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, according to 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

§ 1. CLASSIFICATION AND FUNCTIONS OF CARBOHYDRATES

Even in ancient times, mankind got acquainted with carbohydrates and learned how to use them in their daily lives. Cotton, flax, wood, starch, honey, cane sugar are just some of the carbohydrates that played an important role in the development of civilization. Carbohydrates are among the most common organic compounds in nature. They are integral components of the cells of any organism, including bacteria, plants and animals. In plants, carbohydrates account for 80 - 90% of dry weight, in animals - about 2% of body weight. Their synthesis from carbon dioxide and water is carried out by green plants using the energy of sunlight ( photosynthesis ). The total stoichiometric equation for this process is:

Glucose and other simple carbohydrates are then converted into more complex carbohydrates such as starch and cellulose. Plants use these carbohydrates to release energy through the process of respiration. This process is essentially the reverse of the process of photosynthesis:

Interesting to know! Green plants and bacteria in the process of photosynthesis annually absorb approximately 200 billion tons of carbon dioxide from the atmosphere. In this case, about 130 billion tons of oxygen are released into the atmosphere and 50 billion tons of organic carbon compounds, mainly carbohydrates, are synthesized.

Animals are unable to synthesize carbohydrates from carbon dioxide and water. By consuming carbohydrates with food, animals spend the energy accumulated in them to maintain vital processes. Our foods are high in carbohydrates, such as baked goods, potatoes, cereals, etc.

The name "carbohydrates" is historical. The first representatives of these substances were described by the summary formula C m H 2 n O n or C m (H 2 O) n . Another name for carbohydrates is Sahara - due to the sweet taste of the simplest carbohydrates. According to their chemical structure, carbohydrates are a complex and diverse group of compounds. Among them, there are both fairly simple compounds with a molecular weight of about 200, and giant polymers, the molecular weight of which reaches several million. Along with carbon, hydrogen, and oxygen atoms, carbohydrates can contain atoms of phosphorus, nitrogen, sulfur, and, rarely, other elements.

Classification of carbohydrates

All known carbohydrates can be divided into two large groups - simple carbohydrates and complex carbohydrates. A separate group consists of carbohydrate-containing mixed polymers, for example, glycoproteins- a complex with a protein molecule, glycolipids - complex with lipid, etc.

Simple carbohydrates (monosaccharides, or monoses) are polyhydroxycarbonyl compounds that are not capable of forming simpler carbohydrate molecules upon hydrolysis. If monosaccharides contain an aldehyde group, then they belong to the class of aldoses (aldehyde alcohols), if ketone - to the class of ketoses (keto alcohols). Depending on the number of carbon atoms in a monosaccharide molecule, trioses (C 3), tetroses (C 4), pentoses (C 5), hexoses (C 6), etc. are distinguished:

The most common in nature are pentoses and hexoses.

Complex carbohydrates ( polysaccharides, or polioses) are polymers built from monosaccharide residues. They hydrolyze to form simple carbohydrates. Depending on the degree of polymerization, they are divided into low molecular weight ( oligosaccharides, the degree of polymerization of which, as a rule, is less than 10) and macromolecular. Oligosaccharides are sugar-like carbohydrates that are soluble in water and have a sweet taste. According to their ability to reduce metal ions (Cu 2+, Ag +), they are divided into regenerating and non-reducing. Polysaccharides, depending on the composition, can also be divided into two groups: homopolysaccharides and heteropolysaccharides. Homopolysaccharides are built from monosaccharide residues of the same type, and heteropolysaccharides are built from residues of different monosaccharides.

What has been said with examples of the most common representatives of each group of carbohydrates can be represented as the following diagram:

Functions of carbohydrates

The biological functions of polysaccharides are very diverse.

Energy and storage function

Carbohydrates contain the main amount of calories consumed by a person with food. Starch is the main carbohydrate in food. It is found in bakery products, potatoes, as part of cereals. The human diet also contains glycogen (in the liver and meat), sucrose (as additives to various dishes), fructose (in fruits and honey), lactose (in milk). Polysaccharides, before being absorbed by the body, must be hydrolyzed by digestive enzymes to monosaccharides. Only in this form they are absorbed into the blood. With the blood flow, monosaccharides enter the organs and tissues, where they are used to synthesize their own carbohydrates or other substances, or undergo splitting in order to extract energy from them.

