Chemistry of carbohydrates briefly. Carbohydrates, their classification and significance - Knowledge Hypermarket

Definition

Carbohydrates are natural compounds with the composition C$_n$(H$_2$O)$_m$. The exception is deoxyribose C$_5$H$_(10)$O$_4$.

It should be noted that the molecular formula C$_n$(H$_2$O)$_m$ can describe other classes of compounds.

Carbohydrates are part of all living organisms, they make up about 80% of the dry mass of plants, and the polysaccharide cellulose is the most abundant organic substance on Earth.

In plants and animals, carbohydrates perform a variety of functions: they serve as a source of energy, are the “building material” of plant cell walls, and determine the protective properties of mammals (along with proteins). Carbohydrates serve as starting materials for the production of paper, artificial fibers, explosives, etc. Many carbohydrates are used in medicine.

Among the most well-known carbohydrates are the following (the figures show the structural formulas of carbohydrates and their sources (for “a”, “b”, “c”) or their use (“d”)):

A) glucose - monosaccharide, grape sugar.

b) sucrose- disaccharide, cane sugar.

V) starch - polysaccharide synthesized different plants in chloroplasts, under the influence of light during photosynthesis, the main nutrient in plant cells.

G) cellulose - polysaccharide, the main component of the cell walls of all higher plants.

CLASSIFICATION OF CARBOHYDRATES.

Historically, carbohydrates include substances of a very diverse structure - from low molecular weight, built from just a few carbon atoms (most often five or six), to polymers with molecular weight several million.

The latter, called polysaccharides, as a result of complete hydrolysis they form more simple connections - monosaccharides. The intermediate group consists of oligosaccharides, including a relatively small number of monomer units.

Definition 1

Monosaccharides - monomers, the residues of which make up carbohydrates of a more complex structure. Monosaccharides do not undergo hydrolysis.

Definition 2

Oligosaccharides – oligomers containing from 2 to 10 monosaccharide residues.

Definition 3

Polysaccharides – polymers containing up to several thousand monosaccharide units

Monosaccharides (for example, glucose, fructose, galactose, etc.) belong to a group of substances for which the question of structure is more important than for any other class of compounds. So, monosaccharides can be classified according to:

I. By the number of carbon atoms in the chain

triose - three carbon atoms

tetrose - four carbon atoms in a chain

pentose - five carbon atoms in a chain

hexose - six carbon atoms in the chain

II. By type of carbonyl group

aldose - contains an aldehyde group ($-C(O)H$)

ketose - contains a keto group ($-C(O)-$)

III. According to the configuration of the last chiral carbon atom

D-series carbohydrates

L-series carbohydrates

The diversity of monosaccharides is mainly due to stereochemical differences. For example, pentose or hexose molecules contain from 2 to 4 chiral (asymmetric) carbon atoms, so several isomers correspond to the same structural formula.

Definition

Chiral (or asymmetric ) carbon atom - a carbon atom in $sp^3$-hybridization that has four different substituents. Compounds with a chiral carbon atom (chiral center) have optical activity, i.e. the ability of a substance in solution to rotate the plane of polarized light.

The D,L system has historically been used to designate the spatial structure of monosaccharides.

The position of the hydroxyl group at the last chirality center on the right indicates that the monosaccharide belongs to the D-series, on the left - to the L-series, for example.

Plan:

1. Definition of the concept: carbohydrates. Classification.

2. Composition, physical and chemical properties of carbohydrates.

3.Distribution in nature. Receipt. Application.

Carbohydrates – organic compounds, containing carbonyl and hydroxyl groups of atoms, having the general formula C n (H 2 O) m, (where n and m>3).

