Organic matter in the cell They make up 20-30% of the cell mass. These include biopolymers - proteins, nucleic acids, carbohydrates, fats, ATP, etc. Different types of cells contain different amounts of organic compounds. Complex carbohydrates predominate in plant cells, proteins and fats predominate in animals. Nevertheless, each group of organic substances in any type of cell performs the following functions: providing energy, being a building material, carrying information, etc. Squirrels. Among the organic substances of the cell, proteins occupy the first place in terms of quantity and value. In animals, they account for 50% of the dry mass of the cell. In the human body, there are many types of protein molecules that differ from each other and from the proteins of other organisms. Despite the huge variety and complexity of the structure, proteins are built from 20 amino acids: Amino acids have amphoteric properties, therefore they interact with each other: 
Peptide bond:
When combined, the molecules form: dipeptide, tripeptide or polypeptide. It is a compound of 20 or more amino acids. The order of transformation of amino acids in a molecule is the most diverse. It allows existence 
variants that differ in the requirement and properties of protein molecules. The sequence of amino acids in a molecule is called structure. Primary - linear. Secondary - spiral. Tertiary - globules. Quaternary - association of globules (hemoglobin). The loss of structural organization by a molecule is called denaturation. It is caused by a change in temperature, pH, radiation. With a slight impact, the molecule can restore its properties. It is used in medicine (antibiotics). The functions of proteins in the cell are diverse. The most important is construction. Proteins are involved in the formation of all cell membranes in organelles. The catalytic function is extremely important - all enzymes are proteins. Motor function is provided by contractile proteins. Transport - consists in attaching chemical elements and transferring them to tissues. The protective function is provided by special proteins - antibodies formed in leukocytes. Proteins serve as a source of energy - with complete breakdown of 1 g of protein, 11.6 kJ are released. Carbohydrates. These are compounds of carbon, hydrogen and oxygen. represented by sugars. The cell contains up to 5%. The richest - plant cells - up to 90% of the mass (potatoes, rice). They are divided into simple and complex. Simple - monosugar (glucose) C 6 H 12 O 6, grape sugar, fructose. Disahara - (sucrose) C] 2 H 22 O 11 beet and cane sugar. Polysugar (cellulose, starch) (C 6 H 10 O 5) n. Carbohydrates perform mainly building and energy functions. When 1 g of carbohydrate is oxidized, 17.6 kJ is released. Starch and glycogen serve as the cell's energy reserve. Lipids. These are fats and fat-like substances in the cell. They are esters of glycerol and high molecular weight saturated and unsaturated acids. They can be solid and liquid - oils. Plants contain in seeds, from 5-15% of dry matter. The main function is energy - when 1 g of fat is split, 38.9 kJ is released. Fats are stores of nutrients. Fats perform a building function, are a good heat insulator. Nucleic acids. These are complex organic compounds. They consist of C, H 2, O 2, N 2, P. Contained in the nuclei and cytoplasm. 
a) DNA is a biological polynucleotide consisting of two chains of nucleotides. Nucleotides - consist of 4 nitrogenous bases: 2 purines - Adenine and Valine, 2 pyrimedins Cytosine and Guanine, as well as sugar - deoxyribose and a phosphoric acid residue. In each chain, the nucleotides are connected by covalent bonds. Chains of nucleotides form helices. A helix of DNA packed with proteins forms a structure - a chromosome. b) RNA is a polymer, the monomers of which are nucleotides close to DNA, nitrogenous bases - A, G, C. Instead of thymine, there is Uration. The carbohydrate of RNA is ribose, there is a residue of phosphoric acid.
Double-stranded RNAs are carriers of genetic information. Single-stranded - carry information about the sequence of amino acids in the protein. There are several single-stranded RNAs: - Ribosomal - 3-5 thousand nucleotides; - Information - 300-30000 nucleotides; - Transport - 76-85 nucleotides. Protein synthesis is carried out on ribosomes with the participation of all types of RNA.
test questions
1. Cell - an organism or a part of it? 2. Elementary composition of cells. 3. Water and minerals. 4. Organic substances of the cell. 5. Proteins. 6. Carbohydrates, fats. 7. DNA. 8. RNA.
Topic 2.2 The structure and functions of the cell
test questions
1. What is meant by the level of cell organization? 2. Characteristics of prokaryotes and eukaryotes. 3. The structure of prokaryotes. 4. Morphology of prokaryotes. 5. The structure of eukaryotes. 6. Structure and functions of the nucleus. 7. Karyotype and its features. 8. Structure and functions of the nucleolus. Topic 2.2.1 Golgi complex, lysosomes, mitochondria,
ribosomes, cell center; organelles of movement
Cytoplasm- This is the internal semi-liquid environment of the cell in which all biochemical processes take place. It contains structures - organoids and communicates between them. Organelles have regular features of structure and behavior in different periods of cell life and perform certain functions. There are organelles characteristic of all cells - mitochondria, cell center, Golgi apparatus, ribosomes, ER, lysosomes. Organelles of movement - flagella and cilia are characteristic of unicellular organisms. Various substances are deposited in the cytoplasm - inclusions. These are permanent structures that arise in the process of life. Dense inclusions are granules, liquid inclusions are vacuoles. Their size is determined by the vital activity of the cells. The basis of the structural organization of the cell is the membrane principle of structure. This means that the cell is mainly built of membranes. All membranes have a similar structure. The accepted model is considered to be a fluid-mosaic structure: the membrane is formed by two rows of lipids in which protein molecules are immersed at different depths. Outer cytoplasmic membrane It is present in all cells and separates the cytoplasm from the external environment, forming the surface of the cell. The cell surface is heterogeneous, its physiological properties are different. The cell has high strength and elasticity. In the cytoplasmic membrane there are pores through which the passage of molecules of substances occurs. The entry of substances into the cell is a process that requires energy. The cell membrane has the property of semi-permeability. The mechanism for semipermeability is osmosis. In addition to osmosis, chemicals and solids can enter the cell due to protrusions - these are pinocetosis and phagocytosis. The cytoplasmic membrane also provides communication between cells in the tissues of multicellular organisms due to numerous folds and outgrowths.Organic substances that make up the cell.
Organic compounds make up an average of 20-30% of the cell mass of a living organism. These include biological polymers - proteins, nucleic acids and carbohydrates, as well as fats and a number of small molecules - hormones, pigments, ATP and many others. Different types of cells contain different amounts of organic compounds. Plant cells are dominated by complex carbohydrates - polysaccharides; in animals - more proteins and fats. Nevertheless, each of the groups of organic substances in any type of cells performs similar functions.
Squirrels. Among the organic substances of the cell, proteins occupy the first place both in quantity and in value. In animals, they account for about 50% of the dry mass of the cell. In the human body, there are 5 million types of protein molecules that differ not only from each other, but also from the proteins of other organisms.
Despite such a variety and complexity of structure, they are built from only 20 different amino acids.
