Carbohydrates formed by residues of two monosaccharides. Disaccharides common in animal and plant organisms are sucrose, lactose, maltose, trehalose... Big Encyclopedic Dictionary
DISACCHARIDES, a type of sugar (which includes table sugar), formed by the condensation of two MONOSACHARIDES with the removal of water. Cane sugar (sucrose) is a disaccharide that, when HYDROLYZED in the presence of acid, gives... ... Scientific and technical encyclopedic dictionary
DISACCHARIDES- (sugar-like polyoses, bioses), carbohydrates that are broken down during hydrolysis (inversion) to form 2 molecules of monoses from 1 molecule D. D. are soluble in water, giving true solutions; most crystallize well and have a sweet taste. Leftovers... ... Great Medical Encyclopedia
Bioses, oligosaccharides, molecules are built from two monosaccharide residues linked by a glycosidic bond. In non-reducing D. (sucrose, trehalose), both glycosidic hydroxyls are involved in the formation of bonds between monosaccharides, in ... ... Biological encyclopedic dictionary
BIOSES are oligosaccharides, the molecules of which are built from two monosaccharide residues linked by a glycosidic bond. In non-reducing D. (sucrose, trehalose), both glycosidic hydroxyls are involved in the formation of bonds between monosaccharides, in ... ... Dictionary of microbiology
Carbohydrates formed by residues of two monosaccharides. The following disaccharides are common in animal and plant organisms: sucrose, lactose, maltose, trehalose. * * * DISACCHARIDES DISACCHARIDES, carbohydrates formed by residues of two monosaccharides. IN… … Encyclopedic Dictionary
- (gr. di(s) twice + sakchar sugar + eidos species) a class of organic compounds, carbohydrates, the molecules of which consist of two monosaccharide residues; The most important representatives of disaccharides are sucrose and lactose. New dictionary foreign words. by EdwART,… … Dictionary of foreign words of the Russian language
- (syn. bios) complex sugars, consisting of two monosaccharide residues; are the main sources of carbohydrates in human and animal nutrition (lactose, sucrose, etc.) ... Large medical dictionary
Bioses, carbohydrates, the molecules of which consist of two monosaccharide residues (See Monosaccharides). All D. are constructed according to the type of glycosides (See Glycosides). In this case, the hydrogen atom of the glycosidic hydroxyl of one monosaccharide molecule is replaced... ... Great Soviet Encyclopedia
Same as saccharobioses, see Carbon hydrates... Encyclopedic Dictionary F.A. Brockhaus and I.A. Ephron
An example of the most common disaccharides in nature (oligosaccharides) is sucrose(beet or cane sugar).
Oligosaccharides are condensation products of two or more monosaccharide molecules.
Disaccharides - these are carbohydrates that, when heated with water in the presence of mineral acids or under the influence of enzymes, undergo hydrolysis, splitting into two molecules of monosaccharides.
Physical properties and occurrence in nature
1. It is colorless crystals with a sweet taste and is highly soluble in water.
2. The melting point of sucrose is 160 °C.
3. When molten sucrose hardens, an amorphous transparent mass is formed - caramel.
4. Contained in many plants: in the sap of birch, maple, carrots, melon, as well as in sugar beets and sugar cane.
Structure and chemical properties
1. The molecular formula of sucrose is C 12 H 22 O 11
2. Sucrose has a more complex structure than glucose. The sucrose molecule consists of glucose and fructose residues connected to each other through the interaction of hemiacetal hydroxyls (1→2)-glycosidic bond:
3. The presence of hydroxyl groups in the sucrose molecule is easily confirmed by reaction with metal hydroxides.
If a solution of sucrose is added to copper (II) hydroxide, a bright blue solution of copper sucrose is formed (a qualitative reaction of polyhydric alcohols).
Video experiment “Proof of the presence of hydroxyl groups in sucrose”
4. There is no aldehyde group in sucrose: when heated with an ammonia solution of silver (I) oxide, it does not give a “silver mirror”; when heated with copper (II) hydroxide, it does not form red copper (I) oxide.
5. Sucrose, unlike glucose, is not an aldehyde. Sucrose, when in solution, does not enter into the “silver mirror” reaction, since it is not able to transform into an open form containing an aldehyde group. Such disaccharides are not capable of oxidation (i.e., being reducing agents) and are called non-restorative sugars.
Video experiment “Lack of reducing ability of sucrose”
6. Sucrose is the most important of the disaccharides.
7. It is obtained from sugar beets (it contains up to 28% sucrose from dry matter) or from sugar cane.
Reaction of sucrose with water.
An important chemical property of sucrose is its ability to undergo hydrolysis (when heated in the presence of hydrogen ions). In this case, from one sucrose molecule a glucose molecule and a fructose molecule are formed:
C 12 H 22 O 11 + H 2 O t , H 2 SO 4 → C 6 H 12 O 6 + C 6 H 12 O 6
Video experiment “Acid hydrolysis of sucrose”
Among the isomers of sucrose with the molecular formula C 12 H 22 O 11, maltose and lactose can be distinguished.
During hydrolysis, various disaccharides are broken down into their constituent monosaccharides by breaking the bonds between them ( glycosidic bonds):
Thus, the hydrolysis reaction of disaccharides is the reverse of the process of their formation from monosaccharides.
Application of sucrose
· Food product;
· In the confectionery industry;
· Obtaining artificial honey
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.
