Classification
1) by the number of monosaccharide residues:
Oligosaccharides – contain several monosaccharide residues;
· higher polysaccharides - contain many monosaccharide residues.
2) according to the structure of monosaccharide residues:
Homopolysaccharides - consist of residues of one monosaccharide;
Heteropolysaccharides - consist of residues of various monosaccharides.
Disaccharides
Disaccharides are compounds consisting of two monosaccharide residues linked glycosidic linkage.
Glycosidic bond formed by the interaction of two hydroxyl groups. If one of these hydroxyls is glycosidic and the second is alcoholic, then such a disaccharide is called restorative. If both hydroxyls are glycosidic, then such a disaccharide is called non-restorative.
Reducing disaccharides
Maltose
Malt sugar. It is formed during the hydrolysis of starch by malt enzymes, as well as amylases contained in saliva and pancreatic juice (starch digestion).
The maltose molecule consists of two D-glucopyranose residues connected by an α-(1→4)-glycosidic bond.
Maltose reduces Fehling's reagent, its solutions mutate:
Cellobiose
Formed during incomplete hydrolysis of celludose. Unlike maltose, cellobiose is not broken down by gastrointestinal enzymes and is not digested or absorbed by the body.
The cellobiose molecule consists of two D-glucopyranose residues connected by a β-(1→4)-glycosidic bond.
Cellobiose, like maltose, reduces Fehling's reagent and its solutions mutarotate:
Milk sugar is found in all types of milk in amounts up to 4% (in human milk - 8%). Lactose is broken down by lactase, an enzyme in intestinal juice, and is nutritious product especially for infants. In pharmacy, lactose is used in the manufacture of powders and tablets.
Lactose is a heterodisaccharide. Its molecule consists of D-galactopyranose and D-glucopyranose residues linked by a β-(1→4)-glycosidic bond.
Non-reducing disaccharides
Sucrose
Beet, cane sugar. Contained in the juices of many plants and fruits. Sucrose is broken down by sucrase, an enzyme in intestinal juice, and is a nutritious product.
Carbohydrates- organic substances whose molecules consist of carbon, hydrogen and oxygen atoms, and hydrogen and oxygen are found in them, as a rule, in the same ratio as in a water molecule (2: 1).
The general formula of carbohydrates is C n (H 2 O) m, i.e. they seem to consist of carbon and water, hence the name of the class, which has historical roots. It appeared based on the analysis of the first known carbohydrates. Later it was found that there are carbohydrates in the molecules of which the specified ratio (2: 1) is not observed, for example, deoxyribose - C 5 H 10 O 4. Organic compounds are also known, the composition of which corresponds to the general formula given, but which do not belong to the class of carbohydrates. These include, for example, formaldehyde CH 2 O and acetic acid CH 3 COOH.
However, the name "carbohydrates" has taken root and is now generally accepted for these substances.
Carbohydrates, according to their ability to hydrolyze, can be divided into three main groups: mono-, di- and polysaccharides.
Monosaccharides- carbohydrates that do not hydrolyze (do not decompose with water). In turn, depending on the number of carbon atoms, monosaccharides are divided into trioses (the molecules of which contain three carbon atoms), tetroses (four carbon atoms), pentoses (five), hexoses (six), etc.
In nature, monosaccharides are predominantly represented pentoses And hexoses.
TO pentoses include, for example, ribose - C 5 H 10 O 5 and deoxyribose (ribose from which the oxygen atom has been “removed”) - C 5 H 10 O 4. They are part of RNA and DNA and determine the first part of the names of nucleic acids.
TO hexoses having the general molecular formula C 6 H 12 O 6 include, for example, glucose, fructose, galactose.
Disaccharides- carbohydrates that hydrolyze to form two molecules of monosaccharides, such as hexoses. The general formula of the vast majority of disaccharides is not difficult to derive: you need to “add” two hexose formulas and “subtract” a water molecule from the resulting formula - C 12 H 22 O 11. Accordingly, we can write general equation hydrolysis:
Disaccharides include:
1. Sucrose(common table sugar), which upon hydrolysis forms one molecule of glucose and a molecule of fructose. It is found in large quantities in sugar beets, sugar cane (hence the names beet or cane sugar), maple (Canadian pioneers mined maple sugar), sugar palm, corn, etc.
