Lipids- a collection of organic substances. Found in living organisms and divided into classes of lipids. Lipids are insoluble in water, but can dissolve in ether, chlorophore and benzene. The structure and function of lipids include many chemical compounds; they have the function of storing energy. Steroids and Phospholipids are included in , other lipids, of which there are slightly fewer, may be coenzymes, electron carriers, light absorbing pigments, hormones, hydrophobic “anchors” that contain membrane proteins.

The human body has the ability to break down lipids, although many of these substances must enter the body, these are (omega-3, omega-6)

Lipid groups

Lipids are divided into simple and complex. Elements include esters of fatty acids; complex lipids, in addition to fatty acids and alcohol, contain hydrocarbons, phosphates, lipoproteins and others. Each group is designated by two in English letters:

Glycerophospholipids (GP)

Glycerolipids (GL)

Polyketides (PK).

Sphingolipids (SP);

Steroid lipids (ST)

Prenolni lipids (PR);

Fatty acids (FA)

Sugar lipids (SL);

Chemical composition of lipids

Glycolipids

Glycolipids are a class of lipids containing mono- or oligosaccharide residues. They can be either glycerol or sphingosine derivatives.

(TG) Acylglycerides - glycerides are esters of trihydric alcohol and fatty acids. Hydroxyl classes in the molecule are further divided into groups:

1. triglycerides
2. diglycerides
3. monoglycerides

The most commonthese are triglycerides. They are also called fats. Fats can be simple, containing fatty acids, but mixed fats are more common; they also contain fatty acids. Properties triglycerides depend on its fatty acid composition, for example, the more unsaturated acids, the higher their melting point. Take butter as an example, it contains almost 95% unsaturated fatty acids and melts at room temperature. Animal fats, for example, lard, with room they retain weight at temperature, which is why everything is exactly the opposite for them (the content of saturated fatty acids)

Glycerophospholipids

The formula of glycerophospholipids is R1 and R2 fatty acids, X is the residue of the substance AZT. Glycerophospholipids are also called phosphoglycerides; they produce phosphatidic acids, which in turn consist of glycerin . In it, the first and second groups include R1, R2, and the third group includes phosphate acids; radical X (nitrogen-containing) is already added to it

Fatty acids form the hydrophobic part of glycerophospholipids in the molecule. The phosphate part in a neutral environment carries a negative charge, and nitrogen-containing compounds carry a positive charge; in a nitrogen-containing environment it can be negatively charged, which is why it is sometimes called polar. In an aqueous environment, phosphoglycerols produce micelles, their heads turned outward and their tails inward.

Common membrane phosphoglycerides are lethicin, in which the X radical is a residue of choline and phosphatidylethanolamine. There are also nitrogen-free glycerophospholipids, which include X, inositol and alcohol. Double phosphoglycerides were found in the inner membrane of the mitochondrion. In animals, essential lipids enrich heart, this group of compounds also includes active activation substances platelets.

Glyceroglycolipids

Glyceroglycolipids are a class of diacylglycerols with a carbon atom to which a glycosylmine is attached. The mostwidespreadThe class of lipids is galactolipids, they contain galactose residues. They make up 80% of membrane lipids. Together with galactolipids, a glucose residue can be found in plant membranes

Sphingoglycolipids

Cerebrosides are sphingoglycolipids, the hydrophilic part of which is represented by a monosaccharide residue, usually glucose or galactose. Galactocerebrosides are distributed in neuronal membranes.

Globosides are oligosaccharide derivatives of ceramides. Together with cerebrosides, they are called neutral glycolipids because at pH 7 they are uncharged.

Gangliosides are complex glycolipids, their hydrophilic part is represented by oligosaccharides, at the end of which there is always one or more N-acetylneuraminic (sialic) acid residues, due to which they have acidic properties. Gangliosides are the most common inganglion membranes neurons.

Sphingophospholipids

Structural formula of sphingomyelin in part of it component includes ceramide, which contains long-chain amino alcohols and 1 fatty acid residue, a hydrophilic radical, which in turn connected to sphingosine. found in membrane cells, but nervous tissue is considered the richest. Much of their content is also found in axons, which is where their name comes from.

Phospholipids

The structural classes of lipids are phospholipids; a common feature of phospholipids is their amphiphilicity, and it has a hydrophilic and hydrophobic part. Therefore, they can form micelles and bilayers in an aqueous environment.

