Secondary metabolites are the most important physiologically active compounds in the plant world. Their number, studied by science, is increasing every year. At the moment, about 15% of all plant species have been studied for the presence of these substances. They also have high biological activity in relation to the body of animals and humans, which determines their potential as pharmaceuticals.
What are secondary metabolites?
A distinctive feature of all living organisms is that they have metabolism - metabolism. It is a set of chemical reactions that produce primary and secondary metabolites.
The difference between them is that the former are characteristic of all creatures (the synthesis of proteins, aminocarboxylic and nucleic acids, carbohydrates, purines, vitamins), while the latter are characteristic of certain types of organisms and do not participate in the growth and reproduction process. However, they also perform certain functions.
In the animal world, secondary compounds are rarely produced, more often they enterbody along with plant foods. These substances are synthesized mainly in plants, fungi, sponges and unicellular bacteria.
Features and Features
In biochemistry, the following main signs of secondary plant metabolites are distinguished:
- high biological activity;
- small molecular weight (2-3 kDa);
- production from a small amount of starting substances (5-6 amino acids for 7 alkaloids);
- synthesis is inherent in individual plant species;
- formation at later stages of development of a living organism.
Any of these features are optional. Thus, secondary phenolic metabolites are produced in all plant species, and natural rubber has a high molecular weight. The production of secondary metabolites in plants occurs only on the basis of proteins, lipids and carbohydrates under the influence of various enzymes. Such compounds do not have their own way for synthesis.
They also have the following features:
- presence in different parts of the plant;
- uneven distribution in tissues;
- localization in certain compartments of the cell to neutralize the biological activity of secondary metabolites;
- the presence of a basic structure (most often hydroxyl, methyl, methoxyl groups act in its role), on the basis of which other variants of compounds are formed;
- different types of structure changes;
- the ability to switch to an inactive, "reserve" form;
- lack of direct participation in metabolism.
Secondary metabolism is often viewed as the ability of a living organism to interact with its own enzymes and genetic material. The main process, as a result of which secondary compounds are formed, is dissimilation (decomposition of the products of primary synthesis). This releases a certain amount of energy, which is involved in the production of secondary compounds.
Functions
Initially, these substances were considered unnecessary waste products of living organisms. It is now established that they play a role in metabolic processes:
- phenols - participation in photosynthesis, respiration, electron transfer, production of phytohormones, development of the root system; attraction of pollinating insects, antimicrobial action; coloring of individual parts of the plant;
- tannins - development of resistance to fungal diseases;
- carotenoids - participation in photosynthesis, protection from photooxidation;
- alkaloids - growth regulation;
- isoprenoids - protection against insects, bacteria, animals;
- sterols – regulation of cell membrane permeability.
The main function of secondary compounds in plants is ecological: protection from pests, pathogenic microorganisms,adaptation to external conditions. Since environmental factors differ significantly for different types of flora, the spectrum of these compounds is almost limitless.
Classifications
There are several fundamentally different classifications of secondary metabolites:
- Trivial. Substances are divided into groups according to their specific properties (saponins form foam, bitters have an appropriate taste, and so on).
- Chemical. Based on the characteristics of the chemical structure of compounds. It is currently the most common. The disadvantage of this classification is that substances of the same group may differ in production method and properties.
- Biochemical. At the head of this type of systematization is the method of biosynthesis. It is the most scientifically substantiated, but due to the lack of knowledge of plant biochemistry, the use of this classification is limited.
- Functional. It is based on certain functions of substances in a living organism. The same group may contain secondary metabolites with different chemical structures.
The complexity of classification lies in the fact that each group of secondary metabolites is closely related to the others. Thus, bitters (a class of terpenes) are glycosides, and carotenoids (derivatives of tetraterpenes) are vitamins.
Main Groups
The following types of substances are classified as secondary metabolites of plant cells:
- alkaloids (pyridine,imidazole, purine, betalaines, glycoalkaloids, protoalkaloids and others);
- anthracene derivatives (derivatives of chryzacin, anthrone, alizarin and other compounds);
- phytosteriods (withanolides);
- glycosides (monosides, biosides and oligosides, cyanogenic glycosides and thioglycosides);
- isoprenoids (terpenes and their derivatives - terpenoids and steroids);
- phenolic compounds and others.
Many of these substances have unique properties. So, curare alkaloids are the strongest poison, and some groups of glycosides have a pronounced therapeutic effect and are used to make drugs used in the treatment of heart failure.
Application
Secondary metabolites have an active effect on the organs and systems of humans and animals, so they are widely used in pharmacology and veterinary medicine, are used as flavor and aroma enhancers in food products. Some plants that accumulate these substances in significant quantities are used as raw materials in the production of technical materials.
Abroad, in countries with a developed chemical industry, about a quarter of all compounds used in pharmacy are of plant origin. The valuable therapeutic effect of secondary metabolites is associated with their properties such as:
- wide range of action;
- minimum side effects even with prolongedreception;
- complex effect on the body;
- high efficiency.
Since these compounds are still poorly understood, their further research may lead to the creation of fundamentally new pharmaceuticals.