2. Maltose(malt sugar), which hydrolyzes to form two glucose molecules. Maltose can be obtained by hydrolysis of starch under the action of enzymes contained in malt - sprouted, dried and ground barley grains.
3. Lactose(milk sugar), which hydrolyzes to form glucose and galactose molecules. It is found in mammalian milk (up to 4-6%), has low sweetness and is used as a filler in dragees and pharmaceutical tablets.
The sweet taste of different mono- and disaccharides is different. Thus, the sweetest monosaccharide - fructose - is 1.5 times sweeter than glucose, which is taken as the standard. Sucrose (a disaccharide), in turn, is 2 times sweeter than glucose and 4-5 times sweeter than lactose, which is almost tasteless.
Polysaccharides- starch, glycogen, dextrins, cellulose, etc. - carbohydrates that are hydrolyzed to form many monosaccharide molecules, most often glucose.
To derive the formula of polysaccharides, you need to “subtract” a water molecule from a glucose molecule and write down an expression with the index n: (C 6 H 10 O 5) n, because it is due to the elimination of water molecules that di- and polysaccharides are formed in nature.
The role of carbohydrates in nature and their importance for human life is extremely great. Formed in plant cells as a result of photosynthesis, they act as a source of energy for animal cells. This primarily applies to glucose.
Many carbohydrates (starch, glycogen, sucrose) perform a storage function, role of nutrient reserve.
RNA and DNA acids, which contain some carbohydrates (pentose-ribose and deoxyribose), perform the functions of transmitting hereditary information.
Cellulose- building material of plant cells - plays the role of a frame for the membranes of these cells. Another polysaccharide, chitin, performs a similar role in the cells of some animals: it forms the external skeleton of arthropods (crustaceans), insects, and arachnids.
Carbohydrates ultimately serve as the source of our nutrition: we consume grains that contain starch, or feed them to animals, in whose bodies the starch is converted into proteins and fats. The most hygienic clothing is made from cellulose or cellulose-based products: cotton and linen, viscose fiber, silk acetate. Wooden houses and furniture are built from the same cellulose that makes up wood.
The production of photographic and film films is based on the same cellulose. Books, newspapers, letters, banknotes are all products of the pulp and paper industry. This means that carbohydrates provide us with everything we need for life: food, clothing, shelter.
In addition, carbohydrates are involved in the construction of complex proteins, enzymes, and hormones. Carbohydrates also include such vital substances as heparin (it plays a vital role in preventing blood clotting), agar-agar (it is obtained from seaweed and is used in the microbiological and confectionery industries - remember the famous Bird's Milk cake).
It must be emphasized that the only type of energy on Earth (besides nuclear, of course) is the energy of the Sun, and the only way to accumulate it to ensure the life of all living organisms is the process photosynthesis, which occurs in the cells of living plants and leads to the synthesis of carbohydrates from water and carbon dioxide. It is during this transformation that oxygen is formed, without which life on our planet would be impossible:
Glucose and fructose- solid colorless crystalline substances. Glucose, found in grape juice (hence the name "grape sugar"), together with fructose, which is found in some fruits and fruits (hence the name "fruit sugar"), makes up a significant portion of honey. The blood of humans and animals constantly contains about 0.1% glucose (80-120 mg per 100 ml of blood). Most of it (about 70%) undergoes slow oxidation in tissues with the release of energy and the formation of final products - carbon dioxide and water (glycolysis process):
The energy released during glycolysis largely supplies the energy needs of living organisms.
Exceeding the level of glucose in the blood of 180 mg per 100 ml of blood indicates a violation of carbohydrate metabolism and the development of a dangerous disease - diabetes mellitus.
The structure of the glucose molecule can be judged on the basis of experimental data. It reacts with carboxylic acids to form esters containing from 1 to 5 acid residues. If a glucose solution is added to freshly obtained copper (II) hydroxide, the precipitate dissolves and a bright blue solution of the copper compound is formed, i.e., a qualitative reaction to polyhydric alcohols occurs. Therefore, glucose is a polyhydric alcohol. If the resulting solution is heated, a precipitate will form again, but this time it will be reddish in color, i.e. a qualitative reaction to aldehydes will occur. Similarly, if a glucose solution is heated with an ammonia solution of silver oxide, a “silver mirror” reaction will occur. Consequently, glucose is both a polyhydric alcohol and an aldehyde - an aldehyde alcohol. Let's try to withdraw structural formula glucose. There are six carbon atoms in the C 6 H 12 O 6 molecule. One atom is included in the composition aldehyde group:
The remaining five atoms are associated with five hydroxy groups.
