Carbohydrates. Types of carbohydrates. Glycemic index. What are carbohydrates? Simple and complex carbohydrates

Carbohydrates are one of the most important elements necessary to maintain an optimal state of the human body. They are the main providers of energy, made up of carbon, hydrogen and oxygen. They are found mainly in foods vegetable origin, namely in sugars, baked goods, whole grains and cereals, potatoes, fiber (vegetables, fruits). It is a mistake to believe that dairy and other predominantly protein products do not contain carbohydrates. For example, milk also contains carbohydrates. They are milk sugar - lactose. From this article, you will learn what groups carbohydrates are divided into, examples and differences of these carbohydrates, and you will also be able to understand how to calculate their required daily allowance.

The main groups of carbohydrates

So, now let's figure out what groups carbohydrates are divided into. Experts distinguish 3 main groups of carbohydrates: monosaccharides, disaccharides and polysaccharides. To understand their differences, let's take a closer look at each group.

• Monosaccharides are simple sugars. V a large number found in (glucose), fruit sugar (fructose), etc. Monosugar is perfectly soluble in liquid, giving it a sweet taste.
• Disaccharides are a group of carbohydrates that are broken down into two monosaccharides. They are also completely soluble in water and have a sweet taste.
• Polysaccharides - the last group, which do not dissolve in liquids, do not have a pronounced taste and consist of many monosaccharides. Simply put, these are glucose polymers: the well-known starch cellulose (plant cell wall), glycogens (storage carbohydrate of fungi, as well as animals), chitin, peptidoglycan (murein).

What group of carbohydrates is most needed by the human body

Considering the question of which groups are divided into carbohydrates, it is worth noting that most of them are contained in foods of plant origin. They include great amount vitamins and nutrients, so carbohydrates must be present in the daily diet of every person leading a healthy and active lifestyle. To provide the body with these substances, it is necessary to consume as much grain as possible (cereals, bread, loaves, etc.), vegetables and fruits.

Glucose, i.e. regular sugar is a component that is especially useful for humans, since it has a beneficial effect on mental activity. These sugars are almost instantly absorbed into the blood during the process of digestion, which contributes to an increase in insulin levels. At this time, a person experiences joy and euphoria, therefore sugar is considered to be a drug that, if consumed excessively, causes addiction and negatively affects general state health. That is why, the intake of sugar in the body should be controlled, but it is impossible to completely abandon it, because it is glucose that is a reserve source of energy. In the body, it turns into glycogen and is deposited in the liver and muscles. At the time of the breakdown of glycogen, the work of the muscles is performed, therefore, it is necessary to constantly maintain its optimal amount in the body.

Carbohydrate intake

Since all groups of carbohydrates have their own characteristic features, their consumption should be clearly dosed. For example, polysaccharides, in contrast to monosaccharides, must enter the body in greater quantities. In accordance with modern nutritional standards, carbohydrates should make up half of the daily diet, i.e. approximately 50% - 60%.

Calculation of the amount of carbohydrates required for vital functions

Each group of people requires a different amount of energy. For example, for children aged 1 to 12 months, the physiological need for carbohydrates ranges from 13 grams per kilogram of weight, while one should not forget which groups the carbohydrates present in the child's diet are divided into. For adults between the ages of 18 and 30, the daily intake of carbohydrates varies depending on the area of ​​activity. So, for men and women engaged in mental work, the consumption rate is about 5 grams per 1 kilogram of weight. Therefore, with a normal body weight, a healthy person needs about 300 grams of carbohydrates per day. This indicator also changes depending on gender. If a person is engaged mainly in heavy physical labor or sports, then when calculating the rate of carbohydrates, the following formula is used: 8 grams per 1 kilogram normal weight... Moreover, in this case, it is also taken into account what groups the carbohydrates supplied with food are divided into. The above formulas allow you to calculate mainly the amount of complex carbohydrates - polysaccharides.

Approximate Sugar Intake Rates for Specific Groups of People

As for sugar, in pure form it is sucrose (glucose and fructose molecules). For an adult, only 10% of sugar from the amount of calories consumed per day is considered optimal. To be precise, adult women need about 35-45 grams of pure sugar a day, while for men this figure is higher - 45-50 grams. For those who are actively involved in physical labor, the normal amount of sucrose ranges from 75 to 105 grams. These numbers will allow a person to carry out activities and not experience a decline in strength and energy. As for dietary fiber (fiber), their amount should also be determined individually, taking into account gender, age, weight and activity level (at least 20 grams).

Thus, having determined which three groups carbohydrates are divided into and understanding their importance in the body, each person will be able to independently calculate their required amount for life and normal performance.

