Carbohydrates: monosaccharides, disaccharides and polysaccharides. Chemical properties of disaccharides Physical and chemical properties of disaccharides

Carbohydrates for diabetes

Sugars (saccharides, carbohydrates) are organic compounds common in nature. They are derivatives of polyhydric alcohols. Based on the size and structure of their molecules, they are divided into two groups: simple sugars (monosaccharides) and complex sugars (these include disaccharides and polysaccharides).

Based on the presence of characteristic functional groups, in addition to polyatomic (hydroxyl) groups, which are part of all saccharides, they are distinguished: aldoses - those with aldehyde groups, and - those with ketone groups.

Read more about the different types of carbohydrates below in the articles I collected on this topic.

Carbohydrates are organic compounds, most often of natural origin, consisting only of carbon, hydrogen and oxygen. Carbohydrates play a huge role in the life of all living organisms. This class of organic compounds received its name because the first carbohydrates studied by man had a general formula of the form Cx(H2O)y.

Those. they were conventionally considered compounds of carbon and water. However, it later turned out that the composition of some carbohydrates deviates from this formula. For example, a carbohydrate such as deoxyribose has the formula C5H10O4. At the same time, there are some compounds that formally correspond to the formula Cx(H2O)y, but are not related to carbohydrates, such as formaldehyde (CH2O) and acetic acid (C2H4O2).

However, the term “carbohydrates” has historically been assigned to this class of compounds, and therefore is widely used in our time.

Classification of carbohydrates

Depending on the ability of carbohydrates to be broken down during hydrolysis into other carbohydrates with a lower molecular weight, they are divided into simple (monosaccharides) and complex (disaccharides, oligosaccharides, polysaccharides). As you might guess, from simple carbohydrates, i.e. monosaccharides, it is impossible to obtain carbohydrates with an even lower molecular weight by hydrolysis.

The hydrolysis of one disaccharide molecule produces two monosaccharide molecules, and the complete hydrolysis of one molecule of any polysaccharide produces many monosaccharide molecules.

Chemical properties of monosaccharides using the example of glucose and fructose

As you can see, both the glucose molecule and the molecule contain 5 hydroxyl groups, and therefore they can be considered polyhydric alcohols. The glucose molecule contains an aldehyde group, i.e. in fact, glucose is a polyhydric aldehyde alcohol. In the case of fructose, a ketone group can be found in its molecule, i.e. fructose is a polyhydric keto alcohol.

Chemical properties of glucose and fructose as carbonyl compounds

All monosaccharides can react in the presence of catalysts with hydrogen. In this case, the carbonyl group is reduced to an alcohol hydroxyl group. The glucose molecule contains an aldehyde group, and therefore it is logical to assume that its aqueous solutions give high-quality reactions to aldehydes.

Attention!

Indeed, when an aqueous solution of glucose with freshly precipitated copper (II) hydroxide is heated, just as in the case of any other aldehyde, a brick-red precipitate of copper (I) oxide precipitates from the solution. In this case, the aldehyde group of glucose is oxidized to a carboxyl group - gluconic acid is formed. Glucose also enters into a “silver mirror” reaction when exposed to an ammonia solution of silver oxide.

However, unlike the previous reaction, instead of gluconic acid, its salt is formed - ammonium gluconate, because dissolved ammonia is present in the solution. Fructose and other monosaccharides, which are polyhydric ketoalcohols, do not react qualitatively with aldehydes.

Chemical properties of glucose and fructose as polyhydric alcohols

Because monosaccharides, including glucose and fructose, have several hydroxyl groups in their molecules. All of them give a qualitative reaction to polyhydric alcohols. In particular, freshly precipitated copper (II) hydroxide dissolves in aqueous solutions of monosaccharides. In this case, instead of the blue Cu(OH)2 precipitate, a dark blue solution of copper complex compounds is formed.

Disaccharides. Chemical properties

Disaccharides are carbohydrates whose molecules consist of two monosaccharide residues linked to each other through the condensation of two hemiacetal hydroxyls or one alcohol hydroxyl and one hemiacetal. The bonds formed in this way between monosaccharide residues are called glycosidic. The formula of most disaccharides can be written as C12H22O11.

The most common disaccharide is the familiar sugar, called sucrose by chemists. The molecule of this carbohydrate is formed by cyclic residues of one molecule of glucose and one molecule of fructose. The connection between disaccharide residues in this case is realized due to the elimination of water from two hemiacetal hydroxyls.

Since the bond between monosaccharide residues is formed by the condensation of two acetal hydroxyls, it is impossible for a sugar molecule to open any of the rings, i.e. transition to the carbonyl form is impossible. In this regard, sucrose is not able to give high-quality reactions to aldehydes.

Disaccharides of this kind, which do not give a qualitative reaction to aldehydes, are called non-reducing sugars. However, there are disaccharides that give qualitative reactions to the aldehyde group. This situation is possible when a hemiacetal hydroxyl from the aldehyde group of one of the original monosaccharide molecules remains in the disaccharide molecule.

In particular, maltose reacts with an ammonia solution of silver oxide, as well as copper (II) hydroxide, like aldehydes.

Disaccharides as polyhydric alcohols

Disaccharides, being polyhydric alcohols, give the corresponding qualitative reaction with copper (II) hydroxide, i.e. when their aqueous solution is added to freshly precipitated copper (II) hydroxide, the water-insoluble blue precipitate of Cu(OH)2 dissolves to form a dark blue solution.

Polysaccharides. Starch and cellulose

Polysaccharides are complex carbohydrates, the molecules of which consist of a large number of monosaccharide residues linked together by glycosidic bonds. There is another definition of polysaccharides. Polysaccharides are complex carbohydrates whose molecules form a large number of monosaccharide molecules upon complete hydrolysis.

In general, the formula of polysaccharides can be written as (C6H11O5)n. Starch is a substance that is a white amorphous powder, insoluble in cold water and partially soluble in hot water to form a colloidal solution, commonly called starch paste.

Starch is formed from carbon dioxide and water during photosynthesis in the green parts of plants under the influence of energy from sunlight. Starch is found in the largest quantities in potato tubers, wheat, rice and corn grains. For this reason, these sources of starch are the raw materials for its production in industry.

Cellulose is a substance that, in its pure state, is a white powder that is insoluble in either cold or hot water. Unlike starch, cellulose does not form a paste. Almost pure cellulose consists of filter paper, cotton wool, and poplar fluff.