The energy released from the breakdown of glucose is stored in the form of ATP. There are two processes of glucose breakdown: anaerobic (in the absence of oxygen) and aerobic (in the presence of oxygen). Lactic acid is formed as a result of the anaerobic process

which, during heavy physical exertion, accumulates in the muscles and causes pain.

As a result of the aerobic process, glucose is oxidized to carbon monoxide (IV) and water:

As a result of aerobic breakdown of glucose, much more energy is released than as a result of anaerobic breakdown. In general, the oxidation of 1 g of carbohydrates releases 16.9 kJ of energy.

Glucose can undergo alcoholic fermentation. This process is carried out by yeast under anaerobic conditions:

Alcoholic fermentation is widely used in industry for the production of wines and ethyl alcohol.

Man learned to use not only alcoholic fermentation, but also found the use of lactic acid fermentation, for example, to obtain lactic acid products and pickle vegetables.

In humans and animals there are no enzymes capable of hydrolyzing cellulose; nevertheless, cellulose is the main food component for many animals, in particular for ruminants. The stomach of these animals contains large quantities of bacteria and protozoa that produce the enzyme cellulase catalyzes the hydrolysis of cellulose to glucose. The latter can undergo further transformations, as a result of which butyric, acetic, propionic acids are formed, which can be absorbed into the blood of ruminants.

Carbohydrates also perform a reserve function. So, starch, sucrose, glucose in plants and glycogen in animals they are the energy reserve of their cells.

Structural, supporting and protective functions

Cellulose in plants and chitin in invertebrates and fungi, they perform supporting and protective functions. Polysaccharides form a capsule in microorganisms, thereby strengthening the membrane. Lipopolysaccharides of bacteria and glycoproteins of the surface of animal cells provide selectivity of intercellular interaction and immunological reactions of the body. Ribose is the building block of RNA, while deoxyribose is the building block of DNA.

Performs a protective function heparin. This carbohydrate, being an inhibitor of blood clotting, prevents the formation of blood clots. It is found in the blood and connective tissue of mammals. Cell walls of bacteria, formed by polysaccharides, fastened with short amino acid chains, protect bacterial cells from adverse effects. Carbohydrates are involved in crustaceans and insects in the construction of the external skeleton, which performs a protective function.

Regulatory function

Fiber enhances intestinal motility, thereby improving digestion.

An interesting possibility is the use of carbohydrates as a source of liquid fuel - ethanol. Since ancient times, wood has been used for heating homes and cooking. In modern society, this type of fuel is being replaced by other types - oil and coal, which are cheaper and more convenient to use. However, vegetable raw materials, despite some inconveniences in use, unlike oil and coal, are a renewable source of energy. But its use in internal combustion engines is difficult. For these purposes, it is preferable to use liquid fuel or gas. From low-grade wood, straw or other plant materials containing cellulose or starch, you can get liquid fuel - ethyl alcohol. To do this, you must first hydrolyze cellulose or starch and get glucose:

and then subject the resulting glucose to alcoholic fermentation and obtain ethyl alcohol. Once refined, it can be used as a fuel in internal combustion engines. It should be noted that in Brazil, for this purpose, billions of liters of alcohol are obtained annually from sugar cane, sorghum and cassava and used in internal combustion engines.

, 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

General characteristics, structure and properties of carbohydrates.

Carbohydrates - These are polyhydric alcohols that contain, in addition to alcohol groups, an aldehyde or keto group.

Depending on the type of group in the composition of the molecule, aldoses and ketoses are distinguished.

Carbohydrates are very widespread in nature, especially in the plant world, where they make up 70-80% of the dry matter mass of cells. In the animal body, they account for only about 2% of body weight, but here their role is no less important.