Carbohydrates – substances of primary biochemical importance are widespread in living nature and play an important role in human life. The name carbohydrates arose based on data from the analysis of the first known representatives of this group of compounds. Substances of this group consist of carbon, hydrogen and oxygen, and the ratio of the numbers of hydrogen and oxygen atoms in them is the same as in water, i.e. For every 2 hydrogen atoms there is one oxygen atom. In the last century they were considered to be carbon hydrates. This is where it came from Russian name carbohydrates, proposed in 1844 K. Schmidt. The general formula of carbohydrates, according to what has been said, is C m H 2n O n. When “n” is taken out of brackets, the formula is C m (H 2 O) n, which very clearly reflects the name “carbon - water”. The study of carbohydrates has shown that there are compounds that, in all their properties, should be classified as carbohydrates, although they have a composition that does not exactly correspond to the formula C m H 2p O p. Nevertheless, the ancient name “carbohydrates” has survived to this day, although along with With this name, a newer name is sometimes used to designate the group of substances under consideration - glycides.

Carbohydrates can be divided into three groups : 1) Monosaccharides – carbohydrates that can be hydrolyzed to form simpler carbohydrates. This group includes hexoses (glucose and fructose), as well as pentose (ribose). 2) Oligosaccharides – condensation products of several monosaccharides (for example, sucrose). 3) Polysaccharides – polymer compounds containing 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 (contains a keto group). For example, glucose is an aldose, and fructose is a ketose.

Receipt. Glucose is predominantly found in free form in nature. It is also a structural unit of many polysaccharides. Other monosaccharides are rare in the free state and are mainly known as components of oligo- and polysaccharides. In nature, glucose is obtained as a result of the photosynthesis reaction: 6CO 2 + 6H 2 O ® C 6 H 12 O 6 (glucose) + 6O 2 Glucose was first obtained in 1811 by the Russian chemist G.E. Kirchhoff from the hydrolysis of starch. Later, the synthesis of monosaccharides from formaldehyde in an alkaline medium was proposed by A.M. Butlerov

One of the most important functions in living organisms is performed by carbohydrates. They are a source of energy and are involved in metabolism.

general description

Another name for carbohydrates is sugar. Carbohydrates have two definitions:

• from the point of view of biology - biologically active substances that are a source of energy for living organisms, including humans;
• from a chemical point of view, organic compounds consisting of several carbonyl (-CO) and hydroxyl (-OH) groups.

Elements that form a carbohydrate:

• carbon;
• hydrogen;
• oxygen.

The general formula of carbohydrates is C n (H 2 O) m. The minimum number of carbon and oxygen atoms is three. The ratio of hydrogen and oxygen is always 2:1, as in a water molecule.

The source of carbohydrates is the process of photosynthesis. Carbohydrates make up 80% of dry plant mass and 2-3% of animal matter. Carbohydrates are part of ATP, a universal source of energy.

Kinds

Carbohydrates are a large group of organic substances. They are classified according to two criteria:

• number of carbon atoms;
• number of structural units.

Depending on the number of carbon atoms in one molecule (structural unit), the following are distinguished:

• trioses;
• tetroses;

• pentoses;
• hexoses;
• heptoses.

The molecule can contain up to nine carbon atoms. The most significant are pentoses (C 5 H 10 O 5) and hexoses (C 6 H 12 O 6). Pentoses are components nucleic acids. Hexoses are part of polysaccharides.

Rice. 1. Monosaccharide structure.

According to the second classification criterion, carbohydrates are:

• simple consisting of one molecule or structural unit (monosaccharides);
• complex, including many molecules (oligosaccharides, polysaccharides).

  Features of complex structures are described in the table of carbohydrates.

  

  Rice. 2. Polysaccharide structure.

  One of the most significant types of oligosaccharides is disaccharides, consisting of two monosaccharides. They serve as a source of glucose and perform a construction function in plants.

  Physical properties

  Monosaccharides and oligosaccharides have similar physical properties:

  • crystal structure;
  • sweet taste;
  • solubility in water;
  • transparency;
  • neutral pH in solution;
  • low melting and boiling points.