Both starch and cellulose are plant products. However, the roles they play in plant life are different. Cellulose is mainly a building material; in particular, it mainly forms the membranes of plant cells. Starch primarily has a storage and energy function.

Source: https://scienceforyou.ru/teorija-dlja-podgotovki-k-egje/uglevody

Types of carbohydrates

There are three main types of carbohydrates:

Simple (fast) carbohydrates or sugars: mono- and disaccharides
Complex (slow) carbohydrates: oligo- and polysaccharides
Indigestible, or fibrous, carbohydrates are defined as dietary fiber.

Sahara

There are two types of sugars:

Monosaccharides – Monosaccharides contain one sugar group, such as glucose, fructose or galactose.
disaccharides - disaccharides are formed by residues of two monosaccharides and are represented, in particular, by sucrose (common table sugar) and lactose.

Complex carbohydrates

Polysaccharides are carbohydrates containing three or more molecules of simple carbohydrates. This type of carbohydrate includes, in particular, dextrins, starches, glycogens and celluloses. Sources of polysaccharides are cereals, legumes, potatoes and other vegetables.

Source: http://sportwiki.to/%D0%92%D0%B8%D0%B4%D1%8B_%D1%83%D0%B3%D0%BB%D0%B5%D0%B2%D0%BE %D0%B4%D0%BE%D0%B2

Carbohydrates, monosaccharides, polysaccharides, maltose, glucose, fructose

Carbohydrates

Carbohydrates are a large group of organic compounds that play an important role in the functioning of the body. Carbohydrates are distributed mainly in the plant world. The human body requires 400-500 g of carbohydrates per day (including at least 80 g of sugars). They are an important source of energy.

The digestibility of carbohydrates contained in fruits is 90%; in and dairy products – 98; in table sugar – 99%. Examples of carbohydrates include glucose (C6H2O6), or grape sugar, so named because of its high content in; cane or beet sugar (C6H22011); starch and cellulose (SbH10O5).

These substances consist of carbon, hydrogen and oxygen. Moreover, the ratio of the last two elements is the same as in water, i.e., for two hydrogen atoms there is one oxygen atom. Thus, carbohydrates are, as it were, built from carbon and water, hence their name. Carbohydrates are divided into monosaccharides (such as glucose) and polysaccharides.

Polysaccharides, in turn, are divided into low molecular weight, or oligosaccharides (their representative is beet sugar), and high molecular weight, such as starch and cellulose. Polysaccharide molecules are built from the remains of monosaccharide molecules and, during hydrolysis, are broken down into simpler carbohydrates.

Monosaccharides

Of the monosaccharides, the most important for the human body are glucose, fructose, galactose, etc. All of them are crystalline substances, soluble in water. Glucose in a free state is common in the fruits of many plants. In a bound state, it is found in plants in the form of polysaccharides (sucrose, maltose, starch, dextrin, cellulose, etc.). In industry, glucose is obtained from starch.

Anhydrous glucose melts at a temperature of 146 C, it is highly soluble in water. Glucose is approximately 2 times less sweet than sucrose. When glucose is exposed to strong oxidizing agents, sugar acid is formed. When reduced, it turns into hexahydric alcohol -.

Attention!

There are three types of carbohydrates:

monosaccharides;
disaccharides;
polysaccharides.

The main monosaccharides are glucose and fructose, consisting of one molecule, due to which these carbohydrates are quickly broken down and immediately enter the blood. Brain cells are “fueled” with energy thanks to glucose: for example, the daily requirement of glucose required for the brain is 150 g, which is one fourth of the total amount of this carbohydrate received per day from food.

The peculiarity of simple carbohydrates is that they are quickly processed and are not transformed into fats, while complex carbohydrates (if consumed excessively) can be stored in the body as fat. Monosaccharides are present in large quantities in many fruits and vegetables, as well as honey.

These carbohydrates, which include sucrose, lactose and maltose, cannot be called complex, since they contain residues of two monosaccharides. Disaccharides require a longer time to digest compared to monosaccharides.

Interesting fact! It has been proven that children and adolescents respond to increased consumption of carbohydrates found in refined (or refined) foods with so-called hyperactive (or hyperactive) behavior. By consistently eliminating foods such as sugar, white flour, pasta and white rice from your diet, behavioral disorders will decrease significantly.

At the same time, it is important to increase the consumption of fresh vegetables and fruits, legumes, nuts, and cheese. Disaccharides are present in dairy products, pasta and products containing refined sugar. Polysaccharide molecules include tens, hundreds, and sometimes thousands of monosaccharides.

Polysaccharides (namely starch, fiber, cellulose, pectin, inulin, chitin and glycogen) are most important for the human body for two reasons:

they take a long time to digest and absorb (unlike simple carbohydrates);
contain many useful substances, including vitamins, minerals and proteins.

Many polysaccharides are present in plant fibers, as a result of which one meal, the basis of which is raw or boiled vegetables, can almost completely satisfy the body’s daily requirement for substances that are sources of energy.

Thanks to polysaccharides, firstly, the required sugar level is maintained, and secondly, the brain is provided with the nutrition it needs, which is manifested by increased concentration, improved memory and increased mental activity. Polysaccharides are found in vegetables, fruits, grains, and animal liver.

Benefits of carbohydrates:

Stimulating peristalsis of the gastrointestinal tract.
Absorption and elimination of toxic substances and cholesterol.
Providing optimal conditions for the functioning of normal intestinal microflora.
Strengthening the immune system.
Normalization of metabolism.
Ensuring proper liver function.
Ensuring a constant supply of sugar in the blood.
Prevention of the development of tumors in the stomach and intestines.
Replenishment of vitamins and minerals.
Providing energy to the brain, as well as the central nervous system.
Promoting the production of endorphins, which are called “hormones of joy.”
Relief of premenstrual syndrome.

Daily requirement of carbohydrates

The need for carbohydrates directly depends on the intensity of mental and physical activity, averaging 300–500 g per day, of which at least 20 percent should be easily digestible carbohydrates. Elderly people should include no more than 300 g of carbohydrates in their daily diet, with the amount of easily digestible carbohydrates varying between 15 and 20 percent.

In case of obesity and other diseases, it is necessary to limit the amount of carbohydrates, and this should be done gradually, which will allow the body to adapt to the altered metabolism without any problems. It is recommended to start the restriction with 200 - 250 g per day for a week, after which the amount of carbohydrates consumed with food is increased to 100 g per day.

