Biologically important chemical elements. The chemical composition of the cell

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 the above chemical elements are included in 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, as well as 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 the organic matter- mineral salts and water.

mineral salts are in the cell, as a rule, in the form of cations (K +, Na +, Ca 2+, Mg 2+) and anions (HPO 2-/4, H 2 PO -/4, CI -, HCO 3), the ratio of which determines the acidity of the medium, which is important for the life of cells.

(In many cells, the medium is slightly alkaline and its pH hardly changes, since a certain ratio of cations and anions is constantly maintained in it.)

Of the inorganic substances in wildlife, a huge role is played by water.

Life is impossible without water. It makes up a significant mass of most cells. A lot of water is contained in the cells of the brain and human embryos: more than 80% of water; in adipose tissue cells - only 40%. By old age, the water content in the cells decreases. A person who loses 20% of water dies.

The unique properties of water determine its role in the body. It is involved in thermoregulation, which is due to the high heat capacity of water - consumption a large number energy when heated. What determines the high heat capacity of water?

In a water molecule, an oxygen atom is covalently bonded to two hydrogen atoms. The water molecule is polar because the oxygen atom has a partially negative charge, and each of the two hydrogen atoms has

Partially positive charge. A hydrogen bond is formed between the oxygen atom of one water molecule and the hydrogen atom of another molecule. Hydrogen bonds provide the connection of a large number of water molecules. When water is heated, a significant part of the energy is spent on breaking hydrogen bonds, which determines its high heat capacity.

Water - good solvent. Due to the polarity, its molecules interact with positively and negatively charged ions, thereby contributing to the dissolution of the substance. In relation to water, all substances of the cell are divided into hydrophilic and hydrophobic.

hydrophilic(from Greek. hydro- water and fileo- love) are called substances that dissolve in water. These include ionic compounds (eg salts) and some non-ionic compounds (eg sugars).

hydrophobic(from Greek. hydro- water and phobos- fear) are called substances that are insoluble in water. These include, for example, lipids.

Water plays big role in the chemical reactions that take place in the cell 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 facilitates the movement of various substances within the 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: macronutrients (99%), micronutrients (1%), ultramicronutrients (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.

ORGANIC COMPONENTS OF A CELL

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 enzyme activity. 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).

stored in nucleic acids 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, to write down the sequence of nucleotides in DNA molecules from one human cell (46 chromosomes), one would need a book of about 820,000 pages. The alternation of four types of nucleotides can form an infinite number of variants of DNA molecules. These features of the structure of DNA molecules allow them to store a huge amount of information about all the signs of organisms.

In 1953, the American biologist J. Watson and the English physicist F. Crick created a model for the structure of the DNA molecule. Scientists have found that each DNA molecule consists of two strands interconnected and spirally twisted. It looks like a double helix. In each chain, four types of nucleotides alternate in a specific sequence.

The nucleotide composition of DNA is different different types bacteria, fungi, plants, animals. But it does not change with age, it depends little on changes. environment. Nucleotides are paired, that is, the number of adenine nucleotides in any DNA molecule is equal to the number of thymidine nucleotides (A-T), and the number of cytosine nucleotides is equal to the number of guanine nucleotides (C-G). This is due to the fact that the connection of two chains to each other in a DNA molecule obeys 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 DNA molecule are 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 a macroergic 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.

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 cell consists of approximately 70 basic elements , which can be found in the periodic table. Of these, only 24 are found in all cells.

The main elements are hydrogen, carbon, oxygen and nitrogen. These are the main cellular elements, but elements such as potassium, iodine, magnesium, chlorine, iron, calcium and sulfur play an equally important role. These are macronutrients, which are contained in cells in a relatively small amount (up to tenths of a percent).

There are even fewer trace elements in cells (less than 0.01% of cell mass). These include copper, molybdenum, boron, fluorine, chromium, zinc, silicon and cobalt.

The value and content of elements in the cells of organisms is given in the table.

Table 4.1

The function of macronutrients in the body

Table 4. 1 (end)

The function of microelements and ultramicroelements in the human body

organic matter

Organic compounds make up, on average, 20–30% of the cell mass of a living organism. These include biological polymers - proteins, nucleic acids and polysaccharides, as well as fats and a number of low molecular weight organic substances - amino acids, simple sugars, nucleotides, etc.

Polymers are complex, branched or linear molecules that decompose into monomers upon hydrolysis. If the polymer consists of one type of monomers, then such a polymer is called a homopolymer, if the composition of the polymer molecule includes different monomers, then this is a heteropolymer.

