In living nature, many substances are widespread, the value of which is difficult to overestimate. For example, these include carbohydrates. They are extremely important as an energy source 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 are of great biological importance, play a crucial role in the life of many living things.
Scientists came up with the name of this group after the initial analysis of the substances that make up it was made. Then it was found 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, two oxygen atoms have one oxygen. The first Russian version of the name was proposed in 1844 by Professor C. Schmidt.
Some additions
If you slightly modify the above formula, putting “n” out of the brackets, the expression will be slightly different: See (H 2 O) n. Perhaps it is it that perfectly reflects the very essence of the name “coal - water”.
To date, scientists have precisely 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. And therefore, in foreign literature it is often possible to stumble upon the word "glycides", which is a modern synonym for the term 1844, which turned out to be not entirely 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 the carbohydrates that they contain? Actually, they also do not differ in great complexity:
- Simple are those substances from the group that are not amenable to hydrolysis with the subsequent formation of other carbohydrates. But the main difference is that the number of oxygen atoms in their structure is equal to the similar number of carbon atoms. They are called monosaccharides.
- Accordingly, the definition of “complex” includes all those glycides that decompose upon hydrolysis to form several simple carbohydrates. Of course, their ratio of oxygen and carbon atoms is different. They are called disaccharides. Complex carbohydrates play a very large role in nature, a list of which we partially provide 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 | These include disaccharides, trisaccharides, etc. | There are two types: - Homopolysaccharides.
- Heteropolysaccharides.
From the name it can be understood that the internal molecular structure of these two species is completely different |
Of course, we provided a brief table of carbohydrates, but it is simply impossible to fit into its framework all the specific features that are inherent in some representatives of this vast class. Therefore, we will analyze the main groups each separately, focusing more on 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, are easily able to pass into a crystalline state. They are extremely hygroscopic, perfectly soluble in water, forming a syrup. It is very difficult to isolate them in the form of crystals from there. Their solutions have a neutral reaction, most often sweetish in taste. The taste intensity is different: for example, fructose is approximately 3-3.5 times sweeter than the most common glucose.
About structural form
All these substances are compounds of a bifunctional structure, which necessarily include a carbon skeleton, one carbonyl group and several hydroxyl ones. If an aldehyde group acts as a carbonyl group, the substance is called an aldose. Accordingly, in the case of the presence of a ketone tail, they are called ketoses.
Since these substances are extremely abundant in nature, they can be found both in their free state and in the form of anhydride forms. In general, almost all complex carbohydrates are, to one degree or another, anhydrides of simple sugars, which are quite easily obtained by removing several (or one) water molecules (the prefix "an" is the absence).
Glucose as the most typical representative
The formula of this most typical representative of his group is C 6 H 12 O 6 . These carbohydrates are very common in plant cells. It is not only widespread, but also very important for the body, as it is the main source of energy for it (we are talking about animals and humans, of course). In principle, these are the general 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 general physical properties of carbohydrates in this group? Appearance - small crystals of white color, taste sweetish, dissolve well in water. Solubility increases dramatically if the solution is heated: in this way glucose syrup is obtained .
Brief information about the chemical structure
If you look at the linear formula, then one aldehyde and five hydroxyl groups are clearly visible in the composition of this carbohydrate. When a substance is in a crystalline state, its molecules can be in one of two possible forms (α- or β-glucose). The fact is that a hydroxyl group linked to a fifth carbon atom can interact with a carbonyl residue.
Natural prevalence
Since it is abundant in grape juice, glucose is often called “grape sugar”. Under that name, our distant ancestors still knew her. However, you can find it in any other sweet vegetable or fruit, in the soft tissues of the plant. In the animal kingdom, its prevalence is no lower: approximately 0.1% of our blood is glucose. In addition, you can find these carbohydrates in the cell of almost any internal organ. But especially there are a lot of them in the liver, since it is there that glucose is converted to glycogen.
It (as we have 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 photosynthesis reaction, which occurs exclusively in the cells of plant organisms:
6CO 2 + 6H 2 O chlorophyll C 6 H 12 O 6 + 6O 2 - Q
At the same time, plants fulfill an incredibly important function for the biosphere, accumulating the energy that they receive from the sun. As for industrial conditions, grape sugar has been obtained from starch since ancient times, producing its hydrolysis, and concentrated sulfuric acid is the reaction catalyst:
(C 6 H 10 O 5 ) n + nH 2 O H 2 SO 4 , t nC 6 H 12 O 6
Chemical properties
What are the chemical properties of carbohydrates of this kind? They have all the same characteristics that are characteristic of purely alcohols and aldehydes. In addition, they have some specific features. The synthesis of simple carbohydrates (including glucose) was first performed by the most talented chemist A. M. Butlerov in 1861, and he used formaldehyde as a raw material, breaking it down in the presence of calcium hydroxide. Here is the formula for this process:
6NSON -------> 6 12 6
And now we will consider some properties of two other representatives of the group, the natural value of which is no less great, and therefore biology studies them. Carbohydrates of these species play a very important role in our daily life.
