carbohydrates substances are called with the general formula C n (H 2 O) m, where n and m can have different values. The name "carbohydrates" reflects the fact that hydrogen and oxygen are present in the molecules of these substances in the same ratio as in the water molecule. In addition to carbon, hydrogen and oxygen, carbohydrate derivatives may contain other elements, such as nitrogen.
Carbohydrates are one of the main groups of organic substances of cells. They are the primary products of photosynthesis and the initial products of the biosynthesis of other organic substances in plants (organic acids, alcohols, amino acids, etc.), and are also found in the cells of all other organisms. In an animal cell, the content of carbohydrates is in the range of 1-2%, in plant cells it can reach in some cases 85-90% of the dry matter mass.
There are three groups of carbohydrates:
- monosaccharides or simple sugars;
- oligosaccharides - compounds consisting of 2-10 consecutively connected molecules of simple sugars (for example, disaccharides, trisaccharides, etc.).
- polysaccharides consist of more than 10 molecules of simple sugars or their derivatives (starch, glycogen, cellulose, chitin).
Monosaccharides (simple sugars)
Depending on the length of the carbon skeleton (the number of carbon atoms), monosaccharides are divided into trioses (C 3), tetroses (C 4), pentoses (C 5), hexoses (C 6), heptoses (C 7).
Monosaccharide molecules are either aldehyde alcohols (aldoses) or keto alcohols (ketoses). The chemical properties of these substances are determined primarily by the aldehyde or ketone groups that make up their molecules.
Monosaccharides are highly soluble in water, sweet in taste.
When dissolved in water, monosaccharides, starting with pentoses, acquire a ring shape.
The cyclic structures of pentoses and hexoses are their usual forms: at any given moment, only a small fraction of the molecules exist in the form of an "open chain". The composition of oligo- and polysaccharides also includes cyclic forms of monosaccharides.
In addition to sugars, in which all carbon atoms are bonded to oxygen atoms, there are partially reduced sugars, the most important of which is deoxyribose.
Oligosaccharides
Upon hydrolysis, oligosaccharides form several molecules of simple sugars. In oligosaccharides, simple sugar molecules are connected by so-called glycosidic bonds, connecting the carbon atom of one molecule through oxygen to the carbon atom of another molecule.
The most important oligosaccharides are maltose (malt sugar), lactose (milk sugar) and sucrose (cane or beet sugar). These sugars are also called disaccharides. By their properties, disaccharides are blocks to monosaccharides. They dissolve well in water and have a sweet taste.
Polysaccharides
These are high-molecular (up to 10,000,000 Da) polymeric biomolecules consisting of a large number of monomers - simple sugars and their derivatives.
Polysaccharides may be composed of monosaccharides of the same or different types. In the first case, they are called homopolysaccharides (starch, cellulose, chitin, etc.), in the second - heteropolysaccharides (heparin). All polysaccharides are insoluble in water and do not have a sweet taste. Some of them are able to swell and mucus.
The most important polysaccharides are as follows.
Cellulose- a linear polysaccharide consisting of several straight parallel chains interconnected by hydrogen bonds. Each chain is formed by β-D-glucose residues. This structure prevents the penetration of water, is very tear-resistant, which ensures the stability of plant cell membranes, which contain 26-40% cellulose.
Cellulose serves as food for many animals, bacteria and fungi. However, most animals, including humans, cannot digest cellulose because their gastrointestinal tract lacks the enzyme cellulase, which breaks down cellulose into glucose. At the same time, cellulose fibers play an important role in nutrition, as they give bulk and coarse texture to food, stimulate intestinal motility.
starch and glycogen. These polysaccharides are the main forms of glucose storage in plants (starch), animals, humans and fungi (glycogen). When they are hydrolyzed, glucose is formed in organisms, which is necessary for vital processes.
Chitin formed by molecules of β-glucose, in which the alcohol group at the second carbon atom is replaced by a nitrogen-containing group NHCOCH 3 . Its long parallel chains, like the chains of cellulose, are bundled.
Chitin is the main structural element of the integument of arthropods and the cell walls of fungi.
