What are carbohydrates or saccharides in biology. Brief description of the properties and ecological and biological role of cellulose (cellulose). A few words about the glycemic index

CARBOHYDRATES

Carbohydrates are part of the cells and tissues of all plant and animal organisms and, by weight, constitute the bulk of organic matter on Earth. The share of carbohydrates accounts for about 80% of the dry matter of plants and about 20% of animals. Plants synthesize carbohydrates from inorganic compounds - carbon dioxide and water (CO 2 and H 2 O).

Carbohydrates are divided into two groups: monosaccharides (monoses) and polysaccharides (polyoses).

Monosaccharides

For a detailed study of the material related to the classification of carbohydrates, isomerism, nomenclature, structure, etc., you need to watch the animated films "Carbohydrates. Genetic D - a series of sugars "and" Construction of Haworth's formulas for D - galactose "(this video is available only on CD - ROM ). The texts accompanying these films are in in full moved to this subsection and follow below.

Carbohydrates. Genetic D-series of sugars

"Carbohydrates are widespread in nature and perform various important functions in living organisms. They supply energy for biological processes, and are also the starting material for the synthesis of other intermediate or final metabolites in the body. Carbohydrates have a general formula C n (H 2 O) m , whence the name of these natural compounds originated.

Carbohydrates are divided into simple sugars or monosaccharides and polymers of these simple sugars or polysaccharides. Among polysaccharides, a group of oligosaccharides should be distinguished, containing from 2 to 10 monosaccharide residues in a molecule. These include, in particular, disaccharides.

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 subdivided into aldoses (the monosaccharide contains an aldehyde group) and ketose (contains a keto group). For example, glucose is aldose and fructose is ketosis.

(glucose (aldose))(fructose (ketose))

Depending on the number of carbon atoms in the molecule, the monosaccharide is called tetrose, pentose, hexose, etc. If we combine the last two types of classification, then glucose is aldohexose, and fructose is ketohexose. Most of the naturally occurring monosaccharides are pentoses and hexoses.

Monosaccharides are depicted in the form of Fisher projection formulas, i.e. in the form of a projection of the tetrahedral model of carbon atoms on the plane of the drawing. The carbon chain is written vertically in them. In aldoses, the aldehyde group is placed at the top, in ketosis, the primary alcohol group adjacent to the carbonyl group. The hydrogen atom and hydroxyl group with an asymmetric carbon atom are located on a horizontal line. An asymmetric carbon atom is located in the resulting crosshairs of two straight lines and is not indicated by a symbol. The numbering of the carbon chain begins with the groups at the top. (Let's define an asymmetric carbon atom: it is a carbon atom bonded to four different atoms or groups.)

Establishing an absolute configuration, i.e. the true arrangement in space of the substituents at the asymmetric carbon atom is very laborious, and until some time it was even an impossible task. It is possible to characterize connections by comparing their configurations with those of reference connections, i.e. define relative configurations.

The relative configuration of monosaccharides is determined by the configuration standard - glyceric aldehyde, which at the end of the last century was arbitrarily assigned certain configurations, designated as D - and L - glyceric aldehydes. The configuration of their asymmetric carbon atoms is compared with the configuration of the asymmetric carbon atom of the monosaccharide farthest from the carbonyl group. In pentoses, such an atom is the fourth carbon atom ( C 4 ), in hexoses - the fifth ( S 5 ), i.e. the penultimate in the chain of carbon atoms. If the configuration of these carbon atoms coincides with the configuration D - glyceraldehyde monosaccharide refers to D - a number. Conversely, if the configuration matches L - glyceraldehyde consider that the monosaccharide belongs to L - row. Symbol D means that the hydroxyl group at the corresponding asymmetric carbon atom in the Fisher projection is located to the right of the vertical line, and the symbol L - that the hydroxyl group is on the left.

Genetic D-series of sugars

The ancestor of aldose is glycerol aldehyde. Consider the genetic relationship of sugars D - rows with D - glycerolic aldehyde.

In organic chemistry, there is a method of increasing the carbon chain of monosaccharides by sequentially introducing a group

between a carbonyl group and an adjacent carbon atom. Introduction of this group into a molecule D - glyceraldehyde leads to two diastereomeric tetroses - D - erythrose and D - threose. This is because a new carbon atom introduced into the monosaccharide chain becomes asymmetric. For the same reason, each obtained tetrose, and then pentose, when one more carbon atom is introduced into their molecule, also gives two diastereomeric sugars. Diastereomers are stereoisomers that differ in the configuration of one or more asymmetric carbon atoms.

This is how D is obtained - a series of sugars from D - glyceraldehyde. As you can see, all the terms of the reduced series, being obtained from D - glycerolic aldehyde, retained its asymmetric carbon atom. This is the last asymmetric carbon atom in the carbon chain of the monosaccharides presented.

Each aldose D -series corresponding to stereoisomer L - a series, the molecules of which relate to each other as an object and an incompatible mirror image. Such stereoisomers are called enantiomers.

In conclusion, it should be noted that the given series of aldohexoses is not limited to the four shown. In the above way from D - ribose and D - xylose, you can get two more pairs of diastereomeric sugars. However, we stopped only at aldohexoses, which are the most widespread in nature. "

Construction of the Howorth formulas for D-galactose

"Simultaneously with the introduction of organic chemistry Concepts about the structure of glucose and other monosaccharides as polyhydroxyaldehydes or polyhydroxyketones described by open-chain formulas, facts that were difficult to explain from the standpoint of such structures began to accumulate in the chemistry of carbohydrates. It turned out that glucose and other monosaccharides exist in the form of cyclic hemiacetals formed as a result of the intramolecular reaction of the corresponding functional groups.

Ordinary hemiacetals are formed by the interaction of molecules of two compounds - an aldehyde and an alcohol. In the course of the reaction, the double bond of the carbonyl group is broken, at the site of the break to which the hydroxyl hydrogen atom and the rest of the alcohol are attached. Cyclic hemiacetals are formed due to the interaction of analogous functional groups belonging to the molecule of one compound - a monosaccharide. The reaction proceeds in the same direction: the double bond of the carbonyl group is broken, the hydrogen atom of the hydroxyl is added to the carbonyl oxygen, and a cycle is formed due to the bonding of carbon atoms of the carbonyl and oxygen of the hydroxyl groups.

The most stable hemiacetals are formed due to hydroxyl groups at the fourth and fifth carbon atoms. The resulting five-membered and six-membered rings are called furanose and pyranose forms of monosaccharides, respectively. These names come from the names of five- and six-membered heterocyclic compounds with an oxygen atom in the cycle - furan and pyran.

