Remember!

What substances are called biological polymers?

These are polymers - high-molecular compounds that are part of living organisms. Proteins, some carbohydrates, nucleic acids.

What is the importance of carbohydrates in nature?

Fructose is widely distributed in nature - fruit sugar, which is much sweeter than other sugars. This monosaccharide imparts a sweet taste to plant fruits and honey. The most common disaccharide in nature - sucrose, or cane sugar - consists of glucose and fructose. It is obtained from sugar cane or sugar beets. Starch for plants and glycogen for animals and fungi are a reserve of nutrients and energy. Cellulose and chitin perform structural and protective functions in organisms. Cellulose, or fiber, forms the walls of plant cells. In terms of total mass, it ranks first on Earth among all organic compounds. In its structure, chitin is very close to cellulose, which forms the basis of the external skeleton of arthropods and is part of the cell wall of fungi.

Name the proteins you know. What functions do they perform?

Hemoglobin is a blood protein that transports gases in the blood

Myosin - muscle protein, muscle contraction

Collagen - protein of tendons, skin, elasticity, extensibility

Casein is a milk protein

Review questions and assignments

1. What chemical compounds are called carbohydrates?

This is an extensive group of natural organic compounds. In animal cells, carbohydrates make up no more than 5% of the dry mass, and in some plant cells (for example, tubers or potatoes), their content reaches 90% of the dry residue. Carbohydrates are divided into three main classes: monosaccharides, disaccharides and polysaccharides.

2. What are mono- and disaccharides? Give examples.

Monosaccharides are composed of monomers, low molecular weight organic substances. The monosaccharides ribose and deoxyribose are constituents of nucleic acids. The most common monosaccharide is glucose. Glucose is present in the cells of all organisms and is one of the main sources of energy for animals. If two monosaccharides combine in one molecule, such a compound is called a disaccharide. The most common disaccharide in nature is sucrose, or cane sugar.

3. What simple carbohydrate serves as a monomer of starch, glycogen, cellulose?

4. What organic compounds do proteins consist of?

Long protein chains are built from only 20 different types of amino acids that have a common structural plan, but differ from each other in the structure of the radical. Connecting, amino acid molecules form so-called peptide bonds. The two polypeptide chains that make up the pancreatic hormone insulin contain 21 and 30 amino acid residues. These are some of the shortest "words" in the protein "language". Myoglobin is a protein that binds oxygen in muscle tissue and consists of 153 amino acids. The collagen protein, which forms the basis of connective tissue collagen fibers and ensures its strength, consists of three polypeptide chains, each of which contains about 1000 amino acid residues.

5. How are secondary and tertiary protein structures formed?

Twisting in the form of a spiral, the protein thread acquires a higher level of organization - a secondary structure. Finally, the polypeptide coils up to form a coil (globule). It is this tertiary structure of the protein that is its biologically active form, which has individual specificity. However, for a number of proteins, the tertiary structure is not final. The secondary structure is a polypeptide chain twisted into a helix. For a stronger interaction in the secondary structure, an intramolecular interaction occurs with the help of –S–S– sulfide bridges between the turns of the helix. This ensures the strength of this structure. The tertiary structure is a secondary spiral structure twisted into globules - compact lumps. These structures provide maximum strength and greater abundance in cells compared to other organic molecules.

6. Name the functions of proteins known to you. How can you explain the existing diversity of protein functions?

One of the main functions of proteins is enzymatic. Enzymes are proteins that catalyze chemical reactions in living organisms. An enzymatic reaction is a chemical reaction that takes place only in the presence of an enzyme. Without an enzyme, not one reaction occurs in living organisms. The work of enzymes is strictly specific, each enzyme has its own substrate, which it cleaves. The enzyme approaches its substrate like a "key to a lock". So, the urease enzyme regulates the breakdown of urea, the amylase enzyme regulates starch, and the protease enzymes regulate proteins. Therefore, for enzymes, the expression "specificity of action" is used.

Proteins also perform various other functions in organisms: structural, transport, motor, regulatory, protective, energy. The functions of proteins are quite numerous, since they underlie the variety of manifestations of life. It is a component of biological membranes, the transport of nutrients, such as hemoglobin, muscle function, hormonal function, body defense - the work of antigens and antibodies, and other important functions in the body.

7. What is protein denaturation? What can cause denaturation?

Denaturation is a violation of the tertiary spatial structure of protein molecules under the influence of various physical, chemical, mechanical and other factors. Physical factors are temperature, radiation. Chemical factors are the action of any chemicals on proteins: solvents, acids, alkalis, concentrated substances, and so on. Mechanical factors - shaking, pressure, stretching, twisting, etc.

Think! Remember!

1. Using the knowledge gained in the study of plant biology, explain why there are significantly more carbohydrates in plant organisms than in animals.

Since the basis of life - plant nutrition is photosynthesis, this is the process of formation of complex organic compounds of carbohydrates from simpler inorganic carbon dioxide and water. The main carbohydrate synthesized by plants for air nutrition is glucose, it can also be starch.

2. What diseases can lead to a violation of the conversion of carbohydrates in the human body?

The regulation of carbohydrate metabolism is mainly carried out by hormones and the central nervous system. Glucocorticosteroids (cortisone, hydrocortisone) slow down the rate of glucose transport into tissue cells, insulin accelerates it; adrenaline stimulates the process of sugar formation from glycogen in the liver. The cerebral cortex also plays a certain role in the regulation of carbohydrate metabolism, since psychogenic factors increase the formation of sugar in the liver and cause hyperglycemia.

The state of carbohydrate metabolism can be judged by the content of sugar in the blood (normally 70-120 mg%). With a sugar load, this value increases, but then quickly reaches the norm. Carbohydrate metabolism disorders occur in various diseases. So, with a lack of insulin, diabetes mellitus occurs.

A decrease in the activity of one of the enzymes of carbohydrate metabolism - muscle phosphorylase - leads to muscular dystrophy.

3. It is known that if there is no protein in the diet, even despite the sufficient caloric content of food, growth stops in animals, the composition of the blood changes and other pathological phenomena occur. What is the reason for such violations?

There are only 20 different types of amino acids in the body that have a common structural plan, but differ from each other in the structure of the radical, they form different protein molecules if you do not use proteins, for example, essential ones that cannot be formed in the body on their own, but must be consumed with food . Thus, if there are no proteins, many protein molecules cannot form within the body itself and pathological changes cannot occur. Growth is controlled by the growth of bone cells, the basis of any cell is protein; hemoglobin is the main protein in the blood, which ensures the transport of the main gases in the body (oxygen, carbon dioxide).

4. Explain the difficulties that arise during organ transplantation, based on the knowledge of the specificity of protein molecules in each organism.

Proteins are the genetic material, since they contain the structure of the DNA and RNA of the body. Thus, proteins have genetic characteristics in each organism, the information of genes is encrypted in them, this is the difficulty when transplanting from alien (unrelated) organisms, since they have different genes, and hence proteins.