Proteins isolated from living organisms - animals, plants and microorganisms - include several hundred and sometimes thousands of combinations of 20 basic amino acids. The order of their alternation is the most diverse, which makes possible the existence of a huge number of protein molecules that differ from each other. For example, for a protein consisting of only 20 amino acid residues, about 2,1018 variants are theoretically possible, differing in the alternation of amino acids, and hence in the properties of various protein molecules. The sequence of amino acids in a polypeptide chain is called the primary structure of a protein. However, a protein molecule in the form of a chain of amino acids connected in series by peptide bonds is not yet capable of performing specific functions. This requires a higher structural organization. By forming hydrogen bonds between the residues of carboxyl and amino groups of different amino acids, the protein molecule takes the form of a spiral. This is the secondary structure of a protein. But even it is often not enough to acquire characteristic activity. Only a molecule with a tertiary structure can act as a catalyst or any other. The tertiary structure is formed by the interaction of radicals, in particular radicals of the amino acid cysteine, which contain sulfur. The sulfur atoms of two amino acids located at some distance from each other in the polypeptide chain are connected, forming the so-called disulfide, or 5-3 bonds. Due to these interactions, as well as other less strong bonds, the protein helix coils and takes the form of a ball, or globule. The method of folding polypeptide helices into globules is called the tertiary structure of a protein. Many proteins with a tertiary structure can fulfill their biological role in the cell. However, some functions of the body require the participation of proteins with an even higher level of organization. Such an organization is called a quaternary structure. It is a functional association of several (two, three or more) protein molecules with a tertiary organization. An example of such a complex protein is hemoglobin. Its molecule consists of four interconnected molecules.
The loss of a protein molecule of its structural organization is called denaturation.
Denaturation can be caused by temperature changes, dehydration, exposure to X-rays, and other influences. First, the weakest structure, the quaternary, is destroyed, then the tertiary, secondary, and under the most severe conditions, the primary. If a change in environmental conditions does not lead to the destruction of the primary structure of the molecule, then when normal environmental conditions are restored, the structure of the protein is also completely recreated. This process is called renaturation. This property of proteins to completely restore the lost structure is widely used in the medical and food industries for the preparation of certain medical preparations, such as antibiotics, to obtain food concentrates that retain their nutritional properties for a long time when dried.
The functions of proteins in the cell are extremely diverse. One of the most important is the building function: proteins are involved in the formation of all cell membranes and cell organelles, as well as extracellular structures. The catalytic role of proteins is of exceptional importance. All enzymes are substances of a protein nature, they accelerate the chemical reactions that take place in the cell by tens and hundreds of thousands of times.
The motor function of living organisms is provided by special contractile proteins. These proteins are involved in all types of movement that cells and organisms are capable of: the flickering of cilia and the beating of flagella in protozoa, muscle contraction in multicellular animals, the movement of leaves in plants, etc.
The transport function of proteins is to attach chemical elements (for example, oxygen) or biologically active substances (hormones) and transfer them to various tissues and organs of the body.
When foreign proteins or microorganisms enter the body, white blood cells - leukocytes - form special proteins - antibodies. They bind and neutralize substances that are not characteristic of the body - this is a protective function.
Proteins also serve as one of the sources of energy in the cell, that is, they perform an energy function. With complete breakdown of 1 g of protein, 17.6 kJ of energy is released.
Carbohydrates. Carbohydrates, or saccharides, are organic substances. Most carbohydrates have twice the number of hydrogen atoms as oxygen atoms. Therefore, these substances were called carbohydrates.
In an animal cell, carbohydrates are found in amounts not exceeding 1-2, sometimes 5%. Plant cells are the richest in carbohydrates, where their content in some cases reaches 90% of the dry mass (potato tubers, seeds, etc.).
Carbohydrates are simple and complex. Simple carbohydrates are called monosaccharides. Depending on the number of carbon atoms in the molecule, monosaccharides are called trioses - 3 atoms, tetroses - 4, pentoses - 5 and hexoses - 6 carbon atoms. Of the six-carbon monosaccharides - hexoses, the most important are glucose, fructose and galactose. Glucose is contained in the blood (0.1-0.12%). Pentoses - ribose and deoxyribose - are part of nucleic acids and ATP. If two monosaccharides combine in one molecule, such a compound is called a disaccharide. Dietary sugar, obtained from cane or sugar beets, consists of one molecule of glucose and one molecule of fructose, milk sugar - of glucose and galactose.
Complex carbohydrates formed by many monosaccharides are called polysaccharides. The monomer of such polysaccharides as starch, glycogen, cellulose is glucose.
Carbohydrates perform two main functions: construction and energy. For example, cellulose forms the walls of plant cells; the complex polysaccharide chitin is the main structural component of the external skeleton of arthropods. The construction function of chitin is also performed in fungi. Carbohydrates play the role of the main source of energy in the cell. In the process of oxidation, 1 g of carbohydrates releases 17.6 kJ. Starch in plants and glycogen in animals, deposited in cells, serve as an energy reserve.
Fats and lipoids. Fats (lipids) are compounds of high molecular weight fatty acids and the trihydric alcohol glycerol. Fats do not dissolve in water - they are hydrophobic. There are always other complex hydrophobic fat-like substances in cells called lipoids.
One of the main functions of fats is energy. During the breakdown of 1 g of fat, a large amount of energy is released - 38.9 kJ. The fat content in the cell ranges from 5-15% of the dry matter mass. In adipose tissue cells, the amount of fat increases to 90%. Accumulating in the cells of adipose tissue of animals, in the seeds and fruits of plants, fat serves as a reserve source of energy.
Fats and lipoids also perform a building function, they are part of cell membranes. Due to poor thermal conductivity, fat is able to perform the function of a heat insulator. In some animals (seals, whales), it is deposited in the subcutaneous adipose tissue, which in whales forms a layer up to 1 m thick. The formation of some lipoids precedes the synthesis of a number of hormones. Consequently, these substances also have the function of regulating metabolic processes.
Nucleic acids. The value of nucleic acids in the cell is very high. The peculiarities of their chemical structure provide the possibility of storing, transferring and transmitting by inheritance to daughter cells information about the structure of protein molecules that are synthesized in each tissue at a certain stage of individual development. Since most of the properties and characteristics of cells are due to proteins, it is clear that the stability of nucleic acids is the most important condition for the normal functioning of cells and entire organisms. Any changes in the structure of nucleic acids entail changes in the structure of cells or the activity of physiological processes in them, thus affecting viability. The study of the structure of nucleic acids, which was first established by the American biologist Watson and the English physicist Crick, is extremely important for understanding the inheritance of traits in organisms and the patterns of functioning of both individual cells and cellular systems - tissues and organs.
There are two types of nucleic acids: DNA and RNA. DNA (deoxyribonucleic acid) is a biological polymer consisting of two polynucleotide chains connected to each other. The monomers that make up each of the DNA chains are complex organic compounds, including nitrogenous bases - adenine (A) or thymine (T), cytosine (C) or guanine (G); the five-atom sugar pentose - deoxyribose, after which the name of DNA itself, as well as the residue of phosphoric acid, was named. These compounds are called nucleotides. In each strand, the nucleotides are joined together to form cobalt bonds between the deocaribose of one nucleotide and the phosphoric acid residue of the other. Nucleotides can only connect in pairs: the nitrogenous base A of one chain of polynucleotides is always connected by two hydrogen bonds with the nitrogenous base T of the opposite polynucleotide chain, and G by three hydrogen bonds with C. This ability to selectively combine nucleotides, resulting in the formation of pairs A-T and G-C, is called complementarity.