Monosaccharides having a cyclic form are conveniently represented by the perspective formulas of Heworth. They represent idealized planar five- and six-membered rings with an oxygen atom in the ring, making it possible to see the relative position of all substituents relative to the plane of the ring.

Consider the construction of the Haworth formulas using the example D - galactose.

To construct the Heworth formulas, it is necessary first of all to number the carbon atoms of the monosaccharide in the Fisher projection and turn it to the right so that the chain of carbon atoms occupies horizontal position... Then the atoms and groups located on the left in the projection formula will be at the top, and those on the right will be below the horizontal line, and upon further transition to cyclic formulas, they will be above and below the cycle plane, respectively. In reality, the carbon chain of a monosaccharide is not located in a straight line, but takes a curved shape in space. As can be seen, the hydroxyl at the fifth carbon atom is significantly distant from the aldehyde group, i.e. occupies a position unfavorable for closing the ring. To bring the functional groups closer together, a part of the molecule is rotated around the valence axis connecting the fourth and fifth carbon atoms counterclockwise by one valence angle. As a result of this rotation, the hydroxyl of the fifth carbon atom approaches the aldehyde group, while the other two substituents also change their position - in particular, the group - CH 2 OH is located above the chain of carbon atoms. At the same time, the aldehyde group is also rotated around s - the bond between the first and second carbon atoms approaches the hydroxyl. The approached functional groups interact with each other according to the above scheme, leading to the formation of a hemiacetal with a six-membered pyranose ring.

The resulting hydroxyl group is called a glycoside group. The formation of a cyclic hemiacetal leads to the appearance of a new asymmetric carbon atom, called anomeric. The result is two diastereomers - a - and b - anomers differing in the configuration of only the first carbon atom.

Different configurations of the anomeric carbon atom arise due to the fact that the aldehyde group, which has a planar configuration, due to rotation around s - connections between lane the second and second carbon atoms refers to the attacking reagent (hydroxyl group) both on one and on the opposite sides of the plane. The hydroxyl group then attacks the carbonyl group on either side of the double bond, leading to hemiacetals with different configurations of the first carbon atom. In other words, the main reason for the simultaneous formation a - and b -anomers consists in the non-stereoselectivity of the discussed reaction.

A - anomer, the configuration of the anomeric center is the same with the configuration of the last asymmetric carbon atom, which determines the D - and L - row, and b - anomera - the opposite. Have aldopentosis and aldohexosis D - a series in the Heworth formulas glycosidic hydroxyl group y a - the anomers are located under the plane, and at b - anomers - above the plane of the cycle.

According to similar rules, the transition to the furanose forms of Hewors is carried out. The only difference is that the hydroxyl of the fourth carbon atom participates in the reaction, and to bring the functional groups closer together, it is necessary to rotate a part of the molecule around s - bonds between the third and fourth carbon atoms and clockwise, as a result of which the fifth and sixth carbon atoms are located under the plane of the cycle.

The names of the cyclic forms of monosaccharides include indications of the configuration of the anomeric center ( a - or b -), to the name of the monosaccharide and its series ( D - or L -) and the size of the cycle (furanose or pyranose). For example, a, D - galactopyranose or b, D - galactofuranose. "

Receiving

In the free form, glucose is mainly found in nature. It is also a structural unit of many polysaccharides. Other free monosaccharides are rare and are generally known as components of oligo- and polysaccharides. In nature, glucose is obtained as a result of the photosynthetic reaction:

6CO 2 + 6H 2 O ® C 6 H 12 O 6 (glucose) + 6O 2

For the first time glucose was obtained in 1811 by the Russian chemist G.E. Kirchhoff during the hydrolysis of starch. Later, the synthesis of monosaccharides from formaldehyde in an alkaline medium was proposed by A.M. Butlerov.

In industry, glucose is obtained by hydrolysis of starch in the presence of sulfuric acid.

(C 6 H 10 O 5) n (starch) + nH 2 O –– H 2 SO 4, t ° ® nC 6 H 12 O 6 (glucose)

Physical properties

Monosaccharides are solids that are readily soluble in water, poorly in alcohol and completely insoluble in ether. Aqueous solutions are neutral to litmus. Most monosaccharides have a sweet taste, but less than beet sugar.

Chemical properties

Monosaccharides exhibit the properties of alcohols and carbonyl compounds.

I. Carbonyl group reactions

1. Oxidation.

a) As with all aldehydes, the oxidation of monosaccharides leads to the corresponding acids. So, when glucose is oxidized with an ammonia solution of silver oxide hydrate, gluconic acid is formed (the "silver mirror" reaction).

b) The reaction of monosaccharides with copper hydroxide when heated also leads to aldonic acids.

c) Stronger oxidizing agents oxidize to the carboxyl group not only the aldehyde, but also the primary alcohol group, leading to dibasic sugar (aldaric) acids. Typically, concentrated nitric acid is used for this oxidation.

2. Recovery.

Reduction of sugars leads to polyhydric alcohols. Hydrogen in the presence of nickel, lithium aluminum hydride, etc. are used as a reducing agent.

3. Despite the similarity of the chemical properties of monosaccharides with aldehydes, glucose does not react with sodium hydrosulfite ( NaHSO 3).

II. Reactions on hydroxyl groups

Reactions at the hydroxyl groups of monosaccharides are carried out, as a rule, in a hemiacetal (cyclic) form.

1. Alkylation (formation of ethers).

On action methyl alcohol in the presence of gaseous hydrogen chloride, the hydrogen atom of the glycosidic hydroxyl is replaced by a methyl group.

When using stronger alkylating agents, which are, for example , methyl iodide or dimethyl sulfate, a similar transformation affects all hydroxyl groups of the monosaccharide.

2. Acylation (formation of esters).

When acetic anhydride acts on glucose, an ester is formed - pentaacetylglucose.

3. Like all polyhydric alcohols, glucose with copper hydroxide ( II ) gives an intense blue coloration (qualitative reaction).

III. Specific reactions

In addition to the above, glucose is also characterized by some specific properties - fermentation processes. Fermentation is the breakdown of sugar molecules under the influence of enzymes (enzymes). Sugars with a multiple of three carbon atoms are fermented. There are many types of fermentation, among which the following are best known:

a) alcoholic fermentation

C 6 H 12 O 6 ® 2CH 3 –CH 2 OH (ethyl alcohol) + 2CO 2

b) lactic acid fermentation

c) butyric fermentation

C 6 H 12 O 6 ® CH 3 –CH 2 –CH 2 –СОOH(butyric acid) + 2 H 2 + 2CO 2

The mentioned types of fermentation caused by microorganisms are of wide practical importance. For example, alcohol is used to produce ethyl alcohol, in winemaking, brewing, etc., and lactic acid is used to produce lactic acid and fermented milk products.