  Polysaccharides are more complex substances. They are insoluble and do not have a sweet taste. Cellulose is a type of polysaccharide that is part of the cell walls of plants. Chitin, similar to cellulose, is found in fungi and arthropod shells. Starch accumulates in plants and breaks down into simple carbohydrates, which are a source of energy. In animal cells, glycogen performs a reserve function.

  Chemical properties

  Depending on their structure, each carbohydrate has special chemical properties. Monosaccharides, in particular glucose, undergo multi-stage oxidation (in the absence and presence of oxygen). As a result of complete oxidation, carbon dioxide and water are formed:

  C 6 H 12 O 6 + 6O 2 → 6CO 2 +6H 2 O.

  In the absence of oxygen, fermentation occurs under the action of enzymes:

  • alcohol-

    C 6 H 12 O 6 → 2C 2 H 5 OH (ethanol) + 2CO 2;

  • lactic acid-

    C 6 H 12 O 6 → 2CH 3 -CH(OH)-COOH (lactic acid).

  Otherwise, polysaccharides interact with oxygen, burning to carbon dioxide and water:

  (C 6 H 10 O 5)n + 6O 2 → 6nCO 2 + 5nH 2 O.

  Oligosaccharides and polysaccharides decompose to monosaccharides during hydrolysis:

  • C 12 H 22 O 11 + H 2 O → C 6 H 12 O 6 + C 6 H 12 O 6;
  • (C 6 H 10 O 5)n + nH 2 O → nC 6 H 12 O 6.

  Glucose reacts with copper(II) hydroxide and an ammonia solution of silver oxide (silver mirror reaction):

  • CH 2 OH-(CHOH) 4 -CH=O + 2Cu(OH) 2 → CH 2 OH-(CHOH) 4 -COOH + Cu 2 O↓ + 2H 2 O;
  • CH 2 OH-(CHOH) 4 -CH=O + 2OH → CH 2 OH-(CHOH) 4 -COONH 4 + 2Ag↓ +3NH 3 + H 2 O.

  

  Rice. 3. Reaction of the silver mirror.

  What have we learned?

  From the 10th grade chemistry topic we learned about carbohydrates. These are bioorganic compounds consisting of one or more structural units. One unit or molecule consists of carbonyl and hydroxyl groups. There are monosaccharides, consisting of one molecule, oligosaccharides, including 2-10 molecules, and polysaccharides - long chains of many monosaccharides. Carbohydrates taste sweet and are highly soluble in water (with the exception of polysaccharides). Monosaccharides dissolve in water, oxidize, and interact with copper hydroxide and silver ammonia oxide. Polysaccharides and oligosaccharides undergo hydrolysis. Polysaccharides burn.

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24.02.2015 26958

What are carbohydrates?

• What are carbohydrates?
• What are the “right” sources of carbohydrates and how to include them in your diet?
• What is the glycemic index?
• How are carbohydrates broken down?
• Do they really turn into fat on the body after processing?

Let's start with theory

Carbohydrates (also called saccharides) are organic compounds of natural origin, which are mostly found in the plant world. They are formed in plants during the process of photosynthesis and are found in almost any plant food. Carbohydrates contain carbon, oxygen and hydrogen. Carbohydrates enter the human body mainly from food (found in cereals, fruits, vegetables, legumes and other products), and are also produced from certain acids and fats.

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

Of course, if we consider carbohydrates solely from the point of view of building muscle mass, then they act as an accessible source of energy. In general, the body's energy reserves are contained in fat depots (about 80%), protein depots - 18%, and carbohydrates account for only 2%.

Important: carbohydrates accumulate in the human body in combination with water (1g of carbohydrates requires 4g of water). But fat deposits do not require 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. It also takes part in the process of glycogen formation, and for the normal functioning of red blood cells, about 40 g of glucose per day is needed. Together with food, a person consumes about 18g, and the daily dose is 140g (necessary for the proper functioning of the central nervous system).