Steroids

A steroid is a class of natural lipids, it containscyclopentane perhydrophenanthrenecore. These include alcohols with the hydroxyl class in the 3rd position, sterols with fatty acids - sterides. In animals, the most common sterol is cholesterol, which is also part of the membranes.

Steroids perform many functions in different organisms. For sex hormones, adrenal glands , vitamin functions and others.

Lipids combine a large number of fats and fat-like substances of plant and animal origin, which have a number of common characteristics:

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 high molecular weight compounds and consist of several molecules linked to each other. Lipids may contain alcohols and linear chains of a number of carboxylic acids. In some cases, their individual blocks may consist of high molecular weight acids, various phosphoric acid residues, carbohydrates, nitrogenous bases and other components.

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

1. Simple and complex lipids

When lipids are isolated from oilseed raw materials, a large group of accompanying fat-soluble substances passes into the oil: steroids, pigments, fat-soluble vitamins and some other compounds. A mixture of lipids and compounds soluble in them, extracted from natural objects, is called “crude” fat.

Main components of crude fat

Substances accompanying lipids play an important role in food technology and 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 65-72. The lipid content in them depends not only on the individual characteristics of the plants, but also on the variety, location, and growing conditions. Lipids play an important role in the vital processes of the body.

Their functions are very diverse: their role is important in energy processes, in the body’s defense reactions, in its maturation, aging, etc.

Lipids are part of all structural elements of the cell and primarily cell membranes, influencing their permeability. They are involved in the transmission of nerve impulses, provide intercellular contact, active transport of nutrients across membranes, transport of fats in the blood plasma, protein synthesis and various enzymatic processes.

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

Storage lipids are storage substances that help the body endure adverse environmental influences. Most plants (up to 90%) contain storage lipids, mainly in the 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 oil seeds). These are difficult to extract “bound” lipids.

Natural fatty acids that are part of lipids in animals and plants have many common properties. They usually contain a clear number of carbon atoms and have an unbranched chain. Conventionally, fatty acids are divided into three groups: saturated, monounsaturated and polyunsaturated. Unsaturated fatty acids in 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 have some common structural features, but a strict classification of lipids does not yet exist. One of the approaches to the classification of lipids is chemical, according to which lipids include derivatives of alcohols and higher fatty acids.

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. The most important representatives of simple lipids are acylglycerides (glycerols). They make up the bulk of lipids (95-96%) and are called oils and fats. Fat contains mainly triglycerides, but also contains 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 found in almost all natural oils and fats. Erucic acid is part of rapeseed oil. Most of the most common oils contain unsaturated acids containing 1-3 double bonds. Some acids in natural oils and fats tend to have a cis configuration, i.e. the substituents are distributed on one side of the double bond plane.

Acids with branched carbohydrate chains containing hydroxy, keto and other groups are usually found in small quantities in lipids. The exception is racinolic acid in castor oil. In natural plant triacylglycerols, positions 1 and 3 are preferentially occupied by saturated fatty acid residues, and position 2 is unsaturated. In animal fats the picture is the opposite.

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

Acylglycerols are liquid or solid substances with low melting points and fairly high boiling points, with high 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 coefficient, shows how many free fatty acids are contained in the 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 serves as 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 coefficient, determines the total amount of 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.

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

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

For example: carnauba;

cerotinic;

montanova

The general formula of waxes can be written as follows:

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

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

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

Ormitinolipids are built from fatty acid residues, the amino acid ormitine or lysine, and in some cases including dihydric alcohols. The most important and widespread group of complex lipids are phospholipids. Their molecule is built from residues of alcohols, high-molecular 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.

Scheme 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 are isolated as by-products during 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 participate 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.

Transformation of lipids and their effect on the quality of products during storage and processing:

a) hydrolytic decomposition

b) hydrogenation

c) transesterification

d) autoxidation and enzymatic oxidation (rancidity).

Lipids are the most important source of the body's energy reserves. The fact is obvious even at the nomenclature level: the Greek “lipos” is translated as fat. Accordingly, the category of lipids unites fat-like substances of biological origin. The functionality of the compounds is quite diverse, which is due to the heterogeneity of the composition of this category of biological objects.

What functions do lipids perform?

List the main functions of lipids in the body, which are basic. At the introductory stage, it is advisable to highlight the key roles of fat-like substances in the cells of the human body. The basic list is the five functions of lipids:

1. reserve energy;
2. structure-forming;
3. transport;
4. insulating;
5. signal

The secondary tasks that lipids perform in combination with other compounds include regulatory and enzymatic roles.