Functions of carbohydrates
Energy. Glucose is the main source of energy released in the cells of living organisms during cellular respiration (1 g of carbohydrates releases 17.6 kJ of energy during oxidation).
Structural. Cellulose is part of the cell membranes of plants; chitin is a structural component of the integument of arthropods and the cell walls of fungi.
Some oligosaccharides are part of the cytoplasmic membrane of the cell (in the form of glycoproteins and glycolipids) and form a glycocalyx.
metabolic. Pentoses are involved in the synthesis of nucleotides (ribose is part of RNA nucleotides, deoxyribose is part of DNA nucleotides), some coenzymes (for example, NAD, NADP, coenzyme A, FAD), AMP; take part in photosynthesis (ribulose diphosphate is an acceptor of CO 2 in the dark phase of photosynthesis).
Pentoses and hexoses are involved in the synthesis of polysaccharides; glucose is especially important in this role.
Remember!
What substances are called biological polymers?
These are polymers - high-molecular compounds that are part of living organisms. Proteins, some carbohydrates, nucleic acids.
What is the importance of carbohydrates in nature?
Fructose is widely distributed in nature - fruit sugar, which is much sweeter than other sugars. This monosaccharide imparts a sweet taste to plant fruits and honey. The most common disaccharide in nature - sucrose, or cane sugar - consists of glucose and fructose. It is obtained from sugar cane or sugar beets. 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 the walls of 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.
Name the proteins you know. What functions do they perform?
Hemoglobin is a blood protein that transports gases in the blood
Myosin - muscle protein, muscle contraction
Collagen - protein of tendons, skin, elasticity, extensibility
Casein is a milk protein
Review questions and assignments
1. What chemical compounds are 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, tubers or potatoes), their content reaches 90% of the dry residue. Carbohydrates are divided 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. The monosaccharides ribose and deoxyribose are constituents 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 combine 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 only 20 different types of amino acids that have a common structural plan, but differ from each other in the structure of the radical. Connecting, amino acid molecules form 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 is a protein that binds oxygen in muscle tissue and consists of 153 amino acids. The collagen protein, which forms the basis of the collagen fibers of the 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 polypeptide coils up to form a coil (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 polypeptide chain twisted into a helix. For a stronger interaction in the secondary structure, an intramolecular interaction occurs with the help of –S–S– sulfide bridges between the turns of the helix. This ensures the strength of this structure. The tertiary structure is a secondary spiral structure twisted into globules - compact lumps. These structures provide maximum strength and greater abundance in cells compared to other organic molecules.
6. Name the functions of proteins known to you. How can you explain the existing diversity of protein functions?
One of the main functions of proteins is enzymatic. Enzymes are proteins that catalyze chemical reactions in living organisms. An enzymatic reaction is a chemical reaction that takes place only in the presence of an enzyme. 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 cleaves. The enzyme approaches its substrate like a "key to a lock". So, the urease enzyme regulates the breakdown of urea, the amylase enzyme regulates starch, and the protease enzymes regulate proteins. Therefore, for enzymes, the expression "specificity of action" is used.
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 variety of manifestations of life. It is a component of biological membranes, the transport of nutrients, such as hemoglobin, muscle function, hormonal function, body 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 action of any chemicals on proteins: solvents, acids, alkalis, concentrated substances, and so on. Mechanical factors - shaking, pressure, stretching, twisting, etc.
Think! Remember!
1. Using the knowledge gained in the study of plant biology, explain why there are significantly more carbohydrates in plant organisms than in animals.
Since the basis of life - plant nutrition is photosynthesis, this is the process of 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 lead to a violation of the conversion of carbohydrates in the human body?
The regulation of carbohydrate metabolism is mainly carried out by hormones and the central nervous system. Glucocorticosteroids (cortisone, hydrocortisone) slow down the rate of glucose transport into tissue cells, insulin accelerates it; adrenaline stimulates the process of sugar formation from glycogen in the liver. The cerebral cortex also plays a certain 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. Carbohydrate metabolism disorders 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 calorie content of food, growth stops in animals, 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 that have a common structural 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, essential ones that cannot be formed in the body on their own, but must be consumed with food . Thus, if there are no proteins, many protein molecules cannot form within the body itself and pathological changes cannot occur. Growth is controlled by the growth of bone cells, the basis 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 that arise during organ transplantation, based on the knowledge of the specificity of protein molecules in each organism.