Carbohydrates are organic compounds made up of carbon and oxygen. There are simple carbohydrates, or monosaccharides, such as glucose, and complex, or polysaccharides, which are divided into lower, containing few simple carbohydrate residues, such as disaccharides, and higher, having very large molecules of many simple carbohydrate residues. In animal organisms, the carbohydrate content is about 2% dry weight.

The average daily requirement of an adult in carbohydrates is 500 g, and with intensive muscular work - 700-1000 g.

The amount of carbohydrates per day should be 60% by weight, and 56% by weight of the total amount of food.

Glucose is contained in the blood, in which its amount is maintained at a constant level (0.1-0.12%). After absorption in the intestine, monosaccharides are delivered by the blood to where synthesis of glycogen from monosaccharides, which is part of the cytoplasm, takes place. Glycogen stores are stored mainly in the muscles and in the liver.

The total amount of glycogen in a human body weighing 70 kg is approximately 375 g, of which 245 g is contained in the muscles, 110 g (up to 150 g) in the liver, 20 g in the blood and other body fluids. In the body of a trained person, glycogen is 40 -50% more than untrained.

Carbohydrates are the main source of energy for the life and work of the body.

In the body, under oxygen-free (anaerobic) conditions, carbohydrates break down into lactic acid, releasing energy. This process is called glycolysis. With the participation of oxygen (aerobic conditions), they are split into carbon dioxide and, while releasing much more energy. Of great biological importance is the anaerobic breakdown of carbohydrates with the participation of phosphoric acid - phosphorylation.

Phosphorylation of glucose occurs in the liver with the participation of enzymes. The source of glucose can be amino acids and fats. In the liver, from pre-phosphorylated glucose, huge polysaccharide molecules, glycogen, are formed. The amount of glycogen in the human liver depends on the nature of nutrition and muscle activity. With the participation of other enzymes in the liver, glycogen is broken down to glucose - sugar formation. The breakdown of glycogen in the liver and skeletal muscles during fasting and muscular work is accompanied by simultaneous synthesis of glycogen. Glucose, formed in the liver, enters and is delivered with it to all cells and tissues.

Only a small part of proteins and fats releases energy in the process of desmolytic breakdown and, therefore, serves as a direct source of energy. A significant part of the proteins and fats, even before complete disintegration, is first converted into carbohydrates in the muscles. In addition, from the digestive canal, the products of hydrolysis of proteins and fats enter the liver, where amino acids and fats are converted into glucose. This process is referred to as gluconeogenesis. The main source of glucose formation in the liver is glycogen, a much smaller part of glucose is obtained by gluconeogenesis, during which the formation of ketone bodies is delayed. Thus, carbohydrate metabolism significantly affects the metabolism, and water.

When glucose consumption by working muscles increases 5-8 times, glycogen is formed in the liver from fats and proteins.

Unlike proteins and fats, carbohydrates are easily broken down, so they are quickly mobilized by the body at high energy costs (muscle work, emotions of pain, fear, anger, etc.). The breakdown of carbohydrates keeps the body stable and is the main source of energy for the muscles. Carbohydrates are essential for the normal functioning of the nervous system. A decrease in blood sugar leads to a drop in body temperature, weakness and fatigue of muscles, and disorders of nervous activity.

In tissues, only a very small part of the glucose delivered by the blood is used with the release of energy. The main source of carbohydrate metabolism in tissues is glycogen, previously synthesized from glucose.

During the work of the muscles - the main consumers of carbohydrates - the glycogen reserves in them are used, and only after these reserves are completely used up, the direct use of glucose delivered to the muscles by the blood begins. This consumes glucose, formed from glycogen stores in the liver. After work, the muscles renew their supply of glycogen, synthesizing it from blood glucose, and the liver - due to absorbed monosaccharides in the digestive tract and the breakdown of proteins and fats.

For example, with an increase in blood glucose above 0.15-0.16% due to its abundant content in food, which is referred to as food hyperglycemia, it is excreted from the body with urine - glycosuria.

On the other hand, even with prolonged fasting, the level of glucose in the blood does not decrease, since glucose enters the blood from tissues during the breakdown of glycogen in them.

Brief description of the composition, structure and ecological role of carbohydrates

Carbohydrates are organic substances consisting of carbon, hydrogen and oxygen, having the general formula C n (H 2 O) m (for the vast majority of these substances).

The value of n is either equal to m (for monosaccharides), or greater than it (for other classes of carbohydrates). The above general formula does not correspond to deoxyribose.

Carbohydrates are divided into monosaccharides, di (oligo) saccharides and polysaccharides. Below is a brief description of the individual representatives of each class of carbohydrates.

Brief description of monosaccharides

Monosaccharides are carbohydrates whose general formula is C n (H 2 O) n (the exception is deoxyribose).

Classifications of monosaccharides

Monosaccharides are a rather extensive and complex group of compounds, so they have a complex classification according to various criteria:

1) according to the number of carbon contained in a monosaccharide molecule, tetroses, pentoses, hexoses, heptoses are distinguished; Pentoses and hexoses are of the greatest practical importance;

2) according to functional groups, monosaccharides are divided into ketoses and aldoses;

3) according to the number of atoms contained in the cyclic monosaccharide molecule, pyranoses (contain 6 atoms) and furanoses (contain 5 atoms) are distinguished;

4) based on the spatial arrangement of the "glucosidic" hydroxide (this hydroxide is obtained by attaching a hydrogen atom to the oxygen of the carbonyl group), monosaccharides are divided into alpha and beta forms. Let's take a look at some of the most important monosaccharides of greatest biological and ecological importance in nature.

Brief description of pentoses

Pentoses are monosaccharides, the molecule of which contains 5 carbon atoms. These substances can be both open-chain and cyclic, aldoses and ketoses, alpha and beta compounds. Among them, ribose and deoxyribose are of the most practical importance.

Ribose formula in general form C 5 H 10 O 5. Ribose is one of the substances from which ribonucleotides are synthesized, from which various ribonucleic acids (RNA) are subsequently obtained. Therefore, the furanose (5-membered) alpha form of ribose is of greatest importance (in formulas, RNA is depicted in the form of a regular pentagon).

The formula of deoxyribose in general form is C 5 H 10 O 4. Deoxyribose is one of the substances from which deoxyribonucleotides are synthesized in organisms; the latter are the starting materials for the synthesis of deoxyribonucleic acids (DNA). Therefore, the cyclic alpha form of deoxyribose, which lacks a hydroxide at the second carbon atom in the cycle, is of greatest importance.

The open-chain forms of ribose and deoxyribose are aldoses, that is, they contain 4 (3) hydroxide groups and one aldehyde group. With the complete breakdown of nucleic acids, ribose and deoxyribose are oxidized to carbon dioxide and water; This process is accompanied by the release of energy.