Carbohydrates can be stored as starch in plants and glycogen in animals and humans. These reserves are used as needed. In the human body, carbohydrates are deposited mainly in the liver and muscles, which are its depot.

Among other components of the organism of higher animals and humans, carbohydrates account for 0.5% of body weight. However, carbohydrates are of great importance for the body. These substances, together with proteins in the form proteoglycans underlie connective tissue. Carbohydrate-containing proteins (glycoproteins and mucoproteins) are an integral part of the body's mucus (protective, enveloping functions), plasma transport proteins and immunologically active compounds (group-specific blood substances). Part of the carbohydrates acts as a "reserve fuel" for energy organisms.

Functions of carbohydrates:

• Energy - Carbohydrates are one of the main sources of energy for the body, providing at least 60% of energy costs. For the activity of the brain, blood cells, medulla of the kidneys, almost all the energy is supplied by the oxidation of glucose. With the complete breakdown of 1 g of carbohydrates, 4.1 kcal/mol(17.15 kJ/mol) energy.

• Plastic Carbohydrates or their derivatives are found in all cells of the body. They are part of the biological membranes and organelles of cells, participate in the formation of enzymes, nucleoproteins, etc. In plants, carbohydrates serve mainly as a supporting material.

• Protective - viscous secrets (mucus) secreted by various glands are rich in carbohydrates or their derivatives (mucopolysaccharides, etc.). They protect the inner walls of the hollow organs of the gastrointestinal tract, airways from mechanical and chemical influences, the penetration of pathogenic microbes.

• Regulatory - human food contains a significant amount of fiber, the rough structure of which causes mechanical irritation of the mucous membrane of the stomach and intestines, thus participating in the regulation of the act of peristalsis.

• Specific - individual carbohydrates perform special functions in the body: they are involved in the conduction of nerve impulses, the formation of antibodies, ensuring the specificity of blood groups, etc.

The functional significance of carbohydrates determines the need to provide the body with these nutrients. The daily requirement for carbohydrates for a person is on average 400 - 450 g, taking into account age, type of work, gender and some other factors.

elemental composition. Carbohydrates are made up of the following chemical elements: carbon, hydrogen and oxygen. Most carbohydrates have the general formula C n (H 2 O ) n. Carbohydrates are compounds composed of carbon and water, which is the basis for their name. However, among carbohydrates there are substances that do not correspond to the above formula, for example, rhamnose C 6 H 12 O 5, etc. At the same time, substances are known whose composition corresponds to the general formula of carbohydrates, but they do not belong to them in terms of properties (acetic acid C 2 H 12 O 2). Therefore, the name "carbohydrates" is rather arbitrary and does not always correspond to the chemical structure of these substances.

Carbohydrates- These are organic substances that are aldehydes or ketones of polyhydric alcohols.

Monosaccharides

Monosaccharides - These are polyhydric aliphatic alcohols that contain in their composition an aldehyde group (aldoses) or a keto group (ketoses).

Monosaccharides are solid, crystalline substances, soluble in water and sweet in taste. Under certain conditions, they are easily oxidized, as a result of which aldehyde alcohols are converted into acids, as a result of which aldehyde alcohols are converted into acids, and upon reduction, into the corresponding alcohols.

Chemical properties of monosaccharides :

• Oxidation to mono-, dicarboxylic and glycuronic acids;

• Recovery to alcohols;

• Esters formation;

• The formation of glycosides;

• Fermentation: alcohol, lactic acid, citric acid and butyric.

Monosaccharides that cannot be hydrolyzed into simpler sugars. The type of monosaccharide depends on the length of the hydrocarbon chain. Depending on the number of carbon atoms, they are divided into trioses, tetroses, pentoses, hexoses.

Trioses: glyceraldehyde and dihydroxyacetone, they are intermediate products of glucose breakdown and are involved in the synthesis of fats. both trioses can be obtained from the alcohol glycerol by its dehydrogenation or hydrogenation.

Tetroses: erythrosis - actively involved in metabolic processes.