If a group of different monomers in a polymer molecule is repeated, this is a regular heteropolymer; if there is no repetition of a certain group of monomers, the heteropolymer is irregular.

As part of the cell, they are represented by proteins, carbohydrates, fats, nucleic acids (DNA and RNA) and adenosine triphosphate (ATP).

Squirrels

Of the organic substances of the cell, proteins are in the first place in terms of quantity and value. Proteins, or proteins (from the Greek protos - first, main) - high-molecular heteropolymers, organic substances and decomposing upon hydrolysis to amino acids.

Simple proteins (consisting only of amino acids) are composed of carbon, hydrogen, nitrogen, oxygen, and sulfur.

Some proteins (complex proteins) form complexes with other molecules containing phosphorus, iron, zinc and copper - these are complex proteins containing, in addition to amino acids, also a non-protein - prosthetic group. It can be represented by metal ions (metal proteins - hemoglobin), carbohydrates (glycoproteins), lipids (lipoproteins), nucleic acids (nucleoproteins).

Proteins have a huge molecular weight: One of the proteins - milk globulin - has molecular weight 42000.

Proteins are irregular heteropolymers whose monomers are α-amino acids. More than 170 found in cells and tissues various amino acids, but proteins contain only 20 α-amino acids.

Depending on whether amino acids can be synthesized in the body, there are: nonessential amino acids - ten amino acids synthesized in the body and essential amino acids - amino acids that are not synthesized in the body. Essential amino acids must be ingested with food.

Depending on the amino acid composition, proteins are complete if they contain the entire set of essential amino acids and defective if some essential amino acids are absent in their composition.

The general formula of amino acids is shown in the figure. All α -amino acids at α -carbon atom contain a hydrogen atom, a carboxyl group (-COOH) and an amino group (-NH 2). The rest of the molecule is represented by a radical.

The amino group easily attaches a hydrogen ion, i.e. shows basic properties. The carboxyl group easily gives up a hydrogen ion - it exhibits the properties of an acid. Amino acids are amphoteric compounds, since in solution they can act as both acids and bases. In aqueous solutions, amino acids exist in different ionic forms. It depends on the pH of the solution and whether the amino acid is neutral, acidic, or basic.

Depending on the number of amino groups and carboxyl groups that make up the amino acids, neutral amino acids are distinguished having one carboxyl group and one amino group, basic amino acids having one more amino group in the radical and acidic amino acids having one more carboxyl group in the radical.

Peptides- organic substances consisting of a small number of amino acid residues connected by a peptide bond. The formation of peptides occurs as a result of the condensation reaction of amino acids (Fig. 4.6).

When the amino group of one amino acid interacts with the carboxyl group of another, a covalent nitrogen-carbon bond arises between them, which is called peptide. Depending on the number of amino acid residues that make up the peptide, dipeptides, tripeptides, tetrapeptides, etc. are distinguished. The formation of a peptide bond can be repeated many times. This leads to the formation polypeptides. If a polypeptide consists of a large number of amino acid residues, then it is already called a protein. At one end of the molecule there is a free amino group (it is called the N-terminus), and at the other end there is a free carboxyl group (it is called the C-terminus).

Structure of a protein molecule

The performance of certain specific functions by proteins depends on the spatial configuration of their molecules, in addition, it is energetically unfavorable for the cell to keep proteins in an expanded form, in the form of a chain, therefore, polypeptide chains undergo folding, acquiring a certain three-dimensional structure, or conformation. There are 4 levels of spatial organization of proteins.

Primary Structure protein - the sequence of amino acid residues in the polypeptide chain that makes up the protein molecule. The bond between amino acids is peptide.

The primary structure of a protein molecule determines the properties of protein molecules and its spatial configuration. The replacement of just one amino acid for another in the polypeptide chain leads to a change in the properties and functions of the protein.

For example, the replacement of the sixth glutamine amino acid in the b-subunit of hemoglobin with valine leads to the fact that the hemoglobin molecule as a whole cannot perform its main function - oxygen transport (in such cases, a person develops a disease - sickle cell anemia).

The first protein whose amino acid sequence was identified was the hormone insulin. Research was carried out at the University of Cambridge by F. Sanger from 1944 to 1954. It was found that the insulin molecule consists of two polypeptide chains (21 and 30 amino acid residues) held near each other by disulfide bridges. For his painstaking work, F. Sanger was awarded the Nobel Prize.