RNA (ribonucleic acid), like DNA, is a polymer whose monomers are nucleotides. The nitrogenous bases of the three nucleotides are the same as those that make up DNA (adenine, guanine, cytosine), the fourth - ura-cil - is present in the RNA molecule instead of thymine. RNA nucleotides differ from DNA nucleotides in the structure of their carbohydrate: they include another pentose - ribose (instead of deoxyribose). In an RNA chain, nucleotides are joined by the formation of covalent bonds between the deoxyribose of one nucleotide and the phosphoric acid residue of another.
RNAs carry information about the sequence of amino acids in proteins, that is, about the structure of proteins from chromosomes to the site of their synthesis, and participate in protein synthesis.
There are several types of RNA. Their names are due to their function or location in the cell. Most of the cytoplasmic RNA (up to 80-90%) is ribosomal RNA (rRNA) contained in ribosomes. rRNA molecules are relatively small and consist of 3-5 thousand nucleotides. Another type of RNA is informational RNA (mRNA), which carries information to ribosomes about the sequence of amino acids in proteins that must be synthesized. The size of these RNAs depends on the length of the DNA segment from which they were synthesized. The mRNA molecules can consist of 300-30,000 nucleotides. Transport P/-//((tRNA) include 76-85 nucleotides and perform several functions. They deliver amino acids to the site of protein synthesis, "recognize" (according to the principle of complementarity) the mRNA triplet corresponding to the transferred amino acid, carry out the exact orientation of the amino acid on ribosome.
And 33 look at 31.
Answers to school textbooks
Elements found in living nature are also widely distributed in inanimate nature - the atmosphere, water, and the earth's crust. There are no such elements that would be found exclusively in living organisms. But the ratio of chemical elements, their contribution to the formation of substances that make up a living organism and an inanimate body, differ sharply. In a living organism, most of the elements are in the form of chemical compounds - substances dissolved in water. Only living organisms contain organic substances: proteins, fats, carbohydrates and nucleic acids.
2. Is the chemical composition of plant and animal cells similar?
The chemical composition of plant and animal cells is similar. All living organisms are composed of the same elements, inorganic and organic compounds. However, the content of various elements in different cells varies. Each cell type contains a different number of certain organic molecules. Complex carbohydrates (fiber, starch) predominate in plant cells, while in animals there are more proteins and fats. Each of the groups of organic substances (proteins, carbohydrates, fats, nucleic acids) in any type of cell performs its own functions (nucleic acid - storage and transmission of hereditary information, carbohydrates - energy, etc.).
3. List the elements most common in living organisms.
The cell contains about 80 chemical elements. Depending on the number in which chemical elements are contained in the composition of substances that form a living organism, it is customary to distinguish several of their groups. One group is formed by four elements that make up about 98% of the mass of the cell: oxygen, hydrogen, carbon and nitrogen. They are called macronutrients. These are the dominant constituents of all organic compounds.
The other group includes sulfur and phosphorus, potassium and sodium, calcium and magnesium, manganese, iron and chlorine. They are found in cells in smaller quantities (tenths and hundredths of a percent). Each of them performs an important function in the cell. For example, calcium and phosphorus are involved in the formation of bone tissue, determining bone strength. Iron is part of hemoglobin, a protein in red blood cells (erythrocytes), which is involved in the transfer of oxygen from the lungs to the tissues.
4. What substances are organic?
Organic substances include proteins, nucleic acids, fats, carbohydrates, as well as hormones, pigments, ATP, and some others. They average 20-30% of the cell mass of a living organism.
5. What is the role of proteins in the cell?
Among the organic substances of the cell, proteins occupy the first place both in quantity and in value. In animals, they account for about 50% of the dry mass of the cell.
The role of proteins in the cell is extremely large and varied. One of the most important functions of proteins is construction: proteins are involved in the formation of membranes and non-membrane organelles. Another function is also important - catalytic: certain proteins accelerate chemical reactions occurring in the cell by tens and hundreds of thousands of times.
The motor function of the body is provided by contractile proteins. These proteins are involved in all types of movement that animal cells and organisms are capable of.
The transport function of proteins is to attach chemical elements (for example, oxygen) or biologically active substances (hormones) and transfer them to various tissues and organs of the body.
When foreign proteins or microorganisms enter the body, special proteins are formed in white blood cells (leukocytes) - antibodies. They bind and neutralize substances unusual for the body. This is the protective function of proteins.
Proteins also serve as one of the sources of energy in the cell, that is, they perform an energy function.
6. What substances are the main source of energy?
The main source of energy in the cells of animals and plants are carbohydrates. These include glucose, sucrose, fiber, starch, etc. By “burning” glucose, the body receives the necessary energy for the metabolic processes taking place in it. Living organisms can store carbohydrates in the form of starch (in plants) and glycogen (in animals and fungi). In potato tubers, starch can make up to 80% of the mass, and animals have especially a lot of carbohydrates in liver cells and muscles - up to 5%.
Carbohydrates also perform other functions, such as support and protection. Fiber is part of the wood, chitin forms the outer skeleton of insects, crustaceans and other arthropods.
7. Describe the role of fats in the body.
Fats perform a number of functions in the body, for example, they serve as a reserve source of energy. They give the body up to 30% of all the energy it needs. They also perform a building function, being an essential component in the composition of cell and nuclear membranes. In some animals, fats accumulate in large quantities and serve as a heat insulator, that is, they protect the body from heat loss (for example, in whales, the thickness of the fat layer reaches 1 m).
Fats are also of great importance as an internal reserve of water: as a result of the breakdown of 1 kg of fat, up to 1.1 kg of water is formed. This is very important for hibernating animals - ground squirrels, marmots: due to their subcutaneous fat reserves, they can not drink at this time for up to two months. During desert crossings, camels go without drinking for up to two weeks - they extract the water necessary for the body from their humps - receptacles of fat.
8. What is the role of water in a cell?
The most common inorganic compound in living organisms is water. Its content varies widely: in the cells of tooth enamel - about 10%, and in the cells of the developing embryo - more than 90%. On average, in a multicellular organism, water makes up about 80% of body weight. First of all, water determines the physical properties of the cell, its volume, elasticity. Numerous chemical reactions take place in the aquatic environment, since water is a good solvent. And water itself is involved in many chemical transformations.
Water helps to remove unnecessary and harmful substances from the body resulting from metabolism (excretory function), promotes the movement of oxygen, carbon dioxide and nutrients throughout the body (transport function).
Water has good thermal conductivity and high heat capacity. When the ambient temperature changes, water absorbs or releases heat. As a result, the temperature inside the cell remains unchanged or its fluctuations are much smaller than in the environment surrounding the cell (heat-regulating function).