Disaccharides

Disaccharides (biose) hydrolysis form two identical or different monosaccharides. To establish the structure of disaccharides, you need to know: from which monosaccharides it is built, what is the configuration of the anomeric centers of these monosaccharides ( a - or b -), what are the sizes of the cycle (furanose or pyranose) and with the participation of which hydroxyls two monosaccharide molecules are linked.

Disaccharides are classified into two groups: reducing and non-reducing.

Reducing disaccharides include, in particular, maltose (malt sugar) found in malt, i.e. sprouted and then dried and crushed cereal grains.

(maltose)

Maltose is composed of two residues D - glucopyranoses, which are linked by a (1-4) -glycosidic bond, ie the formation of an ether bond involves a glycosidic hydroxyl of one molecule and an alcoholic hydroxyl at the fourth carbon atom of another monosaccharide molecule. An anomeric carbon atom ( C 1 ) participating in the formation of this connection has a - configuration, and the anomeric atom with free glycosidic hydroxyl (marked in red) can have as a - (a - maltose) and b - configuration (b - maltose).

Maltose is a white crystal, readily soluble in water, sweet in taste, but much less than that of sugar (sucrose).

As you can see, maltose contains free glycosidic hydroxyl, as a result of which the ability to open the ring and transfer to the aldehyde form is retained. In this regard, maltose is capable of entering into reactions characteristic of aldehydes, and, in particular, giving a "silver mirror" reaction, therefore it is called a reducing disaccharide. In addition, maltose enters into many of the reactions characteristic of monosaccharides, for example , forms ethers and esters (see. Chemical properties monosaccharides).

Non-reducing disaccharides include sucrose (beet or canesugar). It is found in sugar cane, sugar beets (up to 28% of dry matter), plant juices and fruits. The sucrose molecule is built from a, D - glucopyranose and b, D - fructofuranose.

(sucrose)

In contrast to maltose, the glycosidic bond (1–2) between monosaccharides is formed due to the glycosidic hydroxyls of both molecules, that is, there is no free glycosidic hydroxyl. As a result, the reducing ability of sucrose is absent, it does not give a "silver mirror" reaction, therefore it is referred to as non-reducing disaccharides.

Sucrose is a white crystalline substance, sweet in taste, well soluble in water.

For sucrose, reactions with hydroxyl groups are characteristic. Like all disaccharides, sucrose is converted by acidic or enzymatic hydrolysis into the monosaccharides from which it is composed.

Polysaccharides

The most important polysaccharides are starch and cellulose (fiber). They are built from glucose residues. The general formula of these polysaccharides ( C 6 H 10 O 5) n ... In the formation of polysaccharide molecules, glycosidic (at the C 1 -atom) and alcohol (at the C 4 -atom) hydroxyls usually take part, i.e. a (1-4) -glycosidic bond is formed.

Starch

Starch is a mixture of two polysaccharides built from a, D - glucopyranose links: amylose (10-20%) and amylopectin (80-90%). Starch is formed in plants during photosynthesis and is deposited as a "reserve" carbohydrate in roots, tubers and seeds. For example, grains of rice, wheat, rye and other cereals contain 60-80% starch, potato tubers - 15-20%. A related role in the animal kingdom is played by the polysaccharide glycogen, which is "stored" mainly in the liver.

Starch is a white powder of fine grains, insoluble in cold water. When processing starch warm water it is possible to isolate two fractions: a fraction soluble in warm water and consisting of amylose polysaccharide, and a fraction that only swells in warm water with the formation of a paste and consisting of amylopectin polysaccharide.

Amylose has a linear structure, a, D - glucopyranose residues are linked by (1-4) -glycosidic bonds. The elementary cell of amylose (and starch in general) is represented as follows:

The amylopectin molecule is built in a similar way, but it has branches in the chain, which creates a spatial structure. At the branching points, the monosaccharide residues are linked by (1-6) -glycosidic bonds. There are usually 20-25 glucose residues between the branching points.

(amylopectin)

Starch is easily hydrolyzed: when heated in the presence of sulfuric acid, glucose is formed.

(C 6 H 10 O 5) n (starch) + nH 2 O –– H 2 SO 4, t ° ® nC 6 H 12 O 6 (glucose)

Depending on the reaction conditions, hydrolysis can be carried out stepwise with the formation of intermediate products.

(C 6 H 10 O 5) n (starch) ® (C 6 H 10 O 5) m (dextrins (m< n )) ® xC 12 H 22 O 11 (мальтоза) ® nC 6 H 12 O 6 (глюкоза)

A qualitative reaction to starch is its interaction with iodine - an intense blue coloration is observed. Such staining appears if a drop of iodine solution is placed on a cut of potatoes or a slice of white bread.

Starch does not react with a "silver mirror".

Starch is a valuable food product. To facilitate its assimilation, products containing starch are subjected to heat treatment, i.e. potatoes and cereals are boiled, bread is baked. The processes of dextrinization (the formation of dextrins), carried out in this case, contribute to a better assimilation of starch by the body and subsequent hydrolysis to glucose.

In the food industry, starch is used in the production of sausages, confectionery and culinary products. It is also used to obtain glucose, in the manufacture of paper, textiles, adhesives, medicines, etc.

Cellulose (fiber)

Cellulose is the most abundant plant polysaccharide. It has great mechanical strength and plays the role of a supporting material for plants. Wood contains 50-70% cellulose, cotton is almost pure cellulose.

Like starch, the structural unit of cellulose is D - glucopyranose, the links of which are linked by (1-4) -glycosidic bonds. However, cellulose differs from starch b - the configuration of glycosidic bonds between the cycles and a strictly linear structure.

Cellulose consists of filamentous molecules, which are bundled by hydrogen bonds of hydroxyl groups within the chain, as well as between adjacent chains. It is this packaging of chains that provides high mechanical strength, fibrousness, insolubility in water and chemical inertness, which makes cellulose an ideal material for building cell walls.

b - The glycosidic bond is not destroyed by human digestive enzymes, therefore cellulose cannot serve as food for him, although in a certain amount it is a ballast substance necessary for normal nutrition. In the stomachs of ruminants there are enzymes that break down cellulose, so these animals use fiber as a component of food.