The main representative of disaccharides is sucrose. The sucrose molecule consists of the residues of the D-glucose and D-fructose molecules. Chemical formula- C 12 H 22 O 11. Sucrose is one of the main carbohydrates in the human body, a colorless crystalline substance. At temperatures above 200°C it decomposes to form so-called caramels. Sucrose is insoluble in non-polar organic solvents, in absolute methanol and ethanol, moderately soluble in ethyl acetate, aniline, and in aqueous solutions of methanol and ethanol. Highly soluble in water. Sucrose does not have reducing properties, so it is resistant to alkalis, but is hydrated under the influence of acids and sucrase enzymes to form D-glucose and D-fructose. Forms saccharates with alkali metals. Sucrose is one of the main disaccharides. It is hydrolyzed by HCl gastric juice and sucrase mucous membrane small intestine person.
Sucrose is a component of sugar (99.75%) used to give food a sweet taste. Sucrose is also called beet sugar.
Another representative of disaccharides is lactose (milk sugar). It consists of gactose and glucose residues. Lactose is an important component of mammalian and human milk. It is formed during lactation in the mammary gland from glucose and is its source for newborns. Lactose facilitates the absorption of calcium from the intestines. The lactose content in human milk is 7 g/100 ml. In the milk of cows and goats - 4.5 g/100 ml.
Disaccharides are carbohydrates that, when heated with water in the presence of mineral acids or under the influence of enzymes, undergo hydrolysis, splitting into two molecules of monosaccharides.
The most common disaccharide is sucrose (cane or beet sugar). It is obtained from sugar cane or sugar beets. Milk contains 5% lactose - milk sugar. Maltose is found in germinating grains and is formed during the hydrolysis of grain starch. Cellobiose is an intermediate product in the enzymatic hydrolysis of cellulose.
Structure
When a glycosidic bond is formed between the anomeric hydroxyl group of one monosaccharide and the OH group of another monosaccharide, a disaccharide is obtained. Since the synthesis of natural disaccharides with the participation of enzymes is strictly stereospecific, the glycosidic bond can only be in one of the possible configurations (α or β). The stereochemistry of the glycosidic bond cannot be changed by mutarotation.
In maltose, which is formed during the breakdown of starch under the action of malt amylases, the anomeric OH group of one glucose molecule is linked by an α-glycosidic bond to C-4 of the second glucose molecule.
Lactose is the most important carbohydrate component of mammalian milk. Cow's milk contains up to 4.5% lactose, human milk - up to 7.5%. In the lactose molecule, the anomeric OH group of the galactose residue is linked by a β-glycosidic bond to the C-4 of the glucose residue. Therefore, the lactose molecule is elongated and both pyranose rings lie approximately in the same plane.
A disaccharide molecule consists of two monosaccharide molecules connected by a glycosidic bond. Depending on which carbon atoms are involved in the formation of the glycosidic bond, the disaccharide molecule may or may not contain a free carbonyl group.
Disaccharides can be divided into two groups: non-reducing and reducing.
Non-reducing sugars do not have an OH group at any anomeric center, while reducing sugars have a free OH group at the anomeric center.
Non-reducing sugars are called glycosyl glycosides; reducing - glycosyl-glycoses.
Maltose is a reducing disaccharide formed during the enzymatic hydrolysis of starch. Maltose consists of two D-glucose residues connected by a glycosidic bond at positions 1,4.
Sucrose consists of glucose and fructose units connected by a 1,2-glycosidic bond. In sucrose, the hemiacetal hydroxyl groups of both monosaccharide molecules participate in the formation of a glycosidic bond, as a result of which sucrose is a non-reducing sugar.
In plants, sucrose serves as a soluble reserve saccharide, as well as a transport form that is easily transported throughout the plant. Humans are attracted to sucrose with its sweet taste. Sources of sucrose are plants with a high sucrose content, such as sugar beets and sugar cane. Honey is formed by enzymatic hydrolysis of flower nectar in the bee's digestive tract and contains approximately equal amounts of glucose and fructose. In sucrose, both anomeric OH groups of glucose and fructose residues are linked by a glycosidic bond and, therefore, sucrose is not a reducing sugar.
Chemical properties disaccharides:
1) the ability to hydrolyze: under the action of an acid or an appropriate enzyme, the glycosidic bond is broken and two monosaccharides are formed;
2) are oxidized by copper, silver, mercury ions, form osazones and enter into all reactions characteristic of compounds containing free carbonyl groups;
3) disaccharides can be oxidized to carbon dioxide and water. Under the action of yeast enzymes, sucrose and maltose produce ethanol, but lactose remains unchanged.
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 got its name because the first carbohydrates studied by man had 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.
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.
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.
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. And indeed, when heated aqueous solution glucose with freshly precipitated copper (II) hydroxide, 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 a blue precipitate of Cu(OH) 2, a dark blue solution of copper complex compounds is formed.
When some enzymes act on glucose, glucose can be converted into ethanol and carbon dioxide:
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:
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. Based on it, 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 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 C 12 H 22 O 11.
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 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. 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.
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, 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 - 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 are formed by complete hydrolysis large number monosaccharide molecules.
IN general case 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.
Starch is formed from carbon dioxide and water during photosynthesis in the green parts of plants under the influence of energy 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 - 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 products plant origin. However, the roles they play in plant life are different. Cellulose is mainly a building material, in particular, it mainly forms shells plant cells. Starch primarily has a storage and energy function.
All polysaccharides, including starch and cellulose, when completely burned in oxygen, form carbon dioxide and water:
With complete hydrolysis of both starch and cellulose, the same monosaccharide is formed - glucose:
When iodine reacts with anything that contains starch, a blue color appears. When heated blue coloring disappears and appears again when cooled.
During the dry distillation of cellulose, in particular wood, its partial decomposition occurs with the formation of such low molecular weight products 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.
