Properties and structure of carbohydrates. Functions of carbohydrates

For the human body, as well as other living beings, energy is needed. Without it, no processes are possible. After all, every biochemical reaction, any enzymatic process or metabolic stage needs an energy source.

Therefore, the importance of substances that give the body strength for life is very large and important. What are these substances? Carbohydrates, proteins, fats. The structure of each of them is different, they belong to completely different classes of chemical compounds, but one of their functions is similar - providing the body with the necessary energy for life. Consider one group of these substances - carbohydrates.

Classification of carbohydrates

The composition and structure of carbohydrates since their discovery were determined by their name. After all, according to early sources, it was believed that this is a group of compounds in whose structure there are carbon atoms associated with water molecules.

A more thorough analysis, as well as accumulated information on the diversity of these substances allowed to prove that not all representatives have only such a composition. However, this sign is still one of those that determines the structure of carbohydrates.

The modern classification of this group of compounds is as follows:

1. Monosaccharides (ribose, fructose, glucose and so on).
2. Oligosaccharides (bioses, trioses).
3. Polysaccharides (starch, cellulose).

Also, all carbohydrates can be divided into the following two large groups:

• Restoring;
• Non-restoring.

The structure of the carbohydrate molecules of each group is discussed in more detail.

Monosaccharides: characteristic

This category includes all simple carbohydrates that contain aldehyde (aldose) or ketone (ketose) grouping and not more than 10 carbon atoms in the chain structure. If you look at the number of atoms in the main chain, then monosaccharides can be divided into:

• Trioses (glycerol aldehyde);
• Tetroses (erythrulosis, erythrose);
• Pentoses (ribose and deoxyribose);
• Hexoses (glucose, fructose).

All other representatives are not so important to the body as listed.

Features of the structure of molecules

In their structure monozems can be represented both in the form of a chain, and in the form of a cyclic carbohydrate. How does this happen? The thing is that the central carbon atom in the compound is an asymmetric center around which the molecule in the solution is able to rotate. Thus, optical isomers of L- and D-form monosaccharides are formed. In this case, the glucose formula, written in the form of a straight chain, can be mentally grasped as an aldehyde grouping (or ketone) and rolled into a ball. We obtain the corresponding cyclic formula.

The chemical structure of carbohydrates of a series of monozones is quite simple: a series of carbon atoms that form a chain or a cycle, from each of which on different or on one side are located hydroxyl groups and hydrogen atoms. If all the same structures on the same side, then the D-isomer is formed, if differently with alternation of each other - then the L-isomer. If we write down the general formula of the most common representative of glucose monosaccharides in molecular form, it will have the form: C ₆ H ₁₂ O ₆ . And this record reflects the structure and fructose too. After all, chemically these two monozems are structural isomers. Glucose - aldehyde alcohol, fructose - ketoalcohol.

The structure and properties of carbohydrates of a number of monosaccharides are closely interrelated. After all, because of the presence of aldehyde and ketone grouping in the structure, they belong to aldehyde and ketone alcohols, which determines their chemical nature and the reactions to which they are able to enter.

Thus, glucose exhibits the following chemical properties:

1. Reactions due to the presence of a carbonyl group:

• Oxidation - reaction of the "silver mirror";
• With freshly precipitated copper (II) hydroxide - aldonic acid;
• Strong oxidants are able to form dibasic acids (Aldar), transforming not only aldehyde, but also one hydroxyl group;
• Recovery - is converted into polyhydric alcohols.

2. In the molecule there are also hydroxyl groups, which reflects the structure. The properties of carbohydrates, which are affected by these groupings:

• Ability to alkylation - formation of ethers;
• Acylation - formation of esters ;
• A qualitative reaction to copper (II) hydroxide.

3. Narrow-specific properties of glucose:

• Oleaginous acid;
• Alcohol;
• Lactic fermentation.

Performed functions in the body

The structure and functions of carbohydrates of a number of monosomes are closely related. The latter are, first of all, participation in the biochemical reactions of living organisms. What role do monosaccharides play in this?

1. The basis for the production of oligo- and polysaccharides.
2. Pentoses (ribose and deoxyribose) are the most important molecules involved in the formation of ATP, RNA, and DNA. And they, in turn, are the main suppliers of hereditary material, energy and protein.
3. Concentration content of glucose in human blood is a correct indicator of osmotic pressure and its changes.

Oligosaccharides: structure

The structure of carbohydrates of this group is reduced to the presence of two (diozy) or three (triozy) molecules of monosaccharides in the composition. There are also those with 4, 5 or more structures (up to 10), but the most common are disaccharides. That is, during hydrolysis such compounds break up with the formation of glucose, fructose, pentose and so on. Which connections are in this category? A typical example is sucrose (ordinary cane sugar), lactose (the main component of milk), maltose, lactulose, isomaltose.

The chemical structure of carbohydrates of this series has the following features:

1. The general formula of the molecular species is: C ₁₂ H ₂₂ O _11.
2. Two identical or different monazide residues in the structure of the disaccharide are joined together by a glycosidic bridge. The character of this compound will depend on the reducing ability of the sugar.
3. Regenerating disaccharides. The structure of carbohydrates of this type consists in the formation of a glycosidic bridge between the hydroxyl of the aldehyde and hydroxyl groups of different mono- molecular molecules. This includes: maltose, lactose and so on.
4. Non-reducing - a typical example of sucrose - when a bridge forms between the hydroxyls of only the corresponding groups, without the participation of the aldehyde structure.