9. Name the carbohydrates you know.
Carbohydrates include the following natural organic compounds: glucose, fructose, sucrose, maltose, lactose, chitin, starch, glycogen and cellulose.
10. What role do nucleic acids play in a cell?
Nucleic acids are responsible for the storage and transmission of hereditary traits from parents to offspring. They are part of chromosomes - special structures located in the cell nucleus. Nucleic acids are also found in the cytoplasm and its organelles.
11. What is the chemical composition of living organisms?
The most common elements in living organisms are oxygen, carbon, hydrogen and nitrogen. The composition of living organisms includes organic substances (proteins, fats, carbohydrates, nucleic acids) and inorganic substances (water, mineral salts).
Organic compounds make up an average of 20-30% of the cell mass of a living organism. These include biological polymers - proteins, nucleic acids and carbohydrates, as well as fats and a number of small molecules - hormones, pigments, ATP and many others.
Different types of cells contain different amounts of organic compounds. In plant cells, complex carbohydrates - polysaccharides predominate, in animals - more proteins and fats. However, each of the groups of organic substances in any type of cell performs similar functions.
Proteins, as a rule, are powerful highly specific enzymes and regulate the metabolism of the cell.
Nucleic acids serve as custodians of hereditary information. In addition, nucleic acids control the formation of the appropriate enzyme proteins in the right amount and at the right time.
Lipids . Among the low molecular weight organic compounds that make up living organisms, lipids play an important role, which include fats, waxes and various fat-like substances. These are hydrophobic compounds that are insoluble in water. Typically, the total lipid content in a cell ranges from 5–15% of the dry matter mass.
However, in the cells of the subcutaneous adipose tissue, their number increases to 90%.
Neutral fats are widely distributed in nature, which are compounds of high molecular weight fatty acids and the trihydric alcohol glycerol.
Model (A) and structure diagram (B) of a neutral fat molecule
In the cytoplasm of cells, neutral fats are deposited in the form of fat droplets.
Fats are a source of energy. When 1 g of fat is oxidized to carbon dioxide and water, 38.9 kJ of energy is released (when 1 g of glucose is oxidized, only 17 kJ).
Fats serve as a source of metabolic water, 1.1 g of water is formed from 1 g of fat. Using their fat reserves, camels or hibernating ground squirrels can do without water for a long time.
Fats are mainly deposited in adipose tissue cells. This tissue serves as the energy depot of the body, protects it from heat loss and performs a protective function. In the body cavity between the internal organs of vertebrates, elastic fatty pads are formed that protect the organs from damage, and the subcutaneous fatty tissue creates a heat-insulating layer.
Waxes - plastic substances with water-repellent properties. In insects, they serve as material for building honeycombs. Wax coating on the surface of leaves, stems, fruits protects plants from mechanical damage, ultraviolet radiation and plays an important role in the regulation of water balance.
Equally important in the body are fatty substances.
Representatives of this group - phospholipids - form the basis of all biological membranes. In their structure, phospholipids are similar to fats, but in their molecule one or two fatty acid residues are replaced by a phosphoric acid residue.
An important role in the life of all living organisms, especially animals, is played by a fat-like substance - cholesterol. In the cortical layer of the adrenal glands, in the gonads and in the placenta, steroid hormones (corticosteroids and sex hormones) are formed from it. In liver cells, bile acids are synthesized from cholesterol, which are necessary for the normal digestion of fats.
Fat-like substances also include fat-soluble vitamins A, D, E, K, which have high biological activity.
carbohydrates called substances with the general formula Сn (H2 O) m. Carbohydrates are one of the main groups of organic substances of cells. They are the primary products of photosynthesis and the initial products of the biosynthesis of other organic substances in plants (organic acids, alcohols, amino acids, etc.), and are also part of the cells of all other organisms. The animal cell contains 1-2% carbohydrates, in plant cells in some cases - 85-90%.
There are three groups of carbohydrates:
- monosaccharides, or simple sugars;
- oligosaccharides - compounds consisting of 2-10 consecutively connected molecules of simple sugars;
- polysaccharides consisting of more than 10 molecules of simple sugars or their derivatives.
Monosaccharides, these are compounds based on an unbranched carbon chain, in which at one of the carbon atoms there is a carbonyl group (C \u003d 0), and at all the others - one hydroxyl group each. Depending on the length of the carbon skeleton (the number of carbon atoms), monosaccharides are divided into trioses (C3), getroses (C4), pentoses (C5), hexoses (C6), heptoses (C7). Examples of pentoses are ribose, deoxyribose, hexose-glucose, fructose, galactose.
Monosaccharides dissolve well in water, they are sweet in taste. In an aqueous solution, monosaccharides, starting from pentoses, acquire a ring shape.
Oligosaccharides. Upon hydrolysis, oligosaccharides form several molecules of simple sugars. In oligosaccharides, simple sugar molecules are connected by so-called glycosidic bonds, connecting the carbon atom of one molecule through oxygen to the carbon atom of another molecule, for example:
The most important oligosaccharides are maltose (malt sugar), lactose (milk sugar) and sucrose (cane or beet sugar):
glucose + glucose = maltose;
glucose + galactose - lactose;
glucose + fructose = sucrose.
These sugars are also called disaccharides.
Polysaccharides. These are high-molecular (up to 10,000,000 Da) biopolymers, consisting of a large number of monomers - simple sugars and their derivatives.
Polysaccharides may be composed of monosaccharides of the same or different types. In the first case, they are called homopolysaccharides (starch, cellulose, chitin, etc.), in the second - heteropolysaccharides (heparin).
Polysaccharides can be linear, unbranched (cellulose) or branched (glycogen). All polysaccharides are insoluble in water and do not have a sweet taste. Some of them are able to swell and mucus.
The most important polysaccharides are:
- Cellulose is a linear polysaccharide consisting of several straight parallel chains linked together by hydrogen bonds.
- Starch (in plants) and glycogen (in animals, humans and fungi) are the main reserve polysaccharides for a number of reasons: being insoluble in water, they do not have any osmotic or chemical effect on the cell, which is important when they stay in a living cell for a long time.
- Chitin is formed by molecules of pVD-glucose, in which the hydroxyl group at the second carbon atom is replaced by the nitrogen-containing group NHCOCH3. Its long parallel chains, like the chains of cellulose, are bundled. Chitin is the main structural element of the integument of arthropods and the cell walls of fungi.
Functions of carbohydrates:
Energy. Glucose is the main source of energy released in the cells of living organisms during cellular respiration. Starch and glycogen make up the energy reserve in the cells.
Structural. Cellulose is part of the cell membranes of plants; chitin serves as a structural component of the integument of arthropods and the cell walls of many fungi. Some oligosaccharides are an integral part of the cytoplasmic membrane of the cell (in the form of glycoproteins and glycolipids), forming a glycocalyx. Pentoses are involved in the synthesis of nucleic acids (ribose is part of RNA, deoxyribose is part of DNA), some coenzymes (for example, NAD, NADP, coenzyme A, FAD), AMP; take part in photosynthesis (ribulose diphosphate is a CO2 acceptor in the dark phase of photosynthesis).