A sharp decrease in carbohydrate intake over a long period of time (as well as a lack of them in the diet) leads to the development of the following disorders:

The listed phenomena disappear after eating sugar or other sweet foods, but the intake of such products should be dosed, which will protect the body from gaining extra pounds. An excess of carbohydrates (especially easily digestible) in the diet is also harmful to the body, as it contributes to an increase in sugar, as a result of which some of the carbohydrates are not used, going to the formation of fat, which provokes the development of atherosclerosis, cardiovascular diseases, flatulence, diabetes, obesity, and caries.

What foods contain carbohydrates?

From the list of carbohydrates below, everyone can create a completely varied diet (taking into account the fact that this is not a complete list of foods that contain carbohydrates). Carbohydrates are found in the following foods:

Only a balanced diet will provide the body with energy and health. But for this you need to properly organize your diet. And the first step to a healthy diet is a breakfast consisting of complex carbohydrates. So, a serving of whole grain porridge (without dressings, meat, etc.) will provide the body with energy for at least three hours.

In turn, when consuming simple carbohydrates (we are talking about sweet baked goods, various refined foods, sweet coffee and tea), we experience an instant feeling of fullness, but at the same time a sharp rise in blood sugar occurs in the body, followed by a rapid decline, after which it appears again. feeling .

Why is this happening? The fact is that the pancreas is very overloaded, since it has to secrete sugar to process refined sugars. The result of such an overload is a decrease in sugar levels (sometimes below normal) and the appearance of a feeling of hunger.

To avoid these violations, let's consider each carbohydrate separately, determining its benefits and role in providing the body with energy.

They are called sugars because they have a naturally sweet taste.

But not all sugars are equally sweet, their degree of sweetness is slightly different, for example, if we take sucrose as one hundred percent sweetness, then the sweetness of the remaining sugars in percentage terms will be as follows:

Fructose – 173%
Glucose – 81%
Maltose and galactose – 32%
Raffinose – 23%
Lactose – 16%

Unlike simple carbohydrates, complex carbohydrates (polysaccharides) do not have a sweet taste, but more on them later.

Monosaccharides and disaccharides in human food come from natural sources: vegetables, fruits, fruits, berries.

Content of simple carbohydrates in some products per 100g

	Total sugar		Fructose	Sucrose
Fruits, berries, citrus,berries, citrus
Grape Apricots Oranges Grapefruit Black currant Strawberry
		Vegetables
Beet Bulb onions White cabbage Corn Sweet green pepper Artichokes

Glucose is a monosaccharide from which, like a chain of links, all the most important polysaccharides for the human body are built - starch, glycogen, cellulose.

Glucose is part of berries, fruits, and vegetables, with which it mainly enters the body.

In addition, glucose forms disaccharides (sucrose, maltose, lactose), which means it is formed during their breakdown in the digestive tract.

Glucose is one of the products that are absorbed in the human digestive tract almost one hundred percent and, moreover, quite quickly.

Once in the blood, glucose penetrates into all tissues and organs, where it is used in oxidative reactions to produce energy.

The human brain uses only glucose as an energy source, so the former suffers from carbohydrate starvation.

The level of glucose in the blood, together with the level of certain amino acids, serves as a signal to the brain structures responsible for modeling human appetite and eating behavior. Excess glucose quickly turns into stored glucose, which means it contributes to nutritional obesity.

The monosaccharide fructose is absorbed in the intestine almost twice as slow as glucose and is retained in the liver to a greater extent.

In the process of cellular metabolism, fructose turns into glucose, but at the same time, the concentration of glucose in the blood increases smoothly and gradually, which does not provoke the release of large amounts of insulin, and therefore reduces the load on the pancreas.

With all this, fructose enters the processes of liponeogenesis faster and easier than glucose and promotes the deposition of fat in the depot.

This is confirmed by new observations obtained from a study of weight gain in people who frequently eat foods rich in fructose (maltodextrous corn syrups).

Excessive intake of fructose leads to an increase in the concentration of C-peptide in the blood, which characterizes the degree of insulin resistance during the development of type 2 diabetes mellitus.

Fructose is found in foods both in free form in honey and fruits, and in the form of the fructose polysaccharide inulin in Jerusalem artichoke, chicory and artichokes.

Galactose enters the body as part of milk sugar (lactose). It can be found free in some fermented dairy products such as yoghurt. Galactose is converted into glucose in the liver.

The main industrially produced disaccharide is sucrose, or table sugar. The raw materials for its production are sugar beets (14...25% sugar) and sugar cane (10 - 15% sugar). Natural sources of sucrose in the diet are melons, watermelons, some vegetables, berries and fruits. Sucrose is easily digestible and quickly breaks down into glucose and fructose, which are then involved in their inherent metabolic processes.

It is the use of sucrose as an essential component of many products (confectionery, candies, jams, desserts, ice cream, soft drinks) that has now led to the fact that monosaccharides and disaccharides are increasing their share in the total volume of incoming carbohydrates to 50% and above (with recommended 20%).

As a result, against the background of physical inactivity and decreasing energy consumption, the nutritional load on the insular apparatus increases, the level of insulin in the blood increases, the deposition of fat in the depot intensifies, and the blood lipid profile is disrupted. All this contributes to an increased risk of developing diabetes mellitus, obesity, atherosclerosis and numerous diseases based on the listed pathological conditions.

The disaccharide lactose is the main carbohydrate in milk and dairy products (consists of galactose and glucose molecules) and is of great importance as a source of simple carbohydrates for children's nutrition.

In adults, its share in the carbohydrate composition of the diet is significantly reduced due to the widespread use of other sources. In addition, in adults and sometimes children, the activity of the lactase enzyme, which breaks down milk sugar, is reduced. The consequences of intolerance to whole milk and products containing it are dyspeptic disorders.

The use of fermented milk products (kefir, yogurt, sour cream), as well as cottage cheese and cheese in the diet, as a rule, does not cause such a clinical picture. Milk intolerance is observed in 30 - 35% of the adult population in Europe, while in Africa - more than 75%.

Maltose, or malt sugar, is found in free form in honey, malt, beer, molasses and products made with the addition of molasses (confectionery and bakery products). In the body, this disaccharide is an intermediate product and is formed as a result of the breakdown of polysaccharides in the gastrointestinal tract. Maltose then dissimilates to two glucose molecules.