Pentoses: ribose and deoxyribose are components of nucleic acids, ribulose and xylulose are intermediate products of glucose oxidation.

Hexoses: they are most widely represented in the animal and plant world and play an important role in metabolic processes. These include glucose, galactose, fructose, etc.

Glucose (grape sugar) . It is the main carbohydrate in plants and animals. The important role of glucose is explained by the fact that it is the main source of energy, forms the basis of many oligo- and polysaccharides, and is involved in maintaining osmotic pressure. The transport of glucose into cells is regulated in many tissues by the pancreatic hormone insulin. In the cell, in the course of multi-stage chemical reactions, glucose is converted into other substances (the intermediate products formed during the breakdown of glucose are used to synthesize amino acids and fats), which are ultimately oxidized to carbon dioxide and water, while releasing energy used by the body to ensure life. The level of glucose in the blood is usually judged on the state of carbohydrate metabolism in the body. With a decrease in the level of glucose in the blood or its high concentration and the impossibility of using it, as happens with diabetes, drowsiness occurs, loss of consciousness (hypoglycemic coma) may occur. The rate of glucose entry into the brain and liver tissues does not depend on insulin and is determined only by its concentration in the blood. These tissues are called insulin-independent. Without the presence of insulin, glucose will not enter the cell and will not be used as fuel..

Galactose. A spatial isomer of glucose, characterized by the location of the OH group at the fourth carbon atom. It is part of lactose, some polysaccharides and glycolipids. Galactose can isomerize to glucose (in the liver, mammary gland).

Fructose (fruit sugar). It is found in large quantities in plants, especially in fruits. A lot of it in fruits, sugar beets, honey. Easily isomerizes to glucose. The pathway of fructose breakdown is shorter and more energetically favorable than that of glucose. 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 carbohydrate source for diabetics. Part of the fructose gets into the liver cells, which turn it into a more versatile "fuel" - glucose, so fructose is also able to increase blood sugar levels, although to a much lesser extent than other simple sugars.

According to the chemical structure, glucose and galactose are aldehyde alcohols, fructose is a keto alcohol. Differences in the structure of glucose and fructose characterize both the differences and some of their properties. Glucose restores metals from their oxides, fructose does not have this property. Fructose is absorbed from the intestine about 2 times slower than glucose.

When the sixth carbon atom in the hexose molecule is oxidized, hexuronic (uronic) acids : from glucose - glucuronic, from galactose - galacturonic.

Glucuronic acid takes an active part in metabolic processes in the body, for example, in the neutralization of toxic products, is part of mucopolysaccharides, etc. Its function is that it combines in the organ with substances that are poorly soluble in water. As a result, the binder becomes water soluble and is excreted in the urine. This route of excretion is especially important for water soluble steroid hormones, their degradation products, and also for the isolation of decay products of medicinal substances. Without interaction with glucuronic acid, further breakdown and excretion of bile pigments from the body are disrupted.

Monosaccharides can have an amino group .

When the hexose molecule of the OH group of the second carbon atom is replaced by an amino group, amino sugars are formed - hexosamines: glucosamine is synthesized from glucose, galactosamine is synthesized from galactose, which are part of the cell membranes and muco- polysaccharides both in free form and in combination with acetic acid.

Amino sugars called monosaccharides, whichplace of the OH group carry an amino group (- N H 2).

Amino sugars are the most important constituent glycosaminoglycans.

Monosaccharides form esters . OH group of a monosaccharide molecule; like any alcohol group, can interact with acid. In the intermediate exchangesugar esters are of great importance. To enableto be metabolized, sugar must becomephosphoric ether. In this case, the terminal carbon atoms are phosphorylated. For hexoses, these are C-1 and C-6, for pentoses, C-1 and C-5, etc. PainMore than two OH groups are not subject to phosphorylation. Therefore, the main role is played by mono- and diphosphates of sugars. In the title phosphorus ester usually indicate the position of the ester bond.