Protective. In animals, heparin prevents blood clotting; in plants, gums and mucus, which are formed when tissues are damaged, perform a protective function.
2.3. The chemical composition of the cell. Macro- and microelements. The relationship of the structure and functions of non-organic and organic substances (proteins, nucleic acids, carbohydrates, lipids, ATP) that make up the cell. The role of chemicals in the cell and the human body.
The chemical composition of the cell
Most of the chemical elements of the Periodic Table of Elements of D. I. Mendeleev discovered to date have been found in the composition of living organisms. On the one hand, they do not contain a single element that would not be in inanimate nature, and on the other hand, their concentrations in bodies of inanimate nature and living organisms differ significantly.
These chemical elements form inorganic and organic substances. Despite the fact that inorganic substances predominate in living organisms, it is organic substances that determine the uniqueness of their chemical composition and the phenomenon of life in general, since they are synthesized mainly by organisms in the process of vital activity and play an important role in reactions.
The study of the chemical composition of organisms and the chemical reactions occurring in them is the science of biochemistry.
It should be noted that the content of chemicals in different cells and tissues can vary significantly. For example, while proteins predominate among organic compounds in animal cells, carbohydrates predominate in plant cells.
| Chemical element | Earth's crust | Sea water | Living organisms |
| O | 49,2 | 85,8 | 65-75 |
| FROM | 0,4 | 0,0035 | 15-18 |
| H | 1,0 | 10,67 | 8-10 |
| N | 0,04 | 0,37 | 1,5-3,0 |
| R | 0,1 | 0,003 | 0,20-1,0 |
| S | 0,15 | 0,09 | 0,15-0,2 |
| To | 2,35 | 0,04 | 0,15-0,4 |
| Sa | 3,25 | 0,05 | 0,04-2,0 |
| Cl | 0,2 | 0,06 | 0,05-0,1 |
| mg | 2,35 | 0,14 | 0,02-0,03 |
| Na | 2,4 | 1,14 | 0,02-0,03 |
| Fe | 4,2 | 0,00015 | 0,01-0,015 |
| Zn | < 0,01 | 0,00015 | 0,0003 |
| Cu | < 0,01 | < 0,00001 | 0,0002 |
| I | < 0,01 | 0,000015 | 0,0001 |
| F | 0,1 | 2,07 | 0,0001 |
Macro- and microelements
About 80 chemical elements are found in living organisms, however, only for 27 of these elements their functions in the cell and organism have been established. The rest of the elements are present in small amounts, and, apparently, enter the body with food, water and air. The content of chemical elements in the body varies significantly. Depending on the concentration, they are divided into macronutrients and microelements.
The concentration of each of the macronutrients in the body exceeds 0.01%, and their total content is 99%. Macronutrients include oxygen, carbon, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, sodium, chlorine, magnesium, and iron. The first four of the listed elements (oxygen, carbon, hydrogen and nitrogen) are also called organogenic, since they are part of the main organic compounds. Phosphorus and sulfur are also components of a number of organic substances, such as proteins and nucleic acids. Phosphorus is essential for the formation of bones and teeth.
Without the remaining macronutrients, the normal functioning of the body is impossible. So, potassium, sodium and chlorine are involved in the processes of excitation of cells. Potassium is also needed for many enzymes to function and to retain water in the cell. Calcium is found in the cell walls of plants, bones, teeth, and mollusk shells and is required for muscle contraction and intracellular movement. Magnesium is a component of chlorophyll - the pigment that ensures the flow of photosynthesis. It also takes part in protein biosynthesis. Iron, in addition to being a part of hemoglobin, which carries oxygen in the blood, is necessary for the processes of respiration and photosynthesis, as well as for the functioning of many enzymes.
Trace elements are contained in the body in concentrations of less than 0.01%, and their total concentration in the cell does not even reach 0.1%. Trace elements include zinc, copper, manganese, cobalt, iodine, fluorine, etc. Zinc is part of the pancreatic hormone molecule insulin, copper is required for photosynthesis and respiration. Cobalt is a component of vitamin B12, the absence of which leads to anemia. Iodine is necessary for the synthesis of thyroid hormones, which ensure the normal course of metabolism, and fluorine is associated with the formation of tooth enamel.
The content of chemical elements in different cells and organisms is not the same, to a large extent it is due to environmental conditions. Thus, the cells of algae contain a relatively large amount of iodine, vertebrates - iron, and mollusks and crustaceans - copper.
Both deficiency and excess or disturbance of the metabolism of macro- and microelements lead to the development of various diseases. In particular, a lack of calcium and phosphorus causes rickets, a lack of nitrogen causes severe protein deficiency, an iron deficiency causes anemia, and a lack of iodine causes a violation of the formation of thyroid hormones and a decrease in metabolic rate. Reducing the intake of fluoride with water and food to a large extent causes a violation of the renewal of tooth enamel and, as a result, a predisposition to caries. Lead is toxic to almost all organisms. Its excess causes irreversible damage to the brain and central nervous system, which is manifested by loss of vision and hearing, insomnia, kidney failure, seizures, and can also lead to paralysis and diseases such as cancer. Acute lead poisoning is accompanied by sudden hallucinations and ends in coma and death.
The lack of macro- and microelements can be compensated by increasing their content in food and drinking water, as well as by taking medications. So, iodine is found in seafood and iodized salt, calcium in eggshells, etc.
Inorganic substances of the cell
The chemical elements of the cell form various compounds - inorganic and organic. The inorganic substances of the cell include water, mineral salts, acids, etc., and the organic substances include proteins, nucleic acids, carbohydrates, lipids, ATP, vitamins, etc.
Water (H 2 0)
- the most common inorganic substance of the cell, which has unique physicochemical properties. It has no taste, no color, no smell. Density and viscosity of all substances are estimated by water. Like many other substances, water can be in three states of aggregation: solid (ice), liquid and gaseous (steam). The melting point of water is 0 ° C, the boiling point is 100 ° C, however, the dissolution of other substances in water can change these characteristics. The heat capacity of water is also quite high - 4200 kJ / mol.K, which makes it possible for it to take part in the processes of thermoregulation. In a water molecule, hydrogen atoms are located at an angle of 105 °, while the common electron pairs are pulled away by the more electronegative oxygen atom. This determines the dipole properties of water molecules (one of their ends is positively charged and the other is negatively charged) and the possibility of the formation of hydrogen bonds between water molecules. The adhesion of water molecules underlies the phenomenon of surface tension, capillarity and the properties of water as a universal solvent. As a result, all substances are divided into soluble in water (hydrophilic) and insoluble in it (hydrophobic). Thanks to these unique properties, it is predetermined that water has become the basis of life on Earth.