In some fruits (apples, pears, peaches) and a number of vegetables, the alcohol form of sugars is found - sorbitol, which is a reduced form of glucose. It is able to maintain blood glucose levels without causing hunger or straining the insulin system. Sorbitol and other polyhydric alcohols, such as xylitol, mannitol or mixtures thereof, having a sweet taste (30 - 40% of the sweetness of glucose), are used to produce a wide range of food products, primarily for feeding patients with diabetes, as well as chewing gum. The disadvantages of polyhydric alcohols include their effect on the intestines, expressed in a laxative effect and increased gas formation.

Carbohydrates - organic compounds, most often of natural origin, consisting only of carbon, hydrogen and oxygen.

Carbohydrates play a huge role in the life of all living organisms.

This class of organic compounds received its name because the first carbohydrates studied by man had a general formula of the form C x (H 2 O) y. Those. they were conventionally considered compounds of carbon and water. However, it later turned out that the composition of some carbohydrates deviates from this formula. For example, a carbohydrate such as deoxyribose has the formula C 5 H 10 O 4. At the same time, there are some compounds that formally correspond to the formula C x (H 2 O) y, but are not related to carbohydrates, such as formaldehyde (CH 2 O) and acetic acid (C 2 H 4 O 2).

However, the term “carbohydrates” has historically been assigned to this class of compounds, and therefore is widely used in our time.

Classification of carbohydrates

As you might guess, from simple carbohydrates, i.e. monosaccharides, it is impossible to obtain carbohydrates with an even lower molecular weight by hydrolysis.

The hydrolysis of one disaccharide molecule produces two monosaccharide molecules, and the complete hydrolysis of one molecule of any polysaccharide produces many monosaccharide molecules.

Chemical properties of monosaccharides using the example of glucose and fructose

The most common monosaccharides are glucose and fructose, having the following structural formulas:

As you can see, both the glucose molecule and the fructose molecule contain 5 hydroxyl groups, and therefore they can be considered polyhydric alcohols.

The glucose molecule contains an aldehyde group, i.e. in fact, glucose is a polyhydric aldehyde alcohol.

In the case of fructose, a ketone group can be found in its molecule, i.e. fructose is a polyhydric keto alcohol.

Chemical properties of glucose and fructose as carbonyl compounds

All monosaccharides can react in the presence of catalysts with hydrogen. In this case, the carbonyl group is reduced to an alcohol hydroxyl group. Thus, in particular, an artificial sweetener, hexaatomic alcohol sorbitol, is produced by industrial hydrogenation of glucose:

The glucose molecule contains an aldehyde group, and therefore it is logical to assume that its aqueous solutions give high-quality reactions to aldehydes. Indeed, when an aqueous solution of glucose with freshly precipitated copper (II) hydroxide is heated, just as in the case of any other aldehyde, a brick-red precipitate of copper (I) oxide precipitates from the solution. In this case, the aldehyde group of glucose is oxidized to a carboxyl group - gluconic acid is formed:

Glucose also enters into a “silver mirror” reaction when exposed to an ammonia solution of silver oxide. However, unlike the previous reaction, instead of gluconic acid, its salt is formed - ammonium gluconate, because dissolved ammonia is present in the solution:

Fructose and other monosaccharides, which are polyhydric ketoalcohols, do not react qualitatively with aldehydes.

Chemical properties of glucose and fructose as polyhydric alcohols

Because monosaccharides, including glucose and fructose, have several hydroxyl groups in their molecules. All of them give a qualitative reaction to polyhydric alcohols. In particular, freshly precipitated copper (II) hydroxide dissolves in aqueous solutions of monosaccharides. In this case, instead of the blue precipitate of Cu(OH) 2, a dark blue solution of copper complex compounds is formed.

Glucose fermentation reactions

Alcoholic fermentation

When some enzymes act on glucose, glucose can be converted into ethyl alcohol and carbon dioxide:

Lactic acid fermentation

In addition to the alcoholic type of fermentation, there are also many others. For example, lactic acid fermentation, which occurs during souring of milk, pickling cabbage and cucumbers:

Features of the existence of monosaccharides in aqueous solutions

Monosaccharides exist in aqueous solution in three forms - two cyclic (alpha and beta) and one non-cyclic (regular). For example, in a glucose solution the following equilibrium exists:

As can be seen, in cyclic forms there is no aldehyde group, due to the fact that it participates in the formation of the ring. On its basis, a new hydroxyl group is formed, which is called acetal hydroxyl. Similar transitions between cyclic and non-cyclic forms are observed for all other monosaccharides.

Disaccharides. Chemical properties.

General description of disaccharides

The most common disaccharide is the familiar sugar, called by chemists sucrose . The molecule of this carbohydrate is formed by cyclic residues of one molecule of glucose and one molecule of fructose. The connection between disaccharide residues in this case is realized due to the elimination of water from two hemiacetal hydroxyls:

Disaccharides of this kind, which do not give a qualitative reaction to aldehydes, are called non-reducing sugars.

However, there are disaccharides that give qualitative reactions to the aldehyde group. This situation is possible when a hemiacetal hydroxyl from the aldehyde group of one of the original monosaccharide molecules remains in the disaccharide molecule.

In particular, maltose reacts with an ammonia solution of silver oxide, as well as copper (II) hydroxide, like aldehydes. This is due to the fact that in its aqueous solutions the following equilibrium exists:

As you can see, in aqueous solutions, maltose exists in two forms - with two rings in the molecule and one ring in the molecule and an aldehyde group. For this reason, maltose, unlike sucrose, gives a qualitative reaction to aldehydes.

Hydrolysis of disaccharides

All disaccharides are capable of undergoing hydrolysis reactions catalyzed by acids and various enzymes. During such a reaction, two monosaccharide molecules are formed from one molecule of the original disaccharide, which can be either the same or different depending on the composition of the original monosaccharide.

For example, the hydrolysis of sucrose leads to the formation of glucose and fructose in equal quantities:

And when maltose is hydrolyzed, only glucose is formed:

Disaccharides as polyhydric alcohols

Polysaccharides. Starch and cellulose

Polysaccharides - complex carbohydrates, the molecules of which consist of a large number of monosaccharide residues linked to each other by glycosidic bonds.

There is another definition of polysaccharides:

Polysaccharides are called complex carbohydrates, the molecules of which form a large number of monosaccharide molecules upon complete hydrolysis.