Thus, the structure of carbohydrates can be briefly represented in the form of a molecular formula. If a detailed detailed structure is required, then it can be represented using Fisher graphical projections or Hevors formulas. And specifically, two cyclic monomers (monozems) are either different, or identical (depending on the oligosaccharide), connected together by a glycosidic bridge. When constructing, it is necessary to take into account the restoring capacity for the correct display of the connection.

Examples of disaccharide molecules

If the task is in the form: "Note the peculiarities of the structure of carbohydrates," then for disaccharides it is best to first indicate from which remnants of monose it consists. The most common types are:

• Sucrose - is constructed from alpha-glucose and betta-fructose;
• Maltose - from the remains of glucose;
• Cellobiose - consists of two residues of beta-glucose D-form;
• Lactose - galactose + glucose;
• Lactulose - galactose + fructose and so on.

Then, on the basis of available residues, a structural formula with a clear prescription for the type of glycosidic bridge should be made.

Significance for living organisms

The role of disaccharides is very great, not only is the structure important. The functions of carbohydrates and fats are generally similar. The basis is the energy component. Nevertheless, for some individual disaccharides, their particular significance should be indicated.

1. Sucrose is the main source of glucose in the human body.
2. Lactose is found in breast milk of mammals, including in women up to 8%.
3. Lactulose is obtained in the laboratory for medical use, and is also added to the production of dairy products.

Any disaccharide, trisaccharide and so on in the human body and other creatures undergoes instant hydrolysis with the formation of monoz. It is this feature that underlies the use of this class of carbohydrates by a person in a raw, unchanged form (beet or sugar cane).

Polysaccharides: molecular features

The functions, composition and structure of carbohydrates of this series are of great importance for the organisms of living beings, as well as for human economic activities. First, it is necessary to understand which carbohydrates belong to polysaccharides.

There are a lot of them:

• starch;
• glycogen;
• Murine;
• Glucomannan;
• cellulose;
• dextrin;
• Galactomannan;
• Muromin;
• Pectin substances;
• Amylose;
• chitin.

This is not a complete list, but only the most significant for animals and plants. If you carry out the task "Note the peculiarities of the structure of carbohydrates of a number of polysaccharides", then first of all you should pay attention to their spatial structure. These are very voluminous, gigantic molecules consisting of hundreds of monomer units, crosslinked with glycoside chemical bonds. Often, the structure of carbohydrate molecules of polysaccharides is a layered composition.

There is a definite classification of such molecules.

1. Homopolysaccharides - consist of identical multiply repeating units of monosaccharides. Depending on the monozoa can be hexoses, pentoses and so on (glucans, mannans, galactans).
2. Heteropolysaccharides are formed by different monomer units.

For compounds with a linear spatial structure, for example, cellulose should be included. Branched structure has the majority of polysaccharides - starch, glycogen, chitin and so on.

The role of living beings in the body

The structure and functions of carbohydrates in this group are closely related to the vital activity of all beings. For example, plants in the form of a reserve nutrient accumulate starch in different parts of the shoot or root. The main source of energy for animals is again polysaccharides, in the splitting of which a lot of energy is generated.

Carbohydrates in the structure of the cells play a very significant role. Of chitin is the cover of many insects and crustaceans, murine - a component of the cell wall of bacteria, cellulose is the basis of plants.

A spare nutrient of animal origin is the molecules of glycogen, or, as it is more often called, animal fat. It is stored in separate parts of the body and performs not only energy, but also a protective function from mechanical influences.

For most organisms, the structure of carbohydrates is of great importance. The biology of every animal and plant is such that it requires a constant source of energy, inexhaustible. And this can only be given by them, and most of all in the form of polysaccharides. So, the complete cleavage of 1 g of carbohydrate as a result of metabolic processes leads to the release of 4.1 kcal of energy! This is the maximum, no more connections. That is why carbohydrates must necessarily be present in the diet of any person and animal. Plants take care of themselves: in the process of photosynthesis, they form a starch inside themselves and store it.

Common properties of carbohydrates

The structure of fats, proteins and carbohydrates in general is similar. After all, they are all macromolecules. Even some of their functions are of a common nature. It is necessary to generalize the role and importance of all carbohydrates in the life of the biomass of the planet.

1. The composition and structure of carbohydrates means their use as a building material for the shell of plant cells, membranes of animals and bacterial, and the formation of intracellular organelles.
2. Protective function. It is characteristic of plant organisms and is manifested in the formation of spikes, thorns, and so on.
3. Plastic role - the formation of vital molecules (DNA, RNA, ATP and others).
4. Receptor function. Polysaccharides and oligosaccharides are active participants in transport transportations through the cell membrane, "guards" that capture the effects.
5. The energy role is the most significant. Provides maximum energy for all intracellular processes, as well as the work of the whole organism as a whole.
6. Regulation of osmotic pressure - glucose performs such control.
7. Some polysaccharides become a reserve nutrient, a source of energy for animal creatures.

Thus, it is obvious that the structure of fats, proteins and carbohydrates, their functions and role in the organisms of living systems are decisive and decisive. These molecules are the creators of life, they are preserving and supporting it.

Carbohydrates with other high-molecular compounds

Also, the role of carbohydrates is known not in pure form, but in combination with other molecules. To such it is possible to carry such most widespread, as:

• Glycosaminoglycans or mucopolysaccharides;
• Glycoproteins.

The structure and properties of carbohydrates of this kind are quite complex, because a variety of functional groups join the complex. The main role of molecules of this type is participation in many life processes of organisms. Representatives are: hyaluronic acid, chondroitin sulfate, heparan, keratan-sulfate and others.

There are also complexes of polysaccharides with other biologically active molecules. For example, glycoproteins or lipopolysaccharides. Their existence is important in the formation of immunological reactions of the body, as they are part of the cells of the lymphatic system.