Despite the insolubility of cellulose in water and common organic solvents, it is soluble in Schweitzer's reagent (a solution of copper hydroxide in ammonia), as well as in a concentrated solution of zinc chloride and in concentrated sulfuric acid.

Like starch, cellulose, upon acid hydrolysis, produces glucose.

Cellulose is a polyhydric alcohol; there are three hydroxyl groups per elementary cell of the polymer. In this regard, cellulose is characterized by esterification reactions (formation of esters). Reactions with nitric acid and acetic anhydride are of the greatest practical importance.

Fully esterified fiber is known as pyroxylin, which, when properly processed, turns into smokeless powder. Depending on the nitration conditions, cellulose dinitrate can be obtained, which is called colloxylin in the art. It is also used in the manufacture of gunpowder and solid rocket fuels. In addition, celluloid is made on the basis of colloxylin.

Triacetylcellulose (or cellulose acetate) is a valuable product for the manufacture of incombustible film and acetate silk. For this, cellulose acetate is dissolved in a mixture of dichloromethane and ethanol, and this solution is forced through spinnerets into a stream of warm air. The solvent evaporates and the trickles of the solution turn into the finest strands of acetate silk.

Cellulose does not give a "silver mirror" reaction.

Speaking about the use of cellulose, one cannot but say that a large amount of cellulose is consumed for the manufacture various paper... Paper is a thin layer of fiber, glued and pressed on a special paper machine.

From the above, it is already clear that the use of cellulose by humans is so wide and varied that an independent section can be devoted to the use of products of chemical processing of cellulose.

END OF SECTION

Remember!

What substances are called biological polymers?

These are polymers - high molecular weight compounds that are part of living organisms. Proteins, some carbohydrates, nucleic acids.

What is the importance of carbohydrates in nature?

Fructose, a fruit sugar that is much sweeter than other sugars, is widespread in nature. This monosaccharide gives sweet taste fruits of plants and honey. The most common disaccharide in nature, sucrose, or cane sugar, is composed of glucose and fructose. It is obtained from sugar cane or sugar beet. Starch for plants and glycogen for animals and fungi are a reserve of nutrients and energy. Cellulose and chitin perform structural and protective functions in organisms. Cellulose, or fiber, forms walls plant cells... In terms of total mass, it ranks first on Earth among all organic compounds. In its structure, chitin is very close to cellulose, which forms the basis of the external skeleton of arthropods and is part of the cell wall of fungi.

What are the proteins you know? What functions do they perform?

Hemoglobin - blood protein, transport of gases in the blood

Myosin - muscle protein, muscle contraction

Collagen - protein of tendons, skin, elasticity, extensibility

Casein - milk protein, nutrient

Review questions and assignments

1. What chemical compounds called carbohydrates?

This is an extensive group of natural organic compounds. In animal cells, carbohydrates make up no more than 5% of the dry mass, and in some plant cells (for example, the club or potatoes), their content reaches 90% of the dry matter. Carbohydrates are classified into three main classes: monosaccharides, disaccharides, and polysaccharides.

2. What are mono- and disaccharides? Give examples.

Monosaccharides are composed of monomers, low molecular weight organic substances. Monosaccharides of ribose and deoxyribose are part of nucleic acids... The most common monosaccharide is glucose. Glucose is present in the cells of all organisms and is one of the main sources of energy for animals. If two monosaccharides are combined in one molecule, such a compound is called a disaccharide. The most common disaccharide in nature is sucrose, or cane sugar.

3. What simple carbohydrate serves as a monomer of starch, glycogen, cellulose?

4. What organic compounds do proteins consist of?

Long protein chains are built from just 20 different types amino acids having overall plan structures, but differing from each other in the structure of the radical. When combined, the amino acid molecules form the so-called peptide bonds. The two polypeptide chains that make up the pancreatic hormone, insulin, contain 21 and 30 amino acid residues. These are some of the shortest "words" in the protein "language". Myoglobin, a protein that binds oxygen in muscle tissue, consists of 153 amino acids. Collagen protein, which forms the basis of collagen fibers of connective tissue and ensures its strength, consists of three polypeptide chains, each of which contains about 1000 amino acid residues.

5. How are secondary and tertiary protein structures formed?

Twisting in the form of a spiral, the protein thread acquires a higher level of organization - a secondary structure. Finally, the helix of the polypeptide folds to form a ball (globule). It is this tertiary structure of the protein that is its biologically active form, which has individual specificity. However, for a number of proteins, the tertiary structure is not final. The secondary structure is a coiled polypeptide chain. For a more lasting interaction during secondary structure, intramolecular interaction occurs with the help of –S – S– sulfide bridges between the turns of the helix. This ensures the strength of this structure. Tertiary structure is a secondary spiral structure twisted into globules - compact lumps. These structures provide maximum strength and more abundance in cells compared to other organic molecules.

6. What are the known functions of proteins? How can you explain the existing variety of functions of proteins?

One of the main functions of proteins is enzymatic. Enzymes are catalytic proteins that speed up chemical reactions in living organisms. An enzymatic reaction is a chemical reaction that only occurs when an enzyme is present. Without an enzyme, not one reaction occurs in living organisms. The work of enzymes is strictly specific, each enzyme has its own substrate, which it breaks down. The enzyme approaches its substrate like a “key to a lock”. Thus, the urease enzyme regulates the breakdown of urea, the amylase enzyme regulates starch, and protease enzymes regulate proteins. Therefore, the expression "action specificity" is used for enzymes.

Proteins also perform various other functions in organisms: structural, transport, motor, regulatory, protective, energy. The functions of proteins are quite numerous, since they underlie the diversity of the manifestation of life. This is a component of biological membranes, the transfer of nutrients, for example, hemoglobin, muscle work, hormonal function, the body's defense - the work of antigens and antibodies, and other important functions in the body.

7. What is protein denaturation? What can cause denaturation?

Denaturation is a violation of the tertiary spatial structure of protein molecules under the influence of various physical, chemical, mechanical and other factors. Physical factors are temperature, radiation, Chemical factors are the effect on proteins of any chemical substances: solvents, acids, alkalis, concentrated substances, etc. Mechanical factors - shaking, pressure, stretching, twisting, etc.

Think! Remember!

1. Using the knowledge gained from the study of plant biology, explain why plant organisms have much more carbohydrates than animals.