Oligosaccharides

Oligosaccharides have two or more monosaccharide. They are found in cells and biological fluids, both in free form and in combination with proteins. Disaccharides are of great importance for the body: sucrose, maltose, lactose, etc. These carbohydrates perform an energy function. It is assumed that, being part of the cells, they participate in the process of "recognition" of cells.

sucrose(beet or cane sugar). Consists of glucose and fructose molecules. She is is a vegetable product and the most important component nutritive food, has the sweetest taste compared to other disaccharides and glucose.

The content of sucrose in sugar is 95%. 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 an "empty calorie carrier" because sugar is a pure carbohydrate and does not contain other nutrients such as vitamins, mineral salts, for example.

Lactose(milk sugar) consists of glucose and galactose, synthesized in the mammary glands during lactation. In the gastrointestinal tract, it is broken down by the action of the enzyme lactase. Deficiency of this enzyme in some people leads to milk intolerance. Deficiency of this enzyme is observed in approximately 40% of the adult population. 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 suppress the activity of the intestinal microflora and reduce the adverse effects of lactose.

Maltose consists of two glucose molecules and is the main structural component of starch and glycogen.

Polysaccharides

Polysaccharides - high molecular weight carbohydrates, composed of a large number of monosaccharides. They have hydrophilic properties and form colloidal solutions when dissolved in water.

Polysaccharides are divided into homo- and gete roposaccharides.

Homopolysaccharides. Contains monosaccharides only one kind. Gak, starch and glycogen fasting swarms only from glucose molecules, inulin - fructose. Homopolysaccharides are highly branched structure and are a mixture of two polymers - amylose and amylopectin. Amylose consists of 60-300 glucose residues connected in chain via an oxygen bridge, formed between the first carbon atom of one molecule and the fourth carbon atom of another (bond 1,4).

amylose soluble in hot water and gives a blue color with iodine.

Amylopectin - a branched polymer consisting of both straight chains (bond 1,4) and branched chains, which are formed due to bonds between the first carbon atom of one glucose molecule and the sixth carbon atom of another with the help of an oxygen bridge (bond 1,6).

Representatives of homopolysaccharides are starch, fiber and glycogen.

Starch(plant polysaccharide)- consists of several thousand glucose residues, 10-20% of which is represented by amylose, and 80-90% by amylopectin. Starch is insoluble in cold water, but in hot water it forms a colloidal solution, commonly called starch paste. Starch accounts for up to 80% of carbohydrates consumed with food. The source of starch is vegetable products, mainly cereals: cereals, flour, bread, and potatoes. Cereals contain the most starch (from 60% in buckwheat (kernel) and up to 70% in rice).

Cellulose, or cellulose,- the most common plant carbohydrate on earth, formed in an amount of approximately 50 kg per inhabitant of the Earth. Cellulose is a linear polysaccharide consisting of 1000 or more glucose residues. In the body, fiber is involved in the activation of the motility of the stomach and intestines, stimulates the secretion of digestive juices, and creates a feeling of satiety.

Glycogen(animal starch) is the main storage carbohydrate of the human body. It consists of approximately 30,000 glucose residues, which form a branched structure. In the most significant amount, glycogen accumulates in the liver and muscle tissue, including the heart muscle. The function of muscle glycogen is that it is a readily available source of glucose used in energy processes in the muscle itself. Liver glycogen is used to maintain physiological blood glucose concentrations, primarily between meals. After 12-18 hours after a meal, the store of glycogen in the liver is almost completely depleted. The content of muscle glycogen decreases markedly only after prolonged and strenuous physical work. With a lack of glucose, it quickly breaks down and restores its normal level in the blood. In cells, glycogen is associated with cytoplasmic protein and partially with intracellular membranes.

Heteropolysaccharides (glycosaminoglycans or mucopolysaccharides) (the prefix "muco-" indicates that they were first obtained from mucin). They consist of various types of monosaccharides (glucose, galactose) and their derivatives (amino sugars, hexuronic acids). Other substances were also found in their composition: nitrogenous bases, organic acids and some others.