Proteins are the genetic material, since they contain the structure of the DNA and RNA of the body. Thus, proteins have genetic characteristics in each organism, the information of genes is encrypted in them, this is the difficulty when transplanting from alien (unrelated) organisms, since they have different genes, and hence proteins.
All carbohydrates are made up of individual "units", which are saccharides. By ability tohydrolysison themonomerscarbohydrates are dividedinto two groups: simple and complex. Carbohydrates containing one unit are calledmonosaccharides, two units -disaccharides, two to ten unitsoligosaccharides, and more than tenpolysaccharides.
Monosaccharides quickly increase blood sugar, and have a high glycemic index, so they are also called fast carbohydrates. They dissolve easily in water and are synthesized in green plants.
Carbohydrates consisting of 3 or more units are calledcomplex. Foods rich in complex carbohydrates gradually increase their glucose content and have a low glycemic index, which is why they are also called slow carbohydrates. Complex carbohydrates are products of the polycondensation of simple sugars (monosaccharides) and, unlike simple ones, in the process of hydrolytic cleavage they are able to decompose 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 mirror image is 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 (ketoses contain one asymmetric carbon atom less than aldoses with the same number of carbon atoms). Naturalhexoses – glucose, fructose, mannoseandgalactose- according to stereochemical configurations, they are classified as D-series compounds.
Polysaccharides - the general name of the class of complex high-molecular carbohydrates,moleculesconsisting of tens, hundreds or thousandsmonomers – monosaccharides. From the point of view of the general principles of structure in the group of polysaccharides, it is possible to distinguish between homopolysaccharides synthesized from the same type of monosaccharide units and heteropolysaccharides, which are characterized by the presence of two or more types of monomeric residues.
https :// en . wikipedia . org / wiki /Carbohydrates
1.6. Lipids - nomenclature and structure. Lipid polymorphism.
Lipids - an extensive 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 other chemical elements. Most often: phosphorus (P), sulfur (S), nitrogen (N).
https:// en. wikipedia. org/ wiki/Lipids
Literature:
1) Cherkasova L. S., Merezhinsky M. F., Metabolism of fats and lipids, Minsk, 1961;
2) Markman A. L., Chemistry of lipids, 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 the liquid-crystal state. Lateral diffusion and flip flops.
membranes delimit the cytoplasm from the environment, and also form the membranes of the nuclei, mitochondria and plastids. They form a labyrinth of the endoplasmic reticulum and flattened stacked vesicles that make up the Golgi complex. The membranes form lysosomes, large and small vacuoles of plant and fungal cells, pulsating vacuoles of protozoa. All these structures are compartments (compartments) designed for certain specialized processes and cycles. Therefore, without membranes, the existence of a cell is impossible.
Diagram of the structure of the membrane: a – three-dimensional model; b - planar image;
1 - proteins adjacent to the lipid layer (A), immersed in it (B) or penetrating it through (C); 2 - layers of lipid molecules; 3 - glycoproteins; 4 - glycolipids; 5 - hydrophilic channel functioning as a pore.
The functions of biological membranes are as follows:
1) Delimit the contents of the cell from the external environment and the contents of the organelles from the cytoplasm.
2) Provide transport of substances into and out of the cell, from the cytoplasm to the organelles and vice versa.
3) They act as receptors (receiving and converting signals from the environment, recognition of cell substances, etc.).
4) They are catalysts (ensuring near-membrane chemical processes).
5) Participate in the transformation of energy.
http:// sbio. info/ page. php? id=15
Lateral diffusion is the chaotic thermal movement of lipid and protein molecules in the plane of the membrane. With lateral diffusion, adjacent lipid molecules jump around, and as a result of such successive jumps from one place to another, the molecule moves along the membrane surface.
