energy by other membrane transport proteins, called ion pumps.

In specialized cells of plants and animals, special regulators or hormones are synthesized, some of which (but not all) are proteins that regulate various physiological processes. Perhaps the most famous of these is insulin, a hormone produced in the pancreas that regulates the level of glucose in the cells of the body. With a lack of insulin in the body, a disease known as diabetes mellitus occurs.

In addition, proteins are capable of performing a protective function. When viruses, bacteria, foreign proteins or other polymers enter the body of animals or humans, special protective proteins are synthesized in the body, which are called antibodies or immunoglobulins. These proteins bind to foreign polymers. The binding of antibodies to proteins of viruses or bacteria inhibits their functional activity and stops the development of infection. Antibodies have a unique property: they are able to distinguish foreign proteins from the body's own proteins. This defense mechanism of the body against pathogens is called immunity. Immunity to infectious diseases can be created by injecting very small amounts of certain biopolymers that are part of the microorganisms or viruses that cause the disease. In this case, antibodies are formed that are subsequently able to protect the body if it is infected with this microorganism or virus. Many living things secrete proteins called toxins, which in most cases are strong poisons, to provide protection.

With a lack of nutrition in animals, the breakdown of proteins to its constituent amino acids sharply increases, the latter, after appropriate transformations, can be used as an energy source (energy function of proteins).

Some bacteria and all plants are able to synthesize all 20 amino acids that make up proteins. However, animals in the process of evolution have lost the ability to synthesize 10 particularly complex amino acids, which they must receive from plant and animal foods. These amino acids are called essential. They are part of the plant and animal proteins obtained from food, which are broken down into amino acids in the digestive tract. In cells, these amino acids are used to build their own proteins that are characteristic of a given organism. Lack of essential amino acids in food causes severe metabolic disorders.

And their role in the life process. At the temperature and acidity of the environment, which is characteristic of the cell, the rate of most chemical reactions is low. However, in reality, reactions in the cell proceed at a very high rate. This is achieved due to the presence in the cell of special catalysts - enzymes, which significantly increase the rate of chemical reactions. Enzymes are the largest and most specialized class of proteins. It is the enzymes that ensure the flow of numerous reactions in the cell, which make up the cellular metabolism. Currently, more than a thousand enzymes are known. Their catalytic efficiency is unusually high: they are able to speed up reactions millions of times.

The catalytic activity of an enzyme is determined not by its entire molecule, but by a certain region of the enzyme molecule, which is called its active site. It is known that chemical catalysis is most often carried out due to the formation of a complex of a substance (substrate) converted in the course of the reaction with a catalyst. And during the enzymatic reaction, the substrate interacts with the enzyme, and the binding of the substrate occurs precisely in the active center. Enzymes are characterized by a spatial correspondence between the substrate and the active center; they fit together, "like a key to a lock." Thus, enzymes are characterized by substrate specificity; therefore, each enzyme ensures the occurrence of one or more reactions of the same type.

The binding of the substrate to the enzyme (the formation of an enzyme-substrate complex) is accompanied by a redistribution of the electronic surrounding the substance (substrate) converted during the reaction due to interaction with the amino acids of the enzyme, which are involved in the formation of the active center. As a result, individual bonds between atoms in the substrate molecule are weakened and destroyed much more easily than in solution. In other cases (reactions in which a bond is formed), two substrate molecules approach each other in the active center of the enzyme so that it is easily formed between them. When the enzyme is denatured, its catalytic activity disappears, since the structure of the active center is disturbed.

Many enzymes contain so-called cofactors - low molecular weight organic or inorganic compounds capable of carrying out certain types of reactions. Cofactors include, for example, NAD dinucleotide (nicotinamide adenine dinucleotide), which ensures the dehydrogenation of various substrates. Its functions will be discussed in detail in the Energy Exchange section. A large number of enzymes are also known, which include metals (iron, copper, cobalt, manganese), which are also involved in the transformation of substrates during the catalytic act.