Glycosaminoglycans are jelly-like, sticky substances. They perform various functions, including structural, protective, regulatory, etc. Glycosaminoglycans, for example, make up the bulk of the intercellular substance of tissues, are part of the skin, cartilage, synovial fluid, and the vitreous body of the eye. In the body, they are found in combination with proteins (proteoglycans and glycoproteins) and fats (glycolipids), in which polysaccharides account for the bulk of the molecule (up to 90% or more). The following are important for the body.

Hyaluronic acid- the main part of the intercellular substance, a kind of "biological cement" that connects the cells, filling the entire intercellular space. It also acts as a biological filter that traps microbes and prevents their penetration into the cell, and is involved in the exchange of water in the body.

It should be noted that hyaluronic acid decomposes under the action of a specific enzyme hyaluronidase. In this case, the structure of the intercellular substance is disturbed, “cracks” are formed in its composition, which leads to an increase in its permeability to water and other substances. This is important in the process of fertilization of the egg by spermatozoa, which are rich in this enzyme. Some bacteria also contain hyaluronidase, which greatly facilitates their penetration into the cell.

X ondroitin sulfates- chondroitin sulfuric acids, serve as structural components of cartilage, ligaments, heart valves, umbilical cord, etc. They contribute to the deposition of calcium in the bones.

Heparin is formed in mast cells, which are found in the lungs, liver and other organs, and is released by them into the blood and intercellular environment. In the blood, it binds to proteins and prevents blood clotting, acting as an anticoagulant. In addition, heparin has an anti-inflammatory effect, affects the exchange of potassium and sodium, and performs an antihypoxic function.

A special group of glycosaminoglycans are compounds containing neuraminic acids and carbohydrate derivatives. Compounds of neuraminic acid with acetic acid are called opal acids. They are found in cell membranes, saliva and other biological fluids.

Carbohydrates

Turning to the consideration of organic substances, it is impossible not to note the importance of carbon for life. Entering into chemical reactions, carbon forms strong covalent bonds, socializing four electrons. Carbon atoms, connecting with each other, are able to form stable chains and rings that serve as the skeletons of macromolecules. Carbon can also form multiple covalent bonds with other carbon atoms, as well as with nitrogen and oxygen. All these properties provide a unique variety of organic molecules.

Macromolecules, which make up about 90% of the mass of a dehydrated cell, are synthesized from simpler molecules called monomers. There are three main types of macromolecules: polysaccharides, proteins, and nucleic acids; monomers for them are, respectively, monosaccharides, amino acids and nucleotides.

Carbohydrates are substances with the general formula C x (H 2 O) y, where x and y are natural numbers. The name "carbohydrates" indicates that in their molecules hydrogen and oxygen are in the same ratio as in water.

Animal cells contain a small amount of carbohydrates, and plant cells contain almost 70% of the total amount of organic matter.

Monosaccharides play the role of intermediate products in the processes of respiration and photosynthesis, are involved in the synthesis of nucleic acids, coenzymes, ATP and polysaccharides, and are released during oxidation during respiration. Derivatives of monosaccharides - sugar alcohols, sugar acids, deoxysugars and amino sugars - are important in the process of respiration, and are also used in the synthesis of lipids, DNA and other macromolecules.

Disaccharides are formed by a condensation reaction between two monosaccharides. They are sometimes used as reserve nutrients. The most common of these are maltose (glucose + glucose), lactose (glucose + galactose) and sucrose (glucose + fructose). found only in milk. (cane sugar) most abundant in plants; this is the same "sugar" that we usually eat.

Cellulose is also a polymer of glucose. It contains about 50% of the carbon contained in plants. In terms of total mass on Earth, cellulose ranks first among organic compounds. The shape of the molecule (long chains with protruding –OH groups) provides a strong bond between adjacent chains. For all their strength, macrofibrils consisting of such chains easily pass water and substances dissolved in it and therefore serve as an ideal building material for plant cell walls. Cellulose is a valuable source of glucose, but its breakdown requires the cellulase enzyme, which is relatively rare in nature. Therefore, only some animals (for example, ruminants) eat cellulose. The industrial value of cellulose is also great - cotton fabrics and paper are made from this substance.