Carbohydrates and their formulas. What are carbohydrates? What we learned
Carbohydrates aldoses, and ketone – ketosis
Functions of carbohydrates in the body.
The main functions of carbohydrates in the body:
1. Energy function. Carbohydrates are one of the main sources of energy for the body, providing at least 60% of energy costs. For the activity of the brain, kidneys, and blood, almost all energy is supplied through the oxidation of glucose. With the complete breakdown of 1 g of carbohydrates, 17.15 kJ/mol or 4.1 kcal/mol of energy is released.
2. Plastic or structural function. Carbohydrates and their derivatives are found in all cells of the body. In plants, fiber serves as the main supporting material; in the human body, bones and cartilage contain complex carbohydrates. Heteropolysaccharides, for example, hyaluronic acid, are part of cell membranes and cell organelles. Participate in the formation of enzymes, nucleoproteins (ribose, deoxyribose), etc.
3. Protective function. Viscous secretions (mucus) secreted by various glands are rich in carbohydrates or their derivatives (mucopolysaccharides, etc.); they protect the internal walls of the genital organs of the gastrointestinal tract, airways, etc. from mechanical and chemical influences, and the penetration of pathogenic microbes. In response to antigens, the body synthesizes immune bodies, which are glycoproteins. Heparin protects blood from clotting (part of the anticoagulant system) and performs an antilipidemic function.
4. Regulatory function. Human food contains a large amount of fiber, the rough structure of which causes mechanical irritation of the mucous membrane of the stomach and intestines, thus participating in the regulation of the act of peristalsis. Glucose in the blood is involved in regulating osmotic pressure and maintaining homeostasis.
5. Specific functions. Some carbohydrates perform special functions in the body: they participate in nerve impulses, ensuring specificity of blood groups, etc.
Classification of carbohydrates.
Carbohydrates are classified according to the size of their molecules into 3 groups:
1. Monosaccharides– contain 1 carbohydrate molecule (aldose or ketose).
· Trioses (glyceraldehyde, dihydroxyacetone).
Tetroses (erythrose).
· Pentoses (ribose and deoxyribose).
· Hexoses (glucose, fructose, galactose).
2. Oligosaccharides- contain 2-10 monosaccharides.
· Disaccharides (sucrose, maltose, lactose).
· Trisaccharides, etc.
3. Polysaccharides- contain more than 10 monosaccharides.
· Homopolysaccharides – contain the same monosaccharides (starch, fiber, cellulose consist only of glucose).
Heteropolysaccharides - contain monosaccharides different types, their vapor-derived and non-carbohydrate components (heparin, hyaluronic acid, chondroitin sulfates).
Scheme No. 1. K classification of carbohydrates.
Carbohydrates
Monosaccharides Oligosaccharides Polysaccharides
1. Trioses 1. Disaccharides 1. Homopolysaccharides
2. Tetroses 2. Trisaccharides 2. Heteropolysaccharides
3. Pentoses 3. Tetrasaccharides
4. Hexoses
Properties of carbohydrates.
1. Carbohydrates are solid, crystalline white substances, almost all of which taste sweet.
2. Almost all carbohydrates are highly soluble in water, and true solutions are formed. The solubility of carbohydrates depends on mass (the greater the mass, the less soluble the substance, for example, sucrose and starch) and structure (the more branched the structure of the carbohydrate, the worse the solubility in water, for example, starch and fiber).
3. Monosaccharides can be found in two stereoisomeric forms: L-shape (leavus - left) and D-shape (dexter - right). These forms have the same chemical properties, but differ in the location of the hydroxide groups relative to the axis of the molecule and optical activity, i.e. rotate the plane of polarized light that passes through their solution through a certain angle. Moreover, the plane of polarized light rotates by one amount, but in opposite directions. Let's consider the formation of stereoisomers using the example of glyceraldehyde:
SNO SNO
BUT-S-N N-S- HE
CH2OH CH2OH
L – shape D – shape
When producing monosaccharides in laboratory conditions, stereoisomers are formed in a 1:1 ratio; in the body, synthesis occurs under the action of enzymes that strictly distinguish between the L - form and the D - form. Since only D-sugars undergo synthesis and breakdown in the body, L-stereoisomers gradually disappeared in evolution (the determination of sugars in biological fluids using a polarimeter is based on this).