§ 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, linen, wood, starch, honey, cane sugar are just a few of the carbohydrates that have played 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 stored 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. According to his 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 (ketal alcohols). Depending on the number of carbon atoms in the monosaccharide molecule, 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, as a rule, is 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 stream, 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. In the stomach of these animals large quantities contains bacteria and protozoa that produce the enzyme cellulase catalyzing 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 serves building material for RNA, and deoxyribose 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 mammals. The cell walls of bacteria, 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 source of energy. 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 obtained annually from sugar cane, sorghum and cassava and used in internal combustion engines.

Plan:

1. Definition of the concept: carbohydrates. Classification.

2. Composition, physical and Chemical properties carbohydrates.

3. Distribution in nature. Receiving. 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 widespread in living nature and play an important role in human life. The name carbohydrates originated from the analysis of the first known representatives of this group of compounds. Substances of this group consist of carbon, hydrogen and oxygen, and the ratio of the numbers of hydrogen and oxygen atoms in them is the same as in water, i.e. for every 2 hydrogen atoms, there is one oxygen atom. In the last century, they were considered carbon hydrates. Hence the Russian name for carbohydrates, proposed in 1844. K. Schmidt. The general formula of carbohydrates, according to what has been said, is Cm H 2n O n. When "n" is taken out of the brackets, the formula C m (H 2 O) n is obtained, which very clearly reflects the name "coal - water". The study of carbohydrates has shown that there are compounds that, according to all their 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 2n O n. Nevertheless, the old name "carbohydrates" has survived to this day, although along with this name, a newer name, glycides, is sometimes used to designate 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) and pentose (ribose). 2) Oligosaccharides - condensation products of several monosaccharides (for example, sucrose). 3) Polysaccharides - polymer compounds containing big number molecules of monosaccharides.

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

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

Carbohydrates

Turning to the consideration of organic substances, one cannot fail to note the importance of carbon for life. Entering into chemical reactions, carbon forms strong covalent bonds, socializing four electrons. Carbon atoms, connecting with each other, are able to form stable chains and rings that serve as skeletons of macromolecules. Carbon can also form multiple covalent bonds with other carbon atoms, as well as nitrogen and oxygen. All of these properties provide a unique variety of organic molecules.

Macromolecules, which make up about 90% of the mass of a dehydrated cell, are synthesized from simpler molecules called monomers. There are three main types of macromolecules: polysaccharides, proteins, and nucleic acids; monomers for them are, respectively, monosaccharides, amino acids and nucleotides.

Carbohydrates are substances with the general formula C x (H 2 O) y, where x and y are integers... The name "carbohydrates" means that in their molecules hydrogen and oxygen are in the same ratio as in water.

Animal cells contain a small amount of carbohydrates, and plant cells - almost 70% of the total amount of organic matter.

Monosaccharides play the role of intermediate products in the processes of respiration and photosynthesis, participate in the synthesis of nucleic acids, coenzymes, ATP and polysaccharides, and serve as released during oxidation during respiration. Monosaccharide derivatives - sugar alcohols, sugar acids, deoxy sugars and amino sugars - have essential in the process of respiration, and are also used in the synthesis of lipids, DNA and other macromolecules.

Disaccharides are formed as a result of a condensation reaction between two monosaccharides. They are sometimes used as reserve nutrients. The most common of these are maltose (glucose + glucose), lactose (glucose + galactose), and sucrose (glucose + fructose). found only in milk. (cane sugar) most abundant in plants; this is the very "sugar" that we usually eat.

Cellulose is also a glucose polymer. It contains about 50% of the carbon contained in plants. In terms of total mass on Earth, cellulose ranks first among organic compounds. The shape of the molecule (long chains with protruding –OH groups) provides strong adhesion between adjacent chains. For all its strength, macrofibrils, consisting of such chains, easily pass water and substances dissolved in it and therefore serve as an ideal building material for the walls of a plant cell. Cellulose is a valuable source of glucose, but the enzyme cellulase, which is relatively rare in nature, is required to break it down. Therefore, only some animals (for example, ruminants) eat cellulose. The industrial value of cellulose is also great - cotton fabrics and paper are made from this substance.

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. By 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, a club or a potato), 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. The 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 provides 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 greater abundance in cells compared to other organic molecules.

6. What are the functions of proteins known to you? 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 chemical reaction, proceeding 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 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 in spite of the sufficient caloric content of food, the growth of animals stops, 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 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 the growth of 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 in organ transplantation based on knowledge of the specificity of protein molecules in each organism.

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