Brief description of hexoses

Hexoses are monosaccharides whose molecules contain six carbon atoms. The general formula of hexoses is C 6 (H 2 O) 6 or C 6 H 12 O 6. All varieties of hexoses are isomers corresponding to the above formula. Among hexoses, there are ketoses, and aldoses, and alpha and beta forms of molecules, open-chain and cyclic forms, pyranose and furanose cyclic forms of molecules. Of greatest importance in nature are glucose and fructose, which are briefly discussed below.

1. Glucose. Like any hexose, it has the general formula C 6 H 12 O 6 . It belongs to aldoses, i.e. it contains an aldehyde functional group and 5 hydroxide groups (characteristic of alcohols), therefore, glucose is a polyatomic aldehyde alcohol (these groups are contained in an open-chain form, the aldehyde group is absent in the cyclic form, since it turns into a hydroxide a group called "glucosidic hydroxide"). The cyclic form can be either five-membered (furanose) or six-membered (pyranose). The most important in nature is the pyranose form of the glucose molecule. The cyclic pyranose and furanose forms can be either alpha or beta forms, depending on the location of the glucosidic hydroxide relative to other hydroxide groups in the molecule.

According to its physical properties, glucose is a white crystalline solid with a sweet taste (the intensity of this taste is similar to sucrose), highly soluble in water and capable of forming supersaturated solutions (“syrups”). Since the glucose molecule contains asymmetric carbon atoms (i.e., atoms connected to four different radicals), glucose solutions have optical activity, therefore, D-glucose and L-glucose are distinguished, which have different biological activity.

From a biological point of view, the ability of glucose to easily oxidize according to the scheme is most important:

С 6 Н 12 O 6 (glucose) → (intermediate stages) → 6СO 2 + 6Н 2 O.

Glucose is a biologically important compound, as it is used by the body through its oxidation as a universal nutrient and a readily available source of energy.

2. Fructose. This is ketosis, its general formula is C 6 H 12 O 6, that is, it is an isomer of glucose, it is characterized by open-chain and cyclic forms. The most important is beta-B-fructofuranose or beta-fructose for short. Sucrose is made from beta-fructose and alpha-glucose. Under certain conditions, fructose is able to turn into glucose during the isomerization reaction. Fructose is similar in physical properties to glucose, but sweeter than it.

Brief description of disaccharides

Disaccharides are products of the reaction of dicondensation of the same or different molecules of monosaccharides.

Disaccharides are one of the varieties of oligosaccharides (a small number of monosaccharide molecules (same or different) are involved in the formation of their molecules.

The most important representative of disaccharides is sucrose (beet or cane sugar). Sucrose is a product of the interaction of alpha-D-glucopyranose (alpha-glucose) and beta-D-fructofuranose (beta-fructose). Its general formula is C 12 H 22 O 11. Sucrose is one of the many isomers of disaccharides.

This is a white crystalline substance that exists in various states: coarse-grained ("sugar heads"), fine-crystalline (granulated sugar), amorphous (powdered sugar). It dissolves well in water, especially in hot water (compared to hot water, the solubility of sucrose in cold water is relatively low), so sucrose is able to form "supersaturated solutions" - syrups that can "candied", i.e., fine-crystalline suspensions are formed. Concentrated solutions of sucrose are capable of forming special glassy systems - caramel, which is used by humans to obtain certain varieties of sweets. Sucrose is a sweet substance, but the intensity of the sweet taste is less than that of fructose.

The most important chemical property of sucrose is its ability to hydrolyze, in which alpha-glucose and beta-fructose are formed, which enter into carbohydrate metabolism reactions.

For humans, sucrose is one of the most important food products, as it is a source of glucose. However, excessive consumption of sucrose is harmful, because it leads to a violation of carbohydrate metabolism, which is accompanied by the appearance of diseases: diabetes, dental diseases, obesity.

General characteristics of polysaccharides

Polysaccharides are called natural polymers, which are products of the reaction of polycondensation of monosaccharides. As monomers for the formation of polysaccharides, pentoses, hexoses and other monosaccharides can be used. In practical terms, the hexose polycondensation products are most important. Polysaccharides are also known, the molecules of which contain nitrogen atoms, such as chitin.

Hexose-based polysaccharides have the general formula (C 6 H 10 O 5)n. They are insoluble in water, while some of them are able to form colloidal solutions. The most important of these polysaccharides are various varieties of vegetable and animal starches (the latter are called glycogens), as well as varieties of cellulose (fiber).

General characteristics of the properties and ecological role of starch

Starch is a polysaccharide that is a product of the polycondensation reaction of alpha-glucose (alpha-D-glucopyranose). By origin, vegetable and animal starches are distinguished. Animal starches are called glycogens. Although, in general, starch molecules have a common structure, the same composition, but the individual properties of starch obtained from different plants are different. So, potato starch is different from corn starch, etc. But all varieties of starch have common properties. These are solid, white, finely crystalline or amorphous substances, “brittle” to the touch, insoluble in water, but in hot water they are able to form colloidal solutions that retain their stability even when cooled. Starch forms both sols (for example, liquid jelly) and gels (for example, jelly prepared with a high starch content is a gelatinous mass that can be cut with a knife).

The ability of starch to form colloidal solutions is related to the globularity of its molecules (the molecule is, as it were, rolled into a ball). Upon contact with warm or hot water, water molecules penetrate between the turns of starch molecules, the molecule increases in volume and the density of the substance decreases, which leads to the transition of starch molecules to a mobile state characteristic of colloidal systems. The general formula of starch is: (C 6 H 10 O 5) n, the molecules of this substance have two varieties, one of which is called amylose (there are no side chains in this molecule), and the other is amylopectin (the molecules have side chains in which the connection occurs through 1 - 6 carbon atoms by an oxygen bridge).

The most important chemical property that determines the biological and ecological role of starch is its ability to undergo hydrolysis, ultimately forming either the disaccharide maltose or alpha-glucose (this is the final product of starch hydrolysis):

(C 6 H 10 O 5) n + nH 2 O → nC 6 H 12 O 6 (alpha-glucose).

The process takes place in organisms under the action of a whole group of enzymes. Due to this process, the body is enriched with glucose - the most important nutrient compound.

A qualitative reaction to starch is its interaction with iodine, in which a red-violet color occurs. This reaction is used to detect starch in various systems.

The biological and ecological role of starch is quite large. This is one of the most important storage compounds in plant organisms, for example, in plants of the cereal family. For animals, starch is the most important trophic substance.

Brief description of the properties and ecological and biological role of cellulose (fiber)

Cellulose (fiber) is a polysaccharide, which is a product of the polycondensation reaction of beta-glucose (beta-D-glucopyranose). Its general formula is (C 6 H 10 O 5) n. Unlike starch, cellulose molecules are strictly linear and have a fibrillar (“filamentous”) structure. The difference in the structures of starch and cellulose molecules explains the difference in their biological and ecological roles. Cellulose is neither a reserve nor a trophic substance, since it is not able to be digested by most organisms (with the exception of some types of bacteria that can hydrolyze cellulose and assimilate beta-glucose). Cellulose is not capable of forming colloidal solutions, but it can form mechanically strong filamentous structures that provide protection for individual cell organelles and the mechanical strength of various plant tissues. Like starch, cellulose is hydrolyzed under certain conditions, and the end product of its hydrolysis is beta-glucose (beta-D-glucopyranose). In nature, the role of this process is relatively small (but it allows the biosphere to “assimilate” cellulose).