A natural question arises: where does the body get the necessary amount of glucose for its work? First things first. 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 level of glucose in the blood 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, insulin takes over, which reduces the amount to the required level. And you don’t have to worry about the portion of carbohydrates you eat; exactly as much as your body requires will enter your bloodstream (due to the work of insulin).

Foods rich in glucose include:

• Grapes - 7.8%;
• Cherries and sweet cherries - 5.5%;
• Raspberries - 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 vegetables and fruits. But it is important to remember that consuming fructose in large quantities not only does not bring benefits, but also causes harm. Huge portions of fructose enter the intestines and cause increased insulin secretion. And if you are not currently engaged in active physical activity, then all glucose is stored in the form of fat deposits. 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. Galactose is almost never found in free form, but is most often a component of milk sugar called lactose.

Disaccharides (simple carbohydrates)

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

Sucrose consists 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 simply 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, molasses, honey, molasses, and any confectionery products. Lactose is mainly found in dairy products, and in the intestines it is broken down and converted into galactose and glucose. The most lactose is found in milk, cottage cheese, and kefir.

Now that we’ve dealt 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 digestible (starch);
• Those that are not digestible (fiber).

Starch is the main source of carbohydrates, which forms the basis of the nutritional pyramid. Most of it is found in grain crops, legumes and potatoes. The main sources of starch are buckwheat, oatmeal, pearl barley, as well as lentils and peas.

Important: Include baked potatoes in your diet, which are high in potassium and other minerals. This is especially important because during cooking, starch molecules swell and reduce the nutritional value of the product. That is, at first the product may contain 70%, but after cooking there may not even be 20% left.

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

Now let's move on to other processes associated with carbohydrates.

How the body stores carbohydrates

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

By mistake, many people who are losing weight, for a more “effective” result, significantly reduce the amount of carbohydrates they consume, hoping that the body will use up fat reserves. In fact, proteins are the first to be consumed, and only then fat deposits. It is important to remember that a large amount of carbohydrates will lead to rapid weight gain only if they enter the body in large portions (and they must also be quickly digested).

Carbohydrate metabolism

Carbohydrate metabolism depends on how much glucose is in the 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;
• Glyconogenesis - the process of breakdown of glycerol, amino acids and lactic acid in the liver and kidneys produces the necessary glucose.

Early in the morning (after waking up), blood glucose reserves drop sharply for a simple reason - lack of replenishment in the form of fruits, vegetables and other foods that contain glucose. The body is also fueled by its own forces, 75% of which is carried out in the process of glycolysis, and 25% occurs in gluconeogenesis. That is, it turns out that the morning time is considered optimal in order to use existing fat reserves as an energy source. And add light cardio exercises to this, and 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, and also in what optimal quantities they should be consumed.

Carbohydrates and bodybuilding: who, what, how much

A few words about the glycemic index

When talking about carbohydrates, one cannot help but mention the term “glycemic index” - that is, the rate at which carbohydrates are absorbed. It is an indicator of how quickly a particular product can 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 fat deposits under the skin. So all foods with high GI values ​​are sure companions for rapidly gaining extra pounds.

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

The body's need for carbohydrates and the right sources

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

• Duration of training;
• Load intensity;
• Metabolic rates in the body.

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

Remember that an ordinary person consumes about 250-300g of carbohydrates per day. For those who train in the gym with weights, daily norm increases and reaches 450-550g. But they still need to be used correctly, and at the right time (in the first half of the day). Why do you need to do this? The scheme is simple: in the first half of the day (after sleep), the body accumulates carbohydrates in order to “feed” its body with them (which is necessary for muscle glycogen). The remaining time (after 12 hours) carbohydrates are quietly deposited in the form of fat. 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 absorb an increased amount of nutrients (used to restore energy and muscle reserves).

It has already become clear that the body needs to constantly receive nourishment in the form of “correct” carbohydrates. To understand the quantitative values, consider the table below.