Rice. 4.6. The primary structure of a protein molecule

secondary structure- ordered folding of the polypeptide chain into α-helix(looks like a stretched spring) and β-structure (folded layer). AT α- spirals NH group of this amino acid residue interacts with CO group the fourth remnant of it. Almost all "CO-" and "NH-groups" take part in the formation of hydrogen bonds. They are weaker than peptide ones, but, repeating many times, they impart stability and rigidity to this configuration. At the level of the secondary structure, there are proteins: fibroin (silk, web), keratin (hair, nails), collagen (tendons).

Tertiary structure- stacking of polypeptide chains globules, resulting from the occurrence of chemical bonds (hydrogen, ionic, disulfide) and the establishment of hydrophobic interactions between radicals of amino acid residues. The main role in the formation of the tertiary structure is played by hydrophilic-hydrophobic interactions. In aqueous solutions, hydrophobic radicals tend to hide from water, grouping inside the globule, while hydrophilic radicals tend to appear on the surface of the molecule as a result of hydration (interaction with water dipoles).

In some proteins, the tertiary structure is stabilized by disulfide covalent bonds that form between the sulfur atoms of the two cysteine ​​residues. At the level of the tertiary structure, there are enzymes, antibodies, some hormones. According to the shape of the molecule, proteins are globular and fibrillar. If fibrillar proteins perform mainly supporting functions, then globular proteins are soluble and perform many functions in the cytoplasm of cells or in the internal environment of the body.

Quaternary structure characteristic of complex proteins, the molecules of which are formed by two or more globules. Subunits are held in the molecule exclusively by non-covalent bonds, primarily hydrogen and hydrophobic.

The most studied protein with a quaternary structure is hemoglobin. It is formed by two a-subunits (141 amino acid residues) and two b-subunits (146 amino acid residues). An iron-containing heme molecule is associated with each subunit. Many proteins with a quaternary structure are intermediate between molecules and cell organelles - for example, microtubules of the cytoskeleton are composed of a protein tubulin consisting of two subunits. The tube elongates as a result of the attachment of dimers to the end.

If for some reason the spatial conformation of proteins deviates from normal, the protein cannot perform its functions.

Rice. 4.7. Structures of protein molecules

Protein Properties

1. Proteins are amphoteric compounds, combine basic and acidic properties determined by amino acid radicals. There are acidic, basic and neutral proteins. The ability to give and attach H + determine buffer properties proteins, one of the most powerful buffers - hemoglobin in erythrocytes, which maintains the pH of the blood at a constant level.
2. eat squirrels soluble, there is insoluble proteins that perform mechanical functions (fibroin, keratin, collagen).
3. There are proteins chemically active(enzymes), there are chemically inactive.
4. There is sustainable to the effects of various environmental conditions and extremely unstable. External factors (changes in temperature, salt composition of the environment, pH, radiation) can cause a violation of the structural organization of the protein molecule.
5. The process of losing the three-dimensional conformation inherent in a given protein molecule is called denaturation. The cause of denaturation is the breaking of bonds that stabilize a particular protein structure. At the same time, denaturation is not accompanied by the destruction of the polypeptide chain. A change in the spatial configuration leads to a change in the properties of the protein and, as a result, makes it impossible for the protein to perform its biological functions.
6. Denaturation can be: reversible, the process of restoring the protein structure after denaturation is called renaturation. If the restoration of the spatial configuration of the protein is impossible, then denaturation is called irreversible.
7. The destruction of the primary structure of a protein molecule is called degradation.

Rice. 4.8. Protein denaturation and renaturation

Functions of proteins

Proteins perform various functions in the cell.

Functional activity is possessed by proteins with tertiary structural organization, but in most cases only the transition of proteins of tertiary organization to a quaternary structure provides a specific function.

Enzymatic function

All biological reactions in a cell proceed with the participation of special biological catalysts - enzymes, and any enzyme is a protein, enzymes are localized in all cell organelles and not only direct the course of various reactions, but also accelerate them tens and hundreds of thousands of times. Each of the enzymes is strictly specific.

So, the breakdown of starch and its transformation into sugar (glucose) causes the amylase enzyme, cane sugar breaks down only the invertase enzyme, etc.

Many enzymes have long been used in the medical and food (bakery, brewing, etc.) industries.

Enzymes are specific - they can catalyze one type of reaction - a certain substrate molecule enters the active center.

Since almost all enzymes are proteins (there are ribozymes, RNA catalyzing some reactions), their activity is highest at physiological normal conditions: most enzymes are most active only when a certain temperature, pH, speed depends on the concentration of the enzyme and substrate.