(C 6 H 10 O 5) n (fiber) + n (H 2 O) → n (C 6 H 12 O 6) (beta-glucose or beta-D-glucopyranose) (with incomplete hydrolysis of fiber, the formation of a soluble disaccharide is possible - cellobiose).

Under natural conditions, fiber (after the death of plants) undergoes decomposition, as a result of which the formation of various compounds is possible. Due to this process, humus (an organic component of the soil), various types of coal are formed (oil and coal are formed from the dead remains of various animal and plant organisms in the absence, i.e., under anaerobic conditions, the whole complex of organic substances is involved in their formation, including carbohydrates).

The ecological and biological role of fiber is that it is: a) protective; b) mechanical; c) a formative compound (for some bacteria it performs a trophic function). The dead remains of plant organisms are a substrate for some organisms - insects, fungi, various microorganisms.

Brief description of the ecological and biological role of carbohydrates

Summarizing the above material related to the characteristics of carbohydrates, we can draw the following conclusions about their ecological and biological role.

1. They perform a building function both in cells and in the body as a whole due to the fact that they are part of the structures that form cells and tissues (this is especially true for plants and fungi), for example, cell membranes, various membranes, etc. in addition, carbohydrates are involved in the formation of biologically necessary substances that form a number of structures, for example, in the formation of nucleic acids that form the basis of chromosomes; carbohydrates are part of complex proteins - glycoproteins, which are of particular importance in the formation of cellular structures and intercellular substance.

2. The most important function of carbohydrates is the trophic function, which consists in the fact that many of them are food products of heterotrophic organisms (glucose, fructose, starch, sucrose, maltose, lactose, etc.). These substances, in combination with other compounds, form food products used by humans (various cereals; fruits and seeds of individual plants, which include carbohydrates in their composition, are food for birds, and monosaccharides, entering into a cycle of various transformations, contribute to the formation of both their own carbohydrates, characteristic for a given organism, and other organo-biochemical compounds (fats, amino acids (but not their proteins), nucleic acids, etc.).

3. Carbohydrates are also characterized by an energy function, which consists in the fact that monosaccharides (in particular glucose) are easily oxidized in organisms (the end product of oxidation is CO 2 and H 2 O), while a large amount of energy is released, accompanied by the synthesis of ATP.

4. They also have a protective function, consisting in the fact that structures (and certain organelles in the cell) arise from carbohydrates that protect either the cell or the body as a whole from various damages, including mechanical ones (for example, chitinous covers of insects that form external skeleton, cell membranes of plants and many fungi, including cellulose, etc.).

5. An important role is played by the mechanical and shaping functions of carbohydrates, which are the ability of structures formed either by carbohydrates or in combination with other compounds to give the body a certain shape and make them mechanically strong; thus, the cell membranes of the mechanical tissue and vessels of the xylem create the frame (internal skeleton) of woody, shrubby and herbaceous plants, the external skeleton of insects is formed by chitin, etc.

Brief description of carbohydrate metabolism in a heterotrophic organism (on the example of a human body)

An important role in understanding metabolic processes is played by knowledge of the transformations that carbohydrates undergo in heterotrophic organisms. In the human body, this process is characterized by the following schematic description.

Carbohydrates in food enter the body through the mouth. Monosaccharides in the digestive system practically do not undergo transformations, disaccharides are hydrolyzed to monosaccharides, and polysaccharides undergo quite significant transformations (this applies to those polysaccharides that are consumed by the body, and carbohydrates that are not food substances, for example, cellulose, some pectins, are removed excreted in the feces).

In the oral cavity, food is crushed and homogenized (becomes more homogeneous than before entering it). Food is affected by saliva secreted by the salivary glands. It contains ptyalin and has an alkaline reaction of the environment, due to which the primary hydrolysis of polysaccharides begins, leading to the formation of oligosaccharides (carbohydrates with a small n value).

Part of the starch can even turn into disaccharides, which can be seen with prolonged chewing of bread (sour black bread becomes sweet).

Chewed food, richly treated with saliva and crushed by teeth, enters the stomach through the esophagus in the form of a food lump, where it is exposed to gastric juice with an acid reaction of the medium containing enzymes that act on proteins and nucleic acids. Almost nothing happens in the stomach with carbohydrates.

Then the food gruel enters the first section of the intestine (small intestine), beginning with the duodenum. It receives pancreatic juice (pancreatic secretion), which contains a complex of enzymes that promote the digestion of carbohydrates. Carbohydrates are converted into monosaccharides, which are water soluble and absorbable. Dietary carbohydrates are finally digested in the small intestine, and in the part where the villi are contained, they are absorbed into the bloodstream and enter the circulatory system.

With the blood flow, monosaccharides are carried to various tissues and cells of the body, but first all the blood passes through the liver (where it is cleared of harmful metabolic products). In the blood, monosaccharides are present mainly in the form of alpha-glucose (but other hexose isomers, such as fructose, are also possible).

If blood glucose is less than normal, then part of the glycogen contained in the liver is hydrolyzed to glucose. An excess of carbohydrates characterizes a serious human disease - diabetes.

From the blood, monosaccharides enter the cells, where most of them are spent on oxidation (in mitochondria), during which ATP is synthesized, which contains energy in a “convenient” form for the body. ATP is spent on various processes that require energy (the synthesis of substances needed by the body, the implementation of physiological and other processes).

Part of the carbohydrates in food is used to synthesize the carbohydrates of a given organism, which are required for the formation of cell structures, or compounds necessary for the formation of substances of other classes of compounds (this is how fats, nucleic acids, etc. can be obtained from carbohydrates). The ability of carbohydrates to turn into fats is one of the causes of obesity - a disease that entails a complex of other diseases.

Therefore, the consumption of excess carbohydrates is harmful to the human body, which must be taken into account when organizing a balanced diet.

In plant organisms that are autotrophs, carbohydrate metabolism is somewhat different. Carbohydrates (monosugar) are synthesized by the body itself from carbon dioxide and water using solar energy. Di-, oligo- and polysaccharides are synthesized from monosaccharides. Part of the monosaccharides is included in the synthesis of nucleic acids. Plant organisms use a certain amount of monosaccharides (glucose) in the processes of respiration for oxidation, in which (as in heterotrophic organisms) ATP is synthesized.

Plan:

1. Definition of the concept: carbohydrates. Classification.

2. Composition, physical and chemical properties of carbohydrates.

3. Distribution in nature. Receipt. Application.

Carbohydrates - organic compounds containing carbonyl and hydroxyl groups of atoms, having the general formula C n (H 2 O) m, (where n and m> 3).