The movement of molecules along the surface of the cell membrane during time t was determined experimentally by the method of fluorescent labels - fluorescent molecular groups. Fluorescent labels make fluorescent molecules, the movement of which on the cell surface can be studied, for example, by examining under a microscope the spreading rate of the fluorescent spot created by such molecules on the cell surface.
flip flop is the diffusion of membrane phospholipid molecules across the membrane.
The rate of jumps of molecules from one membrane surface to another (flip-flop) was determined by the spin label method 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 unpaired electrons on the molecules disappeared: paramagnetic molecules became diamagnetic, which could be detected by a decrease in the area under the curve of the EPR spectrum.
Thus, jumps of molecules from one surface of the bilayer to another (flip-flop) occur much more slowly than jumps during lateral diffusion. The average time for a phospholipid molecule to 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 another in the membrane plane.
The concept of the liquid-crystal state
The solid body can becrystalline , andamorphous. In the first case, there is a long-range order in the arrangement of particles at distances much greater than the 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. The molecules of a liquid and a solid make oscillatory (sometimes rotational) motions around the equilibrium position. After some average time (“time of settled life”), the molecules jump to another equilibrium position. The difference is that the "settled time" in a liquid is much shorter than in a solid state.
Lipid bilayer membranes are liquid under physiological conditions, the “settled life time” 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 approximately parallel to each other. There is also order in the orientation of the 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). There may be various liquid crystal structures: nematic (filamentous), when long molecules are oriented parallel to each other; smectic - molecules are parallel to each other and arranged in layers; cholestic - the molecules are parallel to each other in the same plane, but in different planes the orientations of the molecules are different.
http:// www. studfiles. en/ preview/1350293/
Literature: ON THE. Lemeza, L.V. Kamlyuk, N.D. Lisov. "Biology manual for applicants to universities."
1.8. Nucleic acids. Heterocyclic bases, nucleosides, nucleotides, nomenclature. Spatial structure of nucleic acids - DNA, RNA (tRNA, rRNA, mRNA). Ribosomes and the cell nucleus. Methods for determining the primary and secondary structure of nucleic acids (sequencing, hybridization).
Nucleic acids - phosphorus-containing biopolymers of living organisms that provide storage and transmission of hereditary information.
Nucleic acids are biopolymers. Their macromolecules consist of repeatedly repeating units, which are represented by nucleotides. And they are logically namedpolynucleotides. One of the main characteristics of nucleic acids is their nucleotide composition. The composition of a nucleotide (a structural unit of nucleic acids) includesthree components:
– nitrogenous base. May be pyrimidine or purine. Nucleic acids contain 4 different types of bases: two of them belong to the class of purines and two belong to the class of pyrimidines.
– rest of phosphoric acid.
– Monosaccharide - 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 deoxyribose.
Nucleotide at its core, it is the phosphate ester of the nucleoside.The composition of the nucleoside There are two components: a monosaccharide (ribose or deoxyribose) and a nitrogenous base.
http :// sbio . info / page . php ? id =11
Nitrogenous bases – heterocyclicorganic compounds, derivativespyrimidineandpurine, included innucleic acids. For the abbreviated designation, capital Latin letters are used. The nitrogenous bases areadenine(A)guanine(G)cytosine(C) which are part of both DNA and RNA.Timin(T) is only part of DNA, anduracil(U) occurs only in RNA.
CARBOHYDRATES
Carbohydrates are part of the cells and tissues of all plant and animal organisms and, by mass, make up the bulk of the organic matter on Earth. Carbohydrates account 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 only available on CD-ROM ). The texts accompanying these films have been transferred in full to this subsection and follow below.
Carbohydrates. Genetic D-series of sugars
"Carbohydrates are widely distributed 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 from which 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 containing from 2 to 10 monosaccharide residues in a molecule should be distinguished. 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 divided into aldoses (the monosaccharide contains an aldehyde group) and ketoses (the keto group is contained). For example, glucose is an aldose and fructose is a ketose.
(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 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 in them is written vertically. In aldoses, the aldehyde group is placed at the top, in ketoses, the primary alcohol group adjacent to the carbonyl group. The hydrogen atom and the hydroxyl group at the asymmetric carbon atom are placed 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. From the groups located at the top, the numbering of the carbon chain begins. (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 substituents at an asymmetric carbon atom is a very laborious, and until some time it was even an impossible task. It is possible to characterize compounds by comparing their configurations with those of reference compounds, i.e. define relative configurations.