Since photosynthesis is the basis of life - plant nutrition, this is the process of the formation of complex organic compounds of carbohydrates from simpler inorganic carbon dioxide and water. The main carbohydrate synthesized by plants for air nutrition is glucose, it can also be starch.

2. What diseases can a violation of the conversion of carbohydrates in the human body lead to?

Regulation of carbohydrate metabolism is mainly carried out by hormones and central nervous system... Glucocorticosteroids (cortisone, hydrocortisone) inhibit the rate of glucose transport into tissue cells, insulin accelerates it; adrenaline stimulates the process of sugar formation from glycogen in the liver. Kore large hemispheres also plays a role in the regulation of carbohydrate metabolism, since psychogenic factors increase the formation of sugar in the liver and cause hyperglycemia.

The state of carbohydrate metabolism can be judged by the content of sugar in the blood (normally 70-120 mg%). With a sugar load, this value increases, but then quickly reaches the norm. Disorders of carbohydrate metabolism occur in various diseases. So, with a lack of insulin, diabetes mellitus occurs.

A decrease in the activity of one of the enzymes of carbohydrate metabolism - muscle phosphorylase - leads to muscular dystrophy.

3. It is known that if there is no protein in the diet, even despite the sufficient caloric content of food, animals stop growing, the composition of the blood changes, and other pathological phenomena occur. What is the reason for such violations?

There are only 20 different types of amino acids in the body, which have a general structure plan, but differ from each other in the structure of the radical, they form different protein molecules, if you do not use proteins, for example, irreplaceable ones, which cannot be formed in the body on their own, but must be consumed with food ... Thus, if there are no proteins, many protein molecules will not be able to form inside the body itself and pathological changes will occur. Growth is controlled by growth bone cells, the main cell of any cell is protein; hemoglobin is the main protein in the blood, which ensures the transport of the main gases in the body (oxygen, carbon dioxide).

4. Explain the difficulties encountered in organ transplantation based on knowledge of the specificity of protein molecules in each organism.

Proteins are genetic material, since they contain the structure of the DNA and RNA of the organism. Thus, proteins have genetic characteristics in each organism, the information of genes is encrypted in them, this is the difficulty in transplanting from alien (unrelated) organisms, since they have different genes, and therefore proteins.

All carbohydrates are made up of individual "units" which are saccharides. By ability tohydrolysisonmonomerscarbohydrates are dividedinto two groups: simple and complex. Carbohydrates containing one unit are calledmonosaccharides, two units -disaccharides, from two to ten units -oligosaccharides, and more than ten -polysaccharides.

Monosaccharides quickly increase blood sugar, and have a high glycemic index, which is why they are also called fast carbohydrates. They dissolve easily in water and are synthesized in green plants.

Carbohydrates that are 3 or more units are calledcomplex. Foods rich in complex carbohydrates gradually increase glucose and are low glycemic index, which is why they are also called slow carbohydrates. Complex carbohydrates are polycondensation products of simple sugars (monosaccharides) and, unlike simple ones, in the process of hydrolytic cleavage, they are capable of decomposing into monomers, with the formation of hundreds and thousandsmoleculesmonosaccharides.

Stereoisomerism of monosaccharides: isomerglyceraldehydein which, when the model is projected onto the plane, the OH group at the asymmetric carbon atom is located on the right side, it is considered to be D-glyceraldehyde, and the specular reflection is considered to be L-glyceraldehyde. All isomers of monosaccharides are divided into D- and L- forms according to the similarity of the location of the OH group at the last asymmetric carbon atom near CH 2 OH groups (ketosis contains one less asymmetric carbon atom than aldoses with the same number of carbon atoms). Naturalhexoses – glucose, fructose, mannoseandgalactose- refer to D-series compounds by stereochemical configuration.

Polysaccharides – common name class of complex high molecular weight carbohydrates,moleculeswhich consist of tens, hundreds or thousandsmonomers – monosaccharides... From point of view general principles structure in the group of polysaccharides, it is possible to distinguish between homopolysaccharides synthesized from monosaccharide units of the same type and heteropolysaccharides, which are characterized by the presence of two or more types of monomeric residues.

https :// ru . wikipedia . org / wiki /Carbohydrates

1.6. Lipids - nomenclature and structure. Lipid polymorphism.

Lipids - a wide group of natural organic compounds, including fats and fat-like substances. Simple lipid molecules are composed of alcohol andfatty acids, complex - from alcohol, high molecular weight fatty acids and other components.

Lipid classification

Simple lipids Are lipids that include carbon (C), hydrogen (H) and oxygen (O) in their structure.

Complex lipids - these are lipids that include in their structure, in addition to carbon (C), hydrogen (H) and oxygen (O), and others chemical elements... Most often: phosphorus (P), sulfur (S), nitrogen (N).

https:// ru. wikipedia. org/ wiki/Lipids

Literature:

1) Cherkasova L.S., Merezhinsky M.F., Exchange of fats and lipids, Minsk, 1961;

2) Markman A.L., Lipid Chemistry, V. 12, Tash., 1963 - 70;

3) Tyutyunnikov B.N., Chemistry of fats, M., 1966;

4) Mahler G., Kordes K., Fundamentals of Biological Chemistry, trans. from English, M., 1970.

1.7. Biological membranes. Forms of lipid aggregation. The concept of a liquid-crystalline state. Lateral diffusion and flip flop.

Membranes delimit the cytoplasm from the environment, and also form the membranes of the nuclei, mitochondria and plastids. They form a labyrinth of endo-plasma reticulum and flattened stacked vesicles that make up the Golgi complex. Membranes form lysosomes, large and small vacuoles of plant and fungal cells, pulsating vacuoles of protozoa. All these structures are compartments (compartments) intended for certain specialized processes and cycles. Therefore, without membranes, the existence of a cell is impossible.

Membrane structure diagram: a - three-dimensional model; b - plane image;

1 - proteins adjacent to the lipid layer (A), immersed in it (B) or penetrating it through and through (C); 2 - layers of lipid molecules; 3 - glycoproteins; 4 - glycolipids; 5 - hydrophilic canal that functions as a pore.

The functions of biological membranes are as follows:

1) They delimit the contents of the cell from the external environment and the contents of the organelles from the cytoplasm.

2) Provide the transport of substances into and out of the cell, from the cytoplasm to the organelles and vice versa.

3) They play the role of receptors (receiving and converting signals from the environment, recognizing cell substances, etc.).

4) Are catalysts (providing near-membrane chemical processes).