The average water content in the cells of the body is not the same and may change with age. So, in a one and a half month old human embryo, the water content in the cells reaches 97.5%, in an eight month old - 83%, in a newborn it decreases to 74%, and in an adult it averages 66%. However, body cells differ in water content. So, the bones contain about 20% water, the liver - 70%, and the brain - 86%. In general, we can say that the concentration of water in cells is directly proportional to the intensity of metabolism.
mineral salts
may be in dissolved or undissolved states. Soluble salts dissociate into ions - cations and anions. The most important cations are potassium and sodium ions, which facilitate the transfer of substances through the membrane and participate in the occurrence and conduction of a nerve impulse; as well as calcium ions, which takes part in the processes of contraction of muscle fibers and blood clotting; magnesium, which is part of chlorophyll; iron, which is part of a number of proteins, including hemoglobin. The most important anions are the phosphate anion, which is part of ATP and nucleic acids, and the residue of carbonic acid, which softens fluctuations in the pH of the medium. Ions of mineral salts provide both the penetration of the water itself into the cell and its retention in it. If the concentration of salts in the environment is lower than in the cell, then water penetrates into the cell. Also, ions determine the buffer properties of the cytoplasm, i.e., its ability to maintain a constant slightly alkaline pH of the cytoplasm, despite the constant formation of acidic and alkaline products in the cell.
Insoluble salts (CaCO 3, Ca 3 (P0 4) 2, etc.) are part of the bones, teeth, shells and shells of unicellular and multicellular animals.
In addition, other inorganic compounds, such as acids and oxides, can be produced in organisms. So, parietal cells of the human stomach produce hydrochloric acid, which activates the digestive enzyme pepsin, and silicon oxide impregnates the cell walls of horsetails and forms diatom shells. In recent years, the role of nitric oxide (II) in signaling in cells and the body has also been investigated.
organic matter
General characteristics of the organic substances of the cell
The organic substances of a cell can be represented by both relatively simple molecules and more complex ones. In cases where a complex molecule (macromolecule) is formed by a significant number of repeating simpler molecules, it is called a polymer, and the structural units are called monomers. Depending on whether or not polymer units are repeated, they are classified as regular or irregular. Polymers make up to 90% of the dry matter mass of the cell. They belong to three main classes of organic compounds - carbohydrates (polysaccharides), proteins and nucleic acids. Regular polymers are polysaccharides, while proteins and nucleic acids are irregular. In proteins and nucleic acids, the sequence of monomers is extremely important, since they perform an informational function.
Carbohydrates
- these are organic compounds, which mainly include three chemical elements - carbon, hydrogen and oxygen, although a number of carbohydrates also contain nitrogen or sulfur. The general formula for carbohydrates is C m (H 2 0) n. They are divided into simple and complex carbohydrates.
Simple carbohydrates (monosaccharides) contain a single sugar molecule that cannot be broken down into simpler ones. These are crystalline substances, sweet in taste and highly soluble in water. Monosaccharides take an active part in the metabolism in the cell and are part of complex carbohydrates - oligosaccharides and polysaccharides.
Monosaccharides are classified according to the number of carbon atoms (C 3 -C 9), for example, pentoses (C 5) and hexoses (C 6). Pentoses include ribose and deoxyribose. Ribose is a constituent of RNA and ATP. Deoxyribose is a component of DNA. Hexoses (C 6 H 12 0 6) are glucose, fructose, galactose, etc.
Glucose(grape sugar) is found in all organisms, including human blood, as it is an energy reserve. It is part of many complex sugars: sucrose, lactose, maltose, starch, cellulose, etc.
Fructose(fruit sugar) is found in the highest concentrations in fruits, honey, sugar beet root crops. It not only takes an active part in metabolic processes, but also is part of sucrose and some polysaccharides, such as insulin.
Most monosaccharides are able to give a "silver mirror" reaction and reduce copper by adding Fehling's liquid (a mixture of solutions of copper (II) sulfate and potassium-sodium tartrate) and boiling.
Oligosaccharides are carbohydrates made up of several monosaccharide residues. They are generally also highly soluble in water and are sweet in taste. Depending on the number of these residues, disaccharides (two residues), trisaccharides (three), etc. are distinguished. Disaccharides include sucrose, lactose, maltose, etc.
Sucrose (beet or cane sugar) consists of residues of glucose and fructose, it is found in the storage organs of some plants. There is especially a lot of sucrose in the root-fruits of sugar beet and sugar cane, from where they are obtained industrially. It serves as a benchmark for the sweetness of carbohydrates.
Lactose, or milk sugar, is formed by residues of glucose and galactose, found in mother's and cow's milk.
Maltose(malt sugar) consists of two glucose residues. It is formed during the breakdown of polysaccharides in plant seeds and in the human digestive system, and is used in the production of beer.
Polysaccharides are biopolymers whose monomers are mono- or disaccharide residues. Most polysaccharides are insoluble in water and taste unsweetened. These include starch, glycogen, cellulose and chitin.
Starch is a white powdery substance that is not wetted by water, but forms a suspension when brewed with hot water - a paste. Starch is actually made up of two polymers, the less branched amylose and the more branched amylopectin. The monomer of both amylose and amylopectin is glucose. Starch is the main reserve substance of plants, which accumulates in large quantities in seeds, fruits, tubers, rhizomes and other storage organs of plants. A qualitative reaction to starch is a reaction with iodine, in which starch turns blue-violet.
Glycogen(animal starch) is a reserve polysaccharide of animals and fungi, which in humans accumulates in the largest quantities in the muscles and liver. It is also insoluble in water and tastes unsweetened. The monomer of glycogen is glucose. Compared to starch molecules, glycogen molecules are even more branched.
Cellulose or fiber, - the main reference polysaccharide of plants. The monomer of cellulose is glucose. Unbranched cellulose molecules form bundles that are part of the cell walls of plants and some fungi. Cellulose is the basis of wood, it is used in construction, in the production of textiles, paper, alcohol and many organic substances. Cellulose is chemically inert and does not dissolve in either acids or alkalis. It is also not broken down by the enzymes of the human digestive system, but bacteria in the large intestine help digest it. In addition, fiber stimulates the contraction of the walls of the gastrointestinal tract, helping to improve its work.
Chitin is a polysaccharide, the monomer of which is a nitrogen-containing monosaccharide. It is part of the cell walls of fungi and arthropod shells. In the human digestive system, there is also no enzyme for digesting chitin, only some bacteria have it.
Functions of carbohydrates. Carbohydrates perform plastic (construction), energy, storage and support functions in the cell. They form the cell walls of plants and fungi. The energy value of the breakdown of 1 g of carbohydrates is 17.2 kJ. Glucose, fructose, sucrose, starch and glycogen are reserve substances. Carbohydrates can also be part of complex lipids and proteins, forming glycolipids and glycoproteins, in particular in cell membranes. No less important is the role of carbohydrates in the intercellular recognition and perception of environmental signals, since they act as receptors in the composition of glycoproteins.
Lipids
is a chemically heterogeneous group of low molecular weight substances with hydrophobic properties. These substances are insoluble in water, form emulsions in it, but are readily soluble in organic solvents. Lipids are oily to the touch, many of them leave characteristic non-drying traces on paper. Together with proteins and carbohydrates, they are one of the main components of cells. The content of lipids in different cells is not the same, especially a lot of them in the seeds and fruits of some plants, in the liver, heart, blood.