The relative configuration of monosaccharides is determined by the configuration standard - glyceraldehyde, to which, at the end of the last century, certain configurations were arbitrarily assigned, designated as D- and L - glyceraldehydes. The configuration of the asymmetric carbon atom of the monosaccharide furthest from the carbonyl group is compared with the configuration of their asymmetric carbon atoms. In pentoses, this atom is the fourth carbon atom ( From 4 ), in hexoses - the fifth ( From 5 ), i.e. penultimate in the chain of carbon atoms. If the configuration of these carbon atoms coincides with the configuration D - glyceraldehyde monosaccharide belongs to D - in a row. And vice versa, if it matches the configuration 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 Fischer projection is located to the right of the vertical line, and the symbol L - that the hydroxyl group is located on the left.
Genetic D-series of sugars
The ancestor of aldose is glyceraldehyde. Consider the genetic relationship of sugars D - row with D - glyceraldehyde.
In organic chemistry, there is a method for increasing the carbon chain of monosaccharides by successively introducing a group
|
N– |
I |
-HE |
between the carbonyl group and the adjacent carbon atom. Introduction of this group into the molecule D - glyceraldehyde leads to two diastereomeric tetroses - D - erythrosis and D - treose. This is due to the fact that a new carbon atom introduced into the monosaccharide chain becomes asymmetric. For the same reason, each tetrose obtained, 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 can be seen, all members of the above series, being obtained from D - glyceraldehyde, retained its asymmetric carbon atom. This is the last asymmetric carbon atom in the chain of carbon atoms of the presented monosaccharides.
Each aldose D -number corresponds to a stereoisomer L - a series whose molecules relate to each other as an object and an incompatible mirror image. Such stereoisomers are called enantiomers.
It should be noted in conclusion that the above series of aldohexoses is not limited to the four shown. As shown above, from D - ribose and D - xylose, you can get two more pairs of diastereomeric sugars. However, we focused only on aldohexoses, which are most common in nature.
Construction of Haworth formulas for D-galactose
"Simultaneously with the introduction into organic chemistry of the concept of the structure of glucose and other monosaccharides as polyhydroxy aldehydes or polyhydroxy ketones described by open-chain formulas, facts began to accumulate in the chemistry of carbohydrates that were difficult to explain from the standpoint of such structures. It turned out that glucose and other monosaccharides exist in the form 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. During the reaction, the double bond of the carbonyl group is broken, at the place of the break, the hydrogen atom of the hydroxyl and the remainder of the alcohol are added to it. Cyclic hemiacetals are formed due to the interaction of similar 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 binding of carbon atoms of the carbonyl and oxygen of the hydroxyl groups.
The most stable hemiacetals are formed by hydroxyl groups at the fourth and fifth carbon atoms. The resulting five-membered and six-membered rings are called the 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 that have a cyclic form are conveniently represented by Haworth's promising formulas. They are idealized planar five- and six-membered rings with an oxygen atom in the ring, making it possible to see the mutual arrangement of all substituents relative to the plane of the ring.
Consider the construction of Haworth formulas using the example D - galactose.
To construct the Haworth formulas, it is first necessary 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 takes a horizontal position. Then the atoms and groups located in the projection formula to the left will be at the top, and those located to the right - below the horizontal line, and with a further transition to cyclic formulas - above and below the plane of the cycle, 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 removed from the aldehyde group; 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 CH 2 OH group is located above the chain of carbon atoms. At the same time, the aldehyde group, due to rotation 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 glycosidic group. The formation of a cyclic hemiacetal leads to the appearance of a new asymmetric carbon atom, called anomeric. As a result, two diastereomers are formed - a-and b - anomers differing only in the configuration of the first carbon atom.