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

• Baked or boiled potatoes in their skins;
• Various porridges (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 (grapefruits, apples, pomelo);
• Vegetables are fibrous and starchy (turnips and carrots, pumpkin and zucchini).

These are the foods that should be included in your diet.

The ideal time to consume carbohydrates

The best time to consume a dose of carbohydrates is:

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

Moreover, each of the periods is important and among them there is no more or less suitable one. 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 training (2-3 hours before), you need to fuel your body with carbohydrates with average glycemic index values. For example, eat pasta or corn/rice porridge. This will provide the necessary energy supply for the muscles and brain.

During classes in the gym, you can use intermediate nutrition, that is, drink drinks containing carbohydrates (200 ml every 20 minutes). This will have double benefits:

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

After training, it is best to take a saturated protein-carbohydrate shake, and 1-1.5 hours after completing the training, eat a hearty meal. Buckwheat or pearl barley porridge or potatoes.

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

Do Carbohydrates Help You Build Muscle?

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

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

It must also be remembered that depending on the level of training of the athlete, his muscles can store a larger supply of glycogen. To build muscle mass, you need to take 7g of carbohydrates for every kilogram of body. Don't forget if you start taking large quantity carbohydrates, then the intensity of the load must also be increased.

So that you 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 - medium-heavy work - mechanics, machine operators.
• Group 4 - hard work - builders, oil workers, metallurgists.
• Group 5 - very hard work - miners, steelworkers, loaders, athletes during the competitive period.

And now the results

To ensure that the effectiveness of your training is always at its best, and that 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 average GI values, after training - with low GI;
• Breakfast should be as dense as possible, and in the first half of the day you should eat most of the daily dose of carbohydrates;
• When buying products, check the glycemic index table and choose those that have medium and low GI values;
• If you want to eat foods with high GI values ​​(honey, jam, sugar), it is better to do this in the morning;
• Include more cereals in your diet and consume them regularly;
• Remember, carbohydrates are assistants to proteins in the process of building muscle mass, so if there is no tangible result for a long time, then you need to reconsider your diet and the amount of carbohydrates consumed;
• Eat non-sweet fruits and fiber;
• Remember wholemeal bread and baked potatoes in their skins;
• Constantly update your knowledge about health and bodybuilding.

If you adhere to these simple rules, your energy will noticeably increase, and the effectiveness of your training 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 proper training 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 of achieving the desired result. So think not only in the gym, but also while eating.

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Goals:

educational:

To develop students’ knowledge about carbohydrates, their composition and classification. Consider the dependence of the chemical properties of carbohydrates on the structure of molecules. Qualitative reactions to glucose and starch. Give an idea of ​​the biological role of carbohydrates and their importance in human life.

developing:

Continue to develop in students mental operations: the ability to connect existing knowledge with newly acquired knowledge, the ability to highlight the main thing in the studied material, generalize the studied material and draw conclusions.

educational:

Fostering a responsible attitude towards learning, a desire for creative, cognitive activity.

Type: learning new material

View: lecture

Method : explanatory and illustrative with computer support

Lesson plan

1. Organizing time

2. Motivation for the lesson

Carbohydrates serve as an important source of nutrition: we consume grains, or feed them to animals, in whose bodies the starch is converted into proteins and fats. The most hygienic clothing is made from cellulose or cellulose-based products: cotton and linen, viscose fiber or silk acetate. Wooden houses and furniture are constructed from the same cellulose that forms wood. The production of photographic and film films is based on the same cellulose. Books, newspapers, banknotes are all products of the pulp and paper industry. This means that carbohydrates provide us with everything we need.

In addition, carbohydrates are involved in the construction of complex proteins, enzymes, and hormones. Carbohydrates are also vital necessary substances, like heparin (it plays a crucial role - it prevents blood clotting), agar-agar (it is obtained from seaweed and is used in the microbiological and confectionery industries).