Carbohydrates Substances of paramount biochemical importance are widely distributed in wildlife and play an important role in human life. The name carbohydrates arose on the basis of data from the analysis of the first known representatives of this group of compounds. The substances of this group consist of carbon, hydrogen and oxygen, and the ratio of the numbers of hydrogen and oxygen atoms in them is the same as in water, i.e. There is one oxygen atom for every 2 hydrogen atoms. In the last century they were considered as carbon hydrates. Hence the Russian name carbohydrates, proposed in 1844. K. Schmidt. The general formula for carbohydrates, according to what has been said, is C m H 2p O p. When taking “n” out of brackets, the formula C m (H 2 O) n is obtained, which very clearly reflects the name “carbohydrate”. The study of carbohydrates has shown that there are compounds that, by all properties, must be attributed to the group of carbohydrates, although they have a composition that does not exactly correspond to the formula C m H 2p O p. Nevertheless, the old name "carbohydrates" has survived to this day, although along with with this name, a newer name, glycides, is sometimes used to refer to the group of substances under consideration.

Carbohydrates can be divided into three groups : 1) Monosaccharides - carbohydrates that can be hydrolyzed to form simpler carbohydrates. This group includes hexoses (glucose and fructose), as well as pentose (ribose). 2) Oligosaccharides - condensation products of several monosaccharides (for example, sucrose). 3) Polysaccharides - polymeric compounds containing a large number of monosaccharide molecules.

Monosaccharides. Monosaccharides are heterofunctional compounds. Their molecules simultaneously contain both carbonyl (aldehyde or ketone) and several hydroxyl groups, i.e. monosaccharides are polyhydroxycarbonyl compounds - polyhydroxyaldehydes and polyhydroxyketones. Depending on this, monosaccharides are divided into aldoses (the monosaccharide contains an aldehyde group) and ketoses (the keto group is contained). For example, glucose is an aldose and fructose is a ketose.

Receipt. Glucose is predominantly found in free form in nature. It is also a structural unit of many polysaccharides. Other monosaccharides in the free state are rare and are mainly known as components of oligo- and polysaccharides. In nature, glucose is obtained as a result of photosynthesis reaction: 6CO 2 + 6H 2 O ® C 6 H 12 O 6 (glucose) + 6O 2 For the first time, glucose was obtained in 1811 by the Russian chemist G.E. Kirchhoff during the hydrolysis of starch. Later, the synthesis of monosaccharides from formaldehyde in an alkaline medium was proposed by A.M. Butlerov

For those who want to get fat.

Carbohydrates will help you.

As you know, one molecule of fat is four molecules of glucose plus four molecules of water. That is, with an increased intake of carbohydrates in combination with water intake, you will get the expected result. I will note only one thing, it is desirable to consume more complex carbohydrates, because simple carbohydrates can lead to diabetes, hypertension. I hope that with modern nutrition (a set of products in stores), you will not have difficulties along the way. The main thing about carbohydrates is below, thanks to "Wikipedia"

(sugars, saccharides) - organic substances containing a carbonyl group and several hydroxyl groups. The name of the class of compounds comes from the words "carbon hydrates", it was first proposed by K. Schmidt in 1844. The appearance of such a name is due to the fact that the first carbohydrates known to science were described by the gross formula Cx(H2O)y, formally being compounds of carbon and water.
Carbohydrates are a very broad class of organic compounds, among them there are substances with very different properties. This allows carbohydrates to perform a variety of functions in living organisms. Compounds of this class make up about 80% of the dry mass of plants and 2-3% of the mass of animals.

Simple and complex carbohydrates

On the left is D-glyceraldehyde, on the right is dihydroxyacetone.

Carbohydrates are an integral component of the cells and tissues of all living organisms of the flora and fauna, making up (by mass) the main part of the organic matter on Earth. The source of carbohydrates for all living organisms is the process of photosynthesis carried out by plants. According to the ability to hydrolyze into monomers, carbohydrates are divided into two groups: simple (monosaccharides) and complex (disaccharides and polysaccharides). Complex carbohydrates, unlike simple ones, are able to hydrolyze to form monosaccharides, monomers. Simple carbohydrates are easily soluble in water and synthesized in green plants. Complex carbohydrates are products of the polycondensation of simple sugars (monosaccharides), and in the process of hydrolytic cleavage they form hundreds and thousands of monosaccharide molecules.

Monosaccharides

The most common monosaccharide in nature is beta-D-glucose.

Monosaccharides(from the Greek monos - the only one, sacchar - sugar) - the simplest carbohydrates that do not hydrolyze to form simpler carbohydrates - they are usually colorless, easily soluble in water, poorly in alcohol and completely insoluble in ether, solid transparent organic compounds, one of the main groups of carbohydrates, the simplest form of sugar. Aqueous solutions have a neutral bsp; pH. Some monosaccharides have a sweet taste. Monosaccharides contain a carbonyl (aldehyde or ketone) group, so they can be considered as derivatives of polyhydric alcohols. A monosaccharide with a carbonyl group at the end of the chain is an aldehyde and is called an aldose. At any other position of the carbonyl group, the monosaccharide is a ketone and is called ketose. Depending on the length of the carbon chain (from three to ten atoms), trioses, tetroses, pentoses, hexoses, heptoses, and so on are distinguished. Among them, pentoses and hexoses are the most widespread in nature. Monosaccharides are the building blocks from which disaccharides, oligosaccharides and polysaccharides are synthesized.
In nature, in free form, D-glucose (grape sugar or dextrose, C6H12O6) is the most common - a six-atomic sugar (hexose), a structural unit (monomer) of many polysaccharides (polymers) -disaccharides: (maltose, sucrose and lactose) and polysaccharides (cellulose, starch). Other monosaccharides are generally known as components of di-, oligo- or polysaccharides and are rare in the free state. Natural polysaccharides serve as the main sources of monosaccharides

disaccharides

Maltose (malt sugar) is a natural disaccharide consisting of two glucose residues.

Maltose(malt sugar) - a natural disaccharide consisting of two glucose residues
Disaccharides (from di - two, sacchar - sugar) - complex organic compounds, one of the main groups of carbohydrates, during hydrolysis, each molecule breaks down into two molecules of monosaccharides, are private suchamolygosaccharides. By structure, disaccharides are glycosides, in which two monosaccharide molecules are connected to each other by a glycosidic bond formed as a result of the interaction of hydroxyl groups (two hemiacetal or one hemiacetal and one alcohol). Depending on the structure, disaccharides are divided into two groups: reducing and non-reducing. For example, in the maltose molecule, the second residue of the monosaccharide (glucose) has a free hemiacetal hydroxyl, which gives this disaccharide reducing properties. Disaccharides, along with polysaccharides, are one of the main sources of carbohydrates in the diet of humans and animals.

