Properties of carbohydrates. Functions and properties of carbohydrates: table

In living nature, many substances are widely distributed, the importance of which is difficult to overestimate. For example, these include carbohydrates. They are extremely important as a source of energy for animals and humans, and some properties of carbohydrates make them an indispensable raw material for industry.

What it is?

These are all substances whose structure can be described by the formula Cn (H ₂ O) m. They have a huge biological significance, play a crucial role in the lives of many living beings.

The name of this group of scientists came up after the primary analysis of the substances that included it was made. Then it was found out that their main components are carbon and water. Later it turned out that the name turned out to be extremely accurate, since the properties of carbohydrates are such that the ratio of hydrogen and oxygen atoms in them is completely identical to that in water. Simply put, there is only one oxygen for two hydrogen atoms. The Russian version of the name was first proposed in 1844 by Professor K. Schmidt.

Some additions

If you slightly modify the above formula, putting "n" in parentheses, the expression will become somewhat different: Sm (H ₂ O) n. Perhaps, it reflects the very essence of the name "coal - water" as well as possible.

To date, scientists have accurately established that there are a number of substances that have the properties of carbohydrates, but do not quite correspond to the formula described by us. That is why in foreign literature one can often come across the word "glycides", which is a modern synonym for the term of 1844, which turned out to be not quite accurate.

Simple classification

The entire huge class of substances can be divided into two large groups: simple and complex glycides. What are the properties of carbohydrates that they include? Actually, they are also not very complex:

• Simple are those substances from the group that do not lend themselves to hydrolysis, followed by the formation of other carbohydrates. But the main difference is that the number of oxygen atoms in their structure is equal to the same number of carbon atoms. They are called monosaccharides.
• Accordingly, the definition of "complex" all those glycides that fall into hydrolysis with the formation of several simple carbohydrates. Of course, they have a different ratio of oxygen and carbon atoms. They are called disaccharides. A very large role in nature is played by complex carbohydrates, a list of which we partially mention in the article.

In addition, there is another classification, according to which carbohydrates are divided into three types. Here they are:

• Monosaccharides.
• Oligosaccharides.
• Polysaccharides.

The following table of carbohydrates will certainly help you understand their most important differences.

Mono- (1 molecule)	Oligo- (<10 molecules)	Poly- (> 10 molecules)
Aldoses, ketoses	This includes disaccharides, trisaccharides, and so on.	There are two types: Homopolysaccharides. Heteropolysaccharides. From the name it can be understood that the internal molecular structure of these two species is quite different

Of course, we gave a brief table of carbohydrates, but it's simply impossible to fit all the specific features that are characteristic of some representatives of this vast class. Therefore, we will analyze the main groups each separately, detailing the properties of some individual, most common substances. So, what are the classes of carbohydrates?

Monosaccharides

It should be remembered that they all belong to the category of solids, they are easily capable of transitioning to a crystalline state. They are extremely hygroscopic, perfectly soluble in water, forming a syrup. It is very difficult to distinguish them in the form of crystals from there. Their solutions have a neutral reaction, most often sweetish to taste. The intensity of taste is different: for example, fructose is about 3-3.5 times sweeter than the most commonly found glucose.

About the structural form

All these substances are compounds of bifunctional structure, which necessarily include a carbon skeleton, one carbonyl group and several hydroxyl groups. If the role of the carbonyl group is an aldehyde group, the substance is called aldose. Accordingly, in the case of the presence of a ketone "tail," they are called ketoses.

Since in nature these substances are extremely distributed, they can be found both in their free state and in the form of anhydride forms. In general, almost all complex carbohydrates are to some extent anhydrides of simple sugars, which are rather easily obtained by taking several (or one) water molecules (prefix "an" - absence).

Glucose as the most typical representative

The formula of this most typical representative of his group is C ₆ H ₁₂ O ₆ . Very often, these carbohydrates are found in the plant cell. It is not only widespread, but also very important for the body, since it is the main source of energy for it (talking about animals and man, of course). In principle, these are the common properties of proteins, carbohydrates and fats for all animal organisms. In addition, it is widely used in medicine, veterinary medicine, industry (including food).