4. Monosaccharides in aqueous solutions can be interconverted; this property is called mutation.
HO-CH2 O=C-H
S O NO-S-N
N N N N-S-OH
S S NO-S-N
BUT HE N HE BUT-S-N
C CH2-OH
HO-CH2
N N HE
BUT HE N N
Betta form.
In aqueous solutions, monomers consisting of 5 or more atoms can be found in cyclic (ring) alpha or beta forms and open (open) forms, and their ratio is 1:1. Oligo- and polysaccharides consist of monomers in cyclic form. In the cyclic form, carbohydrates are stable and moloactive, and in the open form they are highly reactive.
5. Monosaccharides can be reduced to alcohols.
6. In open form, they can interact with proteins, lipids, and nucleotides without the participation of enzymes. These reactions are called glycation. The clinic uses a study of the level of glycosylated hemoglobin or fructosamine to diagnose diabetes mellitus.
7. Monosaccharides can form esters. Highest value has the property of carbohydrates to form esters with phosphoric acid, because in order to be included in the metabolism, the carbohydrate must become a phosphorus ester, for example, glucose is converted into glucose-1-phosphate or glucose-6-phosphate before oxidation.
8. Aldolases have the ability to reduce metals from their oxides to oxide or to a free state in an alkaline environment. This property is used in laboratory practice to detect aldoloses (glucose) in biological fluids. Most often used Trommer's reaction in which aldolose reduces copper oxide to oxide, and itself is oxidized to gluconic acid (1 carbon atom is oxidized).
CuSO4 + NaOH Cu(OH)2 + Na2SO4
Blue
C5H11COH + 2Cu(OH)2 C5H11COOH + H2O + 2CuOH
Brick red color
9. Monosaccharides can be oxidized to acids not only in the Trommer reaction. For example, when the 6th carbon atom of glucose is oxidized in the body, glucuronic acid is formed, which combines with toxic and poorly soluble substances, neutralizes them and converts them into soluble ones, in which form these substances are excreted from the body in the urine.
10.Monosaccharides can combine with each other and form polymers. The connection that arises in this case is called glycosidic, it is formed by the OH group of the first carbon atom of one monosaccharide and the OH group of the fourth (1,4-glycosidic bond) or sixth carbon atom (1,6-glycosidic bond) of another monosaccharide. In addition, an alpha glycosidic bond (between two alpha forms of a carbohydrate) or a beta glycosidic bond (between the alpha and beta forms of a carbohydrate) can be formed.
11.Oligo- and polysaccharides can undergo hydrolysis to form monomers. The reaction occurs at the site of the glycosidic bond, and this process is accelerated in an acidic environment. Enzymes in the human body can distinguish between alpha and beta glycosidic bonds, so starch (has alpha glycosidic bonds) is digested in the intestines, but fiber (has beta glycosidic bonds) is not.
12.Mono- and oligosaccharides can undergo fermentation: alcoholic, lactic acid, citric acid, butyric acid.
general characteristics carbohydrates.
Carbohydrates– organic compounds that are aldehydes or ketones of polyhydric alcohols. Carbohydrates containing an aldehyde group are called aldoses, and ketone – ketosis. Most of them (but not all! For example, rhamnose C6H12O5) correspond to the general formula Cn(H2O)m, which is why they received their historical name - carbohydrates. But there are a number of substances, for example, acetic acid C2H4O2 or CH3COOH, which, although they correspond to the general formula, do not belong to carbohydrates. Currently, another name has been adopted, which most accurately reflects the properties of carbohydrates - glucides (sweet), but the historical name has become so firmly established in life that it continues to be used. Carbohydrates are very widespread in nature, especially in the plant world, where they make up 70-80% of the dry matter mass of cells. In the animal body they account for only about 2% of body weight, but here their role is no less important. The share of their participation in the overall energy balance turns out to be very significant, exceeding almost one and a half times the share of proteins and lipids combined. In the body, carbohydrates are able to be stored as glycogen in the liver and used as needed.
>> Chemistry: Carbohydrates, their classification and significance
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 - C5H10O4. 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, the already known formaldehyde CH20 and acetic acid CH3COOH.
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 are carbohydrates that are not hydrolyzed (not decomposed by 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. d.
In nature, monosaccharides are represented mainly by pentoses and hexoses.