Oligosaccharides

Rafinose- natural trisaccharide, consisting of residues of D-galactose, D-glucose and D-fructose.
Oligosaccharides- carbohydrates, the molecules of which are synthesized from 2-10 monosaccharide residues connected by glycosidic bonds. Accordingly, they distinguish: disaccharides, trisaccharides and so on. Oligosaccharides consisting of identical monosaccharide residues are called homopolysaccharides, and those consisting of different monosaccharides are called heteropolysaccharides. Disaccharides are the most common among oligosaccharides.
Among natural trisaccharides, raffinose is the most common - a non-reducing oligosaccharide containing residues of fructose, glucose and galactose - found in large quantities in sugar beet and in many other plants.

Polysaccharides

Polysaccharides- the general name of the class of complex high-molecular carbohydrates, the molecules of which consist of tens, hundreds or thousands of monomers - monosaccharides. From the point of view of the general principles of structure in the group of polysaccharides, it is possible to distinguish between homopolysaccharides synthesized from the same type of monosaccharide units and heteropolysaccharides, which are characterized by the presence of two or more types of monomeric residues.
Homopolysaccharides (glycans), consisting of residues of one monosaccharide, can be hexoses or pentoses, that is, hexose or pentose can be used as a monomer. Depending on the chemical nature of the polysaccharide, glucans (from glucose residues), mannans (from mannose), galactans (from galactose) and other similar compounds are distinguished. The group of homopolysaccharides includes organic compounds of plant (starch, cellulose, pectin), animal (glycogen, chitin) and bacterial (dextrans) origin.
Polysaccharides are essential for the life of animals and plants. It is one of the body's main sources of energy resulting from metabolism. Polysaccharides take part in immune processes, provide adhesion of cells in tissues, and are the bulk of organic matter in the biosphere.

On the left is starch, on the right is glycogen.

Starch

(C6H10O5) n is a mixture of two homopolysaccharides: linear - amylose and branched - amylopectin, the monomer of which is alpha-glucose. White amorphous substance, insoluble in cold water, capable of swelling and partially soluble in hot water. Molecular weight 105-107 Daltons. Starch, synthesized by different plants in chloroplasts, under the action of light during photosynthesis, differs somewhat in the structure of grains, the degree of polymerization of molecules, the structure of polymer chains, and physicochemical properties. As a rule, the content of amylose in starch is 10-30%, amylopectin - 70-90%. The amylose molecule contains, on average, about 1,000 glucose residues linked by alpha-1,4 bonds. Separate linear sections of the amylopectin molecule consist of 20-30 such units, and at the branch points of amylopectin, glucose residues are linked by interchain alpha-1,6 bonds. With partial acid hydrolysis of starch, polysaccharides of a lower degree of polymerization are formed - dextrins (C6H10O5)p, and with complete hydrolysis - glucose.
Glycogen (C6H10O5) n is a polysaccharide built from alpha-D-glucose residues - the main reserve polysaccharide of higher animals and humans, is contained in the form of granules in the cytoplasm of cells in almost all organs and tissues, however, its largest amount accumulates in muscles and liver. The glycogen molecule is built from branching polyglucoside chains, in a linear sequence of which, glucose residues are connected by alpha-1,4 bonds, and at the branch points by interchain alpha-1,6 bonds. The empirical formula of glycogen is identical to that of starch. In chemical structure, glycogen is close to amylopectin with more pronounced chain branching, therefore it is sometimes called the inaccurate term "animal starch". Molecular weight 105-108 Daltons and above. In animal organisms, it is a structural and functional analogue of the plant polysaccharide - starch. Glycogen forms an energy reserve, which, if necessary, to compensate for a sudden lack of glucose can be quickly mobilized - a strong branching of its molecules leads to the presence of a large number of terminal residues, which provide the ability to quickly cleave the required amount of glucose molecules. Unlike the store of triglycerides (fats), the store of glycogen is not so capacious (in calories per gram). Only the glycogen stored in liver cells (hepatocytes) can be converted into glucose to feed the entire body, while hepatocytes are able to store up to 8 percent of their weight in the form of glycogen, which is the highest concentration among all cell types. The total mass of glycogen in the liver of adults can reach 100-120 grams. In muscles, glycogen is broken down into glucose exclusively for local consumption and accumulates in much lower concentrations (no more than 1% of the total muscle mass), however, the total stock in muscles may exceed the stock accumulated in hepatocytes.

Cellulose (fiber) is the most common structural polysaccharide of the plant world, consisting of alpha-glucose residues presented in beta-pyranose form. Thus, in the cellulose molecule, beta-glucopyranose monomeric units are linearly connected to each other by beta-1,4 bonds. With partial hydrolysis of cellulose, the disaccharide cellobiose is formed, and with complete hydrolysis, D-glucose. In the human gastrointestinal tract, cellulose is not digested because the set of digestive enzymes does not contain beta-glucosidase. However, the presence of an optimal amount of plant fiber in food contributes to the normal formation of feces. Possessing high mechanical strength, cellulose acts as a supporting material for plants, for example, in the composition of wood, its share varies from 50 to 70%, and cotton is almost one hundred percent cellulose.
Chitin is a structural polysaccharide of lower plants, fungi and invertebrates (mainly the corneas of arthropods - insects and crustaceans). Chitin, like cellulose in plants, performs supporting and mechanical functions in the organisms of fungi and animals. The chitin molecule is built from N-acetyl-D-glucosamine residues linked by beta-1,4-glycosium bonds. Chitin macromolecules are unbranched and their spatial arrangement has nothing to do with cellulose.
Pectic substances - polygalacturonic acid, found in fruits and vegetables, D-galacturonic acid residues are linked by alpha-1,4-glycosidic bonds. In the presence of organic acids, they are capable of gelation, they are used in the food industry for the preparation of jelly and marmalade. Some pectin substances have an antiulcer effect and are an active component of a number of pharmaceutical preparations, for example, a derivative of the plantain plantaglucid.
Muramine is a polysaccharide, a support-mechanical material of the bacterial cell wall. According to its chemical structure, it is an unbranched chain built from alternating residues of N-acetylglucosamine and N-acetylmuramic acid connected by a beta-1,4-glycosidic bond. Muramine is very close to chitin and cellulose in terms of structural organization (unbranched chain of the beta-1,4-polyglucopyranose skeleton) and functional role.
Dextran half-saccharides of bacterial origin are synthesized under industrial conditions by microbiological means (by the action of Leuconostoc mesenteroides microorganisms on a sucrose solution) and are used as blood plasma substitutes (the so-called clinical "dextrans": Poliglukin and others).

On the left is D-glyceraldehyde, on the right is L-glyceraldehyde.

Spatial isomerism

Isomerism - the existence of chemical compounds (isomers), identical in composition and molecular weight, differing in the structure or arrangement of atoms in space and, as a result, in properties.
Stereoisomerism of monosaccharides: the isomer of glyceraldehyde in which, when the model is projected onto the plane, the OH group at the asymmetric carbon atom is located on the right side is considered to be D-glyceraldehyde, and the mirror reflection is L-glyceraldehyde. All isomers of monosaccharides are divided into D- and L-forms according to the similarity of the location of the OH group at the last asymmetric carbon atom near the CH2OH group (ketoses contain one less asymmetric carbon atom than aldoses with the same number of carbon atoms). Natural hexoses - glucose, fructose, mannose and galactose - according to stereochemical configurations, are classified as D-series compounds.