When the temperature rises to a certain value (on average, up to 50°C), the catalytic activity increases (for every 10°C, the reaction rate increases by about 2 times).

structural function

Proteins are part of all membranes surrounding and penetrating the cell, and organelles.

When combined with DNA, protein makes up the body of chromosomes, and when combined with RNA, it makes up the body of ribosomes.

Solutions of low molecular weight proteins are part of the liquid fractions of cells.

Regulatory function

Some proteins are hormones - biologically active substances released into the blood by various glands that are involved in the regulation of metabolic processes.

Hormones insulin and glucagon regulates the level of carbohydrates in the blood.

transport function

It is with proteins that the transfer of oxygen, as well as hormones in the body of animals and humans, is associated (it is carried out by the blood protein hemoglobin).

motor function

All types of motor reactions of the cell are carried out by special contractile proteins actin and myosin, which cause muscle contraction, the movement of flagella and cilia in protozoa, the movement of chromosomes during cell division, and the movement of plants.

Protective function

Many proteins form a protective cover that protects the body from harmful effects, such as horn formations - hair, nails, hooves, horns. This is mechanical protection. In response to the introduction of foreign proteins (antigens) into the body, substances of a protein nature (antibodies) are produced in the blood cells, which neutralize them, protecting the body from damaging effects. This is immunological protection.

energy function

Proteins can serve as a source of energy. Splitting to the end products of decay - carbon dioxide, water and nitrogen-containing substances, they release the energy necessary for many life processes in the cell 17.6 KJ.

Receptor function

Receptor proteins are protein molecules embedded in the membrane that can change their structure in response to the addition of a specific chemical substance.

Reserve function

This function is performed by the so-called reserve proteins, which are sources of nutrition for the fetus, such as egg proteins (ovalbumins). The main protein of milk (casein) also performs a mainly nutritional function.

A number of other proteins are used in the body as a source of amino acids, which in turn are precursors of biologically active substances that regulate metabolic processes.

Toxic function

toxins, toxic substances natural origin. Usually, high-molecular compounds (proteins, polypeptides, etc.) are classified as toxins, which, when they enter the body, produce antibodies.

According to the target of action, toxins are divided into the following groups:

Hematic poisons are poisons that affect the blood.

Neurotoxins are poisons that affect the nervous system and brain.

Myoxic poisons are poisons that damage muscles.

Hemotoxins are toxins that damage blood vessels and cause bleeding.

Hemolytic toxins are toxins that damage red blood cells.

Nephrotoxins are toxins that damage the kidneys.

Cardiotoxins are toxins that damage the heart.

Necrotoxins are toxins that destroy tissues, causing their necrosis (necrosis).

Poisonous substances phallotoxins and amatoxins are found in various types: pale grebe, smelly fly agaric, spring.

Carbohydrates

Carbohydrates, or saccharides, - organic substances, which include carbon, oxygen, hydrogen. Carbohydrates make up about 1% of the dry matter mass in animal cells, and up to 5% in liver and muscle cells. Plant cells are the richest in carbohydrates (up to 90% of dry mass).

The chemical composition of carbohydrates is characterized by their general formula C m (H 2 O) n, where m≥n. The number of hydrogen atoms in carbohydrate molecules is usually twice the number of oxygen atoms (that is, as in a water molecule). Hence the name carbohydrates.

They are much more abundant in plant cells than in animal cells. Carbohydrates contain only carbon, hydrogen and oxygen.

The simplest carbohydrates are simple sugars (monosaccharides). They contain five (pentoses) or six (hexoses) carbon atoms and the same number of water molecules.

Examples of monosaccharides are glucose and fructose found in many plant fruits. In addition to plants, glucose is also part of the blood.

Complex carbohydrates are made up of several molecules of simple carbohydrates. Two monosaccharides form a disaccharide.

Dietary sugar (sucrose), for example, consists of a glucose molecule and a fructose molecule.

Much more molecules of simple carbohydrates are included in such complex carbohydrates as starch, glycogen, fiber (cellulose).

In a fiber molecule, for example, from 300 to 3000 glucose molecules.

Functions of carbohydrates

Energy function

one of the main functions of carbohydrates. Carbohydrates (glucose) are the main sources of energy in the animal body. Provide up to 67% of daily energy consumption (at least 50%). When splitting 1 g of carbohydrate, 17.6 kJ, water and carbon dioxide are released.

storage function

expressed in the accumulation of starch by plant cells and glycogen by animal cells, which play the role of sources of glucose, easily releasing it as needed.