The only source of energy on Earth (besides nuclear) is the energy of the Sun, and the only way to accumulate it to ensure the life of all living organisms is the process of photosynthesis, which occurs in plant cells and leads to the synthesis of carbohydrates from water and carbon dioxide. By the way, it is during this transformation that oxygen is formed, without which life on our planet would be impossible.

Lecture outline

1. The concept of carbohydrates. Classification of carbohydrates.

2. Monosaccharides

3. Disaccharides

4. Polysaccharides

1. The concept of carbohydrates. Classification of carbohydrates.

Carbohydrates- a wide class of natural compounds that play an important role in the life of humans, animals and plants .

These compounds received the name “carbohydrates” because the composition of many of them is expressed by the general formula Cn (H 2 O) m, i.e. formally they are compounds of carbon and water. With the development of carbohydrate chemistry, compounds were discovered whose composition does not correspond to the given formula, but which have the properties of substances of their class (for example, deoxyribose C 5 H 10 O 4). At the same time, there are substances that correspond to the general formula of carbohydrates, but do not exhibit their properties (for example, inositol alcohol C 6 H 12 O 6).

Classification of carbohydrates

All carbohydrates can be divided into two groups: simple carbohydrates (monosaccharides) and complex carbohydrates.

Simple carbohydrates(monosaccharides)- These are the simplest carbohydrates that do not hydrolyze to form simpler carbohydrates.

Complex carbohydrates - these are carbohydrates whose molecules consist of two or more monosaccharide residues and decompose into these monosaccharides during hydrolysis.

2. Monosaccharides

Monosaccharides are compounds with mixed functions. They contain an aldehyde or keto group and several hydroxyl groups, i.e. are aldehyde alcohols or ketone alcohols.

Monosaccharides with an aldehyde group are called aldoses, and with a keto group - ketoses.

Based on the number of carbon atoms in the molecule, monosaccharides are divided into tetroses, pentoses, hexoses etc.

Highest value Monosaccharides include hexoses and pentoses.

Monosaccharide structure

Projection projections are used to depict the structure of monosaccharides. Fisher's formulas. In Fischer's formulas, the chain of carbon atoms is arranged in one chain. The chain numbering starts from the atom of the aldehyde group (in the case of aldoses) or from the outermost carbon atom to which the keto group is located closer (in the case of ketoses).

Depending on the spatial arrangement of H atoms and OH groups at the 4th carbon atom in pentoses and the 5th carbon atom in hexoses, monosaccharides are classified as D - or L - series.

A monosaccharide is classified as a D series if the OH group of these atoms is located to the right of the chain.

Almost all naturally occurring monosaccharides belong to the D series.

However, monosaccharides can also exist in cyclic forms. The cyclic forms of hexoses and pentoses are called pyranose and furanose, respectively.

In solutions of monosaccharides, a mobile equilibrium is established between the acyclic and cyclic forms - tautomerism.

Cyclic forms are usually depicted promising Haworth formulas.

In the cyclic forms of monosaccharides, an asymmetric carbon atom appears (C-1 in aldoses, C-2 in ketoses). This carbon atom is called anomeric. If the OH group of an anomeric atom is located below the plane, then an α-anomer is formed, the opposite arrangement leads to the formation of a β-anomer.

Physical properties

Colorless crystalline substances, sweet in taste, highly soluble in water, poorly soluble in alcohol. The sweetness of monosaccharides varies. For example, fructose is 3 times sweeter than glucose.

(slide 8 – 12.)

Chemical properties

The chemical properties of monosaccharides are determined by the peculiarities of their structure.

Let's look at the chemical properties using glucose as an example.

