White crystals, soluble in water and have a pleasant sweet taste - what is it? We are talking about carbohydrates familiar to everyone - fructose, glucose or sucrose. Complex substances of this class, called polysaccharides, the properties of which we will consider in our article, have characteristics that are not characteristic of mono- or oligosaccharides.
For example, starch, eatable, is an amorphous compound that is not soluble in water. Its colloidal solution does not have a sweet taste, and the chemical characteristic is fundamentally different from simple carbohydrates. What substances are polysaccharides (other than starch)? Cellulose is another complex carbohydrate. It is better known as wood. Inedible, completely insoluble in water, however, it has the same molecular formula (C 5 H 10 O 5 ) n as starch. How can this be explained? Let's figure it out.
How the structure of a substance affects its properties
Polysaccharides: starch, cellulose, glycogen, are giant macromolecules, consisting of repeatedly repeating similar units - monomers. They can be represented by molecules, for example, glucose, having a cyclic structure. At the same time, glucose, represented by an individual substance, has an open carbon skeleton form. The spatial form of its molecule determines good solubility in water, sweet taste and crystalline structure of the substance. Polysaccharides whose formula (C 5 H 10 O 5 ) n is starch and cellulose. Being isomers, the compounds have a different structure not only of the polymer chains themselves, but also of the structural elements - glucose particles. All this dramatically affects the properties of starch and cellulose, which differ from each other.
What substances relate to polysaccharides
In addition to starch and cellulose, the most common in plants, complex carbohydrates that are part of human, animal, insect or fungal organisms can be called. It is glycogen and chitin. Animal starch glycogen is a reserve energy compound. It is synthesized with an excess of glucose by the cells of the liver and muscles of higher mammals in the processes of assimilation. During periods of food shortage or during intense physical or emotional stress, glycogen breaks down to glucose. It enters the bloodstream and is supplied to the cells as the main energy material. Chitin is a structural carbohydrate that serves as the basis for the external skeleton of invertebrate animals. It is also part of the cell walls of fungi and integuments of crustaceans, spiders, ticks and insects.
Starch characterization
The composition of the polymer, which is the main product of photosynthetic activity of plants, includes cyclic alpha-glucose. The process of photosynthesis itself can be expressed as follows:
Photosynthesis reaction equation: 6CO2 + 6H2O → C6H12O6 + 6O2
Starch contains cyclic alpha-glucose molecules. This is a complex carbohydrate that looks like a white powder, in hot water it turns into a paste - a colloidal solution, but in cold water it remains practically insoluble. When eating potatoes, bread, rice and other starchy foods in the oral cavity, stomach and duodenum, the polysaccharide splits. This process is called hydrolysis, it occurs under the action of an enzyme - amylase. The reaction products are glucose molecules:
(6105) n + n H2O → n C6H12O6
Other polysaccharides can be synthesized in plants, the formula and molecules of which contain not glucose residues, but D-fructose, for example, inulin. It contains the roots of chicory or dahlia. The substance is used as a substitute for sugar in diseases of the pancreas.
Cellulose
Speaking about which substances belong to polysaccharides, we mentioned a plant polymer - cellulose. It has the same molecular formula as starch, yj is characterized by other properties. It's all about the structure of cellulose macromolecules. Its monomers are cyclic beta-glucose particles, and the relative molecular weight is several million. This significantly exceeds this indicator for starch, whose molecular weight is approximately 100,000 amu. Hydrolysis of wood in the presence of acids and when heated leads to the production of glucose, and from it - large volumes of ethyl alcohol.
Cellulose nitration is the way to get the ester - cellulose trinitrate. It is the starting material in the production of gunpowder. Crude glucose obtained by hydrolysis of woodworking waste products is used as an additive in feed in animal husbandry.
In our article, we found out which substances belong to polysaccharides, and also studied their properties and applications in industry.