lipid compounds. The importance of lipids in the life of the human body and their functions

organic matter. general characteristics. Lipids

organic matter are complex carbon-containing compounds. These include proteins, fats, carbohydrates, enzymes, hormones, vitamins and products of their transformations present in living organisms.

The name "organic compounds" appeared on early stage development of chemistry and speaks for itself: scientists of that era believed that living beings consist of special organic compounds.

Among all chemical elements carbon most closely associated with living organisms. More than a million different molecules based on it are known. interesting unique ability carbon atoms enter into a covalent bond with each other, forming long chains, complex rings and other structures.

Most organic compounds in nature are formed as a result of the process of photosynthesis - from carbon dioxide and water with energy solar radiation in chlorophyll-containing organisms.

Low molecular weight organic compounds They got their name because of their small molecular weight. These include amino acids, lipids, organic acids, vitamins, coenzymes (vitamin derivatives that determine the activity of enzymes) and others.

Low molecular weight organic compounds make up 0.1 - 0.5% of the cell mass.

High molecular weight organic compounds (biopolymers)

A macromolecule made up of monomers is calledpolymer(from Greek poly - "a lot of"). Therefore, a polymer is a multi-link chain in which a relatively simple substance is a link.

Polymers- These are molecules consisting of repeating structural units - monomers.

The properties of biopolymers depend on the number and variety of monomeric units that form the polymer. If you combine 2 types of monomers together BUT and B, then you can get a variety of polymers, the structure and properties of which will depend on the number, ratio and order of alternation of monomers in the chains.

Let's say there are 16 units in paraffin. You won’t repeat methylene - methylene - methylene 16 times ... For such long word there is a simplification - "hexadecane". What if there are a thousand units in a molecule? We speak simplistically poly- "a lot of". For example, take a thousand links ethylene, connect, get everyone familiar polyethylene.

Homopolymers (or regular) are built from monomers of the same type (for example, glycogen, starch and cellulose made up of molecules glucose).

Heteropolymers(or irregular) are built from differing monomers (for example, proteins consisting of 20 amino acids, and nucleic acids built from 8 nucleotides).

Each of the monomers determines some property of the polymer. For example, BUT- high strength, B- electrical conductivity. Alternating them in different ways, you can get a huge number of polymers with different properties. This principle underlies the diversity of life on our planet.

Lipids, their structure, properties and functions

Lipids are esters of the trihydric alcohol glycerol and higher fatty acids. Each of them has an acidic COOH residue, which, losing a hydrogen atom, combines with glycerol, and a carbon chain is connected to the residue. Lipids are low molecular weight hydrophobic organic compounds.

« Bold» acids are named because some of the high molecular weight members of this group are part of fats. General formula of fatty acids: CH 3 - (CH 2) p - COOH. Most of fatty acids contains an even number of carbon atoms (from 14 to 22).

Fatty acids are synthesized from cholesterol in the liver, then they enter the duodenum with bile, where they contribute to the digestion of fats, emulsifying them, thereby stimulating their absorption.

Lipids include fats, waxes, steroids, phospholipids, terpenes, glycolipids, lipoproteins.

Lipids are usually divided into fats and oils, depending on whether they remain solid at 20 ° C (fats) or have a liquid consistency at this temperature (oils).

There is always pure fat white color, a pure oil always colorless. The yellow, orange and brown color of the oil is due to the presence of carotene or similar compounds. Olive oil, on the other hand, sometimes has a greenish tint: it contains a little chlorophyll.

Fats have a high boiling point. Thanks to this, it is convenient to fry food on fats. They do not evaporate from a hot pan, they begin to burn only at a temperature of 200 - 300 0 C.

Neutral Fats(triglycerides) are compounds of high molecular weight fatty acids and the trihydric alcohol glycerol. In the cytoplasm of cells, triglycerides are deposited in the form of fat droplets.

Excess fat can cause fatty degeneration. The main sign of the appearance of fatty degeneration is an increase and thickening of the liver due to the accumulation of fat in hepatocytes (liver cells).

Waxes- plastic substances with water-repellent properties. In insects, they serve as material for building honeycombs. Wax coating on the surface of leaves, stems, fruits protects plants from mechanical damage, ultraviolet radiation and plays an important role in the regulation of water balance.

Phospholipids- representatives of the class of fat-like substances, which are esters of glycerol and fatty acids, containing a residue of phosphoric acid.