1. Reactions involving the aldehyde group of glucose

A) reduction (hydrogenation) with the formation of the polyhydric alcohol sorbitol

CH=O CH 2 OH

│ kat , t 0 │

(CHOH) 4 + H 2 → (CHOH) 4

CH 2 OH CH 2 OH

b) oxidation

“silver mirror” reaction (with an ammonia solution of silver oxide,t 0 ),

reaction with copper hydroxide (II ) Cu (OH ) 2 in an alkaline environment,t 0 )

CH=O COOH

│ NH 4 OH, t 0 │

(CHOH) 4 + Ag 2 O → (CHOH) 4

CH 2 OH CH 2 OH

The oxidation product is gluconic acid (the salt of this acid is calcium gluconate, a well-known drug).

CH=OCOOH

│ t 0 │

(CHOH) 4 + 2Cu(OH) 2 → (CHOH) 4 + Cu 2 O↓ + 2H 2 O

│ blue │ brick red

CH 2 OH CH 2 OH

These reactions are qualitative for glucose as an aldehyde.

Under the influence of strong oxidizing agents (for example, nitric acid), dibasic glucaric acid is formed.

CH=OCOOH

│ t 0 │

(CHOH) 4 + HNO 3 → (CHOH) 4

CH2OHCOOH

2. Reaction of glucose with the participation of hydroxyl groups (i.e. properties of glucose as a polyhydric alcohol)

A) interaction Cu (OH ) 2 in the cold with the formation of copper (II) gluconate - a qualitative reaction to glucose as a polyhydric alcohol.

3. Fermentation of monosaccharides

A) alcoholic fermentation

C 6 H 12 O 6 → 2C 2 H 5 OH + 2CO 2

b) butyric acid fermentation

C 6 H 12 O 6 → CH 3 ─CH 2 ─CH 2 ─COOH + 2H 2 + 2CO 2

V) lactic acid fermentation

C 6 H 12 O 6 → 2CH 3 ─ CH ─ COOH

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Biological role of glucose

D-glucose (grape sugar) is widespread in nature: found in grapes and other fruits, and in honey. It is an essential component of the blood and tissues of animals and a direct source of energy for cellular reactions. The level of glucose in human blood is constant and ranges from 0.08-0.11%. The entire blood volume of an adult contains 5-6 g of glucose. This amount is enough to cover the body’s energy costs for 15 minutes. his life activity. In some pathologies, for example, when diabetes mellitus, the glucose level in the blood increases, and its excess is excreted in the urine. In this case, the amount of glucose in the urine can increase to 12% compared to the usual 0.1%.

3. Disaccharides

(slide 13.)

Disaccharides – condensation products of two monosaccharides.

The most important natural representatives: sucrose (cane or beet sugar), maltose (malt sugar), lactose (milk sugar), cellobiose. They all have the same empirical formula C 12 H 22 O 11, i.e. are isomers.

Disaccharides are typical sugar-like carbohydrates; These are crystalline solids that have a sweet taste.

(slide 14-15.)

Structure

1. Disaccharide molecules can contain two residues of one monosaccharide or two residues of different monosaccharides;

2. The bonds formed between monosaccharide residues can be of two types:

a) hemiacetal hydroxyls of both monosaccharide molecules take part in the formation of the bond. For example, the formation of a sucrose molecule;

b) the hemiacetal hydroxyl of one monosaccharide and the alcohol hydroxyl of another monosaccharide take part in the formation of the bond. For example, the formation of maltose, lactose and cellobiose molecules.

(slide 16-17.)

Chemical properties of disaccharides

1. Disaccharides, in the molecules of which hemiacetal hydroxyl is preserved (maltose, lactose, cellobiose), in solutions are partially converted into open aldehyde forms and enter into reactions characteristic of aldehydes, in particular in the “silver mirror” reaction and with copper (II) hydroxide . Such disaccharides are called restorative.

Disaccharides whose molecules do not contain hemiacetal hydroxyl (sucrose) cannot transform into open carbonyl groups. These disaccharides are called non-restorative(do not reduce Cu (OH) 2 and Ag 2 O).