And finally, we distribute the hydrogen atoms in the molecule, taking into account the fact that carbon is tetravalent:
However, it has been established that in a glucose solution, in addition to linear (aldehyde) molecules, there are molecules of a cyclic structure that make up crystalline glucose. The transformation of linear molecules into cyclic ones can be explained if we remember that carbon atoms can freely rotate around σ bonds located at an angle of 109° 28′. In this case, the aldehyde group (1st carbon atom) can approach the hydroxyl group of the fifth carbon atom. In the first, under the influence of the hydroxy group, the π-bond is broken: a hydrogen atom is added to the oxygen atom, and the oxygen of the hydroxy group that has “lost” this atom closes the cycle:
As a result of this rearrangement of atoms, a cyclic molecule is formed. The cyclic formula shows not only the order of bonding of atoms, but also their spatial arrangement. As a result of the interaction of the first and fifth carbon atoms, a new hydroxy group appears at the first atom, which can occupy two positions in space: above and below the plane of the cycle, and therefore two cyclic forms of glucose are possible:
A) α-form of glucose- hydroxyl groups at the first and second carbon atoms are located on one side of the ring of the molecule;
b) β-form of glucose- hydroxyl groups are located on opposite sides of the ring of the molecule:
In an aqueous solution of glucose, three of its isomeric forms are in dynamic equilibrium - the cyclic α-form, the linear (aldehyde) form and the cyclic β-form:
In the established dynamic equilibrium, the β-form predominates (about 63%), since it is energetically preferable - it has OH groups at the first and second carbon atoms on opposite sides of the ring. In the α-form (about 37%), the OH groups on the same carbon atoms are located on one side of the plane, so it is energetically less stable than the β-form. The share of the linear form in equilibrium is very small (only about 0.0026%).
The dynamic equilibrium can be shifted. For example, when glucose is exposed to an ammonia solution of silver oxide, the amount of its linear (aldehyde) form, which is very small in the solution, is replenished all the time due to cyclic forms, and glucose is completely oxidized to gluconic acid.
The isomer of the aldehyde alcohol of glucose is the ketone alcohol - fructose:
The chemical properties of glucose, like any other organic substance, are determined by its structure. Glucose has a dual function, being both aldehyde, And polyhydric alcohol, therefore, it is characterized by the properties of both polyhydric alcohols and aldehydes.
Reactions of glucose as a polyhydric alcohol.
Glucose qualitatively reacts polyhydric alcohols (think glycerol) with freshly prepared copper(II) hydroxide, producing a bright blue solution of the copper(II) compound.
Glucose, like alcohols, can form esters.
Reactions of glucose as an aldehyde
1. Oxidation of the aldehyde group. Glucose, as an aldehyde, can be oxidized into the corresponding (gluconic) acid and give qualitative aldehyde reactions.
Silver mirror reaction:
Reaction with freshly obtained Cu(OH) 2 when heated:
Reduction of aldehyde group. Glucose can be reduced to the corresponding alcohol (sorbitol):
Fermentation reactions
These reactions occur under the influence of special biological catalysts of a protein nature - enzymes.
1. Alcoholic fermentation:
has long been used by man to obtain ethyl alcohol and alcoholic beverages.
2. Lactic acid fermentation:
which forms the basis of the life activity of lactic acid bacteria and occurs during souring of milk, pickling cabbage and cucumbers, and ensiling green fodder.\
Chemical properties of glucose - summary
Starch- white amorphous powder, insoluble in cold water. IN hot water it swells and forms a colloidal solution - starch paste.
Starch is contained in the cytoplasm of plant cells in the form of storage grains nutrient. Potato tubers contain about 20% starch, wheat and corn grains - about 70%, and rice grains - almost 80%.
Cellulose(from Latin cellula - cell), isolated from natural materials (for example, cotton wool or filter paper), is a solid fibrous substance, insoluble in water.
Both polysaccharides are of plant origin, but play different roles in plant cells: cellulose has a building, structural function, and starch has a storage function. Therefore cellulose is mandatory element plant cell membrane. Cotton fibers contain up to 95% cellulose, flax and hemp fibers - up to 80%, and wood contains about 50%.