Support and construction function

Carbohydrates are part of cell membranes and cell walls (cellulose is part of the cell wall of plants, the shell of arthropods is formed from chitin, murein forms the cell wall of bacteria). Combined with lipids and proteins, they form glycolipids and glycoproteins. Ribose and deoxyribose are part of the monomers of nucleotides.

Receptor function

Oligosaccharide fragments of glycoproteins and glycolipids of cell walls perform a receptor function, perceiving signals from the external environment.

Protective function

Mucus secreted by various glands is rich in carbohydrates and their derivatives (for example, glycoproteins). They protect the esophagus, intestines, stomach, bronchi from mechanical damage, prevent the penetration of bacteria and viruses into the body.

Lipids

Lipids are a group of organic compounds that do not have a single chemical characteristic. They are united by the fact that they are all insoluble in water, but highly soluble in organic solvents (ether, chloroform, gasoline).

Distinguish between simple and complex lipids.

Simple lipids are two-component substances that are esters of higher fatty acids and any alcohol, more often glycerol.

Complex lipids consist of multicomponent molecules.

From simple lipids consider fats and waxes.

Fats widely distributed in nature. Fats are esters of higher fatty acids and a trihydric alcohol, glycerol. In chemistry, this group of organic compounds is usually called triglycerides, since all three hydroxyl groups of glycerol are associated with fatty acids.

More than 500 fatty acids have been found in the composition of triglycerides, the molecules of which have a similar structure.

Like amino acids, fatty acids have the same grouping for all acids - a hydrophilic carboxyl group (-COOH) and a hydrophobic radical that distinguishes them from each other. Therefore, the general formula of fatty acids is R-COOH. The radical is a hydrocarbon tail, which differs in different fatty acids in the number of -CH 2 groups.

Most of fatty acids contains an even number of carbon atoms in the "tail", from 14 to 22 (most often 16 or 18). In addition, the hydrocarbon tail may contain varying amounts of double bonds. By the presence or absence of double bonds in the hydrocarbon tail, saturated fatty acids, not containing double bonds in the hydrocarbon tail and unsaturated fatty acids having double bonds between carbon atoms (-CH=CH-). If saturated fatty acids predominate in triglycerides, then they are solid at room temperature (fats), if unsaturated fatty acids are liquid (oils). The density of fats is lower than that of water, so they float in water and are on the surface.

Wax- a group of simple lipids, which are esters of higher fatty acids and higher high-molecular alcohols. They are found both in the animal and plant kingdoms, where they perform mainly protective functions.

In plants, for example, they cover leaves, stems and fruits with a thin layer, protecting them from wetting with water and the penetration of microorganisms. The shelf life of fruits depends on the quality of the wax coating. Honey is stored under the cover of beeswax and larvae develop.

to complex lipids include phospholipids, glycolipids, lipoproteins, steroids, steroid hormones, vitamins A, D, E, K.

Phospholipids- esters of polyhydric alcohols with higher fatty acids containing a phosphoric acid residue. Sometimes additional groupings (nitrogenous bases, amino acids) can be associated with it.

As a rule, a phospholipid molecule has two higher fatty acid residues and one phosphoric acid residue. Phospholipids are present in all cells of living beings, participating mainly in the formation of the phospholipid bilayer of cell membranes - phosphoric acid residues are hydrophilic and always directed towards the outer and inner surfaces of the membrane, and hydrophobic tails are directed towards each other inside the membrane.

Glycolipids are carbohydrate derivatives of lipids. The composition of their molecules, along with polyhydric alcohol and higher fatty acids, also includes carbohydrates. They are localized predominantly on the outer surface of the plasma membrane, where their carbohydrate components are among other cell surface carbohydrates.

Lipoproteins- lipid molecules associated with proteins. There are a lot of them in membranes, proteins can penetrate the membrane through, are located under or above the membrane, can be immersed in the lipid bilayer to different depths.

Lipoids- fat-like substances. These include steroids(widespread in animal tissues cholesterol and its derivatives - hormones of the adrenal cortex - mineralocorticoids, glucocorticoids, estradiol and testosterone - female and male sex hormones, respectively). Terpenes are lipoids ( essential oils, on which the smell of plants depends), gibberellins (growth substances of plants), some pigments (chlorophyll, bilirubin), fat-soluble vitamins (A, D, E, K).

Lipid functions are shown in Table 4.1.

Table 4.2.