Physical properties

What are the common physical properties of carbohydrates in this group? Appearance - small crystals of white color, taste sweet, in water dissolve well. Dissolubility sharply increases if the solution is heated: in this way glucose syrup is obtained .

Brief information on the chemical structure

If we look at the linear formula, one aldehyde and five hydroxyl groups are clearly visible in this carbohydrate. When the substance is in a crystalline state, its molecules can be in one of two possible forms (α- or β-glucose). The fact is that the hydroxyl group linked to the fifth carbon atom can interact with the carbonyl residue.

Prevalence in natural conditions

Since it is exceptionally abundant in grape juice, glucose is often called "grape sugar". Under this name, our distant ancestors also knew it. However, it can be found in any other sweet vegetable or fruit, in the soft tissues of the plant. In the animal world, its prevalence is not lower: about 0.1% of our blood is glucose. In addition, you can find these carbohydrates in the cage of almost any internal organ. But especially there are a lot of them in the liver, since it is there that glucose is processed into glycogen.

It (as we already said) is a valuable source of energy for our body, it is part of almost all complex carbohydrates. Like other simple carbohydrates, in nature it occurs after the reaction of photosynthesis, which occurs exclusively in the cells of plant organisms:

6CO ₂ + 6H ₂ O chlorophyll C ₆ H ₁₂ O ₆ + 6 O ₂ - Q

Plants at the same time perform an incredibly important function for the biosphere, accumulating the energy that they receive from the sun. With regard to industrial conditions, grape sugar has been obtained from starch from time to time, producing its hydrolysis, with the reaction catalyst being concentrated sulfuric acid:

(C ₆ H ₁₀ O ₅ ) n + n H ₂ O H ₂ SO ₄ , t n C ₆ H ₁₂ O ₆

Chemical properties

What are the chemical properties of carbohydrates of this kind? Have all the same characteristics that are peculiar to alcohol and aldehyde. In addition, they also have some specific features. The first synthesis of simple carbohydrates (including glucose) was produced by the talented chemist A. M. Butlerov in 1861, and as raw material he used formaldehyde, splitting it in the presence of calcium hydroxide. Here is the formula for this process:

6HSSON -------> C6H ₁₂ O ₆

And now we will consider some properties of two other representatives of the group, whose natural value is no less great, and therefore they are studied by biology. Carbohydrates of these species play a very important role in our daily lives.

Fructose

The formula for this glucose isomer is CeH ₁₂ O. Like the "progenitor" can exist in a linear and cyclical form. Enter all the reactions that are typical for polyhydric alcohols, but, thus, differing from glucose, does not interact with an ammoniacal solution of silver oxide.

Ribose

Ribose and deoxyribose are of great interest. If you remember the biology program a little, you yourself know very well that these carbohydrates in the body are part of DNA and RNA, without which the very existence of life on the planet is impossible. The name "deoxyribose" means that in its molecule, one oxygen atom is less (if compared with ordinary ribose). Being similar in this respect to glucose, they can also have a linear and cyclic structure.

Disaccharides

In principle, these substances in their structure and functions in many ways repeat the previous class, and therefore there is no reason to dwell on this in more detail. What are the chemical properties of carbohydrates related to this group? The most important representatives of the family are sucrose, maltose and lactose. All of them can be described by the formula C ₁₂ H ₂₂ O ₁₁ , since they are isomers, but this does not cancel out the huge differences in their structure. So what is characteristic of complex carbohydrates, a list and description of which you can see below?

Sucrose

Its molecule consists of two cycles at once: one of them is a six-membered (α-glucose residue), and the other is a five-membered (β-fructose residue). The whole construction is connected by glycoside hydroxyl glucose.

Getting and general value

According to the preserved historical information, even three centuries before the Nativity of Christ, sugar from sugar cane learned to receive in Ancient India. Only in the middle of the 19th century it turned out that much more sucrose with lesser efforts could be extracted from sugar beet. Some of its grades contain up to 22% of this carbohydrate, while in cane the content can be within 26%, but this is possible only under ideal growing conditions and a favorable climate.