The composition of these polysaccharides can be expressed by the general formula (C6H10O5)n. The number of repeating units in a starch macromolecule can vary from several hundred to several thousand. Cellulose differs significantly a large number units and, therefore, a molecular weight that reaches several millions.
Carbohydrates differ not only in molecular weight, but also in structure. Starch is characterized by two types of macromolecular structures: linear and branched. The smaller macromolecules of that part of starch, which is called amylose, have a linear structure, and the molecules of another component of starch, amylopectin, have a branched structure.
In starch, the share of amylose is 10-20%, and the share of amylopectin is 80-90%. Starch amylose dissolves in hot water, and amylopectin only swells.
The structural units of starch and cellulose are built differently. If the starch unit includes residues α-glucose, then cellulose is residue β-glucose oriented to natural fibers:
1. Glucose formation. Starch and cellulose undergo hydrolysis to form glucose in the presence of mineral acids, such as sulfuric acid:
IN digestive tract animal starch undergoes complex stepwise hydrolysis:
The human body is not adapted to digest cellulose, since it does not have the enzymes necessary to break the bonds between β-glucose residues in the cellulose macromolecule.
Only in termites and ruminants (for example, cows) digestive system microorganisms live that produce the enzymes necessary for this.
2. Formation of esters. Starch can form esters due to hydroxy groups, but these esters have not found practical use.
Each cellulose unit contains three free alcohol hydroxy groups. Therefore, the general formula of cellulose can be written as follows:
Due to these alcohol hydroxy groups, cellulose can form esters, which are widely used.
When cellulose is treated with a mixture of nitric and sulfuric acids, mono-, di- and trinitrocellulose is obtained, depending on the conditions:
A mixture of mono- and dinitrocellulose is called colloxylin. A solution of colloxylin in a mixture of alcohol and diethyl ether - collodion - is used in medicine for sealing small wounds and for gluing bandages to the skin.
When a solution of colloxylin and camphor in alcohol dries, it turns out celluloid- one of the plastics that first became widely used in everyday life humans (photographic and film films are made from it, as well as various consumer goods). Solutions of colloxylin in organic solvents are used as nitrovarnishes. And when dyes are added to them, durable and aesthetic nitro paints are obtained, widely used in everyday life and technology.
Like other organic substances containing nitro groups in their molecules, all types of nitrocellulose are flammable. Particularly dangerous in this regard trinitrocellulose- the strongest explosive. Under the name pyroxylin, it is widely used for the production of weapon shells and blasting operations, as well as for the production of smokeless powder.
With acetic acid (in industry, a more powerful esterifying substance, acetic anhydride, is used for these purposes), similar (di- and tri-) esters of cellulose and acetic acid are obtained, which are called cellulose acetate:
Cellulose acetate It is used to produce varnishes and paints; it also serves as a raw material for the production of artificial silk. To do this, it is dissolved in acetone, and then this solution is forced through the thin holes of dies (metal caps with numerous holes). The flowing streams of solution are blown with warm air. In this case, the acetone quickly evaporates, and the drying cellulose acetate forms thin shiny threads that are used to make yarn.
Starch, unlike cellulose, gives a blue color when reacting with iodine. This reaction is qualitative for starch or iodine, depending on the presence of which substance needs to be proven.
Reference material for taking the test:
Periodic table
Solubility table
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 the molecules, they are divided into two groups: simple sugars(monosaccharides) and complex (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 various types carbohydrates, read 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.
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 can easily 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.
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.
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.
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 are carbohydrates whose molecules consist of two monosaccharide residues linked to each other by 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 relationship between disaccharide residues in 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, 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 are 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 complex carbohydrates whose molecules form a large number of monosaccharide molecules upon complete hydrolysis.
IN general case the polysaccharide formula 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. IN the largest quantities starch is found 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 products plant origin. 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
There are three main types of carbohydrates:
There are two types of sugars:
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 are a large group of organic compounds that play an important role in the functioning of the body. Carbohydrates are distributed mainly in flora. 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.
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:
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. Digestion of disaccharides requires more long time 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:
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 fully satisfy daily norm organism in 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:
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, while the amount of easily digestible carbohydrates should vary 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 consuming sugar or other sweet food, but the intake of such products must 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.