Nucleic acids

Another important class of biopolymers are nucleic acids, which are genetic carriers and also take part in the process of protein synthesis. Two types of nucleic acids have been found in wildlife, namely: Deoxyribonucleic acid(abbreviated DNA) and ribonucleic acid(RNA). DNA and RNA are found in all prokaryotes and eukaryotes, with the exception of viruses, some of which contain only RNA, while others contain only DNA. DNA and RNA are made up of monomers called mononucleotides. The mononucleotides that make up DNA and RNA have a similar, but not the same, structure. Mononucleotides consist of three main components: 1) nitrogenous base, 2) pentose sugars and 3) phosphoric acid.

The mononucleotides that make up DNA contain the five-carbon sugar deoxyribose and one of four nitrogenous bases: adenine, guanine, cytosine and thymine(abbreviated A, G, C and T).

Mononucleotides that make up RNA contain a five-carbon saccharribose, as well as one of four bases: adenine, guanine, cytosine and uracil(abbreviated as A, G, C and U).

Deoxyribonucleic acid (DNA). DNA is the carrier of genetic information and is concentrated in the cell mainly in the nucleus, where it is the main component of chromosomes (in eukaryotes, DNA is also found in mitochondria and chloroplasts). DNA is a polymer consisting of covalently linked mononucleotides, which include deoxyribose and four nitrogenous bases (adenine, guanine, cytosine and thymine). The number of mononucleotides that make up DNA is very large: in prokaryotic cells containing a single chromosome, all DNA is present in the form of one macromolecule with a molecular weight of more than 2*10 9 .

The structure of the DNA molecule was deciphered by Watson and Crick in 1953. The DNA molecule consists of two strands located parallel to each other and forming a right-handed helix. The width of the helix is ​​about 2 nm, while the length can reach hundreds of thousands of nanometers. The mononucleotides that make up one chain are sequentially connected due to the formation of covalent bonds between the deoxyribose of one and the phosphoric acid of the other mononucleotide. The nitrogenous bases, which are located on one side of the formed backbone of one DNA strand, form hydrogen bonds with the nitrogenous bases of the second strand. Thus, in a helical double-stranded DNA molecule, the nitrogenous bases are located inside the helix. The structure of the helix is ​​such that its constituent polynucleotide chains can be separated only after unwinding the helix.

The DNA molecule is arranged in such a way that the number of nitrogenous bases of one type (adenine and guanine) included in its composition is equal to the number of nitrogenous bases of another type (thymine and cytosine), that is, A + G \u003d T + C. This is due to the size of nitrogenous bases: the length of the structure formed during the formation of a hydrogen bond between adenine-thymine and guanine-cytosine pairs is approximately 11 A. The dimensions of these pairs correspond to the size of the inner part of the DNA helix. The A-G pair would be too large and the C-T pair would be too small to form a spiral. Thus, a nitrogenous base located in one strand of DNA determines a base located in the same place in another strand. The strict correspondence of nucleotides located parallel to each other in the paired chains of the DNA molecule is called complementarity (additionality). It is due to this property of the DNA molecule that accurate reproduction (replication) of genetic information is possible. In a cell, DNA replication (self-doubling) occurs as a result of the breaking of hydrogen bonds between the nitrogenous bases of adjacent DNA strands and the subsequent synthesis of two new (daughter) DNA molecules using the parent strands as a matrix. Such reactions were called matrix synthesis reactions.

Ribonucleic acid. RNA is a polymer consisting of covalently linked mononucleotides, which include ribose and four nitrogenous bases (adenine, guanine, cytosine and uracil). There are three different types of ribonucleic acids in cells: messenger RNA (mRNA or mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). The molecules of all three types of RNA are single-stranded. And they all have a much smaller molecular weight than DNA molecules. In most cells, the RNA content is many times (from 5 to 10) higher than the DNA content. All three types of RNA are essential for protein synthesis in the cell.