Energy reserve of the body

This is not only one of the important, but the priority role of fat-like compounds. In fact, part of the lipids is the source of energy for the entire cellular mass. Indeed, fat for cells is an analogue of fuel in a car tank. The energy function of lipids is realized in the following way. Fats and similar substances are oxidized in the mitochondria, breaking down to water and carbon dioxide. The process is accompanied by the release of a significant amount of ATP - high-energy metabolites. Their supply allows the cell to participate in energy-dependent reactions.

Building Blocks

At the same time, lipids perform a construction function: with their help, the cell membrane is formed. The following groups of fat-like substances are involved in the process:

1. cholesterol is a lipophilic alcohol;
2. glycolipids – compounds of lipids with carbohydrates;
3. Phospholipids are esters of complex alcohols and higher carboxylic acids.

It should be noted that the formed membrane does not contain fats directly. The resulting wall between the cell and the external environment turns out to be two-layered. This is achieved due to biphilicity. This characteristic of lipids indicates that one part of the molecule is hydrophobic, that is, insoluble in water, and the second, on the contrary, is hydrophilic. As a result, a cell wall bilayer is formed due to the ordered arrangement of simple lipids. The molecules turn their hydrophobic regions toward each other, while their hydrophilic tails point inward and outward of the cell.

This determines the protective functions of membrane lipids. First, the membrane gives the cell its shape and even maintains it. Secondly, the double wall is a kind of passport control point that does not allow unwanted visitors to pass through.

Autonomous heating system

Of course, this name is quite arbitrary, but it is quite applicable if we consider what functions lipids perform. The compounds do not so much heat the body as they retain heat inside. A similar role is assigned to fatty deposits that form around various organs and in the subcutaneous tissue. This class of lipids is characterized by high heat-insulating properties, which protects vital organs from hypothermia.

Did you order a taxi?

The transport role of lipids is considered a secondary function. Indeed, the transfer of substances (mainly triglycerides and cholesterol) is carried out by separate structures. These are linked complexes of lipids and proteins called lipoproteins. As is known, fat-like substances are insoluble in water, respectively, in blood plasma. In contrast, the functions of proteins include hydrophilicity. As a result, the lipoprotein core is a collection of triglycerides and cholesterol esters, while the shell is a mixture of protein molecules and free cholesterol. In this form, lipids are delivered to the tissues or back to the liver for removal from the body.

Minor Factors

The list of the 5 functions of lipids already listed complements a number of equally important roles:

• enzymatic;
• signal;
• regulatory

Signal function

Some complex lipids, in particular their structure, allow the transmission of nerve impulses between cells. Glycolipids mediate this process. No less important is the ability to recognize intracellular impulses, also realized by fat-like structures. This allows you to select substances needed by the cell from the blood.

Enzymatic function

Lipids, regardless of their location in the membrane or outside it, are not part of enzymes. However, their biosynthesis occurs with the presence of fat-like compounds. Additionally, lipids are involved in protecting the intestinal wall from pancreatic enzymes. The excess of the latter is neutralized by bile, where cholesterol and phospholipids are included in significant quantities.

Structure of lipids, fatty acids

Lipids - a fairly large group of organic compounds present in all living cells that do not dissolve in water, but dissolve well in non-polar organic solvents (gasoline, ether, chloroform, benzene, etc.).

Note 1

Lipids have a wide variety of chemical structures, but true lipids are esters of fatty acids and any alcohol.

U fatty acids the molecules are small and have a long chain, most often consisting of 19 or 18 carbon atoms. The molecule also contains hydrogen atoms and carboxyl group(-COOH). Their hydrocarbon “tails” are hydrophobic, and the carboxyl group is hydrophilic, so esters are easily formed.

Sometimes fatty acids contain one or more double bonds (C–C). In this case, fatty acids, as well as the lipids that contain them, are called unsaturated .

Fatty acids and lipids whose molecules lack double bonds are called saturated . They are formed by the addition of an additional pair of hydrogen atoms at the site of the double bond of an unsaturated acid.

Unsaturated fatty acids melt at lower temperatures than saturated fatty acids.

Example 1

Oleic acid (Mp = 13.4˚C) is liquid at room temperature, while palmitic and stearic acids (Mp = 63.1 and 69.9˚C, respectively) remain solid under these conditions.