Fructose
The formula for this glucose isomer is CeH
12 O
b . Like a "grandparent" can exist in a linear and cyclic form. It enters into all reactions that are characteristic of polyhydric alcohols, but, thereby differing from glucose, does not interact in any way with an ammonia solution of silver oxide.
Ribose
Of great interest is ribose and deoxyribose. If you even remember a little the biology program, then you yourself are well aware that these very 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 there is one less oxygen atom in its molecule (if compared with ordinary ribose). Being similar in this respect to glucose, can also have a linear and cyclic structure.
Disaccharides
In principle, these substances in their structure and functions largely repeat the previous class, and therefore it makes no sense to dwell on this in more detail. What are the chemical properties of carbohydrates belonging to this group? The most important members 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 negate 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 contains two cycles at once: one of them is six-membered (α-glucose residue), and the other five-membered (β-fructose residue). All this construction is connected due to glycosidic hydroxyl glucose.
Receiving and general meaning
According to preserved historical information, even three centuries before the birth of Christ, sugar from sugarcane was learned in ancient India. Only in the middle of the 19th century it turned out that much more sucrose with less effort can be obtained from sugar beets. Some of its varieties contain up to 22% of this carbohydrate, while the reed content can be up to 26%, but this is only possible under ideal growing conditions and a favorable climate.
We have already said that carbohydrates dissolve well in water. It is on this principle that sucrose production is based when diffusers are used for this purpose. To precipitate possible impurities, the solution is filtered through filters, which include 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, getting the already familiar sugar at the output.
Lactose
This carbohydrate in industrial conditions is released from ordinary milk, which contains excess fats and carbohydrates. It contains quite a lot of this substance: for example, cow's milk contains about 4-5.5% lactose, and in the milk of women its volume fraction reaches 5.5-8.4%.
Each molecule of this glycide consists of 3-galactose and a-glucose residues in pyranose form, which form bonds through the first and fourth carbon atoms.
Unlike other sugars, lactose has one exceptional property. It is a complete absence of hygroscopicity, so even in a humid room, this glycide does not dampen at all. This property is actively used in pharmaceuticals: if regular sucrose is part of a medicine in powder form, then lactose is definitely added to it. It is completely natural and harmless to the human body, unlike many artificial additives that prevent caking and getting wet. What are the functions and properties of carbohydrates of this type?
The biological significance of lactose is extremely high, since lactose is an essential nutrient component of milk of all animals and humans. As for maltose, its properties are somewhat different.
Maltose
It is an intermediate product that is obtained by hydrolysis of starch. The name "maltose" received due to the fact that it is formed largely under the influence of malt (in Latin malt - maltum). Widely distributed not only in plant, but also in animal organisms. In large quantities, it is formed in the digestive tract of ruminants.
Chemical structure and properties
The molecule of this carbohydrate consists of two parts of α-glucose in pyranose form, which are interconnected by the first and fourth carbon atoms. It looks like colorless, white crystals. On the palate - sweetish, 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 b N 10 O 5 ) p. In 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 and is deposited in large quantities in the roots and seeds of plant organisms. What are the physical properties of carbohydrates of this kind? It looks like a white powder with poor crystallinity, insoluble in cold water. In a hot liquid it forms a colloidal structure (paste, jelly). In the digestive tract of animals there are many enzymes that contribute to its hydrolysis with the formation of glucose.
It is the most common natural polymer, which is formed from many a-glucose residues. In nature, two of its forms occur simultaneously: amylose and amshopectin. Amylose, being a linear polymer, can be dissolved in water. The molecule consists of alpha-glucose residues that are linked through the first and fourth carbon atoms.
It must 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%, while in potato tubers - only 15-20%. By the way, by the type of starch grains under a microscope, it is possible to accurately determine the species affiliation of the plant, since they are all different.
If the
carbohydrate is quickly heated, its huge molecule will quickly decompose to form small polysaccharides, which are known as dextrins. They have one common chemical formula with starch (C
6 H
12 O
5 ) x, but there is a difference in the value of the variable "x", which is less than the value of "n" in starch.
Finally, we present a table that reflects not only the main classes of carbohydrates, but also their properties.
Main groups | Features of the molecular structure | Distinctive properties of carbohydrates |
Monosaccharides | They differ in the number of carbon atoms: - Trioses (C3)
- Tetrosis (C4)
- Pentoses (C5)
- Hexoses (C6)
| Colorless or white crystals, highly soluble in water, sweet to taste |
Oligosaccharides | The complex structure. Depending on the species, they contain 2-10 residues of simple monosaccharides | Appearance is the same, slightly soluble in water, less sweet taste |
Polysaccharides | Consist of a very large amount of monosaccharide residues | White powder, crystalline structure is weakly expressed, does not dissolve in water, but they tend to swell in it. It tastes neutral |
Here are the functions and properties of carbohydrates of the main classes.