In general, the formula of polysaccharides can be written as (C 6 H 10 O 5) n.

Starch – a substance that is a white amorphous powder, insoluble in cold water and partially soluble in hot water to form a colloidal solution, commonly called starch paste.

Cellulose - a substance in its pure state that is a white powder, insoluble in either cold or hot water. Unlike starch, cellulose does not form a paste. Almost pure cellulose consists of filter paper, cotton wool, and poplar fluff. Both starch and cellulose are plant products. However, the roles they play in plant life are different. Cellulose is mainly a building material; in particular, it mainly forms the membranes of plant cells. Starch primarily has a storage and energy function.

Chemical properties of starch and cellulose

Combustion

All polysaccharides, including starch and cellulose, when completely burned in oxygen, form carbon dioxide and water:

Glucose formation

With complete hydrolysis of both starch and cellulose, the same monosaccharide is formed - glucose:

Qualitative reaction to starch

When iodine reacts with anything that contains starch, a blue color appears. When heated, the blue color disappears, and when cooled it appears again.

During the dry distillation of cellulose, in particular wood, its partial decomposition occurs with the formation of low molecular weight products such as methyl alcohol, acetic acid, acetone, etc.

Since both starch molecules and cellulose molecules contain alcohol hydroxyl groups, these compounds are able to enter into esterification reactions with both organic and inorganic acids.

One of the types of organic compounds necessary for the full functioning of the human body are carbohydrates.

They are divided into several types according to their structure - monosaccharides, disaccharides and polysaccharides. You need to figure out why they are needed and what their chemical and physical properties are.

Carbohydrates are compounds that contain carbon, hydrogen and oxygen. Most often they are of natural origin, although some are created industrially. Their role in the life of living organisms is enormous.

Their main functions are the following:

Energy. These compounds are the main source of energy. Most organs can function fully using the energy obtained from the oxidation of glucose.
Structural. Carbohydrates are necessary for the formation of almost all cells in the body. Fiber plays the role of supporting material, and complex carbohydrates are found in bones and cartilage tissue. One of the components of cell membranes is hyaluronic acid. Also, carbohydrate compounds are required in the process of enzyme production.
Protective. During the functioning of the body, the work of glands is carried out, secreting secretory fluids necessary to protect internal organs from pathogenic influences. A significant portion of these liquids are carbohydrates.
Regulatory. This function is manifested in the effect on the human body of glucose (maintains homeostasis, controls osmotic pressure) and fiber (affects gastrointestinal peristalsis).
Special Features. They are characteristic of certain types of carbohydrates. Such special functions include: participation in the process of transmitting nerve impulses, the formation of different blood groups, etc.

Based on the fact that the functions of carbohydrates are quite diverse, it can be assumed that these compounds should differ in their structure and characteristics.

This is true, and their main classification includes such varieties as:

. They are considered the simplest. Other types of carbohydrates enter the process of hydrolysis and break down into smaller components. Monosaccharides do not have this ability; they are the final product.
Disaccharides. In some classifications they are classified as oligosaccharides. They contain two monosaccharide molecules. It is into them that the disaccharide is divided during hydrolysis.
Oligosaccharides. This compound contains from 2 to 10 molecules of monosaccharides.
Polysaccharides. These compounds are the largest variety. They contain more than 10 molecules of monosaccharides.

Each type of carbohydrate has its own characteristics. We need to look at them to understand how each of them affects the human body and what its benefits are.

These compounds are the simplest form of carbohydrates. They contain one molecule, so during hydrolysis they are not divided into small blocks. When monosaccharides combine, disaccharides, oligosaccharides and polysaccharides are formed.

They are distinguished by their solid state of aggregation and sweet taste. They have the ability to dissolve in water. They can also dissolve in alcohols (the reaction is weaker than with water). Monosaccharides almost do not react to mixing with esters.

Natural monosaccharides are most often mentioned. Some of them are consumed by people in food. These include glucose, fructose and galactose.

chocolate;
fruits;
some types of wine;
syrups, etc.

The main function of carbohydrates of this type is energy. This is not to say that the body cannot do without them, but they have properties that are important for the full functioning of the body, for example, participation in metabolic processes.

The body absorbs monosaccharides faster than anything that happens in the gastrointestinal tract. The process of assimilation of complex carbohydrates, unlike simple compounds, is not so simple. First, complex compounds must be separated into monosaccharides, only after which they are absorbed.

This is one of the common types of monosaccharides. It is a white crystalline substance that is formed naturally - during photosynthesis or hydrolysis. The formula of the compound is C6H12O6. The substance is highly soluble in water and has a sweet taste.

Glucose provides muscle and brain tissue cells with energy. Once ingested, the substance is absorbed, enters the bloodstream and spreads throughout the body. There it oxidizes and releases energy. This is the main source of energy for the brain.

When there is a lack of glucose in the body, hypoglycemia develops, which primarily affects the functioning of brain structures. However, its excessive content in the blood is also dangerous, since it leads to the development of diabetes mellitus. Also, when consuming large amounts of glucose, body weight begins to increase.

Fructose

It is a monosaccharide and is very similar to glucose. It has a slower rate of absorption. This is because fructose must first be converted into glucose in order to be absorbed.

Therefore, this compound is considered harmless for diabetics, since its consumption does not lead to a sharp change in the amount of sugar in the blood. However, with such a diagnosis, caution is still necessary.

Fructose has the ability to quickly convert into fatty acids, which causes the development of obesity. This compound also reduces insulin sensitivity, which causes type 2 diabetes.

This substance can be obtained from berries and fruits, and also from honey. Usually it is there in combination with glucose. The compound is also white in color. The taste is sweet, and this feature is more intense than in the case of glucose.

Other connections

There are other monosaccharide compounds. They can be natural or semi-artificial.

Galactose is a natural one. It is also found in food products, but is not found in its pure form. Galactose is the result of the hydrolysis of lactose. Its main source is milk.

Other naturally occurring monosaccharides are ribose, deoxyribose and mannose.

There are also varieties of such carbohydrates, for the production of which industrial technologies are used.

These substances are also found in food and enter the human body:

rhamnose;
erythrulose;
ribulose;
D-xylose;
L-allose;
D-sorbose, etc.

Each of these connections has its own characteristics and functions.