Pentoses include, for example, ribose - C5H10O5 and deoxyribose (ribose from which the oxygen atom has been “removed”) - C5H10O4. They are part of RNA and DNA and determine the first part of the names of nucleic acids.
Hexoses with the general molecular formula C6H1206 include, for example, glucose, fructose, and galactose.
Disaccharides are carbohydrates that hydrolyze to form two monosaccharide molecules, 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 - C12H22O11 - from the resulting formula. Accordingly, we can write the general hydrolysis equation:
С12Н22O11 + Н2O -> 2С6Н12O6
hexose disaccharide
Disaccharides include:
Sucrose (common table sugar), which when hydrolyzed produces 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.;
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;
Lactose (milk sugar), which hydrolyzes to form the molecule glucose and galactose. 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. So the sweetest monosaccharide - fructose - is one and a half 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... - 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: (C6H10O5)n - after all, 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, the role of a reserve of nutrients.
RNA and DNA acids, which contain some carbohydrates (pentoses - ribose and deoxyribose), perform the function of transmitting hereditary information.
Cellulose - construction material plant cells - plays the role of a framework 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 our source of nutrition: we consume grains, which contain starch, or feed them to animals, in whose bodies the starch is converted into proteins and fats. Our most hygienic clothing is made from cellulose or cellulose-based products: cotton and linen, viscose fiber, silk acetate. Wooden houses and furniture are constructed from the same cellulose that forms 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 necessary 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 source of energy on Earth (besides nuclear energy, 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 of photosynthesis, which occurs in the cells of living plants and leads to the synthesis of carbohydrates from water and carbon dioxide. By the way, it is during this transformation that oxygen is formed, without which life on our planet would be impossible.
Photosynthesis
6С02 + 6Н20 ------> С6Н1206 + 602
Carbohydrates (sugar A , saccharides) - organic substances containing a carbonyl group and several hydroxyl groups. The name of the class of compounds comes from the words “carbon hydrates” and was first proposed by K. Schmidt in 1844. The appearance of this name is due to the fact that the first carbohydrates known to science were described by the gross formula C x (H 2 O) y, formally being compounds of carbon and water.
All carbohydrates are made up of individual “units”, which are saccharides. Based on their ability to hydrolyze into monomers, carbohydrates are divided into two groups: simple and complex. Carbohydrates containing one unit are called monosaccharides, two units are disaccharides, two to ten units are oligosaccharides, and more than ten units are polysaccharides. Common monosaccharides are polyoxy-aldehydes (aldoses) or polypoxyketones (ketoses) with a linear chain of carbon atoms (m = 3-9), each of which (except the carbonyl carbon) is linked to a hydroxyl group. The simplest of monosaccharides, glyceraldehyde, contains one asymmetric carbon atom and is known in the form of two optical antipodes (D and L). Monosaccharides quickly increase blood sugar and have a high glycemic index, which is why they are also called fast carbohydrates. They are easily soluble in water and synthesized in green plants. Carbohydrates made up of 3 or more units are called complex carbohydrates. Foods rich in slow carbohydrates gradually increase glucose levels and have low glycemic index, which is why they are also called slow carbohydrates. Complex carbohydrates are products of polycondensation of simple sugars (monosaccharides) and, unlike simple ones, during the process of hydrolytic cleavage they can decompose into monomers, forming hundreds and thousands of monosaccharide molecules
In living organisms, carbohydrates perform following functions:
1. Structural and support functions. Carbohydrates are involved in the construction of various supporting structures. Thus, cellulose is the main structural component of plant cell walls, chitin performs a similar function in fungi, and also provides rigidity to the exoskeleton of arthropods.
2. Protective role in plants. Some plants have protective structures (thorns, prickles, etc.) consisting of cell walls of dead cells.
3. Plastic function. Carbohydrates are part of complex molecules (for example, pentoses (ribose and deoxyribose) are involved in the construction of ATP, DNA and RNA).
4. Energy function. Carbohydrates serve as a source of energy: the oxidation of 1 gram of carbohydrates releases 4.1 kcal of energy and 0.4 g of water.
5. Storage function. Carbohydrates act as reserve nutrients: glycogen in animals, starch and inulin in plants.
6. Osmotic function. Carbohydrates are involved in the regulation of osmotic pressure in the body. Thus, the blood contains 100-110 mg/% glucose, and the osmotic pressure of the blood depends on the concentration of glucose.