From the list of carbohydrates below, everyone can create a completely varied diet (taking into account the fact that this is far from full list products containing 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 healthy eating will be 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.
To widespread and important as components food products, include disaccharides: sucrose, lactose, maltose, etc.
According to their chemical structure, disaccharides are glycosides of monosaccharides. Most disaccharides are composed of hexoses, but disaccharides consisting of one hexose molecule and one pentose molecule are known in nature.
When a disaccharide is formed, one monosaccharide molecule always forms a bond with a second molecule using its hemiacetal hydroxyl. Another monosaccharide molecule can be joined either by a hemiacetal hydroxy acid or by one of the alcohol hydroxyls. In the latter case, one hemiacetal hydroxyl will remain free in the disaccharide molecule.
Maltose– reserve oligosaccharide – found in many plants in small quantities, accumulates in large quantities in malt – usually in barley seeds sprouted under certain conditions. Therefore, maltose is often called malt sugar. Maltose is formed in plant and animal organisms as a result of the hydrolysis of starch under the action of amylases.
Maltose contains two D-glucopyranose residues connected to each other by an a(1®4) glycosidic bond.
Maltose has restorative properties, which is used in its quantification. It is easily soluble in water. The solution exhibits mutarotation.
Under the action of the enzyme a-glucosidase (maltase), malt sugar is hydrolyzed to form two glucose molecules:
Maltose is fermented by yeast. This ability of maltose is used in fermentation technology in the production of beer, ethyl alcohol, etc. from starch-containing raw materials.
Lactose– reserve disaccharide (milk sugar) – found in milk (4-5%) and obtained in the cheese industry from whey after separating the curd. It is fermented only with special lactose yeast contained in kefir and kumiss. Lactose is composed of b-D-galactopyranose and a-D-glucopyranose residues connected to each other by a b-(1→4)-glycosidic bond. Lactose is a reducing disaccharide, with the free hemiacetal hydroxyl belonging to the glucose residue and an oxygen bridge linking the first carbon atom of the galactose residue to the fourth carbon atom of the glucose residue.
Lactose is hydrolyzed by the enzyme b-galactosidase (lactase):
Lactose differs from other sugars in that it is not hygroscopic - it does not dampen. Milk sugar is used as pharmaceutical drug and as a nutritional product for infants. Aqueous solutions of lactose mutate, lactose has a 4-5 times less sweet taste than sucrose.
Sucrose(cane sugar, beet sugar) is a reserve disaccharide - extremely widespread in plants, especially in beet roots (14 to 20%), as well as in sugar cane stems (14 to 25%). Sucrose is a transport sugar in the form of which carbon and energy are transported throughout the plant. It is in the form of sucrose that carbohydrates move from the sites of synthesis (leaves) to the place where they are stored (fruits, roots, seeds).
Sucrose consists of a-D-glucopyranose and b-D-fructofuranose, connected by an a-1→b-2 bond via glycosidic hydroxyls:
Sucrose does not contain a free hemiacetal hydroxyl, so it is not capable of oxy-oxo tautomerism and is a non-reducing disaccharide.
When heated with acids or under the action of the enzymes a-glucosidase and b-fructofuranosidase (invertase), sucrose is hydrolyzed to form a mixture of equal amounts of glucose and fructose, which is called invert sugar.
The most important disaccharides- sucrose, maltose and lactose. They all have the general formula C12H22O11, but their structure is different.
Sucrose consists of 2 cycles interconnected by glycosidic hydroxide:
Maltose consists of 2 glucose residues:
Lactose:
All disaccharides are colorless crystals, sweet in taste, and highly soluble in water.
1) Hydrolysis. As a result, the connection between the 2 cycles is broken and monosaccharides are formed:
Reducing dicharides are maltose and lactose. They react with an ammonia solution of silver oxide:
Can reduce copper(II) hydroxide to copper(I) oxide:
The reducing ability is explained by the cyclicity of the form and the content of glycosidic hydroxyl.
There is no glycosidic hydroxyl in sucrose, so the cyclic form cannot open and transform into an aldehyde.
The most common disaccharide is sucrose.
It is a source of carbohydrates in human food.
Lactose is found in milk and is obtained from it.
Maltose is found in sprouted cereal seeds and is formed during the enzymatic hydrolysis of starch.