5) Participate in the transformation of energy.

http:// sbio. info/ page. php? id=15

Lateral diffusion Is a chaotic thermal movement of lipid and protein molecules in the membrane plane. With lateral diffusion, adjacent lipid molecules abruptly change places, and as a result of such successive hops from one place to another, the molecule moves along the membrane surface.

Movement of molecules over the surface of the cell membrane during time t was determined experimentally by the method of fluorescent labels - fluorescent molecular groups. Fluorescent labels make molecules fluorescent, whose movement along the cell surface can be studied, for example, by examining under a microscope the rate at which a fluorescent spot created by such molecules spreads over the cell surface.

Flip flop Is the diffusion of membrane phospholipid molecules across the membrane.

The rate of jumping of molecules from one membrane surface to another (flip-flop) was determined by the method of spin labels in experiments on model lipid membranes - liposomes.

Some of the phospholipid molecules from which liposomes were formed were labeled with spin labels attached to them. Liposomes were exposed to ascorbic acid, as a result of which the unpaired electrons on the molecules disappeared: paramagnetic molecules became diamagnetic, which could be detected by a decrease in the area under the EPR spectrum curve.

Thus, jumps of molecules from one bilayer surface to another (flip-flop) occur much more slowly than jumps during lateral diffusion. The average time after which a phospholipid molecule performs a flip-flop (T ~ 1 hour) is tens of billions of times longer than the average time for a molecule to jump from one place to an adjacent one in the membrane plane.

The concept of the liquid-crystalline state

A solid body can be likecrystalline andamorphous. In the first case, there is long-range order in the arrangement of particles at distances much larger than intermolecular distances (crystal lattice). In the second, there is no long-range order in the arrangement of atoms and molecules.

The difference between an amorphous body and a liquid is not in the presence or absence of long-range order, but in the nature of particle motion. Molecules of a liquid and a solid perform oscillatory (sometimes rotational) movements around the equilibrium position. After some average time ("time sedentary life») The molecules jump to another equilibrium position. The difference is that the “sedentary life” in a liquid is much shorter than in a solid state.

Lipid bilayer membranes under physiological conditions are liquid, the "sedentary life" of a phospholipid molecule in the membrane is 10 −7 – 10 −8 with.

Molecules in the membrane are not randomly arranged; long-range order is observed in their arrangement. Phospholipid molecules are in a double layer, and their hydrophobic tails are roughly parallel to each other. There is order in the orientation of polar hydrophilic heads.

The physiological state in which there is a long-range order in the mutual orientation and arrangement of molecules, but the state of aggregation is liquid, is calledliquid crystal state. Liquid crystals can form not in all substances, but in substances from "long molecules" (the transverse dimensions of which are smaller than the longitudinal ones). Various liquid crystal structures can exist: nematic (filamentary), when long molecules are oriented parallel to each other; smectic - molecules are parallel to each other and arranged in layers; cholestic - the molecules are located parallel to each other in the same plane, but in different planes the orientations of the molecules are different.

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Literature: ON. Lemeza, L.V. Kamlyuk, N.D. Lisov. "A guide to biology for university applicants."

1.8. Nucleic acids. Heterocyclic bases, nucleosides, nucleotides, nomenclature. The spatial structure of nucleic acids - DNA, RNA (tRNA, rRNA, mRNA). Ribosomes and cell nucleus. Methods for determining the primary and secondary structure of nucleic acids (sequencing, hybridization).

Nucleic acids - phosphorus-containing biopolymers of living organisms, providing storage and transmission of hereditary information.

Nucleic acids are biopolymers. Their macromolecules are composed of repeating units that are represented by nucleotides. And they were logically namedpolynucleotides. One of the main characteristics of nucleic acids is their nucleotide composition. The composition of the nucleotide (structural unit of nucleic acids) includesthree components:

– Nitrous base. It can be pyrimidine and purine. Nucleic acids contain 4 different types of bases: two of them belong to the purine class and two to the pyrimidine class.

– The remainder of the phosphoric acid.

– The monosaccharide is ribose or 2-deoxyribose. Sugar, which is part of the nucleotide, contains five carbon atoms, i.e. is a pentose. Depending on the type of pentose present in the nucleotide, two types of nucleic acids are distinguished.- ribonucleic acids (RNA), which contain ribose, anddeoxyribonucleic acids (DNA), containing disoxyribose.

Nucleotide in essence, it is a phosphoric ester of a nucleoside.The composition of the nucleoside includes two components: a monosaccharide (ribose or deoxyribose) and a nitrogenous base.

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Nitrous bases – heterocyclicorganic compounds, derivativespyrimidineandpurineincluded innucleic acids... For abbreviations, use capital Latin letters. Nitrogenous bases includeadenine(A),guanine(G),cytosine(C), which are part of both DNA and RNA.Timin(T) is part of only DNA, anduracil(U) is found only in RNA.

In this material, we have to completely deal with such information as:

• What are carbohydrates?
• What are the “right” carbohydrate sources and how to include them in your diet?
• What is the glycemic index?
• How is the breakdown of carbohydrates?
• After processing, do they really turn into a fat layer on the body?

We start with theory

Carbohydrates (also called saccharides) are organic compounds of natural origin, which are mostly found in the vegetable world. They are formed in plants during photosynthesis and are found in almost any plant food. The composition of carbohydrates includes carbon, oxygen and hydrogen. V human body carbohydrates come mainly from food (found in cereals, fruits, vegetables, legumes and other foods), and are also produced from some acids and fats.

Carbohydrates are not only the main source of human energy, but they also perform a number of other functions:

Of course, if you think of carbohydrates solely in terms of building muscle mass, then they act as an affordable source of energy. In general, in the body, the energy reserve is contained in fat depots (about 80%), in proteins - 18%, and carbohydrates account for only 2%.

Important: carbohydrates accumulate in the human body in conjunction with water (1 g of carbohydrates requires 4 g of water). But fatty deposits do not need water, so it is easier to accumulate them, and then use them as a backup source of energy.

All carbohydrates can be divided into two types (see image): simple (monosaccharides and disaccharides) and complex (oligosaccharides, polysaccharides, fiber).

Monosaccharides (simple carbohydrates)

They contain one sugar group, for example: glucose, fructor, galactose. And now about each in more detail.

Glucose- is the main "fuel" of the human body and supplies energy to the brain. She also takes part in the formation of glycogen, and for the normal functioning of erythrocytes, about 40 g of glucose per day are needed. Together with food, a person consumes about 18g, and the daily dose is 140g (necessary for correct work central nervous system).