Biological role
In living organisms, carbohydrates perform the following functions:
Structural and support functions. Carbohydrates are involved in the construction of various supporting structures. Since cellulose is the main structural component of plant cell walls, chitin performs a similar function in fungi, and also provides rigidity to the exoskeleton of arthropods.
Protective role in plants. Some plants have protective formations (thorns, prickles, etc.) consisting of cell walls of dead cells.
plastic function. Carbohydrates are part of complex molecules (for example, pentoses (ribose and deoxyribose) are involved in the construction of ATP, DNA and RNA).
Energy function. Carbohydrates serve as a source of energy: when 1 gram of carbohydrates are oxidized, 4.1 kcal of energy and 0.4 g of water are released.
storage function. Carbohydrates act as reserve nutrients: glycogen in animals, starch and inulin in plants.
osmotic function. Carbohydrates are involved in the regulation of osmotic pressure in the body. Thus, the blood contains 100-110 mg /% glucose, the osmotic pressure of the blood depends on the concentration of glucose.
receptor function. Oligosaccharides are part of the receptive part of many cell receptors or ligand molecules Biosynthesis
Carbohydrates predominate in the daily diet of humans and animals. Herbivores get starch, fiber, sucrose. Carnivores get glycogen from meat.
Animal organisms are not able to synthesize carbohydrates from inorganic substances. They get them from plants with food and use them as the main source of energy obtained in the process of oxidation: In the green leaves of plants, carbohydrates are formed during photosynthesis - a unique biological process of converting inorganic substances into sugars - carbon monoxide (IV) and water, which occurs with the participation chlorophyll due to solar energy: The metabolism of carbohydrates in the human body and higher animals consists of several processes:
Hydrolysis (breakdown) in the gastrointestinal tract of food polysaccharides and disaccharides to monosaccharides, followed by absorption from the intestinal lumen into the bloodstream.
Glycogenogenesis (synthesis) and glycogenolysis (breakdown) of glycogen in tissues, mainly in the liver.
Aerobic (pentose phosphate pathway of glucose oxidation or pentose cycle) and anaerobic (without oxygen consumption) glycolysis are ways of breaking down glucose in the body.
Interconversion of hexoses.
Aerobic oxidation of the product of glycolysis - pyruvate (the final stage of carbohydrate metabolism).
Gluconeogenesis is the synthesis of carbohydrates from non-carbohydrate raw materials (pyruvic, lactic acid, glycerol, amino acids and other organic compounds).
[edit] Key sources
The main sources of carbohydrates from food are: bread, potatoes, pasta, cereals, sweets. The net carbohydrate is sugar. Honey, depending on its origin, contains 70-80% glucose and fructose.
To indicate the amount of carbohydrates in food, a special bread unit is used.
In addition, fiber and pectins that are poorly digested by the human body adjoin the carbohydrate group.

List of the most common carbohydrates

• Monosaccharides

• Oligosaccharides

• sucrose (regular sugar, cane or beet)

• Polysaccharides

• galactomannans

• Glycosaminoglycans (Mucopolysaccharides)

• chondroitin sulfate

• hyaluronic acid

• heparan sulfate

• dermatan sulfate

• keratan sulfate

Glucose is the most important of all monosaccharides, since it is the structural unit of most food di- and polysaccharides. In the process of metabolism, they are broken down into individual molecules of monosaccharides, which, in the course of multi-stage chemical reactions, are converted into other substances and ultimately oxidized to carbon dioxide and water - used as "fuel" for cells. Glucose is an essential component of metabolism carbohydrates. With a decrease in its level in the blood or a high concentration and the inability to use, as happens with diabetes, drowsiness occurs, loss of consciousness (hypoglycemic coma) may occur. Glucose "in its pure form", as a monosaccharide, is found in vegetables and fruits. Especially rich in glucose are grapes - 7.8%, cherries, cherries - 5.5%, raspberries - 3.9%, strawberries - 2.7%, plums - 2.5%, watermelon - 2.4%. Of the vegetables, most glucose is found in pumpkin - 2.6%, in white cabbage - 2.6%, in carrots - 2.5%.

Glucose is less sweet than the most famous disaccharide, sucrose. If we take the sweetness of sucrose as 100 units, then the sweetness of glucose will be 74 units.

Fructose is one of the most common carbohydrates fruits. Unlike glucose, it can penetrate from the blood into tissue cells without the participation of insulin. For this reason, fructose is recommended as the safest source. carbohydrates for diabetic patients. Part of the fructose enters the liver cells, which turn it into a more universal "fuel" - glucose, so fructose is also able to increase blood sugar, although to a much lesser extent than other simple sugars. Fructose is more easily converted into fat than glucose. The main advantage of fructose is that it is 2.5 times sweeter than glucose and 1.7 times sweeter than sucrose. Its use instead of sugar can reduce overall intake carbohydrates.

The main sources of fructose in food are grapes - 7.7%, apples - 5.5%, pears - 5.2%, cherries, sweet cherries - 4.5%, watermelons - 4.3%, black currants - 4.2% , raspberries - 3.9%, strawberries - 2.4%, melons - 2.0%. In vegetables, the fructose content is low - from 0.1% in beets to 1.6% in white cabbage. Fructose is found in honey - about 3.7%. Fructose, which has a much higher sweetness than sucrose, has been well proven to not cause tooth decay, which is promoted by sugar consumption.

Galactose does not occur in free form in products. It forms a disaccharide with glucose - lactose (milk sugar) - the main carbohydrate milk and dairy products.

Lactose is broken down in the gastrointestinal tract to glucose and galactose by the action of an enzyme. lactase. Deficiency of this enzyme in some people leads to milk intolerance. Undigested lactose serves as a good nutrient for the intestinal microflora. At the same time, abundant gas formation is possible, the stomach “swells”. In fermented milk products, most of the lactose is fermented to lactic acid, so people with lactase deficiency can tolerate fermented milk products without unpleasant consequences. In addition, lactic acid bacteria in fermented milk products inhibit the activity of the intestinal microflora and reduce the adverse effects of lactose.

Galactose, formed during the breakdown of lactose, is converted into glucose in the liver. With a congenital hereditary deficiency or absence of an enzyme that converts galactose into glucose, a serious disease develops - galactosemia, which leads to mental retardation.

A disaccharide made up of glucose and fructose molecules is sucrose. The content of sucrose in sugar is 99.5%. That sugar is the "white death", sweet lovers know as well as smokers that a drop of nicotine kills a horse. Unfortunately, both of these common truths are more often an occasion for jokes than for serious reflection and practical conclusions.