They form the basis of all biological membranes. In their structure, phospholipids are similar to fats, but in their molecule one or two fatty acid residues are replaced by a phosphoric acid residue.

Glycolipids- substances formed as a result of the combination of carbohydrates and lipids. The carbohydrate components of glycolipid molecules are polar, and this determines their role: like phospholipids, glycolipids are part of cell membranes.

To fat-like substances (lipoids) include precursors and derivatives of simple and complex lipids: cholesterol, bile acids, fat-soluble vitamins, steroid hormones, glycerol and others.

General properties of lipids:

1) have a high energy intensity;
2) have a density lower than that of water;
3) have an advantageous boiling point;
4) high-calorie substances.

General functions of lipids

What are lipids?

Lipids are a series organic matter, which is part of all living cells. It also includes fats and fat-like substances contained in the cells and tissues of animals as part of adipose tissue, which plays an important physiological role.

The human body itself is able to synthesize all the essential lipids. Only fat-soluble vitamins and essential polyunsaturated fatty acids cannot be synthesized in the body of animals and humans. Basically, lipid synthesis occurs in the liver and epithelial cells of the small intestine. A number of lipids are characteristic of certain organs and tissues, the remaining lipids are present in the cells of all tissues. The amount of lipids contained in organs and tissues is different. Most lipids are found in adipose and nervous tissue.

The lipid content in the human liver varies from 7 to 14% (dry weight). In the case of liver diseases, such as fatty liver, the lipid content in the liver tissue reaches 45%, mainly due to an increase in the amount of triglycerides. Lipids in blood plasma are found in combination with proteins and in this composition they are transported to other organs and tissues.

Lipids perform the following biological functions:

1. Structural. In combination, phospholipids with proteins form biological membranes.

2. Energy. In the process of fat oxidation, a large amount of energy is released, and it is she who goes to the formation of ATP. Most of the body's energy reserves are stored precisely in the form of lipids, and are consumed in case of a lack of energy. nutrients. For example, animals fall into hibernation, and pre-accumulated fats and oils are used to maintain life. Due to the high content of lipids in the seeds of plants, the embryo and seedling develop until they feed on their own. Seeds of plants such as coconut palm, castor bean, sunflower, soybean, rapeseed are the raw material from which vegetable oil is made industrially.

3. Heat-insulating and protective. It is deposited in the subcutaneous tissue and around organs such as the intestines and kidneys. The resulting layer of fat protects the body of the animal and its organs from mechanical damage. Since subcutaneous fat has a low thermal conductivity, it perfectly retains heat, which allows animals to live in cold climates. For whales, for example, this fat helps buoyancy.

4. Lubricating and water repellent. The skin, wool and feathers have a layer of wax that keeps them supple and protects them from moisture. Such a layer of wax is also found on the leaves and fruits of various plants.

5. Regulatory. Sex hormones, testosterone, progesterone and corticosteroids, as well as others, are derivatives of cholesterol. Vitamin D, derivatives of cholesterol, play an important role in calcium and phosphorus metabolism. Bile acids are involved in digestion (emulsification of fats), as well as the absorption of higher carboxylic acids.

Lipids are the source of metabolic water formation. So to get 105 grams of water, you need to oxidize 100 grams of fat. For desert dwellers, such water is vital, for example, for camels, who have to go without water for 10-12 days, such fat is deposited in their hump and used to obtain water. The process of fat oxidation is very important for hibernating animals, such as marmots, bears, etc.

Composition, properties and functions of lipids in the body

Nutritional value of oils and fats used in the baking and confectionery industry.

cyclic lipids. Role in food technology and life of the organism.

Simple and complex lipids.

Composition, properties and functions of lipids in the body.

Lipids in raw materials and food products

Lipids unite a large number of fats and fat-like substances of plant and animal origin, having a number of common features:

a) insolubility in water (hydrophobicity and good solubility in organic solvents, gasoline, diethyl ether, chloroform, etc.);

b) the presence in their molecules of long-chain hydrocarbon radicals and esters

groupings().

Most lipids are not macromolecular compounds and consist of several molecules linked to one another. Lipids can include alcohols and linear chains of a number of carboxylic acids. In some cases, their individual blocks may consist of macromolecular acids, various phosphoric acid residues, carbohydrates, nitrogenous bases, and other components.