The various configurations of the anomeric carbon atom result from the fact that the aldehyde group, which has a planar configuration, due to rotation around s - links between lanes with the first and second carbon atoms refers to the attacking reagent (hydroxyl group) both on one and opposite sides of the plane. The hydroxyl group then attacks the carbonyl group from 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 lies in the non-stereoselectivity of the discussed reaction.
a - anomer, the configuration of the anomeric center is the same as the configuration of the last asymmetric carbon atom, which determines belonging to D - and L - in a row, and b - anomer - opposite. In aldopentosis and aldohexosis D - series in Haworth's formulas glycosidic hydroxyl group y a - anomer is located under the plane, and y b - anomers - above the plane of the cycle.
According to similar rules, the transition to the furanose forms of Haworth is carried out. The only difference is that the hydroxyl of the fourth carbon atom is involved in the reaction, and for the convergence of functional groups, it is necessary to rotate 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 will be 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 -), the name of the monosaccharide and its series ( D - or L -) and cycle size (furanose or pyranose). For example , a , D - galactopyranose or b, D - galactofuranose."
Receipt
Glucose is predominantly found in free form in nature. It is also a structural unit of many polysaccharides. Other monosaccharides in the free state are rare and are mainly known as components of oligo- and polysaccharides. In nature, glucose is obtained as a result of photosynthesis 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 solid substances, readily soluble in water, poorly soluble 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. Reactions at the carbonyl group
1. Oxidation.
a) As with all aldehydes, oxidation of monosaccharides leads to the corresponding acids. So, when glucose is oxidized with an ammonia solution of silver hydroxide, 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 not only the aldehyde group, but also the primary alcohol group into the carboxyl group, leading to dibasic sugar (aldaric) acids. Typically, concentrated nitric acid is used for this oxidation.
2. Recovery.
The 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 ( NaHSO3).
II. Reactions on hydroxyl groups
Reactions on the hydroxyl groups of monosaccharides are carried out, as a rule, in the hemiacetal (cyclic) form.
1. Alkylation (formation of ethers).
Under the action of 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, such as for example , methyl iodide or dimethyl sulfate, such a transformation affects all the 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 color (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 most famous are the following:
a) alcoholic fermentation
C 6 H 12 O 6 ® 2CH 3 -CH 2 OH (ethyl alcohol) + 2CO 2
b) lactic fermentation
c) butyric fermentation
C6H12O6® CH 3 -CH 2 -CH 2 -COOH(butyric acid) + 2 H 2 + 2CO 2
The mentioned types of fermentation caused by microorganisms are of wide practical importance. For example, alcohol - for the production of ethyl alcohol, in winemaking, brewing, etc., and lactic acid - for the production of lactic acid and fermented milk products.
disaccharides
Disaccharides (bioses) upon hydrolysis form two identical or different monosaccharides. To establish the structure of disaccharides, it is necessary to know: from which monosaccharides it is built, what is the configuration of the anomeric centers in these monosaccharides ( a - or b -), what are the sizes of the ring (furanose or pyranose) and with the participation of which hydroxyls two monosaccharide molecules are linked.
Disaccharides are divided into two groups: reducing and non-reducing.
Reducing disaccharides include, in particular, maltose (malt sugar) contained in malt, i. sprouted, and then dried and crushed grains of cereals.
(maltose)
Maltose is made up of two residues D - glucopyranoses, which are linked by a (1–4) -glycosidic bond, i.e. the glycosidic hydroxyl of one molecule and the alcohol hydroxyl at the fourth carbon atom of another monosaccharide molecule participate in the formation of an ether bond. An anomeric carbon atom ( From 1 ) participating in the formation of this bond has a - configuration, and an anomeric atom with a free glycosidic hydroxyl (indicated in red) can have both a - (a - maltose) and b - configuration (b - maltose).
Maltose is a white crystal, highly soluble in water, sweet in taste, but much less than that of sugar (sucrose).
As can be seen, maltose contains a 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 able to enter into reactions characteristic of aldehydes, and, in particular, to give the "silver mirror" reaction, therefore it is called a reducing disaccharide. In addition, maltose enters into many reactions characteristic of monosaccharides, for example , forms ethers and esters (see chemical properties of 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 made up of a , D - glucopyranose and b, D - fructofuranoses.
(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, there is no reducing ability of sucrose, it does not give the "silver mirror" reaction, therefore it is referred to as non-reducing disaccharides.