Sugar is rapidly broken down in the gastrointestinal tract, glucose and fructose are absorbed into the blood and serve as a source of energy and the most important precursor of glycogen and fats. It is often referred to as the "empty calorie carrier" since sugar is pure carbohydrate and does not contain other nutrients, such as, for example, vitamins, mineral salts. Of the vegetable products, the most sucrose is found in beets - 8.6%, peaches - 6.0%, melons - 5.9%, plums - 4.8%, tangerines - 4.5%. In vegetables, except for beets, a significant content of sucrose is noted in carrots - 3.5%. In other vegetables, the sucrose content ranges from 0.4 to 0.7%. In addition to sugar itself, the main sources of sucrose in food are jam, honey, confectionery, sweet drinks, ice cream.

When two glucose molecules combine, they form maltose- malt sugar. It contains honey, malt, beer, molasses and bakery and confectionery products made with the addition of molasses.

All polysaccharides present in human food, with rare exceptions, are polymers of glucose.

Starch is the main digestible polysaccharide. It accounts for up to 80% of food intake. carbohydrates.

The source of starch is vegetable products, mainly cereals: cereals, flour, bread, and potatoes. Cereals contain the most starch: from 60% in buckwheat (kernel) to 70% in rice. Of the cereals, the least amount of starch is found in oatmeal and its processed products: oatmeal, Hercules oatmeal - 49%. Pasta contains from 62 to 68% starch, rye flour bread, depending on the variety, from 33% to 49%, wheat bread and other products made from wheat flour - from 35 to 51% starch, flour - from 56 (rye) to 68% (wheat premium). There is also a lot of starch in legumes - from 40% in lentils to 44% in peas. For this reason, dry peas, beans, lentils, chickpeas are classified as legumes. Soybean, which contains only 3.5% starch, and soy flour (10-15.5%) stand apart. Due to the high starch content in potatoes (15-18%) in nutrition, it is not classified as a vegetable, where the main carbohydrates represented by monosaccharides and disaccharides, and to starchy foods along with cereals and legumes.

In Jerusalem artichoke and some other plants carbohydrates stored in the form of a polymer of fructose - inulin. Food products with the addition of inulin are recommended for diabetes and especially for its prevention (recall that fructose puts less stress on the pancreas than other sugars).

Glycogen- "Animal starch" - consists of highly branched chains of glucose molecules. It is found in small amounts in animal products (2-10% in the liver, 0.3-1% in muscle tissue).

Diabetes mellitus (DM)- an endocrine disease characterized by a syndrome of chronic hyperglycemia, which is the result of insufficient production or action of insulin, which leads to disruption of all types of metabolism, primarily carbohydrate metabolism, vascular damage (angiopathy), nervous system (neuropathy), as well as other organs and systems. According to the WHO definition (1985) - diabetes mellitus is a state of chronic ...

, depending on its origin, contains 70-80% sugar. In addition, poorly digestible by the human body adjoins the carbohydrate group fiber and pectins.

Of all the food substances consumed by humans, carbohydrates are undoubtedly the main source of energy. On average, they account for 50 to 70% of daily caloric intake. Despite the fact that a person consumes significantly more carbohydrates than fats and proteins, their reserves in the body are small. This means that the supply of them to the body must be regular.

The need for carbohydrates to a very large extent depends on the energy expenditure of the body. On average, in an adult male engaged mainly in mental or light physical labor, the daily requirement for carbohydrates ranges from 300 to 500 g. In manual workers and athletes, it is much higher. Unlike proteins and, to a certain extent, fats, the amount of carbohydrates in diets can be significantly reduced without harm to health. Those who want to lose weight should pay attention to this: carbohydrates are mainly energy value. When 1 g of carbohydrates are oxidized in the body, 4.0 - 4.2 kcal is released. Therefore, at their expense, it is easiest to regulate the calorie intake.

Carbohydrates(saccharides) is the common name for a large class of naturally occurring organic compounds. The general formula of monosaccharides can be written as C n (H 2 O) n. In living organisms, sugars with 5 (pentoses) and 6 (hexoses) carbon atoms are most common.

Carbohydrates are divided into groups:

Simple carbohydrates are easily soluble in water and synthesized in green plants. In addition to small molecules, large ones are also found in the cell, they are polymers. Polymers are complex molecules that are made up of separate "units" connected to each other. Such "links" are called monomers. Substances such as starch, cellulose and chitin are polysaccharides - biological polymers.

Monosaccharides include glucose and fructose, which add sweetness to fruits and berries. The food sugar sucrose consists of covalently attached to each other glucose and fructose. Sucrose-like compounds are called disaccharides. Poly-, di-, and monosaccharides are collectively referred to as carbohydrates. Carbohydrates are compounds that have diverse and often completely different properties.

Table: Variety of carbohydrates and their properties.

group of carbohydrates	Examples of carbohydrates	Where do they meet	properties
monosugar	ribose	RNA
	deoxyribose	DNA
	glucose	beet sugar
	fructose	Fruit, honey
	galactose	The composition of milk lactose
oligosaccharides	maltose	malt sugar	Sweet in taste, soluble in water, crystalline,
	sucrose	Cane sugar
	Lactose	Milk sugar in milk
Polysaccharides (built from linear or branched monosaccharides)	Starch	Vegetable storage carbohydrate	Not sweet, white, insoluble in water.
	glycogen	Reserve animal starch in the liver and muscles
	Fiber (cellulose)
	chitin
	murein	water . For many human cells (for example, brain and muscle cells), glucose brought in by the blood serves as the main source of energy. Starch and a very similar substance of animal cells - glycogen - are glucose polymers, they serve to store it inside the cell. 2. structural function, that is, they participate in the construction of various cellular structures. Polysaccharide cellulose forms the cell walls of plant cells, characterized by hardness and rigidity, it is one of the main components of wood. Other components are hemicellulose, also belonging to polysaccharides, and lignin (it has a non-carbohydrate nature). Chitin also performs structural functions. Chitin performs supporting and protective functions. The cell walls of most bacteria consist of murein peptidoglycan- the composition of this compound includes residues of both monosaccharides and amino acids. 3. Carbohydrates play a protective role in plants (cell walls, consisting of cell walls of dead cells, protective formations - spikes, spines, etc.). The general formula of glucose is C 6 H 12 O 6, it is an aldehyde alcohol. Glucose is found in many fruits, plant juices and flower nectar, as well as in the blood of humans and animals. The content of glucose in the blood is maintained at a certain level (0.65-1.1 g per l). If it is artificially lowered, then brain cells begin to experience acute starvation, which can result in fainting, coma, and even death. A long-term increase in blood glucose is also not at all useful: at the same time, diabetes mellitus develops. Mammals, including humans, can synthesize glucose from certain amino acids and breakdown products of glucose itself, such as lactic acid. They do not know how to get glucose from fatty acids, unlike plants and microbes. Interconversions of substances. Excess protein------carbohydrates Excess fat--------------carbohydrates