7. Receptor function. Oligosaccharides are part of the receptor portion of many cellular receptors or ligand molecules.
18. Monosaccharides: trioses, tetroses, pentoses, hexoses. Structure, open and cyclic forms. Optical isomerism. Chemical properties glucose, fructose. Qualitative reactions to glucose.
Monosaccharides(from Greek monos- the only one, sacchar- sugar) - the simplest carbohydrates that do not hydrolyze to form simpler carbohydrates - are usually colorless, easily soluble in water, poorly soluble in alcohol and completely insoluble in ether, solid transparent organic compounds, one of the main groups of carbohydrates, the simplest form of sugar . Aqueous solutions have a neutral pH. Some monosaccharides have a sweet taste. Monosaccharides contain a carbonyl (aldehyde or ketone) group, so they can be considered as derivatives of polyhydric alcohols. A monosaccharide with a carbonyl group at the end of the chain is an aldehyde and is called aldose. At any other position of the carbonyl group, the monosaccharide is a ketone and is called ketosis. Depending on the length of the carbon chain (from three to ten atoms) there are trioses, tetroses, pentoses, hexoses, heptoses and so on. Among them greatest distribution pentoses and hexoses were obtained in nature. Monosaccharides are the building blocks from which disaccharides, oligosaccharides and polysaccharides are synthesized.
In nature, the most common free form is D-glucose (grape sugar or dextrose, C 6 H 12 O 6) - hexatom sugar ( hexose), a structural unit (monomer) of many polysaccharides (polymers) - disaccharides: (maltose, sucrose and lactose) and polysaccharides (cellulose, starch). Other monosaccharides are mainly known as components of di-, oligo- or polysaccharides and are rarely found in the free state. Natural polysaccharides serve as the main sources of monosaccharides.
Qualitative reaction:
Add a few drops of copper (II) sulfate solution and an alkali solution to the glucose solution. No copper hydroxide precipitate is formed. The solution turns bright blue. In this case, glucose dissolves copper (II) hydroxide and behaves like a polyhydric alcohol, forming complex compound.
Let's heat the solution. Under these conditions, the reaction with copper(II) hydroxide demonstrates the reducing properties of glucose. The color of the solution begins to change. First, a yellow precipitate of Cu 2 O is formed, which over time forms larger red CuO crystals. Glucose is oxidized to gluconic acid.
2HOCH 2 -(CHOH) 4)-CH=O + Cu(OH) 2 2HOCH 2 -(CHOH) 4)-COOH + Cu 2 O↓ + 2H 2 O
19. Oligosaccharides: structure, properties. Disaccharides: maltose, lactose, cellobiose, sucrose. Biological role.
The bulk oligosaccharides is represented by disaccharides, among which sucrose, maltose and lactose play an important role for the animal body. The disaccharide cellobiose is essential for plant life.
Disaccharides (bioses) upon hydrolysis form two identical or different monosaccharides. To establish their structure, it is necessary to know from which monosaccharides the disaccharide is built; in what form, furanose or pyranose, is the monosaccharide in the disaccharide; Which hydroxyls are involved in the bonding of two simple sugar molecules?
Disaccharides can be divided into two groups: non-reducing sugars and reducing sugars.
The first group includes trehalose (mushroom sugar). It is incapable of tautomerism: the ester bond between two glucose residues is formed with the participation of both glucosidic hydroxyls
The second group includes maltose (malt sugar). It is capable of tautomerism, since only one of the glucosidic hydroxyls is used to form the ester bond and, therefore, contains an aldehyde group in a latent form. The reducing disaccharide is capable of mutarotation. It reacts with reagents on the carbonyl group (similar to glucose), is reduced to a polyhydric alcohol, and oxidized to an acid
Hydroxyl groups of disaccharides undergo alkylation and acylation reactions.
Sucrose(beet, cane sugar). Very common in nature. It is obtained from sugar beets (content up to 28% of dry matter) and sugar cane. It is a non-reducing sugar, since the oxygen bridge is formed with the participation of both glycosidic hydroxyl groups
Maltose(from 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. 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
Cellobiose- 4-(β-glucosido)-glucose, a disaccharide consisting of two glucose residues connected by a β-glucosidic bond; basic structural unit of cellulose. Cellobiose is formed during the enzymatic hydrolysis of cellulose by bacteria living in the gastrointestinal tract of ruminants. Cellobiose is then broken down by the bacterial enzyme β-glucosidase (cellobiase) into glucose, which ensures the absorption of the cellulose part of the biomass by ruminants.