Messenger RNA. Messenger RNA is synthesized in the nucleus during transcription, during which template synthesis of the RNA molecule is provided on one of the DNA strands. An mRNA molecule consists of approximately 300-30,000 nucleotides and is a structure that is complementary to a specific section of a single-stranded DNA molecule (gene). After synthesis, mRNA passes into the cytoplasm, where it attaches to ribosomes and is used as a template that determines the amino acid sequence in the growing polypeptide chain. Thus, the sequence of nucleotides in the DNA chain, and then the mRNA synthesized using it as a template, determines the amino acid sequence in the synthesized protein. Each of the thousands of proteins synthesized by a cell is encoded by a specific mRNA.

transport RNA. The function of tRNA is to transport certain amino acids to the newly synthesized polypeptide chain during protein synthesis carried out on ribosomes. The molecular weight of tRNA is small: the molecules contain from 75 to 90 mononucleotides.

Ribosomal RNA. Ribosomal RNA is part of the ribosomes - the organelles through which protein synthesis is carried out. rRNA molecules consist of 3-5 thousand mononucleotides.

Carbohydrates

Carbohydrates, or saccharides, are compounds with the general formula (CH 2 O) p, which are aldehyde alcohols or keto alcohols. Carbohydrates are divided into mono-, di- and polysaccharides.

Monosaccharides, or simple sugars, most often consist of a strand (pentose) or six (hexose) carbon atoms and have the formulas (CH 2 O) 5 and (CH 2 O) 6.

The most common simple sugar is the six-carbon sugar glucose, which is the parent monomer from which many polysaccharides are built. Glucose is also the main source of energy in the cell. Pentoses (ribose and deoxyribose) are part of nucleic acids and ATP.

Two simple sugars are combined in a disaccharide molecule. The most famous representatives of disaccharides is sucrose, or food sugar, the molecule of which consists of glucose and fructose molecules.

Polysaccharide molecules are long chains built from many monosaccharide units, and the chains can be either linear or branched. Most polysaccharides contain repeating units of the same type or two alternating types as monomers, so they cannot play the role of informational biopolymers.

Living nature contains a huge amount of carbohydrates. This is due primarily to the wide distribution of two polysaccharides: starch and cellulose. Starch is found in large quantities in plants. It is the form of polysaccharide in which fuel is stored. Cellulose is the main component of extracellular fibrous and lignified plant tissues. In the digestive tract of animals there are no enzymes capable of breaking down cellulose into monomers. However, these enzymes are present in bacteria that live in the digestive tract of some animals, allowing them to use cellulose as a food source.

Polysaccharides are part of the hard walls of plant and bacterial cells, they are also an integral element of the softer shells of animal cells. Thus, carbohydrates perform two main functions in the cell: energy and construction.

Lipids

Lipids are water-insoluble organic compounds that make up cells. These substances can be extracted (dissolved) with non-polar solvents such as chloroform, benzene or ether. Several classes of lipids are known, but the most important function in the body is apparently performed by phospholipids, which are esters of the trihydric alcohol glycerol and phosphoric acid. When a phospholipid molecule is formed, two hydroxyl groups of glycerol interact with high molecular weight fatty acids containing 16-18 carbon atoms, and one hydroxyl group interacts with phosphoric acid. All phospholipids contain a polar head and a non-polar tail formed by two fatty acid molecules. At the oil-water interface, phospholipid molecules orient themselves in such a way that their polar heads are immersed in water and their hydrophobic tails are immersed in oil. Phospholipids spread over the water surface in the form of a monolayer, in which the fatty acid tails are oriented towards the hydrophobic air, and the charged heads are directed towards the aquatic environment.

Phospholipid molecules are able to form two-dimensional structures, which are called bilayers: the bilayer is formed from two monolayers of phospholipids oriented relative to each other so that the hydrophobic tails of the phospholipids are located inside the bilayer, and the polar heads are directed outward. Such a bilayer is characterized by a very high electrical resistance. It is the bilayers, consisting of phospholipids, that are the most important component of biological membranes. Biological membranes are natural films 5-7 nm thick formed by a phospholipid bilayer containing protein molecules. Thus, lipids perform a building function in the cell.