Disaccharides and their uses

The next type of carbohydrate compounds are disaccharides. They are considered complex substances. As a result of hydrolysis, two molecules of monosaccharides are formed from them.

This type of carbohydrate has the following features:

hardness;
solubility in water;
poor solubility in concentrated alcohols;
sweet taste;
color - from white to brown.

The main chemical properties of disaccharides are the reactions of hydrolysis (breaking of glycosidic bonds and formation of monosaccharides) and condensation (polysaccharides are formed).

There are 2 types of such connections:

Restorative. Their peculiarity is the presence of a free hemiacetal hydroxyl group. Due to this, such substances have restorative properties. This group of carbohydrates includes cellobiose, maltose and lactose.
Non-restorative. These compounds cannot be reduced because they lack a hemiacetal hydroxyl group. The most well-known substances of this type are sucrose and trehalose.

These compounds are widely distributed in nature. They can occur both in free form and as part of other compounds. Disaccharides are a source of energy because they produce glucose when hydrolyzed.

Lactose is very important for children, as it is the main component of baby food. Another function of carbohydrates of this type is structural, since they are part of cellulose, which is necessary for the formation of plant cells.

Characteristics and features of polysaccharides

Another type of carbohydrates are polysaccharides. This is the most complex type of connection. They consist of a large number of monosaccharides (their main component is glucose). Polysaccharides are not absorbed in the gastrointestinal tract; they are first broken down.

The features of these substances are:

insolubility (or weak solubility) in water;
yellowish color (or no color);
they have no smell;
almost all of them are tasteless (some have a sweetish taste).

The chemical properties of these substances include hydrolysis, which is carried out under the influence of catalysts. The result of the reaction is the decomposition of the compound into structural elements - monosaccharides.

Another property is the formation of derivatives. Polysaccharides can react with acids.

The products formed during these processes are very diverse. These are acetates, sulfates, esters, phosphates, etc.

Examples of polysaccharides:

starch;
cellulose;
glycogen;
chitin.

Educational video material about the functions and classification of carbohydrates:

These substances are important for the full functioning of the body as a whole and individual cells. They supply the body with energy, participate in the formation of cells, and protect internal organs from damage and adverse effects. They also play the role of reserve substances that animals and plants need in case of difficult periods.

Chemistry

Lecture

Topic: Carbohydrates, their classification and properties

Carbohydrates They are widely distributed in living nature, especially in the plant world, and make up the bulk of organic matter on our planet. Thus, carbohydrates account for up to 80% of the dry mass of plants. Carbohydrates include various sugary substances (glucose, fructose, sucrose), starch, and fiber. The name “carbohydrates” is historical, it has been preserved since those times when the structure of these compounds was unknown, but their composition has been established, corresponding to the general formulaWITH n (N 2 O)m, Wheren, m> 3. In this formula, carbohydrates appear as compounds of carbon with water - “carbon-water”. The composition of carbohydrates in most cases corresponds to this formula.

Depending on their structure, carbohydrates are divided into monosaccharides, disaccharides (oligosaccharides) and polysaccharides.

Monosaccharides

Monosaccharides - These are carbohydrates that do not hydrolyze to form simpler carbohydrates.

Monosaccharide molecules can contain from four to ten carbon atoms. Their names are formed from the corresponding Greek numerals with the addition of the ending-osa.Therefore, according to the number of carbon atomsVmolecule, monosaccharides are divided intotetroses, pentoses, hexoses etc. Hexoses C are of greatest importance 6 N 12 ABOUT 6 and pentose C 5 N 10 ABOUT 5 .

The most common monosaccharides areglucose and fructose.

Glucose

Glucose is a colorless crystalline substance, highly soluble in water, sweet in taste (from the Greek.glykys- sweet). It is found in grape juice, which is why it is called grape sugar, as well as in ripe fruits and berries, and in honey.

Molecule structure. The composition of glucose (established by I. Berzelius) is expressed by the formulaWITH 6 N 12 ABOUT 6 , its structure has been proven experimentally. So:

When glucose is reduced, hexane is formed. This indicates that the basis of the molecular skeleton isnunbranched carbon chain;

an aqueous solution of glucose has a neutral reaction (does not change the color of the indicators), it does not form salts. Therefore, glucosedoes not contain a carboxyl group;

it gives a “silver mirror” reaction, which indicates presence of an aldehyde groupin its molecule;

a glucose ester was obtained, the molecule of which contains five residues of acetic acid, which proves the presence in its moleculefive hydroxyl groups.

Based on these data, the chemical structure of glucose can be expressed by the formula:

6 5 4 3 2 1 ABOUTABOUT

CH 2 OH – CHON-CHON-CHON-CHON-S or CH 2 HE – (SNON) 4 - WITH

N N

Thus, glucose is an aldehyde alcohol (aldose).

Chemical properties. Glucose is a bifunctional compound, which is characterized by the properties of aldehydes and polyhydric alcohols, as well as a number of specific properties.

I.Reactions involving aldehyde groupsp s. These reactions occur with the aldehyde form of glucose.

Oxidation reactions (qualitative reactions).

Glucose, as an aldehyde, has reducing properties and reacts with an ammonia solution of silver oxide (the “silver mirror” reaction), oxidizing into gluconic acid:

Oh Oh

CH 2 OH-(SNON) 4 - WITH+ Ag 2 ABOUTammonia rrCH 2 OH-(SNON) 4 - WITH+ 2 Ag

glucoseNgluconic acidN

The oxidation of glucose and freshly prepared copper (II) hydroxide proceeds similarly.when heated:

Glucose is oxidized with bromine water to gluconic acid:

Medicinecalcium gluconateis a salt of gluconic acid.

Recovery reactions. Under the influence of hydrogen in the presence of a catalyst, the aldehyde group of glucose is reduced to an alcohol group, forming a hexahydric alcohol -sorbitol;

CH 2 OH-(SNON) 4 - WITH+ N 2 NiCH 2 OH-(SNON) 4 -CH 2 HE

Sorbitol is the starting material for the industrial synthesis of vitamin C; it is a sugar substitute for patients with diabetes.

II.Reactions involving hydroxylgroups.

Glucose, as a polyhydric alcohol, reacts in a cyclic form.

Interaction with copper hydroxide (II) without heating.

Glucose as a polyhydric alcohol (for example, glycerol) reacts with freshly prepared copper (II) hydroxidewithout heating (in the cold), forming a complex compound of bright blue color. This reaction is used to detect sugar in urine. It is a qualitative reaction to glucose.