Lactose(milk sugar) C12H22O11 - a carbohydrate of the disaccharide group, found in milk. The lactose molecule consists of residues of glucose and galactose molecules. Used for cooking nutrient media, for example in the production of penicillin. Used as an excipient (excipient) in the pharmaceutical industry. From lactose, lactulose is obtained - a valuable drug for the treatment of intestinal disorders, such as constipation.
20. Homopolysaccharides: starch, glycogen, cellulose, dextrins. Structure, properties. Biological role. Qualitative reaction to starch.
Homopolysaccharides ( glycans ), consisting of residues of one monosaccharide, can be hexoses or pentoses, that is, hexose or pentose can be used as a monomer. Depending on the chemical nature of the polysaccharide, glucans (from glucose residues), mannans (from mannose), galactans (from galactose) and other similar compounds are distinguished. The group of homopolysaccharides includes organic compounds of plants (starch, cellulose, pectin substances), animals (glycogen, chitin) and bacterial ( dextrans) origin.
Polysaccharides are necessary for the life of animal and plant organisms. This is one of the main sources of energy in the body, generated as a result of metabolism. Polysaccharides take part in immune processes, provide cell adhesion in tissues, and constitute the bulk of organic matter in the biosphere.
Starch (C 6 H 10 O 5) n - a mixture of two homopolysaccharides: linear - amylose and branched - amylopectin, the monomer of which is alpha-glucose. White amorphous substance, insoluble in cold water, capable of swelling and partially soluble in hot water. Molecular weight 10 5 -10 7 Dalton. Starch, synthesized by different plants in chloroplasts under the influence of light during photosynthesis, differs somewhat in the structure of grains, the degree of polymerization of molecules, the structure of polymer chains and physicochemical properties. As a rule, the amylose content in starch is 10-30%, amylopectin - 70-90%. The amylose molecule contains on average about 1,000 glucose residues linked by alpha-1,4 bonds. Individual linear sections of the amylopectin molecule consist of 20-30 such units, and at the branching points of amylopectin, glucose residues are connected by interchain alpha-1,6 bonds. With partial acid hydrolysis of starch, polysaccharides of a lower degree of polymerization are formed - dextrins ( C 6 H 10 O 5) p, and with complete hydrolysis - glucose.
Glycogen (C 6 H 10 O 5) n - a polysaccharide built from alpha-D-glucose residues - the main reserve polysaccharide of higher animals and humans, found in the form of granules in the cytoplasm of cells in almost all organs and tissues, however, the largest amount accumulates in muscles and liver. The glycogen molecule is built from branching polyglucoside chains, in the linear sequence of which the glucose residues are connected through alpha-1,4 bonds, and at branching points by interchain alpha-1,6 bonds. The empirical formula of glycogen is identical to the formula of starch. In terms of its chemical structure, glycogen is close to amylopectin with more pronounced chain branching, which is why it is sometimes called the inaccurate term “animal starch.” Molecular weight 10 5 -10 8 Dalton and higher. In animal organisms it is a structural and functional analogue of plant polysaccharide - starch. Glycogen forms an energy reserve, which, if necessary, can be quickly mobilized to compensate for a sudden lack of glucose - the strong branching of its molecule leads to the presence of a large number of terminal residues, providing the ability to quickly cleave off the required number of glucose molecules. Unlike triglyceride (fat) storage, glycogen storage is not as large (calories per gram). Only glycogen stored in liver cells (hepatocytes) can be converted into glucose to power the entire body, and hepatocytes are able to accumulate up to 8 percent of their weight in the form of glycogen, which is the highest concentration of any cell type. The total mass of glycogen in the liver of adults can reach 100-120 grams. In muscles, glycogen is broken down into glucose exclusively for local consumption and accumulates in much lower concentrations (no more than 1% of the total muscle mass), however, the total reserve in muscles may exceed the reserve accumulated in hepatocytes.