In addition, lipids are an important source of energy-. With the complete conversion of 1 g of lipids into water and carbon dioxide in a cell, about 2 times more energy is released than with the same conversion of carbohydrates. The fat accumulated in the subcutaneous tissue is a good heat-insulating material. In addition, lipids are a source of water, which is released in significant quantities during their oxidation. That is why many animals that store fats (for example, camels during desert crossings, bears, marmots, ground squirrels during hibernation) can do without water for a long time.

Some substances related to lipids have high biological activity: a number of vitamins, such as vitamins A and B, as well as some hormones (steroid). An important function in the animal body is performed by cholesterol, which is a component of cell membranes: improper cholesterol metabolism in humans leads to atherosclerosis, a disease in which cholesterol is deposited in the form of plaques on the walls of blood vessels, narrowing their lumen. This leads to disruption of the blood supply to organs and is the cause of such severe cardiovascular diseases as stroke or myocardial infarction.

Chemical elements of the cell

In living organisms, there is not a single chemical element that would not be found in the bodies of inanimate nature (which indicates the commonality of animate and inanimate nature).
Different cells include practically the same chemical elements (which proves the unity of living nature); and at the same time, even the cells of one multicellular organism, performing different functions, can differ significantly from each other in chemical composition.
Of the currently known more than 115 elements, about 80 are found in the composition of the cell.

All elements according to their content in living organisms are divided into three groups:

1. macronutrients- the content of which exceeds 0.001% of body weight.
   98% of the mass of any cell falls on four elements (they are sometimes called organogens): - oxygen (O) - 75%, carbon (C) - 15%, hydrogen (H) - 8%, nitrogen (N) - 3%. These elements form the basis of organic compounds (and oxygen and hydrogen, in addition, are part of the water, which is also contained in the cell). About 2% of the cell mass accounts for another eight macronutrients: magnesium (Mg), sodium (Na), calcium (Ca), iron (Fe), potassium (K), phosphorus (P), chlorine (Cl), sulfur (S);
2. The remaining chemical elements are contained in the cell in very small quantities: trace elements- those that account for from 0.000001% to 0.001% - boron (B), nickel (Ni), cobalt (Co), copper (Cu), molybdenum (Mb), zinc (Zn), etc.;
3. ultramicroelements- the content of which does not exceed 0.000001% - uranium (U), radium (Ra), gold (Au), mercury (Hg), lead (Pb), cesium (Cs), selenium (Se), etc.

Living organisms are able to accumulate certain chemical elements. So, for example, some algae accumulate iodine, buttercups - lithium, duckweed - radium, etc.

Cell chemicals

Elements in the form of atoms are part of the molecules inorganic and organic cell compounds.

To inorganic compounds include water and mineral salts.

organic compounds are characteristic only for living organisms, while inorganic exist in inanimate nature.

To organic compounds include carbon compounds with a molecular weight of 100 to several hundred thousand.
Carbon is the chemical basis of life. It can enter into contact with many atoms and their groups, forming chains, rings that make up the skeleton of organic molecules that differ in chemical composition, structure, length and shape. They form complex chemical compounds that differ in structure and function. These organic compounds that make up the cells of living organisms are called biological polymers, or biopolymers. They make up more than 97% of the cell's dry matter.

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?

1. 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;
2. Carbon. Its content reaches 20%. Main function: included in all;
3. 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;
4. 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.
Phosphorus (P)		It is part of the most important source of energy - ATP.
		Participates in the formation of disulfide bridges during protein folding into a tertiary structure. Included in the composition of cysteine ​​and methionine, some vitamins.
		Potassium ions are involved in cells and also affect the membrane potential.
		Major anion in the body
Sodium (Na)		Analogue of potassium involved in the same processes.
Magnesium (Mg)		Magnesium ions are the regulators of the process In the center of the chlorophyll molecule, there is also a magnesium atom.
		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 macronutrients.

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).
		Participates in the processes of photosynthesis, synthesis of hemocyanin and some enzymes.
		It is a structural component of the hormones T3 and T4 of the thyroid gland
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.
		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.