A natural question arises, where does the body then draws the necessary amount of glucose for its work? Everything in order. In the human body, everything is thought out to the smallest detail, and glucose reserves are stored in the form of glycogen compounds. And as soon as the body requires "refueling", some of the molecules are broken down and used.

The blood glucose level is a relatively constant value and is regulated by a special hormone (insulin). As soon as a person consumes a lot of carbohydrates, and the glucose level rises sharply, he takes insulin for work, which lowers the amount to required level... And you don't have to worry about a portion of eaten carbohydrates, as much as the body requires (due to the work of insulin) will enter the bloodstream.

Foods rich in glucose include:

• Grapes - 7.8%;
• Cherries and cherries - 5.5%;
• Raspberry - 3.9%;
• Pumpkin - 2.6%;
• Carrots - 2.5%.

Important: the sweetness of glucose reaches 74 units, and sucrose - 100 units.

Fructose is a naturally occurring sugar found in fruits and vegetables. But it is important to remember that consuming large amounts of fructose is not only not beneficial, but also harmful. Huge portions of fructose enter the intestines and cause increased insulin secretion. And if now you are not engaged in active physical activity, then all glucose is stored in the form of body fat. The main sources of fructose are foods such as:

• Grapes and apples;
• Melons and pears;

Fructose is much sweeter than glucose (2.5 times), but despite this, it does not destroy teeth and does not cause caries. Free galactose is practically not found anywhere, but most often it is a component of milk sugar called lactose.

Disaccharides (simple carbohydrates)

Disaccharides always contain simple sugars (in the amount of 2 molecules) and one glucose molecule (sucrose, maltose, lactose). Let's take a closer look at each of them.

Sucrose is composed of fructose and glucose molecules. Most often, it is found in everyday life in the form of ordinary sugar, which we use during cooking and just put in tea. So it is this sugar that is deposited in the layer of subcutaneous fat, so you should not get carried away with the amount consumed, even in tea. The main sources of sucrose are sugar and beets, plums and jam, ice cream and honey.

Maltose is a compound of 2 glucose molecules, which are found in large quantities in products such as: beer, young, honey, molasses, any confectionery... Lactose is mainly found in dairy products, and in the intestine it is broken down and converted into galactose and glucose. Most of all lactose is found in milk, cottage cheese, kefir.

So we figured out with simple carbohydrates, it's time to move on to complex ones.

Complex carbohydrates

All complex carbohydrates can be divided into two categories:

• Those that are digested (starch);
• Those that are not digested (fiber).

Starch is the main source of carbohydrates and is at the heart of the food pyramid. Most of all it is found in cereals, legumes and potatoes. The main sources of starch are buckwheat, oatmeal, pearl barley, as well as lentils and peas.

Important: Use baked potatoes in your diet that contain a large number of potassium and other minerals. This is especially important as the starch molecules swell during cooking and reduce the nutritional value of the product. That is, in the beginning, the product may contain 70%, and after cooking, 20% may not remain.

Fiber plays a very important role in the work of the human body. With its help, the work of the intestines and the entire gastrointestinal tract as a whole is normalized. It also creates the necessary breeding ground for the development of important microorganisms in the intestine. The body practically does not digest fiber, but it provides a feeling of quick satiety. Vegetables, fruits, and wholemeal breads (which are high in fiber) are used to prevent obesity (because they quickly make you feel full).

Now let's move on to other processes related to carbohydrates.

How the body stores carbohydrates

The reserves of carbohydrates in the human body are located in the muscles (2/3 of the total amount), and the rest in the liver. The total supply is only enough for 12-18 hours. And if you do not replenish reserves, then the body begins to experience a shortage, and synthesizes the substances it needs from proteins and intermediate metabolic products. As a result, the stores of glycogen in the liver can be significantly depleted, which will cause the deposition of fat in its cells.

By mistake, many people who lose weight, for a more "effective" result, significantly cut the amount of carbohydrates consumed, hoping that the body will use up fat reserves. In fact, proteins are the first to be "consumed", and only then are fat deposits. It is important to remember that large amounts of carbohydrates will lead to quick dial masses only if they enter the body in large portions (and they must also be quickly absorbed).

Carbohydrate metabolism

Carbohydrate metabolism depends on how much glucose is in circulatory system and is divided into three types of processes:

• Glycolysis - glucose is broken down, as well as other sugars, after which the required amount of energy is produced;
• Glycogenesis - glycogen and glucose are synthesized;
• Glyconeogenesis - in the process of splitting glycerol, amino acids and lactic acid in the liver and kidneys, the necessary glucose is formed.

In the early morning (after waking up), blood glucose reserves drop sharply for a simple reason - the lack of nutrition in the form of fruits, vegetables and other foods that contain glucose. The body also feeds on its own, 75% of which is carried out in the process of glycolysis, and 25% falls on glyconeogenesis. That is, it turns out that the morning time is considered optimal in order to use the available fat reserves as a source of energy. And if you add light cardio loads to this, you can get rid of a few extra pounds.

Now we are finally moving on to the practical part of the question, namely: what carbohydrates are good for athletes, as well as in what optimal quantities they should be consumed.

Carbohydrates and bodybuilding: who, what, how much

A few words about the glycemic index

When we talk about carbohydrates, one cannot fail to mention such a term as "glycemic index" - that is, the rate at which carbohydrates are absorbed. It is an indicator of how fast a product is able to increase the amount of glucose in the blood. The highest glycemic index is 100 and refers to glucose itself. The body, after consuming food with a high glycemic index, begins to store calories and deposits fatty deposits under the skin. So all products with high GI values ​​are faithful companions in order to rapidly gain extra pounds.

Products with a low GI index are a source of carbohydrates, which for a long time, constantly and evenly feeds the body and ensures a systematic flow of glucose into the blood. With their help, you can maximally adjust the body for a long-term feeling of satiety, as well as prepare the body for active physical activity in the gym. There are even special tables for food that indicate the glycemic index (see image).

The body's need for carbohydrates and the right sources

So the moment has come when we will figure out how many carbohydrates you need to consume in grams. It is logical to assume that bodybuilding is a very energy-intensive process. Therefore, if you want the quality of training not to suffer, you need to provide your body with a sufficient amount of "slow" carbohydrates (about 60-65%).

• The duration of the workout;
• Load intensity;
• The metabolic rate in the body.

It is important to remember that you do not need to go below the 100 g per day bar, and also have 25-30 g in stock, which are fiber.