Lipids, together with proteins and carbohydrates, make up the bulk of organic matter in all living organisms, being an indispensable component of every cell.

When lipids are isolated from oilseed raw materials, it passes into oil large group accompanying fat-soluble substances: steroids, pigments, fat-soluble vitamins and some other compounds. The mixture extracted from natural objects, consisting of lipids and compounds soluble in them, was called "raw" fat.

Main components of crude fat

Substances associated with lipids play big role in food technology, affect the nutritional and physiological value of the resulting food products. Vegetative parts of plants accumulate no more than 5% of lipids, mainly in seeds and fruits. For example, the lipid content in various plant products is (g / 100g): sunflower 33-57, cocoa (beans) 49-57, soybeans 14-25, hemp 30-38, wheat 1.9-2.9, peanuts 54- 61, rye 2.1-2.8, flax 27-47, corn 4.8-5.9, coconut palm 65-72. The content of lipids in them depends not only on the individual characteristics of plants, but also on the variety, place, and growing conditions. Lipids play an important role in the life processes of the body.

Their functions are very diverse: their role in energy processes, in the protective reactions of the body, in its maturation, aging, etc.

Lipids are part of all structural elements of the cell and, first of all, cell membranes, affecting their permeability. They are involved in the transmission of a nerve impulse, provide intercellular contact, active transfer of nutrients through membranes, transport of fats in blood plasma, protein synthesis and various enzymatic processes.

According to their functions in the body, they are conditionally divided into two groups: spare and structural. Spare (mainly acylglycerols) have a high calorie content, are the body's energy reserve and are used by it in case of malnutrition and diseases.

Spare lipids are reserve substances that help the body to endure adverse effects. external environment. Most plants (up to 90%) contain storage lipids, mainly in seeds. They are easily extracted from fat-containing material (free lipids).

Structural lipids(primarily phospholipids) form complex complexes with proteins and carbohydrates. They are involved in a variety of complex processes occurring in the cell. By weight, they constitute a significantly smaller group of lipids (3-5% in oilseeds). These are hard-to-remove “bound” lipids.

Natural fatty acids, which are part of lipids, animals and plants, have many common properties. They contain, as a rule, a clear number of carbon atoms and have an unbranched chain. Fatty acids are conventionally divided into three groups: saturated, monounsaturated and polyunsaturated. Unsaturated fatty acids of animals and humans usually contain a double bond between the ninth and tenth carbon atoms, the remaining carboxylic acids that make up fats are as follows:

Most lipids share some common structural features, but there is no strict classification of lipids yet. One of the approaches to the classification of lipids is chemical, according to which derivatives of alcohols and higher fatty acids belong to lipids.

Lipid classification scheme.

simple lipids. Simple lipids are represented by two-component substances, esters of higher fatty acids with glycerol, higher or polycyclic alcohols.

These include fats and waxes. Most important representatives simple lipids are acylglycerides (glycerols). They make up the bulk of lipids (95-96%) and they are called oils and fats. The composition of fats includes mainly triglycerides, but there are mono- and diacylglycerols:

The properties of specific oils are determined by the composition of the fatty acids involved in the construction of their molecules and the position occupied by the residues of these acids in the molecules of oils and fats.

Up to 300 carboxylic acids of various structures have been found in fats and oils. However, most of them are present in small quantities.

Stearic and palmitic acids are part of almost all natural oils and fats. Erucic acid is found in rapeseed oil. Most of the most common oils contain unsaturated acids containing 1-3 double bonds. Some acids in natural oils and fats are usually in the cis configuration, i.e. substituents are distributed on one side of the plane of the double bond.

Branched carbohydrate acids containing hydroxy, keto and other groups are usually found in small amounts in lipids. The exception is racinoleic acid in castor oil. In natural plant triacylglycerols, positions 1 and 3 are preferably occupied by saturated fatty acid residues, and position 2 is unsaturated. In animal fats, the picture is reversed.

The position of fatty acid residues in triacylglycerols significantly affects their physicochemical properties.

Acylglycerols are liquids or solids with low melting points and fairly high temperatures boiling, with increased viscosity, colorless and odorless, lighter than water, non-volatile.

Fats are practically insoluble in water, but form emulsions with it.

In addition to the usual physical indicators, fats are characterized by a number of physicochemical constants. These constants for each type of fat and its grade are provided by the standard.