Reducing disaccharides include maltose or malt sugar. Maltose is obtained by partial hydrolysis of starch in the presence of enzymes or aqueous solution acids. Maltose is made up of two glucose molecules (i.e. it is a glucoside). Glucose is present in maltose in the form of a cyclic hemiacetal. Moreover, the bond between the two cycles is formed by the glycosidic hydroxyl of one molecule and the hydroxyl of the fourth tetrahedron of the other. The peculiarity of the structure of the maltose molecule is that it is built from α-anomers of glucose:
The presence of free glycosidic hydroxyl determines the main properties of maltose:
Ability for tautomerism and mutarotation:
Maltose can be oxidized and reduced:
For the reducing disaccharide, phenylhydrazone and osazone can be prepared:
The reducing disaccharide can be alkylated methyl alcohol in the presence of hydrogen chloride:
Whether reducing or non-reducing, the disaccharide can be alkylated with methyl iodide in the presence of wet silver oxide or acetylated with acetic anhydride. In this case, all hydroxyl groups of the disaccharide react:
Another product of hydrolysis of a higher polysaccharide is cellobiose disaccharide:
Cellobiose, like maltose, is built from two glucose residues. The fundamental difference is that in the cellobiose molecule the residues are linked by β-glycosidic hydroxyl.
Judging by the structure of the cellobiose molecule, it should be a reducing sugar. It also has all the chemical properties of disaccharides.
Another reducing sugar is lactose, milk sugar. This disaccharide is found in all milk and gives the taste of milk, although it is less sweet than sugar. Constructed from β-D-galactose and α-D-glucose residues. Galactose is an epimer of glucose and differs in the configuration of the fourth tetrahedron:
Lactose has all the properties of reducing sugars: tautomerism, mutarotation, oxidation to lactobionic acid, reduction, formation of hydrazones and osazones.
Formation of glycosides
The glycosidic bond has an important biological significance, because it is with the help of this bond that the covalent binding of monosaccharides in the composition of oligo- and polysaccharides is carried out. When a glycosidic bond is formed, the anomeric OH group of one monosaccharide interacts with the OH group of another monosaccharide or alcohol. In this case, the water molecule is split off and the formation O-glycosidic bond. All linear oligomers (except disaccharides) or polymers contain monomeric residues involved in the formation of two glycosidic bonds, except for the terminal residues. Some glycosidic residues can form three glycosidic bonds, which is typical for branched oligo- and polysaccharides. Oligo- and polysaccharides may have a terminal monosaccharide residue with a free anomeric OH group not used in the formation of the glycosidic bond. In this case, when the ring opens, a free carbonyl group capable of oxidation may be formed. Such oligo- and polysaccharides have reducing properties and are therefore called reducing or reducing.
Figure - Polysaccharide structure.
A. Formation of a-1,4- and a-1,6-glycosidic bonds.
B. Structure of a linear polysaccharide:
1 – a-1,4-glycosidic bonds between manomers;
2 – non-reducing end (the formation of a free carbonyl group in an anomeric carbohydrate is not possible);
3 – reducing end (possible ring opening with the formation of a free carbonyl group at the anomeric carbon).
The anomeric OH group of a monosaccharide can interact with the NH2 group of other compounds, resulting in the formation of an N-glycosidic bond. A similar bond is present in nucleotides and glycoproteins.
Figure - Structure of the N-glycosidic bond
Question 2. Disaccharides
Oligosaccharides contain from two to ten monosaccharide residues connected by a glycosidic bond. Disaccharides are the most common oligomeric carbohydrates found in free form, i.e. not connected to other connections. By chemical nature, disaccharides are glycosides that contain 2 monosaccharides connected by a glycosidic bond in an a- or b-configuration. Food contains mainly disaccharides such as sucrose, lactose and maltose.
Figure - Food disaccharides
Sucrose – a disaccharide consisting of a-D-glucose and b-D-fructose connected by an a,b-1,2-glycosidic bond. In sucrose, both anomeric OH groups of glucose and fructose residues participate in the formation of the glycosidic bond. Therefore, sucrose not a reducing sugar. Sucrose is a soluble disaccharide with a sweet taste.
The source of sucrose is plants, especially sugar beets and sugar cane. The latter explains the origin of the trivial name for sucrose - “cane sugar”.