III.Specific properties of glucose.

UnderThrough the action of biological catalysts - enzymes produced by microorganisms, glucose can be broken down. This reaction is calledfermentation. Depending on the nature of the enzyme, alcoholic, lactic, butyric, etc. fermentation is distinguished. The name of the process is determined by the final product of the reaction. Thus, under the influence of yeast enzymes,alcohol fermentation, used in winemaking, brewing:

WITH 6 N 12 ABOUT 6 yeast enzymesWITH 2 N 5 OH + 2CO 2

ethanol

WITH 6 N 12 ABOUT 6 enzymes2CH 3 – CH - COOH

HElactic acid

This reaction underlies the production of lactic acid products (yogurt, sour cream, cottage cheese, cheese). Lactic acid is also formed during the pickling of cabbage and cucumbers, and silage of green feed for livestock. At the same time, it performs a preservative effect, preventing the development of decay processes.

Biological role and use of glucose. In nature, glucose is formed during photosynthesis, which occurs under the influence of solar energy in green plants.

photosynthesis

6СО 2 + 6H 2 O C 6 N 12 ABOUT 6 + 6O 2 - 2816 kJ

During this reactionglucose accumulates energy from the sun, which becomes available to living organisms. Every year, as a result of photosynthesis, approximately 20 tons of organic matter are formed for each inhabitant of the Earth, while about 200 billion tons of carbon dioxide are absorbed and about 145 billion tons of free oxygen are released into the atmosphere.

In living organisms, most of the glucose (about 70% is subject to oxidation by atmospheric oxygen in a reaction reverse to the process of photosynthesis:

6СО 2 + 6H 2 ABOUT breathWITH 6 N 12 ABOUT 6 + 6O 2 + 2816 kJ

In this case, the same amount of energy is released that was absorbed during the formation of glucose. This energy is used to ensure the vital processes of the body (muscle contraction, synthesis of substances, etc.).

Glucose is not only a source of energy, but it also servesoriginal a substance for the synthesis of many other compounds necessary for a living organism(glycogen, fats, amino acids) - this is its second important biochemical role.

Glucose is an essential component of blood; its level is in the range of 0.08-0.11%. In some diseases, such as diabetes, the glucose level in the blood increases and excess is excreted in the urine. In this case, the amount of glucose in the urine can increase to 12% compared to the usual 0.1%.

Glucose is used in medicine as a means of enhanced nutrition and as a medicinal substance, in the confectionery industry (making caramel, marmalade, gingerbread, etc.),it is included in drinks. Glucose is a reducing agent, so it is used for making mirrors, Christmas tree decorations (silvering), and also in the textile industry for dyeing.

In industry, glucose is obtained by hydrolysis of starch and cellulose.

Fructose (fruit sugar) has the same molecular formula as glucose (C 6 N 12 ABOUT 6 ), but differs in structure:

CH 2 OH - SNON - SNON - SNON - S - CH 2 HE

Fructose -ketone alcohol (ketosis),it is a structural isomer of glucose.

Fructose, like glucose, can exist in linear and cyclic forms, but, unlike glucose, its cycle isfive-membered, containing an oxygen atom. In aqueous solutions, different forms of fructose are in equilibrium with each other.

Fructose is a crystalline substance, highly soluble in water, three times sweeter than glucose. It is found in free form in berries and fruits. Bee honey is a mixture of glucose and fructose.

Chemical properties. Fructose has the properties of polyhydric alcohols and ketones. As a polyhydric alcohol, fructose gives a bright blue color with copper (II) hydroxide without heating, and forms ethers and esters. And the presence of a carbonyl group in the molecule is proven by the fact that when it is reduced, a hexahydric alcohol is formed -sorbitol

Unlike glucosefructose is not oxidized by an ammonia solution of silver (I) oxide (does not give a “silver mirror” reaction), it is not oxidized by bromine water. Explain why?

Questions.

The “silver mirror” reaction is given by:

a) ethylene, ethylene glycol, glucose;b) ribose, glycerol, sucrose;

c) fructose, acetic acid, acetaldehyde;G)formic acid, glucose, formaldehyde.

Calculate how much glucose and fructose can be obtained from the hydrolysis of 5 moles of sucrose.

Sucrose weighing 25 g was subjected to acid hydrolysis. Calculate the mass fraction of the yield of the reaction products if, when they were heated with an ammonia solution of silver (I) oxide, 27 g of precipitate was formed.

Disaccharides – carbohydrates that hydrolyze to form two molecules of monosaccharides.

They are widespread in nature and are found in many fruits and vegetables. The most common are sucrose, maltose and lactose.

General formula of disaccharidesWITH 12 N 22 ABOUT 11

Receipt and application. Sucrose is the most common of all sugars. It is found in all parts of green plants. The richest in sucrose are sugar beets (16-20%) and sugar cane (14-26%). Sucrose is obtained from these plants, calling it beet or cane sugar, respectively. It is used mainly in the food industry. Sucrose is one of the main sources of carbohydrates in human food.

Polysaccharides - These are natural high-molecular carbohydrates, the macromolecules of which contain hundreds and thousands of monosaccharide residues.

Polysaccharide molecules can be considered as a product of polycondensation of monosaccharides. What their structure has in common is that monosaccharide residues are linked by the glycosidic hydroxyl of one molecule and the alcohol hydroxyl of another, etc. Each monosaccharide residue is linked to neighboring residues by glycosidic bonds.

The most important of the polysaccharides arestarch, glycogen (animal starch),fiber (cellulose). All these polysaccharides consist of cyclic glucose molecules connected to each other in various ways. Their composition is expressed by the general formula

(WITH 6 N 10 ABOUT 5 ) n

Unlike mono- and disaccharides, polysaccharides do not have a sweet taste and are insoluble in water.

Starch

Structure. Starch isheterogeneous substance. It is a mixture of two polysaccharides that differnumber elementary links andstructure macromolecular chain: amylose has a linear structure; Amylopectin – has a branched structure.

Physical and chemical properties. Starch is an amorphous white powder, insoluble in cold water; in hot water it swells, forming a colloidal solution - a paste.

Starch, like sucrose, does not give a “silver mirror” reaction and does not reduce copper hydroxide(II).

Since starch ishigh molecular weight polyhydric alcohol, it can react to form ethers and esters. But starch esters are of no practical importance.