Functions of fats

Rice. 9. Chemical structure of lipids and carbohydrates

Adenosine triphosphate (ATP)

It is part of any cell, where it performs one of the most important functions - an energy store. ATP molecules are composed of the nitrogenous base adenine, the carbohydrate ribose, and three molecules of phosphoric acid.

The unstable chemical bonds that connect phosphoric acid molecules in ATP are very rich in energy (macroergic bonds): when these bonds are broken, energy is released and used in a living cell to ensure vital processes and the synthesis of organic substances.

Rice. 4.10. The structure of the ATP molecule

4.4. Practical task

Instruction

The main elements found in cells are hydrogen, carbon, oxygen and nitrogen. These chemical elements are called biogenic because they play decisive role in cell activity. They account for ninety-five percent of the total cell mass. These elements are supplemented by substances such as sulfur and phosphorus, which, together with biogenic elements, form the molecules of the main organic compounds in cells.

Equally important for functioning is the presence of macronutrients. Their number is small, less than a percent of the total mass, but invaluable. Macronutrients include substances such as sodium, potassium, chlorine, magnesium and calcium.

All macronutrients are found in cells in the form of ions and are directly involved in a number of cellular processes, for example, calcium ions are involved in muscle contractions, motor functions and blood clotting, and ions are responsible for the work of ribosomes. Plant cells also cannot do without magnesium - it is part of chlorophyll and ensures the functioning of mitochondria. Sodium and potassium, elements contained in human cells, are in turn responsible for the transmission of nerve impulses and heart rate.

Microelements are of no less important functional significance - substances that do not exceed their content of one hundredth of a percent of the total mass of cells. These are iron, zinc, manganese, copper, cobalt, zinc, and for a certain type of cell also boron, aluminum, chromium, fluorine, selenium, molybdenum, iodine and silicon.

The importance of the elements that make up the cells is not reflected in percentage terms. For example, without copper, the functioning of redox processes will be a big question, moreover, this element, despite its low content in cells, has great importance in the life of mollusks, being responsible for transporting oxygen throughout the body.

Iron is the same trace element as copper, and its content in cells is low. But without this substance healthy person it is simply impossible to imagine. Hemoglobin heme and many enzymes cannot do without this element. Iron is also an electron carrier.

Cells of algae, sponges, horsetails and molluscs need an element such as silicon. Its role in vertebrates is no less pronounced - its highest content is in ligaments and cartilage. Fluorine is found in large quantities in the cells of the enamel of teeth and bones, and boron is responsible for the growth of plant organisms. Even the smallest content of trace elements in cells has its own meaning and plays its inconspicuous, but important role.

A separate group among macronutrients is organogenic elements(O, C, H, N), which form the molecules of all organic substances.

Macronutrients, their role in the cell.Organogenic elements - oxygen, carbon, hydrogen and nitrogen make up ≈ 98% of the chemical content of the cell. They easily form covalent bonds by sharing two electrons (one from each atom) and due to this they form a wide variety of organic substances in the cell.

Other macronutrients in animal and human cells (potassium, sodium, magnesium, calcium, chlorine, iron) are also vital, accounting for about 1.9%.

So, potassium and sodium ions regulate the osmotic pressure in the cell, determine the normal rhythm of cardiac activity, the emergence and conduction of a nerve impulse. Calcium ions are involved in blood clotting, contraction of muscle fibers. Insoluble calcium salts take part in the formation of bones and teeth.

Magnesium ions play an important role in the functioning of ribosomes and mitochondria. Iron is part of hemoglobin.

Trace elements, their role in the cell. The biological role of micro- and ultramicroelements is determined not by their percentage, but by the fact that they are part of enzymes, vitamins and hormones. For example, Cobalt is part of vitamin B 12, Iodine is part of the hormone thyroxine, Copper is part of enzymes that catalyze redox processes.

Ultramicroelements, their role in the cell. Their concentration does not exceed 0.000001%. These are the following elements: gold, silver, lead, uranium, selenium, cesium, beryllium, radium, etc. The physiological role of many chemical elements has not yet been established, but they are necessary for the normal functioning of the body. For example, a deficiency of the ultramicroelement Selenium leads to the development of cancer.

General information about biological significance the main chemical elements contained in the cells of living organisms are presented in table 4.1.

With a lack of an important chemical element in the soil of a certain region, which causes its deficiency in the body local residents, there are so-called endemic diseases.

All chemical elements are contained in the cell in the form of ions or are part of chemicals.

Tab. 4.1. The main chemical elements of the cell and their importance for the life and activity of organisms

Cell chemicals