Lactose– milk sugar. Lactose is hydrolyzed to form glucose and galactose. The most important disaccharide in mammalian milk. IN cow's milk contains up to 5% lactose, in women's - up to 8%. In lactose, the anomeric OH group on the first carbon atom of the D-galactose residue is linked by a b-glycosidic bond to the fourth carbon atom of D-glucose (b-1,4 bond). Since the anomeric carbon atom of the glucose residue does not participate in the formation of the glycosidic bond, therefore lactose refers to reducing sugars.
Maltose comes with products containing partially hydrolyzed starch, for example, malt, beer. Maltose is formed during the breakdown of starch in the intestines and partially in oral cavity. Maltose consists of two D-glucose residues connected by an a-1,4-glycosidic bond. Refers to reducing sugars.
Question 3. Polysaccharides:
Classification
Depending on the structure of monosaccharide residues, polysaccharides can be divided into homopolysaccharides(all monomers are identical) and heteropolysaccharides(monomers are different). Both types of polysaccharides can have either a linear arrangement of monomers or a branched one.
The following structural differences between polysaccharides are distinguished:
Depending on the functions they perform ( biological role) polysaccharides can be divided into 3 main groups:
Structural formula
Molecular weight: 342.297
Maltose(from the English malt - malt) - malt sugar, 4-O-α-D-glucopyranosyl-D-glucose, a natural disaccharide consisting of two glucose residues; found in large quantities in sprouted grains (malt) of barley, rye and other grains; also found in tomatoes, pollen and nectar of a number of plants.
The biosynthesis of maltose from β-D-glucopyranosylphosphate and D-glucose is known only in some bacterial species. In animal and plant organisms, maltose is formed during the enzymatic breakdown of starch and glycogen (see Amylase).
Maltose is easily absorbed by the human body. The breakdown of maltose into two glucose residues occurs as a result of the action of the enzyme a-glucosidase, or maltase, which is found in the digestive juices of animals and humans, in sprouted grains, in molds and yeast. The genetically determined absence of this enzyme in the human intestinal mucosa leads to congenital maltose intolerance - serious illness, requiring the exclusion of maltose, starch and glycogen from the diet or the addition of the enzyme maltase to the food.
Chemical name
α-Maltose - (2R,3R,4S,5R,6R)-5-[(2R,3R,4S,5R,6R)-2,3,4-trihydroxy-6-(hydroxymethyl)oxanyl]oxy-6- (hydroxymethyl)oxane-2,3,4-triol
β-Maltose - (2S,3R,4S,5R,6R)-5-[(2R,3R,4S,5R,6R)-2,3,4-trihydroxy-6-(hydroxymethyl)oxanyl]oxy-6- (hydroxymethyl)oxane-2,3,4-triol
Physical properties
Maltose is a reducing sugar because it has an unsubstituted hemiacetal hydroxyl group.
When maltose is boiled with dilute acid and under the action of an enzyme, maltose is hydrolyzed (two glucose molecules C6H12O6 are formed).
C12H22O11 + H2O → 2C6H12O6
(from the English malt ≈ malt), malt sugar, a natural disaccharide consisting of two glucose residues; found in large quantities in sprouted grains (malt) of barley, rye and other grains; also found in tomatoes, pollen and nectar of a number of plants. M. is easily soluble in water and has a sweet taste; is a reducing sugar because it has an unsubstituted hemiacetal hydroxyl group. Biosynthesis of M. from b-D-glucopyranosylphosphate and D-glucose is known only in some species of bacteria. In animal and plant organisms M.
is formed during the enzymatic breakdown of starch and glycogen (see Amylase). The breakdown of M. into two glucose residues occurs as a result of the action of the enzyme a-glucosidase, or maltase, which is found in the digestive juices of animals and humans, in sprouted grains, in molds and yeast. The genetically determined absence of this enzyme in the human intestinal mucosa leads to congenital intolerance to M., a serious disease that requires the exclusion of M., starch, and glycogen from the diet or the addition of the enzyme maltase to food.
Lit.: Chemistry of carbohydrates, M., 1967; Harris G., Fundamentals of human biochemical genetics, translation from English, M., 1973.
If proteins are considered organic compounds, the most diverse in structure and function, then carbohydrates are the most common in nature. We encounter them everywhere: sugar, starch, paper, cotton fabric and many other substances and materials are built from disaccharides and polysaccharides. We will consider the chemical properties of these compounds and their significance for human life in our article.