Definition 1

Most lipids are esters formed by the trihydric alcohol glycerol and three fatty acid residues. These connections are called triglycerides, or triacylglycerols.

Fats and oils

Lipids are divided into fats and oils . It depends on what state they remain in at room temperature: solid (fats) or liquid (oils).

The lower the melting point of lipids, the greater the proportion of unsaturated fatty acids in them.

Oils tend to have more unsaturated fatty acids than fats.

Example 2

The bodies of animals living in cold climate zones (fish of the Arctic seas) usually contain more unsaturated triacylglycerols than those living in southern latitudes. Therefore, their body remains flexible even at low ambient temperatures.

Functions of lipids

Important groups of lipids also include

• steroids (cholesterol, bile acids, vitamin D, sex hormones, etc.),
• terpenes (carotenoids, vitamin K, plant growth substances – gibberellins),
• waxes,
• phospholipids,
• glycolipids,
• lipoproteins.

Note 2

Lipids are an important source of energy.

As a result of oxidation, lipids provide twice as much energy as proteins and carbohydrates, that is, they are an economical form of storing reserve nutrients. This is due to the fact that lipids contain more hydrogen and very little oxygen compared to proteins and carbohydrates.

Example 3

Hibernating animals accumulate fats, and dormant plants accumulate oils. They spend them later in the process of life. Due to their high lipid content, plant seeds provide energy for the development of the embryo and sprout until it begins to feed itself. The seeds of many plants (sunflower, soybean, flax, corn, mustard, coconut palm, castor oil, etc.) are raw materials for producing oils industrially.

Due to their insolubility in water, lipids are important structural component cell membranes consisting mainly of phospholipids. In addition, they contain glycolipids and lipoproteins.

Lipids (from the Greek lipos - ether) are a complex mixture of ether-like organic compounds with similar physical and chemical properties. Lipids are widely used in the production of many food products; they are important components of food products, largely determining their nutritional and biological value and taste.

In plants, lipids accumulate mainly in seeds and fruits and vary from a few percent in cereals and cereals to tens of percent in oilseeds. In animals and fish, lipids are concentrated in the subcutaneous, brain and nervous tissues. The lipid content in fish varies from 8 to 25%; in carcasses of terrestrial animals it varies greatly: 33% (pork), 9.8% (beef). In the milk of various animal species, the lipid content ranges from 1.7% in mare's milk to 34.5% in the milk of a female reindeer.

Lipids are insoluble in water (hydrophobic*), highly soluble in organic solvents (gasoline, diethyl ether, chloroform, etc.).

According to their chemical structure, lipids are derivatives of fatty acids, alcohols, and aldehydes, built using ester, ether, phosphoester, and glycosidic bonds. Lipids are divided into two main groups: simple and complex lipids. Simple neutral lipids include derivatives of higher fatty acids and alcohols: glycerolipids, waxes, cholesterol esters, glycolipids and other compounds. The molecules of complex lipids contain not only residues of high molecular weight carboxylic acids, but also phosphoric, sulfuric acids or nitrogen.

The most important and widespread group of simple neutral lipids are acylglycerols (or glycerides). These are esters of glycerol and higher carboxylic acids. They make up the bulk of lipids (sometimes up to 95%) and, essentially, they are called fats or oils. The composition of fats includes mainly triacylglycerols (I), less often diacylglycerols (II) and monoacylglycerols (III):

The most important representatives of complex lipids are phospholipids– essential components of plants (0.3-1.7%). Their molecules are built from alcohol residues (glycerol, sphingosine), fatty acids, phosphoric acid (H 3 PO 4), and also contain nitrogenous bases, amino acid residues and some other compounds.

The molecules of most phospholipids are built according to a general principle. Their composition includes, on the one hand, hydrophobic groups, characterized by low affinity for water, and on the other hand, hydrophilic groups (residues of phosphoric acid and nitrogenous base). They are called "polar heads". Due to this property (amphiphilicity), phospholipids often create an interface (membrane) between water and the hydrophobic phase in living systems and food products.

Lipids perform not only an energy function (free lipids), but also perform a structural function: together with proteins and carbohydrates, they are part of cell membranes and cellular structures. By weight, structural lipids constitute a significantly smaller group of lipids (3-5% in oil seeds). These are difficult to extract “bound” and “tightly bound” lipids.

	|	next lecture ==>