Starch is characterized by:

formation with iodine solution of a complex compound of blue color- qualitative reaction to starch;

This reaction is due to the presence in starchamilo PS Amylopectin turns purple when exposed to iodine.

ability sequentially (stepwise)hydrolyze. First, chain fragments of shorter length are formeddextrins, thenmaltose and then the final product glucose.

starch N 2 ABOUTdextrin N 2 ABOUTmaltose N 2 ABOUTglucose wherem < n

(WITH 6 N 12 ABOUT 5 ) n(WITH 6 N 12 ABOUT 5 ) mWITH 12 N 22 ABOUT 11 WITH 6 N 12 ABOUT 6

Being in nature. Starch is widely distributed in nature. It is one of the productsphotosynthesis.Some of the glucose produced in green plants during photosynthesis is converted into starch:

6СО 2 + 6H 2 ABOUT photosynthesisWITH 6 N 12 ABOUT 6 + 6O 2 nС 6 N 12 ABOUT 6 photosynthesis(WITH 6 N 10 ABOUT 5 ) P + nN 2 ABOUT,

glucose starch

or in general:

6 nCO 2 + 5 nN 2 O photosynthesis(WITH 6 N 10 ABOUT 5 ) n+ 6nO 2 ,

which accumulates in tubers, fruits, and plant seeds as a reserve nutrient. Thus, potato tubers contain up to 24% starch, wheat grains - up to 64%, rice - 75%, corn - 70%.

Receipt and application. Starch is obtained from potato tubers or from corn and rice. It is used in the food industry as thickeners and gelling agents.

In the confectionery industry, starch is processed into molasses (a mixture of dextrins and glucose), which is used to make jams, marmalade, sweets, etc. Glucose obtained by hydrolysis of starch is used to produce ethanol, lactic acid and other valuable products. It is used in medicine as fillers (in ointments and powders) and as an adhesive.

Starch is used for starching linen. Under a hot iron, starch is partially hydrolyzed and converted into dextrins. The latter form a dense film on the fabric, which adds shine to the fabric and protects it from contamination.

Biological role of starch. Glycogen. Starch is a valuable nutritious product and, along with sucrose, the main source of carbohydrates in the human body. It is included in bread and potatoes, cereals, pasta and confectionery. Starch is not directly absorbed by the body; it is first hydrolyzed under the influence of enzymes. This process begins when chewing food in the oral cavity under the action of the enzyme saliva -ptyalina. At the same time, a sweet taste is felt, which is not characteristic of starch, but is due to the presence of dextrins. The latter, unlike starch, are soluble in water. Hydrolysis of starch to glucose continues in the digestive tract. Part of the resulting glucose is immediately absorbed by the body, and the rest (excess) is converted into glycogen (animal starch).

Glycogen - polysaccharide, similar in structure to starch amylopectin, butits molecules are more branched and have a higher relative molecular weight(from 1 to 15 million). Glycogen accumulates in the liver and muscles. In humans and animals, it is a reserve nutrient, like starch in plants, which is hydrolyzed to glucose as needed.

Questions.

1. Explain why frozen potatoes have a sweet taste, and boiled potatoes have adhesive properties.

2. Explain why foods containing starch are exposed to high temperatures (potatoes are boiled, bread is baked).

3. To establish the ripeness of a fruit, it is necessary to act on it:

a) water; b) alkali; c) sulfuric acid; d) iodine solution.

4. Recognize solutions of glucose, sucrose and starch. Make up the experiment and reaction equations.

5. Carry out the following transformations:

starch -> glucose -> ethanol -> carbon monoxide(IV)-> glucose.

Calculate the amount of carbon monoxide (IV) formed in the third stage if 243 g of starch was taken.

6. Draw up reaction schemes that need to be carried out to obtain calcium gluconate from starch.

7. From one ton of potatoes containing 20% starch, 100 liters of ethanol were obtained (p = 0.8 g/cm 3 ). Calculate the yield of the reaction product.

Cellulose

Structure. Cellulose (fiber), like starch, is a natural polymer, the structural unit of which is a cyclic glucose residue. These substances have the same molecular formula (C 6 N 10 ABOUT 5 ) n. However, cellulose macromolecules, unlike starch:

- contain a greater number of structural links(glucose residues) - up to 40 thousand; their relative molecular number reaches several million;

have only a linear structure(type of threads);

connected to each other by hydrogen bonds,in the formation of which hydroxyl groups of glucose residues participate. This ensures high mechanical strength of cellulose.

Physical and chemical properties. The difference in the structure of the macromolecules of starch and cellulose causes some differences in their physical and chemical properties. Cellulose is a solid, white or gray fibrous substance, insoluble in water and common organic solvents.

Thermal decomposition of cellulose. When wood is heated without air access, cellulose decomposes with the formation of:charcoal, methane, methanol, acetic acid, acetone, water and other substances.

Cellulose, like starch,does not give “silver mirror” reactions.

Occurrence in nature, biological role, production and use of cellulose. Cellulose is even more common in nature than starch. It is the building material of plants, forming cell membranes in them. The fibers of cotton, flax, and hemp consist mainly of cellulose. Wood contains approximately 50% of it, grass and green leaves contain up to 25%. Cellulose, like starch, is formed in green plants during the process of photosynthesis.

Cellulose is industrially extracted from wood. The production of cellulose comes down to separating it from other compounds present in wood. Examples of almost pure cellulose are wadding obtained from purified cotton and filter paper.

In the bodies of many animals and humans there is no enzyme capable of hydrolyzing cellulose, therefore, unlike starch and glycogen, it is not digestible and cannot serve as a food product. But such an enzyme is produced by some microorganisms that live in the stomachs of ruminants (cows, sheep), some insects (for example, termites), as well as in the soil. These animals can eat cellulozoy.

Cellulose is of great importance as a source of glucose and unit alcohol. It is used in construction and carpentry and as fuel (wood); in the form of fibrous materials (flax, hemp, cotton) it is used to make fabrics - cotton and linen. Cellulose is a raw material for the production of paper and cardboard, artificial silk and livestock feed.

Questions.

1. Indicate: a) what is common in the structure of the macromolecules of starch and cellulose;

b)Cellulose macromolecules differ in structure from starch.

2. Calculate how many links C 6 N 10 ABOUT 5 contained in the cellulose molecule of flax fiber (M G=5 900 000).