The acid number, or acidity index, indicates how much free fatty acids are in a fat. It is expressed as the number of mg of KOH required to neutralize free fatty acids in 1 g of fat. The acid number is an indicator of the freshness of the fat. On average, it varies for different types of fat from 0.4 to 6.

The saponification number, or saponification factor, determines total acids, both free and bound in triacylglycerols, found in 1 g of fat. Fats containing residues of high molecular weight fatty acids have a lower saponification number than fats formed by low molecular weight acids.

The iodine number is an indicator of the unsaturation of fat. O is determined by the number of grams of iodine added to 100 g of fat. The higher the iodine number, the more unsaturated the fat is.

Waxes. Waxes are esters of higher fatty acids and high molecular weight alcohols (18-30 carbon atoms). The fatty acids that make up waxes are the same as for fats, but there are also specific ones that are characteristic only for waxes.

For example: carnauba;

cerotinic;

montana.

The general formula for waxes can be written as follows:

Waxes are widely distributed in nature, covering the leaves, stems, fruits of plants with a thin layer, they protect them from wetting with water, drying out, and the action of microorganisms. The content of wax in grains and fruits is low.

complex lipids. Complex lipids have multicomponent molecules, individual parts of which are connected by chemical bonds. various types. These include phospholipids, consisting of residues of fatty acids, glycerol and other polyhydric alcohols, phosphoric acid and nitrogenous bases. In the structure of glycolipids, along with polyhydric alcohols and high molecular weight fatty acids, there are also carbohydrates (usually residues of galactose, glucose, mannose).

There are also two groups of lipids, which include both simple and complex lipids. These are diol lipids, which are simple and complex lipids of dihydric alcohols and high molecular weight fatty acids, containing in some cases phosphoric acid, nitrogenous bases.

Ormitinolipids are built from fatty acid residues, the amino acid ormitin or lysine, and in some cases include dihydric alcohols. The most important and widespread group of complex lipids are phospholipids. Their molecule is built from residues of alcohols, high molecular weight fatty acids, phosphoric acid, nitrogenous bases, amino acids and some other compounds.

The general formula of phospholipids (phosphotides) is as follows:

Therefore, the phospholipid molecule has two types of groups: hydrophilic and hydrophobic.

Phosphoric acid residues and nitrogenous bases act as hydrophilic groups, and hydrocarbon radicals act as hydrophobic groups.

Schematic diagram of the structure of phospholipids

Rice. 11. Phospholipid molecule

The hydrophilic polar head is a residue of phosphoric acid and a nitrogenous base.

Hydrophobic tails are hydrocarbon radicals.

Phospholipids have been isolated as by-products in the production of oils. They are surfactants that improve the baking properties of wheat flour.

They are also used as emulsifiers in the confectionery industry and in the production of margarine products. They are an essential component of cells.

Together with proteins and carbohydrates, they are involved in the construction of cell membranes and subcellular structures that perform the functions of supporting membrane structures. They promote better absorption of fats and prevent fatty liver, playing an important role in the prevention of atherosclerosis.

Lipids are involved in the following functions:

1. Structural or the plastic role of lipids consists in the fact that they are part of the structural components of the cell (phospho- and glycolipids), the nucleus, cytoplasm, membranes and largely determine their properties (the nervous tissue contains up to 25%, in cell membranes up to 40% of fats).

2. Energy function - provides 25-30% of all the energy needed by the body (with the breakdown of 1 g of fat, 38.9 kJ is formed.). In an adult woman, the share of adipose tissue in the body is on average 20-25% of body weight, which is almost a widow more than in a man (12-14%, respectively). It should be assumed that fat also performs specific functions in the female body. In particular, adipose tissue provides a woman with a reserve of energy necessary for gestation and breastfeeding.

3. Fats are the source of endogenous water formation. During the oxidation of 100 g of fat, 107 ml of H 2 O are released.

4. Nutrient storage function (fat depot) . Fats are a kind of "energy canned food".

5.Protective. Fats Protect organs from injury (pillow near the eyes, perirenal capsule) .

6. Perform a transport function - carriers of fat-soluble vitamins.

7. Thermoregulatory. Fats protect the body from heat loss. .

8. Fats are source of steroid hormone synthesis.

9. Participate in the synthesis of thromboplastin and myelin of nervous tissue, bile acids, prostaglandins and vitamin D.

