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Properties and structure of carbohydrates. Carbohydrate functions

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 value of substances that provide the body with the force of life is very great 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.

carbohydrate structure

Carbohydrate classification

The composition and structure of carbohydrates from the moment of their discovery was determined by their name. Indeed, according to early sources, it was believed that this is such a group of compounds in the structure of which there are carbon atoms bound to water molecules.

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

The current 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:

  • restorative;
  • non-reducing.

The structure of carbohydrate molecules of each group will be considered in more detail.

Monosaccharides: Characterization

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

  • trioses (glycerin aldehyde);
  • tetrosis (erythrulose, erythrosis);
  • pentoses (ribose and deoxyribose);
  • hexoses (glucose, fructose).

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

the structure of protein fats and carbohydrates

Structural Features of Molecules

In their structure, monoses 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 solution is able to rotate. Thus, the optical isomers of L- and D-type monosaccharides are formed. In this case, the glucose formula, written in the form of a straight chain, can be mentally grasped by the aldehyde group (or ketone) and rolled up into a ball. The corresponding cyclic formula is obtained.

The chemical structure of the carbohydrates of a number of monoses is quite simple: a series of carbon atoms forming a chain or cycle, from each of which hydroxyl groups and hydrogen atoms are located on different or one side. If all the structures of the same name are on the same side, then the D-isomer is formed, if on different with alternating each other - then the L-isomer. If you write down the general formula of the most common representative of glucose monosaccharides in molecular form, then it will look like: C 6 H 12 O 6 . Moreover, this entry reflects the structure and fructose, too. After all, chemically these two monoses are structural isomers. Glucose - aldehyde alcohol, fructose - keto alcohol.

The structure and properties of carbohydrates of a number of monosaccharides are closely interrelated. Indeed, due to the presence of the aldehyde and ketone groups in the structure, they belong to aldehyde and keto alcohols, which determines their chemical nature and the reactions in which they are able to enter.

So, glucose exhibits the following chemical properties:

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

  • oxidation is the reaction of a silver mirror;
  • with freshly precipitated copper (II) hydroxide - aldonic acid;
  • strong oxidizing agents are able to form dibasic acids (aldaric), transforming not only the aldehyde, but also one hydroxyl group;
  • recovery - converted to polyhydric alcohols.

chemical structure of carbohydrates

2. The molecule also contains hydroxyl groups, which reflects the structure. Properties of carbohydrates that are affected by these groups:

  • the ability to alkylate - the formation of ethers;
  • acylation - the formation of esters ;
  • high-quality reaction to copper (II) hydroxide.

3. Narrow-specific properties of glucose:

  • butyric acid;
  • alcohol;
  • lactic acid fermentation.

Functions in the body

The structure and functions of carbohydrates of a number of monoses are closely related. The latter are, first of all, in the participation in 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. The concentration of glucose in human blood is a reliable indicator of osmotic pressure and its changes.

note the structural features of carbohydrates

Oligosaccharides: structure

The structure of carbohydrates of this group is reduced to the presence of two (dioses) or three (trioses) monosaccharide molecules in the composition. There are those with 4, 5 or more structures (up to 10), but disaccharides are the most common. That is, upon hydrolysis, such compounds decompose to form glucose, fructose, pentose, and so on. What compounds belong to 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. General molecular formula: C 12 H 22 O 11.
  2. Two identical or different monose residues in the structure of the disaccharide are interconnected using a glycosidic bridge. The regenerative ability of sugar will depend on the nature of this compound.
  3. Reducing 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 monosis molecules. These include: maltose, lactose, and so on.
  4. Non-reducing - a typical example of sucrose - when the bridge is formed 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 needed, then it can be represented using Fischer graphic projections or Heworth's formulas. Specifically, two cyclic monomers (monoses) are either different or the same (depending on the oligosaccharide), interconnected by a glycosidic bridge. When building, you should take into account the restoring ability to correctly display the connection.

composition and structure of carbohydrates

Examples of disaccharide molecules

If the task is in the form: "Mark the structural features of carbohydrates," then for disaccharides it is best to first indicate what residues the monosis consists of. The most common types are:

  • sucrose - built from alpha glucose and beta-fructose;
  • maltose - from glucose residues;
  • cellobiose - consists of two residues of beta-glucose D-form;
  • lactose - galactose + glucose;
  • lactulose - galactose + fructose and so on.

Then, using the available residues, a structural formula should be drawn up with a clear prescription of the type of glycosidic bridge.

Value for living organisms

The role of disaccharides is very great, not only the structure is important. The functions of carbohydrates and fats are generally similar. The basis is the energy component. Nevertheless, for some individual disaccharides, their special 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 female 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 monosis. It is this feature that underlies the use of this class of carbohydrates by humans in raw, unchanged form (beet or cane sugar).

structure and properties of carbohydrates

Polysaccharides: Features of Molecules

The functions, composition and structure of carbohydrates of this series are of great importance for living organisms, as well as for human economic activity. First, you need to figure out which carbohydrates belong to polysaccharides.

There are a lot of them:

  • starch;
  • glycogen;
  • murein;
  • 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 structural features of the carbohydrates of a number of polysaccharides", then first of all you should pay attention to their spatial structure. These are very voluminous, giant molecules consisting of hundreds of monomeric units crosslinked by glycosidic chemical bonds. Often the structure of polysaccharide carbohydrate molecules is layered composition.

There is a certain classification of such molecules.

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

Compounds with a linear spatial structure should include, for example, cellulose. The branched structure has the majority of polysaccharides - starch, glycogen, chitin and so on.

the structure of carbohydrate molecules

Role in the body of living things

The structure and functions of carbohydrates of this group are closely related to the life of all creatures. So, 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, which, when broken down, generate a lot of energy.

Carbohydrates play a very significant role in the structure of cells . The cover of many insects and crustaceans consists of chitin, murein is a component of the bacterial cell wall, cellulose is the basis of plants.

A reserve nutrient of animal origin is glycogen molecules, or, as it is 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 each animal and plant is such that it requires a constant source of energy, inexhaustible. And only they can give it, and most of all it is in the form of polysaccharides. So, the complete breakdown 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 connection anymore. That is why carbohydrates must be present in the diet of any person and animal. Plants take care of themselves: in the process of photosynthesis, they form starch inside themselves and store it.

Common carbohydrate properties

The structure of fats, proteins and carbohydrates is generally similar. After all, they are all macromolecules. Even some of their functions are of a common nature. The role and importance of all carbohydrates in the life of the planet’s biomass should be generalized.

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

Thus, it is obvious that the structure of fats, proteins and carbohydrates, their functions and role in living organisms are crucial and decisive. These molecules are the creators of life, they also preserve and support it.

Carbohydrates with other high molecular weight compounds

The role of carbohydrates is not known in its pure form, but in combination with other molecules. These include the most common, such as:

  • glycosaminoglycans or mucopolysaccharides;
  • glycoproteins.

The structure and properties of carbohydrates of this kind are quite complex, because a variety of functional groups are combined into a 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, since they are part of the cells of the lymphatic system.

Source: https://habr.com/ru/post/G39879/

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