Remember also that a common person consumes about 250-300 g of carbohydrates per day. For those who train in a weighted gym, the daily rate increases and reaches 450-550g. But they still need to be used correctly, and at the right time (in the morning). Why do you need to do this? The scheme is simple: in the first half of the day (after sleep), the body stores carbohydrates in order to "feed" their body with them (which is needed for muscle glycogen). The remaining time (after 12 hours), carbohydrates are safely deposited in the form of a fat layer. So stick to the rule: more in the morning, less in the evening. After training, it is important to adhere to the rules of the protein-carbohydrate window.

Important: protein-carbohydrate window - a short period of time during which the human body becomes able to assimilate an increased amount of nutrients (spent on restoring energy and muscle reserves).

It has already become clear that the body needs to constantly receive nutrition in the form of "correct" carbohydrates. And to understand the quantitative values, consider the table below.

The concept of "correct" carbohydrates includes those substances that have a high biological value (amount of carbohydrates / 100 g. Of the product) and a low glycemic index. These include products such as:

• Baked or boiled potatoes in their skins;
• Various cereals (oatmeal, pearl barley, buckwheat, wheat);
• Bakery products made from wholemeal flour and bran;
• Pasta (from durum wheat);
• Fruits that are low in fructose and glucose (grapefruit, apples, pomelo);
• Fibrous and starchy vegetables (turnips and carrots, pumpkin and zucchini).

It is these foods that must be present in your diet.

Ideal time to consume carbohydrates

The best time to consume your carbohydrate dose is:

• Time after morning sleep;
• Before training;
• After workout;
• During training.

Moreover, each of the periods is important and there is no more or less suitable one among them. Also in the morning, in addition to healthy and slow carbohydrates, you can eat something sweet (a small amount of fast carbohydrates).

Before you go to workout (2-3 hours), you need to feed the body with carbohydrates with average glycemic index values. For example, eat pasta or corn / rice porridge. This will provide the necessary supply of energy for the muscles and brain.

During classes in the hall, you can use intermediate meals, that is, consume drinks with carbohydrates (200 ml each 20 minutes). This will have a double benefit:

• Replenishment of fluid reserves in the body;
• Replenishment of muscle glycogen depot.

After training, it is best to take a rich protein-carbohydrate cocktail, and after 1-1.5 hours after completing the training, eat a hearty meal. Buckwheat or pearl barley porridge or potatoes are best suited for this.

Now is the time to talk about the role carbohydrates play in muscle building.

Do carbohydrates help you build muscle?

It is generally accepted that only proteins are building material for muscles and only they need to be consumed in order to build muscle mass. In fact, this is not entirely true. What's more, carbohydrates not only help build muscle, they can help fight extra pounds... But all this is possible only if they are consumed correctly.

Important: In order for the body to appear 0.5 kg of muscle, you need to burn 2500 calories. Naturally, proteins cannot provide such an amount, therefore carbohydrates come to the rescue. They provide the necessary energy to the body and protect proteins from destruction, allowing them to act as building blocks for muscles. Also, carbohydrates contribute to the rapid burning of fat. This is due to the fact that a sufficient amount of carbohydrates contributes to the consumption of fat cells, which are constantly burned during exercise.

It should also be remembered that depending on the level of training of the athlete, his muscles can store a greater store of glycogen. To build muscle mass, you need to take 7g of carbohydrates for every pound of body. Do not forget that if you began to take more carbohydrates, then the intensity of the load should also be increased.

So that you already fully understand all the characteristics of nutrients and understand what and how much you need to consume (depending on age, physical activity and gender), carefully study the table below.

• Group 1 - predominantly mental / sedentary work.
• Group 2 - service sector / active sedentary work.
• Group 3 - work of medium severity - locksmiths, machine operators.
• Group 4 - hard work - builders, oil workers, metallurgists.
• Group 5 - very hard work - miners, steelworkers, loaders, athletes during the competition period.

And now the results

In order for the effectiveness of training to always be at its best, and you have a lot of strength and energy for this, it is important to adhere to certain rules:

• The diet should consist of 65-70% carbohydrates, and they should be "correct" with a low glycemic index;
• Before training, you need to consume foods with an average GI, after exercise - with a low GI;
• Breakfast should be as rich as possible, and in the morning you need to eat most daily intake of carbohydrates;
• When buying food, check the glycemic index table and choose those with medium and low GI values;
• If you want to eat foods with high GI values ​​(honey, jam, sugar), it is better to do it in the morning;
• Include more cereals in your diet and consume them regularly;
• Remember, carbohydrates are helpers of proteins in the process of building muscle mass, so if there is no tangible result for a long time, then you need to revise your diet and the amount of carbohydrates consumed;
• Eat non-sweet fruits and fiber;
• Remember about wholemeal bread and potatoes baked in skins;
• Constantly improve your health and bodybuilding knowledge.

If you stick to these simple rules, then your energy will noticeably increase, and the effectiveness of your workouts will increase.

Instead of a conclusion

As a result, I would like to say that you need to approach training intelligently and competently. That is, you need to remember not only what exercises, how to do them and how many approaches. But also pay attention to nutrition, remember proteins, fats, carbohydrates and water. After all, it is the combination of correct workouts and high-quality nutrition that will allow you to quickly achieve your intended goal - a beautiful athletic body. Products should be not just a set, but a means to achieve the desired result. So think not only in the gym, but also while eating.

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§ 1. CLASSIFICATION AND FUNCTIONS OF CARBOHYDRATES

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

Then glucose and other simple carbohydrates are converted into more complex carbohydrates, such as starch and cellulose. Plants use these carbohydrates to release energy during respiration. This process is essentially the opposite of the process of photosynthesis:

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

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

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

Classification of carbohydrates

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

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

Pentoses and hexoses are most common in nature.

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

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

Functions of carbohydrates

The biological functions of polysaccharides are very diverse.

Energy and storage function

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

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

which with heavy physical activity builds up in the muscles and causes pain.

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

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

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

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

Man learned to use not only alcoholic fermentation, but also found application of lactic acid fermentation, for example, for obtaining lactic acid products and pickling vegetables.

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

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

Structural, supporting and protective functions

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

The protective function is performed by heparin... This carbohydrate, as a blood clotting inhibitor, prevents blood clots. It is found in the blood and connective tissue of mammals. The bacterial cell walls formed by polysaccharides are held together by short amino acid chains and protect bacterial cells from adverse effects. Carbohydrates are involved in crustaceans and insects in the construction of the external skeleton, which performs a protective function.

Regulatory function

Fiber enhances intestinal motility, thereby improving digestion.

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

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