Sucrose is one of the most important disaccharides synthesized by plants, such as sugar cane or sugar beets. The compound performs an energetic function, so its splitting leads to the release of a large amount of energy. Hydrolysis of sucrose occurs in cells human body and leads to the formation of glucose and fructose molecules:
C 12 H 22 O 11 + H 2 O = C 6 H 12 O 6 + C 6 H 12 O 6
The main factors for carrying out hydrolysis in laboratory or industrial conditions are heat and an excess of hydrogen ions, which perform a catalytic function in the reacting mixture. The fructose and glucose residues in the disaccharide are presented in their cyclic form and are interconnected by an oxygen atom. Sucrose is devoid of free aldehyde groups, which is why the silver mirror reaction does not occur in it, and the carbohydrate does not exhibit reducing properties.
This is confirmed by the above reaction equations for disaccharides. The chemical properties of substances, namely, formed the basis for the classification of carbohydrates.
Substances that are not broken down by water, such as fructose, found in honey and most fruits, as well as glucose, are monosaccharides or monosaccharides. If, during the process of hydrolysis, a carbohydrate is decomposed into two molecules of simple sugars, it is classified as a disaccharide. This class includes sucrose and lactose. If many monosaccharide residues are formed from one macromolecule of an organic substance, they speak of polysaccharides. These include a well-known plant polymer - starch, which accumulates in the leaves, fruits and seeds of plants during photosynthesis.
In the shells of arthropods and fungal cells there is a carbohydrate, which, unlike the previously discussed compounds, contains not only carbon, oxygen and hydrogen atoms, but also nitrogen. Interesting structure and characteristics of reactions that distinguish it from chemical properties disaccharides, has hyaluronic acid, representing the basis of the intercellular substance in animals and humans. linear structure, which is, in fact, one giant macromolecule containing up to 50,000 monomer units. Its greatest quantity is found in the dermis, cartilage, vitreous body organ of vision. Animal starch - glycogen is synthesized in animal and human cells from glucose residues and is deposited as a reserve energy material in liver cells - hepatocytes.
Milk is the first and most important product nutrition for young mammals: animals and humans. In addition to milk protein - casein, fat, water, mineral salts and vitamins, it contains a carbohydrate - lactose or milk sugar. Its molecules consist of monosaccharide residues - glucose and galactose, containing six carbon atoms each. During the digestion of milk in gastrointestinal tract lactose is broken down into monosaccharides.
They are absorbed by the capillaries of the villi small intestine. All chemical properties of disaccharides take place with the participation of enzymes, for example, lactase, which accelerates the hydrolysis of milk sugar. A decrease in the level of this substance, associated both with genetic predisposition and with individual characteristics (age, specific nutrition), causes the disease - hypolactasia.
Lactose molecules consist of galactose and glucose residues, which have open carbon chains and free aldehyde complexes. The presence of a functional group makes it possible to carry out reduction reactions, for example, with hydrogen. As a result, the complex of -CHO atoms, which is part of glucose, is reduced to a hydroxyl group, and a hexahydric alcohol - sorbitol - is formed. The reduction process that occurs can be expressed by equations, and the chemical properties of the disaccharides will thus have the following form:
CH 2 OH - (CHOH) 4 - COH + H 2 = (temperature, Ni catalyst) => CH 2 OH -(CHOH) 4 -CH 2 OH
They depend on what forms of glucose are included in the carbohydrate: cyclic or with an open carbon skeleton.
A white powder that does not dissolve in cold water, but in hot water, forms a paste - this is starch. Its highest content is typical for rice and corn seeds, potato tubers. The macromolecule of the substance consists of cyclic alpha-glucose residues. IN acidic environment its reaction has the following form:
(C 6 H 10 O 5) n + nH 2 O - H 2 SO 4 → nC 6 H 12 O 6
The chemical properties of disaccharides and polysaccharides have similarities: they are all capable of hydrolysis.
Cellulose, which is part of wood, contains monomers - beta-glucose residues. Heating a substance with concentrated nitrate acid leads to the formation ester- three cellulose nitrates, used in pyrotechnics.
In our article, we studied the features of the chemical properties of disaccharides and polysaccharides and examined their distribution in nature.