Depending on the structure of the molecule, lipids are divided into simple and complex. Simple lipids include neutral lipids (fats), waxes, sterols, and steroids. Complex lipids also contain another, non-lipid component. The most important of them are phospholipids, glycolipids, etc.
Fats are derivatives of the trihydric alcohol glycerol and higher fatty acids. Most fatty acids contain 14-22 carbon atoms. Among them there are both saturated and unsaturated, that is, containing double bonds. Of the saturated fatty acids, palmitic and stearic acids are most common, and of the unsaturated fatty acids, oleic. Some unsaturated fatty acids are not synthesized in the human body or are synthesized in insufficient quantities, and therefore are indispensable. Glycerol residues form hydrophilic heads, while fatty acid residues form tails.
Squirrels
- These are high-molecular compounds, biopolymers, the monomers of which are amino acids linked by peptide bonds.
amino acid called an organic compound having an amino group, a carboxyl group and a radical. In total, about 200 amino acids are found in nature, which differ in radicals and the mutual arrangement of functional groups, but only 20 of them can be part of proteins. Such amino acids are called proteinogenic.
Unfortunately, not all proteinogenic amino acids can be synthesized in the human body, so they are divided into interchangeable and irreplaceable.
Non-essential amino acids are formed in the human body in the required amount, while essential ones are not. They must come from food, but can also be partially synthesized by intestinal micro-organisms. There are 8 completely irreplaceable amino acids. These include valine, isoleucine, leucine, lysine, methionine, threonine, tryptophan and phenylalanine. Despite the fact that absolutely all proteinogenic amino acids are synthesized in plants, vegetable proteins are incomplete because they do not contain a complete set of amino acids, moreover, the presence of protein in the vegetative parts of plants rarely exceeds 1-2% of the mass. Therefore, it is necessary to eat proteins not only of vegetable, but also of animal origin.
A sequence of two amino acids linked by peptide bonds is called a dipeptide, of three, a tripeptide, etc. Among the peptides, there are such important compounds as hormones (oxytocin, vasopressin), antibiotics, etc. A chain of more than ten amino acids is called a polypeptide, and polypeptides containing more than 50 amino acid residues are proteins.
Levels of protein structural organization. Proteins can have primary, secondary, tertiary and quaternary structures.
Primary structure of a protein is a sequence of amino acids connected by a peptide bond. The primary structure ultimately determines the specificity of the protein and its uniqueness, because even if we assume that the average protein contains 500 amino acid residues, then the number of possible combinations is 20,500. Therefore, a change in the location of at least one amino acid in the primary structure entails a change secondary and higher structures, as well as the properties of the protein as a whole.
Structural features of the protein determine its spatial packing - the emergence of secondary and tertiary structures.
secondary structure is a spatial arrangement of a protein molecule in the form of a helix or folds held by hydrogen bonds between oxygen and hydrogen atoms of peptide groups of different turns of the helix or folds. Many proteins contain more or less long regions with a secondary structure. These are, for example, keratins of hair and nails, silk fibroin.
Tertiary structure protein is also a form of spatial packing of the polypeptide chain, held by hydrophobic, hydrogen, disulfide (S-S) and other bonds. It is characteristic of most body proteins, such as muscle myoglobin.
Quaternary structure- the most complex, formed by several polypeptide chains connected mainly by the same bonds as in the tertiary (hydrophobic, ionic and hydrogen), as well as other weak interactions. The quaternary structure is characteristic of a few proteins, such as hemoglobin, chlorophyll, etc.
According to the shape of the molecule, fibrillar and globular proteins are distinguished. The first of them are elongated, like, for example, connective tissue collagen or hair and nail keratins. Globular proteins are in the form of a ball (globules), like muscle myoglobin.
Simple and complex proteins. Proteins can be simple or complex. Simple proteins consist only of amino acids, while complex proteins (lipoproteins, chromoproteins, glycoproteins, nucleoproteins, etc.) contain protein and non-protein parts. Chromoproteins contain a colored non-protein part. These include hemoglobin, myoglobin, chlorophyll, cytochromes, etc.
So, in the composition of hemoglobin, each of the four polypeptide chains of the globin protein is associated with a non-protein part - heme, in the center of which there is an iron ion, which gives hemoglobin a red color. Non-protein part of lipoproteins is lipid, aglycoproteins - carbohydrate. Both lipoproteins and glycoproteins are part of cell membranes. Nucleoproteins are complexes of proteins and nucleic acids (DNA and RNA). They perform the most important functions in the processes of storage and transmission of hereditary information.
Protein properties. Many proteins are highly soluble in water, but there are some among them that dissolve only in solutions of salts, alkalis, acids, or organic solvents. The structure of a protein molecule and its functional activity depend on environmental conditions. The loss of a protein molecule of its structure, up to the primary one, is called denaturation.
Denaturation occurs due to changes in temperature, pH, atmospheric pressure, under the action of acids, alkalis, salts of heavy metals, organic solvents, etc. The reverse process of restoring secondary and higher structures is called renaturation, however, it is not always possible. The complete destruction of a protein molecule is called destruction.
Proteins perform a number of functions in the cell: plastic (construction), catalytic (enzymatic), energy, signal (receptor), contractile (motor), transport, protective, regulatory and storage.
The building function of proteins is associated with their presence in cell membranes and structural components of the cell. Energy - due to the fact that during the breakdown of 1 g of protein, 17.2 kJ of energy is released. Membrane receptor proteins are actively involved in the perception of environmental signals and their transmission through the cell, as well as in intercellular recognition. Without proteins, the movement of cells and organisms as a whole is impossible, since they form the basis of flagella and cilia, and also provide muscle contraction and movement of intracellular components. In the blood of humans and many animals, the protein hemoglobin carries oxygen and part of carbon dioxide, while other proteins transport ions and electrons. The protective role of proteins is associated primarily with immunity, since the interferon protein is able to destroy many viruses, and antibody proteins suppress the development of bacteria and other foreign agents. There are many hormones among proteins and peptides, for example, pancreatic hormone, insulin, which regulates the concentration of glucose in the blood. In some organisms, proteins can be stored in reserve, as in legumes in seeds, or the proteins of a chicken egg.
Nucleic acids
are biopolymers whose monomers are nucleotides. Currently, two types of nucleic acids are known: ribonucleic (RNA) and deoxyribonucleic (DNA).
A nucleotide is formed by a nitrogenous base, a pentose sugar residue, and a phosphoric acid residue. The features of nucleotides are mainly determined by the nitrogenous bases that make up their composition, therefore, even conditionally, nucleotides are designated by the first letters of their names.
The composition of nucleotides can include five nitrogenous bases: adenine (A), guanine (G), thymine (T), uracil (U) and cytosine (C). The pentoses of nucleotides - ribose and deoxyribose - determine which nucleotide will be formed - ribonucleotide or deoxyribonucleotide. Ribonucleotides are RNA monomers, they can act as signal molecules (cAMP) and be part of macroergic compounds, such as ATP, and coenzymes, such as NADPH + H +, NADH + H +, FADH 2, etc., and deoxyribonucleotides are part of DNA.