Cellulose(fiber) - the most common structural polysaccharide flora, consisting of alpha-glucose residues presented in beta-pyranose form. Thus, in a cellulose molecule, beta-glucopyranose monomer units are linearly connected to each other by beta-1,4 bonds. With partial hydrolysis of cellulose, the disaccharide cellobiose is formed, and with complete hydrolysis, D-glucose is formed. In the human gastrointestinal tract, cellulose is not digested, since the set of digestive enzymes does not contain beta-glucosidase. However, the presence of an optimal amount of plant fiber in food contributes to the normal formation of feces. Having great mechanical strength, cellulose acts as a supporting material for plants; for example, in wood its share varies from 50 to 70%, and cotton is almost one hundred percent cellulose.
A qualitative reaction to starch is carried out with an alcohol solution of iodine. When interacting with iodine, starch forms a complex compound of blue-violet color
Plan:
1. Definition of the concept: carbohydrates. Classification.
2. Composition, physical and chemical properties of carbohydrates.
3.Distribution in nature. Receipt. Application.
Carbohydrates – organic compounds containing carbonyl and hydroxyl groups of atoms, having the general formula C n (H 2 O) m, (where n and m>3).
Carbohydrates – substances of primary biochemical importance are widespread in living nature and play an important role in human life. The name carbohydrates arose based on data from the analysis of the first known representatives of this group of compounds. Substances of this group consist of carbon, hydrogen and oxygen, and the ratio of the numbers of hydrogen and oxygen atoms in them is the same as in water, i.e. For every 2 hydrogen atoms there is one oxygen atom. In the last century they were considered to be carbon hydrates. This is where it came from Russian name carbohydrates, proposed in 1844 K. Schmidt. The general formula of carbohydrates, according to what has been said, is C m H 2n O n. When “n” is taken out of brackets, the formula is C m (H 2 O) n, which very clearly reflects the name “carbon - water”. The study of carbohydrates has shown that there are compounds that, in all their properties, should be classified as carbohydrates, although they have a composition that does not exactly correspond to the formula C m H 2p O p. Nevertheless, the ancient name “carbohydrates” has survived to this day, although along with With this name, a newer name is sometimes used to designate the group of substances under consideration - glycides.
Carbohydrates can be divided into three groups : 1) Monosaccharides – carbohydrates that can be hydrolyzed to form simpler carbohydrates. This group includes hexoses (glucose and fructose), as well as pentose (ribose). 2) Oligosaccharides – condensation products of several monosaccharides (for example, sucrose). 3) Polysaccharides – polymer compounds containing big number monosaccharide molecules.
Monosaccharides. Monosaccharides are heterofunctional compounds. Their molecules simultaneously contain both carbonyl (aldehyde or ketone) and several hydroxyl groups, i.e. monosaccharides are polyhydroxycarbonyl compounds - polyhydroxyaldehydes and polyhydroxyketones. Depending on this, monosaccharides are divided into aldoses (the monosaccharide contains an aldehyde group) and ketoses (contains a keto group). For example, glucose is an aldose, and fructose is a ketose.
Receipt. Glucose is predominantly found in free form in nature. It is also a structural unit of many polysaccharides. Other monosaccharides are rare in the free state and are mainly known as components of oligo- and polysaccharides. In nature, glucose is obtained as a result of the photosynthesis reaction: 6CO 2 + 6H 2 O ® C 6 H 12 O 6 (glucose) + 6O 2 Glucose was first obtained in 1811 by the Russian chemist G.E. Kirchhoff from the hydrolysis of starch. Later, the synthesis of monosaccharides from formaldehyde in an alkaline medium was proposed by A.M. Butlerov
Carbohydrates are organic substances whose molecules consist of carbon, hydrogen and oxygen atoms. Moreover, hydrogen and oxygen in them are in the same ratios as in water molecules (1:2)
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 hydrocarbons. Later it was found that there are carbohydrates in the molecules of which there is no 1H: 2O ratio, for example, deoxyribose - C 5 H 10 O 4. Organic compounds are also known, the composition of which matches 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 “hydrocarbons” has taken root and is generally accepted for these substances.
Hydrocarbons, 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 atoms), pentoses(five), hexoses(six), etc.
In nature, monosaccharides are predominantly provided pentoses And hexoses. Pentoses include, for example, ribose C5H10O5 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.
Hexoses having the general molecular formula C 6 H 12 O 6 include, for example, glucose, fructose, galactose.
Disaccharides– carbohydrates that are hydrolyzed 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 10. Accordingly, we can write the general hydrolysis equation:
C 12 H 22 O 10 + H 2 O → 2C 6 H 12 O 6
Disaccharides include:
1) C acharose(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 and 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 the milk of mammals, has a 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(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. After all, it is due to the splitting off of water molecules that di- and polysaccharides are formed in nature.
