If proteins are considered organic compounds, the most diverse in structure and function, then carbohydrates are the most common in nature. We encounter them everywhere: sugar, starch, paper, cotton and many other substances and materials are built from disaccharides and polysaccharides. The chemical properties of these compounds and their significance for human life, we will consider in our article.
Carbohydrate metabolism in the cell
Sucrose is one of the most important disaccharides synthesized by plants, such as sugarcane or sugar beets. The compound performs an energy function, so its splitting leads to the release of a large amount of energy. Hydrolysis of sucrose occurs in the cells of the human body and leads to the formation of glucose and fructose molecules:
12 22 11 + 2 = 6 12 6 + 6 12 6
The main factors for hydrolysis in laboratory or industrial conditions are heating and an excess of hydrogen ions that perform a catalytic function in the reacting mixture. The residues of fructose and glucose in the disaccharide are represented by their cyclic form and are interconnected due to the oxygen atom. Sucrose lacks free aldehyde groups, which is why it does not have a silver mirror reaction, and the carbohydrate does not exhibit reducing properties.
This is confirmed by the above equations for the reactions of disaccharides. The chemical properties of substances, namely the hydrolysis reaction, formed the basis for the classification of carbohydrates.
Types of carbohydrates
Substances that do not break down under the influence of water, for example, fructose found in honey and most fruits, as well as glucose, are monosaccharides or monoses. If, during hydrolysis, a carbohydrate decomposes into two simple sugar molecules, it refers to a disaccharide. This class includes sucrose and lactose. In the event that many monosaccharide residues are formed from one macromolecule of organic matter, they speak of polysaccharides. These include the well-known plant polymer - starch, which accumulates in the leaves, fruits, and seeds of plants during photosynthesis.
In the shell of arthropods and fungal cells is chitin. This carbohydrate, which in contrast to the earlier compounds containing not only carbon, hydrogen and oxygen, but also nitrogen. An interesting structure and features of the reaction that distinguish it from the chemical properties of disaccharides have hyaluronic acid, which is the basis of the intercellular substance in animals and humans. This is a linear polysaccharide , which is, in fact, one giant macromolecule containing up to 50,000 monomeric units. Its greatest amount is in the dermis, cartilage, vitreous body of the organ of vision. Animal starch - glycogen is synthesized in animal and human cells from glucose residues and is deposited in the form of reserve energy material in the liver cells - hepatocytes.
Chemical properties of disaccharides as an example of lactose
Milk is the first and most important food product for young mammals: animals and humans. In addition to milk protein - casein, fat, water, mineral salts and vitamins, it contains a carbohydrate - lactose or milk sugar. Its molecules consist of monosaccharide residues - glucose and galactose, each containing six carbon atoms. During the digestion of milk in the gastrointestinal tract, lactose breaks down to monosaccharides.
They are absorbed by the capillaries of the villi of the small intestine. All chemical properties of disaccharides pass with the participation of enzymes, for example, lactase, accelerating the hydrolysis of milk sugar. A decrease in the level of this substance, associated both with a genetic predisposition and with individual characteristics (age, specifics of nutrition), causes a disease - hypolactasia.
Restorative properties of carbohydrates
Lactose molecules are composed of galactose and glucose residues having open carbon chains and free aldehyde complexes. The presence of a functional group makes it possible to carry out reduction reactions, for example, with hydrogen. As a result, the -CHO atom complex, which is part of glucose, is reduced to the hydroxyl group, and a six-atom alcohol sorbitol forms. The ongoing reduction process can be expressed by equations, and the chemical properties of disaccharides, thus, will have the following form:
CH 2 OH - (CHOH) 4 - COH + H 2 = (temperature, Ni catalyst) => CH 2 OH - (CHOH) 4 -CH 2 OH
They depend on what forms of glucose are part of the carbohydrate: cyclic or with an open carbon skeleton.
The most important polysaccharides and their structural features
White powder, insoluble in cold water, and in hot, forming a paste - is starch. Its highest content is characteristic of rice and corn seeds, potato tubers. The macromolecule of a substance consists of cyclic alpha-glucose residues. In an acidic medium, it is hydrolyzed, the reaction equation has the following form:
(C 6 H 10 O 5 ) n + nH 2 O - H 2 SO 4 → nC 6 H 12 O 6
The chemical properties of disaccharides and polysaccharides have similarities: they are all capable of hydrolysis.
Cellulose, which is part of wood, contains monomers - beta-glucose residues. Heating a substance with concentrated nitric acid leads to the formation of an ester - three cellulose nitrate used in pyrotechnics.
In our article, we studied the chemical properties of disaccharides and polysaccharides and examined their distribution in nature.