10 . There is evidence that part of the male sex steroid hormones in adipose tissue is converted into female hormones, which is the basis for the indirect participation of adipose tissue in humoral regulation bodily functions.

Metabolism of fats in the body.

Neutral fats are the most important source of energy. Due to oxidation, 50% of all the energy needed by the body is formed. Neutral fats, which make up the bulk of animal food and body lipids (10-20% of body weight), are a source of endogenous water. Physiological deposition of neutral fats is performed by lipocytes , accumulating them in the subcutaneous fatty tissue, omentum, fatty capsules of various organs - increasing in volume. It is believed that the number of fat cells is formed in childhood and can only increase in size in the future. Fats deposited in the subcutaneous tissue protect the body from heat loss, and the surrounding internal organs from mechanical damage. Fat can be deposited in the liver and muscles. The amount of fat deposited in the depot depends on the nature of nutrition, constitution, gender, age, type of activity, lifestyle, etc.

Phospho- and glycolipids are part of all cells (cellular lipids), especially nerve cells. This type of fat is an indispensable component of biological membranes. Phospholipids are synthesized in the liver and in the intestinal wall, but only hepatocytes are able to release them into the blood. Therefore, the liver is the only organ that determines the level of blood phospholipids.

brown fat It is represented by a special adipose tissue located in newborns and infants in the neck and upper back (its amount in the body is 1-2% of the total body weight). In a small amount (0.1-0.2% of the total body weight), brown fat is also present in an adult. A feature of the composition of brown fat is a huge number of mitochondria with reddish-brown pigments in which intense oxidation processes occur that are not associated with the formation of ATP. The most important role in the mechanisms of this phenomenon is played by the thermogenin protein, which makes up 10–15% of the total brown fat mitochondrial protein. The production of heat by brown fat (per unit mass of its tissue) is 20 or more times higher than that of ordinary adipose tissue.

In newborns, the low functional activity of the body and the immaturity of the central and peripheral mechanisms of thermoregulation do not provide sufficient heat production, so brown fat performs the function of an additional specific heat generator. In adults, the need for an additional source of heat disappears, since heat production is provided by other, more advanced mechanisms.

It should be noted that brown fat is also a source of endogenous water.

higher fatty acids are the main product of lipid hydrolysis in the intestine. Their absorption into the blood occurs in the form of micellar complexes consisting of fatty and bile acids, phospholipids and cholesterol.

For normal life, the presence of essential fatty acids in food, which are not synthesized in the body, is necessary. These acids include oleic, linoleic, linolenic and arachidonic. The daily requirement for them is 10-12 g. Linoleic and linolenic acids are found mainly in vegetable fats, arachidonic - only in animals. Deficiency of essential fatty acids in food leads to a slowdown in the growth and development of the body, a decrease in reproductive function and various skin lesions. Polyunsaturated fatty acids are necessary for the construction and maintenance of lipoprotein cell membranes, for the synthesis of prostaglandins and sex hormones.

Fats can be formed in the body from carbohydrates and proteins when they are excessively supplied from outside. A person receives a significant amount of fat from sausages - from 20 - 40%, fat - 90%, butter – 72- 82%, cheese - 15 - 50%, sour cream - 20 - 30%.

On average, a person needs 70-125 g of fat per day, of which 70% is animal, and 30% is vegetable. Excess fat is deposited in the body in certain parts of the body in the form of fat depots.

cholesterol belongs to the class of sterols, which also includes steroid hormones, vitamin D and bile acids. Cholesterol enters the body with food and synthesized in the body. At the same time, a significant part of it is synthesized in the liver, where it is also split into bile acids secreted as part of bile into the intestine. Transport cholesterol in the blood is carried out as part of high, low and very low density lipoproteins.

An increase in the fraction of low-density lipoproteins carries the risk of developing atherosclerosis due to their accumulation in the vascular wall. High-density lipoproteins, on the contrary, contribute to the removal of cholesterol from cells,

The total amount of fat in the human body is 10 - 20% of body weight. Weight gain by 20 - 25% is considered the maximum allowable physiological limit. More than 30% of the population of economically developed countries have a body weight exceeding normal levels.

Lipids are derivatives of fatty acids, alcohols, built using an ester bond. In lipids, a simple ether bond, a phosphoether bond, and a glycosidic bond are also found. Lipids are a complex mixture of organic compounds with similar physicochemical properties.