Deoxyribonucleic acid (DNA)- double-stranded biopolymer, the monomers of which are deoxyribonucleotides. The composition of deoxyribonucleotides includes only four nitrogenous bases out of five possible - adenine (A), thymine (T), guanine (G) and cytosine (C), as well as deoxyribose and phosphoric acid residues. Nucleotides in the DNA chain are interconnected through orthophosphoric acid residues, forming a phosphodiester bond. When a double-stranded molecule is formed, the nitrogenous bases are directed inward of the molecule. However, the connection of DNA chains does not occur randomly - the nitrogenous bases of different chains are interconnected by hydrogen bonds according to the principle of complementarity: adenine is connected to thymine by two hydrogen bonds (A \u003d T), and guanine and cytosine by three (G≡C).
For her were set Chargaff rules
:
1. The number of DNA nucleotides containing adenine is equal to the number of nucleotides containing thymine (A=T).
2. The number of DNA nucleotides containing guanine is equal to the number of nucleotides containing cytosine (G≡C).
3. The sum of deoxyribonucleotides containing adenine and guanine is equal to the sum of deoxyribonucleotides containing thymine and cytosine (A + G = T + C).
4. The ratio of the sum of deoxyribonucleotides containing adenine and thymine to the sum of deoxyribonucleotides containing guanine and cytosine depends on the type of organisms.
The structure of DNA was deciphered by F. Crick and D. Watson (Nobel Prize in Physiology or Medicine, 1962). According to their model, the DNA molecule is a right-handed double helix. The distance between nucleotides in a DNA chain is 0.34 nm.
The most important property of DNA is the ability to replicate (self-doubling). The main function of DNA is the storage and transmission of hereditary information, which is written in the form of nucleotide sequences. The stability of the DNA molecule is maintained by powerful repair (recovery) systems, but even they are not able to completely eliminate adverse effects, which ultimately leads to mutations. The DNA of eukaryotic cells is concentrated in the nucleus, mitochondria and plastids, while prokaryotic cells are located directly in the cytoplasm. Nuclear DNA is the basis of chromosomes, it is represented by open molecules. DNA of mitochondria, plastids and prokaryotes has a circular shape.
Ribonucleic acid (RNA)- a biopolymer whose monomers are ribonucleotides. They also contain four nitrogenous bases - adenine (A), uracil (U), guanine (G) and cytosine (C), thereby differing from DNA in one of the bases (uracil is found in RNA instead of thymine). The pentose sugar residue in ribonucleotides is represented by ribose. RNA is mostly single-stranded molecules, with the exception of some viral ones. There are three main types of RNA: informational, or template (mRNA, mRNA), ribosomal (rRNA) and transport (tRNA). All of them are formed in the process of transcription - rewriting from DNA molecules.
mRNAs make up the smallest fraction of RNA in a cell (2-4%), which is offset by their diversity, since one cell can contain thousands of different mRNAs. These are single-stranded molecules that are templates for the synthesis of polypeptide chains. Information about the structure of the protein is recorded in them in the form of sequences of nucleotides, and each amino acid encodes a triplet of nucleotides - a codon.
rRNAs are the most numerous type of RNA in the cell (up to 80%). Their molecular weight averages 3000-5000; are formed in the nucleoli and are part of the cellular organelles - ribosomes. rRNAs also appear to play a role in protein synthesis.
tRNA is the smallest of the RNA molecules, as it contains only 73-85 nucleotides. Their share of the total amount of cell RNA is about 16%. The function of tRNA is the transport of amino acids to the site of protein synthesis (on ribosomes). The shape of the tRNA molecule resembles a clover leaf. At one end of the molecule there is a site for attaching an amino acid, and in one of the loops there is a triplet of nucleotides that is complementary to the mRNA codon and determines which amino acid the tRNA will carry - the anticodon.
All types of RNA take an active part in the implementation of hereditary information, which is rewritten from DNA to mRNA, and on the latter protein synthesis is carried out. tRNA in the process of protein synthesis delivers amino acids to ribosomes, and rRNA is part of the ribosomes directly.
Adenosine triphosphoric acid (ATP)
is a nucleotide containing, in addition to the nitrogenous base of adenine and a ribose residue, three phosphoric acid residues.
The bonds between the last two phosphorus residues are macroergic (42 kJ / mol of energy is released during splitting), while the standard chemical bond during splitting gives 12 kJ / mol. If energy is needed, the macroergic bond of ATP is split, adenosine diphosphoric acid (ADP), a phosphorus residue are formed, and energy is released:
ATP + H 2 0 → ADP + H 3 P0 4 + 42 kJ.
ADP can also be broken down to form AMP (adenosine monophosphoric acid) and a phosphoric acid residue:
ADP + H 2 0 → AMP + H 3 P0 4 + 42 kJ.
In the process of energy metabolism (during respiration, fermentation), as well as in the process of photosynthesis, ADP attaches a phosphorus residue and turns into ATP. The ATP recovery reaction is called phosphorylation. ATP is a universal source of energy for all life processes of living organisms.
The study of the chemical composition of the cells of all living organisms has shown that they contain the same chemical elements, chemicals that perform the same functions. Moreover, a piece of DNA transferred from one organism to another will work in it, and a protein synthesized by bacteria or fungi will act as a hormone or enzyme in the human body. This is one of the proofs of the unity of the origin of the organic world.
Fats
perform in cells mainly a storage function and serve as a source of energy. They are rich in subcutaneous fatty tissue, which performs shock-absorbing and thermal insulation functions, and in aquatic animals it also increases buoyancy. Plant fats mostly contain unsaturated fatty acids, as a result of which they are liquid and are called oils. Oils are found in the seeds of many plants, such as sunflower, soybeans, rapeseed, etc.
Waxes are complex mixtures of fatty acids and fatty alcohols. In plants, they form a film on the surface of the leaf, which protects against evaporation, the penetration of pathogens, etc. In a number of animals, they cover the body or serve to build honeycombs.
Sterols include a lipid such as cholesterol, an essential component of cell membranes, and steroids include the sex hormones estradiol, testosterone, etc.
Phospholipids, in addition to glycerol and fatty acid residues, contain an orthophosphoric acid residue. They are part of cell membranes and provide their barrier properties.
Glycolipids are also components of membranes, but their content there is low. The non-lipid part of glycolipids are carbohydrates.
Functions of lipids. Lipids perform plastic (building), energy, storage, protective and regulatory functions in the cell, in addition, they are solvents for a number of vitamins. It is an essential component of cell membranes. When splitting 1 g of lipids, 38.9 kJ of energy is released. They are deposited in the reserve in various organs of plants and animals. In addition, subcutaneous fatty tissue protects internal organs from hypothermia or overheating, as well as shock. The regulatory function of lipids is due to the fact that some of them are hormones.
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