The role of carbohydrates in nature and their price in human life is extremely important. 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, the role of a reserve of nutrients.
DNA and RNA acids, which contain some carbohydrates (pentose-ribose and deoxyribose), perform the functions of transmitting hereditary information.
Cellulose, the building material of plant cells, plays the role of a framework for the membranes of these cells. Another polysaccharide - chitin- performs a similar role in the cells of some animals: the external skeleton of arthropods (crustaceans), insects, and arachnids is formed.
Carbohydrates ultimately serve as our source of nutrition: we consume grains, which contain starch, or feed them to animals, in whose bodies the starch is converted into fats and proteins. 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 film and photographic film 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 the essentials for life: food, clothing, shelter.
In addition, carbohydrates are involved in the construction of complex proteins, enzymes, and hormones. Carbohydrates also include vital substances such 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 of photosynthesis, which occurs in cells 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:
6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2
Physical properties and occurrence in nature
Glucose And fructose– solid and colorless substances, crystalline substances. Glucose, found in grape juice (hence the name "grape sugar"), along with fructose, which is found in some fruits and vegetables (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). The largest part of it (about 70%) undergoes slow oxidation in tissues with the release of energy and the formation of final products - water and carbon dioxide (glycolysis process):
C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + 2920 kJ
The energy released during glycolysis largely supplies the energy needs of living organisms.
An increase in blood glucose level of 180 mg per 100 ml indicates a violation of carbohydrate metabolism and the development of a dangerous disease - diabetes mellitus.
Structure of the glucose molecule
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 hydroxide (||), the precipitate dissolves and a bright blue solution of the copper compound is obtained, i.e., a qualitative reaction to polyhydric alcohols occurs. Hence , glucose is a polyhydric alcohol. If the resulting solution is heated, a precipitate forms again, this time reddish in color, i.e. there will be a qualitative reaction to aldehydes. Similarly, if a glucose solution is heated with an ammonia solution of silver oxide, a “silver mirror” reaction will occur. Therefore, glucose is both a polyhydric alcohol and an aldehyde - 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 part of the aldehyde group:
The remaining five atoms are associated with hydroxy groups. And finally, taking into account the fact that carbon is tetravalent, we will arrange the hydrogen atoms:
or:
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 molecules of a linear form into a cyclic one can be explained if we remember that carbon atoms can freely rotate around σ-bonds located at an angle of 109 o 28 / while 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:
1) α-form of glucose - hydroxyl groups at the first and second carbon atoms are located on one side of the ring of the molecule;
2) β-forms of glucose - hydroxyl groups are located on opposite sides of the ring of the molecule:
In an aqueous solution of glucose, its three 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 cycle. 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.
Chemical properties of glucose
The chemical properties of glucose, like any organic substance, are determined by its structure. Glucose has a dual function, being both an aldehyde and a 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 hydroxide (ǀǀ), forming a bright blue solution of copper compound (ǀǀ).
Glucose, like alcohols, can form esters.
Reactions of glucose as an aldehyde
1. Oxidation of the aldehyde group. Glucose, as an aldehyde, is capable of oxidizing to the corresponding (gluconic) acid and giving qualitative reactions to aldehydes. Reaction of the “Silver Mirror” (when heated):
CH 2 -OH-(CHOH) 4 -COH + Ag 2 O → CH 2 OH-(CHOH) 4 -COOH + 2Ag↓
Reaction with freshly obtained Cu(OH) 2 when heated:
CH 2 -OH-(CHOH) 4 -COH + 2 Cu(OH) 2 → CH 2 -OH-(CHOH) 4 -COOH + Cu 2 O↓ +H 2 O
2. Reduction of the aldehyde group. Glucose can be reduced to the corresponding alcohol (sorbitol):
CH 2 -OH-(CHOH) 4 -COH + H 2 → CH 2 -OH-(CHOH) 4 - CH 2 -OH
Fermentation reactions
These reactions occur under the influence of special biological catalysts of a protein nature - enzymes.
1.Alcoholic fermentation:
C 6 H 12 O 6 → 2C 2 H 5 OH + 2CO 2
It has long been used by humans to produce 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, ensiling green feed
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