2. All disaccharides are polyhydric alcohols, they are characterized by the properties of polyhydric alcohols, they give a qualitative reaction to polyhydric alcohols - a reaction with Cu (OH) 2 in the cold.

3. All disaccharides are hydrolyzed to form monosaccharides:

H+, t 0

C 12 H 22 O 11 + H 2 O → C 6 H 12 O 6 + C 6 H 12 O 6

sucrose glucose fructose

In living organisms, hydrolysis occurs under the action of enzymes.

4. Polysaccharides

(slide 18 - 20.)

Polysaccharides– high molecular weight non-sugar-like carbohydrates containing from ten to hundreds of thousands of monosaccharide residues (usually hexoses) linked by glycosidic bonds.

The most important natural representatives: starch, glycogen, cellulose. These are natural polymers (NMPs), the monomer of which is glucose. Their general empirical formula is (C 6 H 10 O 5) n.

Starch– amorphous powder white, tasteless and odorless, poorly soluble in water, in hot water forms a colloidal solution. Starch macromolecules are made from large numberα-glucose residues linked by α-1,4-glycosidic bonds.

Starch consists of two fractions: amylose (20-30%) and amylopectin (70-80%).

Amylose molecules are very long unbranched chains consisting of α-glucose residues. Amylopectin molecules, unlike amylose, are highly branched.

Chemical properties of starch:

(slide 21.)

1. hydrolysis

H 2 O, enzymes

(C 6 H 10 O 5) n → (C 6 H 10 O 5) m → C 12 H 22 O 11 → n C 6 H 12 O 6

starch dextrins maltose glucose

The reaction of converting starch into glucose under the catalytic action of sulfuric acid was discovered in 1811 by the Russian scientist K. Kirchhoff.

2. Qualitative reaction to starch

(C 6 H 10 O 5) n + I 2 → complex compound blue-violet color.

When heated, the color disappears (the complex is destroyed); when cooled, it appears again.

Starch is one of the products of photosynthesis, the main reserve nutrient of plants. Glucose residues in starch molecules are connected quite firmly and at the same time can be easily split off under the action of enzymes. As soon as the need for an energy source arises.

Glycogen is the equivalent of starch synthesized in the animal body, i.e. This is also a reserve polysaccharide, the molecules of which are built from a large number of α-glucose residues. Glycogen is found mainly in liver muscles.

Cellulose or fiber

The main component of the plant cell, synthesized in plants (in wood up to 60% cellulose). Pure cellulose is a white fibrous substance, tasteless and odorless, insoluble in water.

Cellulose molecules are long chains consisting of β-glucose residues that are linked by the formation of β-1,4-glycosidic bonds.

Unlike starch molecules, cellulose consists only of unbranched molecules in the form of threads, because the shape of β-glucose residues precludes helicalization.

Cellulose is not a food product for humans and most animals, because their bodies do not have enzymes that break down stronger β-1,4-glycosidic bonds.

(slide 22-23.)

Chemical properties of cellulose:

1. hydrolysis

With prolonged heating with mineral acids or under the action of enzymes (in ruminants and rabbits), stepwise hydrolysis occurs:

H 2 O

(C 6 H 10 O 5) n → y (C 6 H 10 O 5) x → n /2 C 12 H 22 O 11 → n C 6 H 12 O 6

cellulose cellobiose β-glucose

2. formation of esters

a) interaction with inorganic acids

b) interaction with organic acids

3. combustion

(C 6 H 10 O 5) n +6nO 2 → 6nCO 2 +5nH 2 O

4. thermal decomposition of cellulose without air access:

t 0

(C 6 H 10 O 5) n → charcoal+H 2 O +volatile organic matter

Being component wood, cellulose is used in construction and carpentry; as fuel; wood is used to produce paper, cardboard, ethanol. In the form of fibrous materials (cotton, linen), cellulose is used to make fabrics and threads. Cellulose ethers are used in the production of nitro varnishes, plastics, medical collodion, and artificial fiber.