Sucrose is a white crystalline substance, sweet in taste, highly soluble in water.
Sucrose is characterized by reactions on hydroxyl groups. Like all disaccharides, sucrose is converted by acidic or enzymatic hydrolysis into the monosaccharides of which it is composed.
Polysaccharides
The most important polysaccharides are starch and cellulose (fiber). They are built from glucose residues. The general formula for these polysaccharides ( C 6 H 10 O 5 n . Glycosidic (at C 1 -atom) and alcohol (at C 4 -atom) hydroxyls usually take part in the formation of polysaccharide molecules, 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 world is played by the polysaccharide glycogen, which is "stored" mainly in the liver.
Starch is a white powder consisting of small grains, insoluble in cold water. When starch is treated with warm water, it is possible to isolate two fractions: a fraction that is soluble in warm water and consists of amylose polysaccharide, and a fraction that only swells in warm water to form a paste and consists of amylopectin polysaccharide.
Amylose has a linear structure, a , D - glucopyranose residues are linked by (1–4)-glycosidic bonds. The elemental cell of amylose (and starch in general) is represented as follows:
The amylopectin molecule is built in a similar way, but has branches in the chain, which creates a spatial structure. At branch points, monosaccharide residues are linked by (1–6)-glycosidic bonds. Between the branch points are usually 20-25 glucose residues.
(amylopectin)
Starch easily undergoes hydrolysis: 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 color is observed. Such staining appears if a drop of iodine solution is placed on a slice of potato or a slice of white bread.
Starch does not enter into the "silver mirror" reaction.
Starch is a valuable food product. To facilitate its absorption, 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 better absorption 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 common plant polysaccharide. It has great mechanical strength and acts as 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 connected by (1-4) -glycosidic bonds. However, cellulose is different from starch. b - the configuration of glycosidic bonds between cycles and a strictly linear structure.
Cellulose consists of filamentous molecules, which are assembled into bundles by hydrogen bonds of hydroxyl groups within the chain, as well as between adjacent chains. It is this chain packing that provides high mechanical strength, fiber content, water insolubility, 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. Ruminant animals have cellulose-digesting enzymes in their stomachs, so ruminant animals use fiber as a food component.
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 undergoes acid hydrolysis to form glucose.
Cellulose is a polyhydric alcohol; there are three hydroxyl groups per unit cell of the polymer. In this regard, cellulose is characterized by esterification reactions (the formation of esters). Of greatest practical importance are reactions with nitric acid and acetic anhydride.
Fully esterified fiber is known as pyroxylin, which, after appropriate processing, turns into smokeless powder. Depending on the nitration conditions, cellulose dinitrate can be obtained, which is called colloxylin in the technique. It is also used in the manufacture of gunpowder and solid propellants. In addition, celluloid is made on the basis of colloxylin.
Triacetylcellulose (or cellulose acetate) is a valuable product for the manufacture of non-combustible film and acetate silk. To do 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 streams of the solution turn into the thinnest threads 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 of various papers. Paper is a thin layer of fiber fibers, 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
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 paramount biochemical importance are widely distributed in wildlife and play an important role in human life. The name carbohydrates arose on the basis of data from the analysis of the first known representatives of this group of compounds. The 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. There is one oxygen atom for every 2 hydrogen atoms. In the last century they were considered as carbon hydrates. Hence the Russian name carbohydrates, proposed in 1844. K. Schmidt. The general formula for carbohydrates, according to what has been said, is C m H 2p O p. When taking “n” out of brackets, the formula C m (H 2 O) n is obtained, which very clearly reflects the name “carbohydrate”. The study of carbohydrates has shown that there are compounds that, according to all properties, must be attributed to the group of carbohydrates, although they have a composition that does not exactly correspond to the formula C m H 2p O p. Nevertheless, the old name "carbohydrates" has survived to this day, although along with with this name, a newer name, glycides, is sometimes used to refer to the group of substances under consideration.
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 - polymeric compounds containing a large number of 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 (the keto group is contained). 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 in the free state are rare and are mainly known as components of oligo- and polysaccharides. In nature, glucose is obtained as a result of photosynthesis 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