We have already said that carbohydrates dissolve well in water. It is on this principle that the production of sucrose is based, when diffusion apparatuses are used for this purpose. To precipitate possible impurities, the solution is filtered through filters containing lime. To remove calcium hydroxide from the resulting solution, ordinary carbon dioxide is passed through it. The precipitate is filtered off, and the sugar syrup is evaporated in special ovens, obtaining the sugar we already know.

Lactose

This carbohydrate in industrial conditions is extracted from regular milk, in which fat and carbohydrates are abundant. It contains a lot of this substance: thus, cow's milk contains about 4-5.5% of lactose, and in the milk of women its volume fraction reaches 5.5-8.4%.

Each molecule of this glycid consists of the residues of 3-galactose and a-glucose in the pyranose form, which form bonds through the first and fourth carbon atoms.

Unlike other sugars, lactose has one exceptional property. This is a complete lack of hygroscopicity, so that even in a damp room this glycid does not damp at all. This property is actively used in pharmaceuticals: if the composition of a drug in the powder form includes the usual sucrose, then lactose is necessarily added to it. It is completely natural and harmless to the human body, unlike many artificial additives that prevent caking and wetting. What are the functions and properties of carbohydrates of this type?

The biological significance of lactose is extremely high, since lactose is the most important nutrient component of milk of all animals and humans. As for maltose, its properties are somewhat different.

Maltose

It is an intermediate product, which is obtained by hydrolysis of starch. The name "maltose" was received due to the fact that it is formed largely under the influence of malt (maltum in Latin maltum). It is widely distributed not only in plant, but also in animal organisms. In large quantities, it forms in the digestive tract of ruminant animals.

Chemical structure and properties

The molecule of this carbohydrate consists of two parts of α-glucose in the pyranose form, which are connected together by the first and fourth carbon atoms. In appearance it is colorless, white crystals. The taste is sweet, perfectly soluble in water.

Polysaccharides

It should be remembered that all polysaccharides can be considered from the point of view that they are products of polycondensation of monosaccharides. Their general chemical formula is (C ₆ H ₁₀ O ₅ ) n. In the framework of this article, we will consider starch, since it is the most typical representative of the family.

Starch

It is formed as a result of photosynthesis, in large quantities it is deposited in the roots and seeds of plant organisms. What are the physical properties of carbohydrates of this species? In appearance it is a white powder with a poor crystallinity, insoluble in cold water. In a hot liquid, it forms a colloidal structure (paste, kissel). In the digestive tract of animals, there are many enzymes that promote its hydrolysis with the formation of glucose.

It is the most common natural polymer, which is formed from a variety of a-glucose residues. In nature, simultaneously there are two of its forms: amylose and amshopectin. Amylose, being a linear polymer, can be dissolved in water. The molecule consists of the residues of alpha-glucose, which are linked through the first and fourth carbon atoms.

It should be remembered that it is starch that is the first visible product of plant photosynthesis. In wheat and other cereals it contains up to 60-80%, whereas in potato tubers it is only 15-20%. By the way, according to the type of starch grains under a microscope, it is possible to accurately determine the species belonging of a plant, since they are all different.

If the carbohydrate is heated quickly , its huge molecule will quickly decompose with the formation of small polysaccharides, which are known as dextrins. They have one common chemical formula (C ₆ H ₁₂ O ₅ ) x with starch, but there is a difference in the value of the variable "x", which is less than the value "n" in starch.

Finally, we give a table, which reflects not only the main classes of carbohydrates, but also their properties.

Basic Groups	Features of molecular structure	Distinctive properties of carbohydrates
Monosaccharides	Differences in the number of carbon atoms: Trioses (C3) Tetrose (C4) Pentoses (C5) Hexoses (C6)	Colorless or white crystals, perfectly soluble in water, sweet to taste
Oligosaccharides	Complex structure. Depending on the species, they contain 2-10 residues of simple monosaccharides	Appearance is the same, slightly more soluble in water, less sweet taste
Polysaccharides	Consist of a very large number of monosaccharide residues	White powder, the crystal structure is weakly expressed, do not dissolve in water, but have a property in it to swell. Neutral

Here are the functions and properties of carbohydrates of the main classes.