Lipids are insoluble in water (hydrophobic), but highly soluble in organic solvents (gasoline, chloroform). There are lipids of plant origin and animal origin. In plants, it accumulates in seeds and fruits, most of all in nuts (up to 60%). In animals, lipids are concentrated in the subcutaneous, brain, and nervous tissues. The fish contains 10-20%, pork meat up to 33%, beef meat 10% lipids.

According to their structure, lipids are divided into two groups:

- simple lipids

- complex lipids.

to simple lipids include complex (fat and oil) or simple (wax) esters of higher fatty acids and alcohols.

The structure of fats and oils can be represented by the general formula:

CH 2 - O - CO - R 1

CH - O - CO - R 2

CH 2 - O - CO - R 3

Where: fatty acid radicals - R 1, R 2, R 3.

Complex lipids contain compounds containing nitrogen, sulfur, phosphorus atoms. This group includes phospholipids. They are represented phosphotidic acid, which contain only phosphoric acid, which takes the place of one of the fatty acid residues, and phospholipids, which include three nitrogenous bases. Nitrogenous bases are added to the phosphoric acid residue of phosphotidic acid. Phosphotidylethanolamine contains the nitrogenous base ethanolamine HO - CH 2 - CH 2 - NH 2. Phosphotidylcholine contains the nitrogenous base choline [HO-CH 2 - (CH 3) 3 N] + (OH), this substance is called lecithin. Phosphotidylserine contains the amino acid serine HO-CH (NH 2) - COOH.

Complex lipids contain carbohydrate residues - glycolipids, protein residues lipoproteins, alcohol sphingosine (instead of glycerol) contain sphingolipids.

Glycolipids perform structural functions, are part of cell membranes, and are part of grain gluten. Most often in the composition of glycolipids there are monosaccharides D-galactose, D-glucose.

Lipoproteins are part of cell membranes, in the protoplasm of cells, affect metabolism.

Sphingolipids are involved in the activity of the central nervous system. In violation of the metabolism and functioning of sphingolipids, disturbances in the activity of the central nervous system develop.

The most common simple lipids are acylglycerides. The composition of acylglycerides includes alcohol glycerol and high molecular weight fatty acids. The most common among fatty acids are saturated acids (not containing multiple bonds) palmitic (C 15 H 31 COOH) and stearic (C 17 H 35 COOH) acids and unsaturated acids (containing multiple bonds): oleic with one double bond(C 17 H 33 COOH), linoleic with two multiple bonds (C 17 H 31 COOH), linolenic with three multiple bonds (C 17 H 29 COOH). Among simple lipids, triacylglycerides are mainly found (containing three identical or different fatty acid residues). However, simple lipids can be presented as diacylglycerides and monoacylglycerides.

Fats are predominantly saturated fatty acids. Fats are hard and have a high melting point. Contained mainly in lipids of animal origin. Oils contain mainly unsaturated fatty acids, have a liquid consistency and low temperature melting. Contained in lipids of plant origin.

Waxes are called esters, which include one high molecular weight monohydric alcohol with 18 - 30 carbon atoms, and one high molecular weight fatty acid with 18 - 30 carbon atoms. Waxes are found in flora. Wax covers leaves and fruits with a very thin layer, protecting them from waterlogging, drying, and exposure to microorganisms. The wax content is low and amounts to 0.01 - 0.2%.

Phospholipids are common among complex lipids. Phospholipids contain two types of substituents: hydrophilic and hydrophobic. Fatty acid radicals are hydrophobic, while phosphoric acid residues and nitrogenous bases are hydrophilic. Phospholipids are involved in the construction of cell membranes, regulate the flow of nutrients into the cell.

When lipids are extracted from oilseed raw materials, various fat-soluble compounds pass into oil: phospholipids, pigments, fat-soluble vitamins, sterols and sterols. The mixture that is extracted is called "crude fat". When cleaning (refining) vegetable oils almost all components associated with oils are removed, which significantly reduces nutritional value oils.

Of the fat-soluble pigments, a group of carotenoids, the precursors of vitamin A, should be noted. By chemical nature, these are hydrocarbons. These substances are red-orange in color. Chlorophyll is the green dye of plants.

Steroids are cyclic compounds having the structure of. From steroids big influence cholesterol exerts on a person. It is involved in the metabolism of hormones, bile acids.