Sphingomyelin
The first part of the word “sphingo” indicates that the molecule contains, instead of glycerol, a dihydric unsaturated alcohol - sphingosine. The most widespread representative of this group of compounds in the body is sphingomyelin. Sphingomyelin is found in the membranes of plant and animal cells; Nervous tissue, and in particular the brain, is especially rich in sphingophospholipids.A characteristic feature of phospholipids is their diphilicity, that is, the ability to dissolve both in an aqueous environment and in neutral lipids. This is due to the presence of pronounced polar properties in phospholipids. At pH 7.0, their phosphate group always carries a negative charge. Nitrogen-containing groups in the composition of phosphatidylcholine (choline) and phosphatidylethanolamine (ethanolamine) at pH 7.0 carry a positive charge. Thus, at pH 7.0, these glycerophospholipids are bipolar zwitterions and their net charge is zero. The serine residue in the phosphatidylserine molecule contains an α-amino group and a carboxyl group. Therefore, at pH 7.0, the phosphatidylserine molecule has two negatively and one positively charged groups and carries a total negative charge.
At the same time, fatty acid radicals in phospholipids do not have an electrical charge in an aqueous environment and thus determine the hydrophobicity of part of the phospholipid molecule. The presence of polarity due to the charge of polar groups determines hydrophilicity. Therefore, at the oil-water interface, phospholipids are arranged in such a way that polar groups are in the aqueous phase and non-polar groups are in the oil phase. Due to this, in an aqueous environment they form a bimolecular layer, and upon reaching a certain critical concentration - micelles.]
This is the basis for the participation of phospholipids in the construction of biological membranes.
Ultrasound treatment of a diphilic lipid in an aqueous medium leads to the formation of liposomes. A liposome is a closed lipid bilayer, inside which is part of the aqueous environment. Liposomes are used in the clinic and cosmetology as unique containers and carriers of drugs, nutrients to certain organs and for a combined effect on the skin.
The functional role of phospholipids is not limited to their participation in the construction of biomembranes. Thus, they are regulators of enzyme activity. For example, phosphatidylcholine, phosphatidylserine, sphingomyelin activate or inhibit the activity of enzymes that catalyze blood clotting processes. The regulatory function of lipids lies in the fact that a number of hormones (sex hormones, adrenal hormones) are derivatives of lipids. In addition, phospholipids
They perform a detergent function in the intestines and gall bladder. They are an important structural component of bile, along with free cholesterol and bile acids. A change in the ratio of any of these components leads to the precipitation and formation of gallstones. Phospholipids are also an important component of mixed micelles that are formed during lipid digestion.
It is a source of arachidonic acid, a precursor of eicosanoids.
They are sources of secondary messengers - diacylglycerol and inositol triphosphate, as mentioned above
Provide attachment of proteins to the membrane. Some extracellular proteins are attached to the outside of the plasma membrane by forming covalent bonds with phosphatidylinositol. Examples of such proteins are enzymes: alkaline phosphatase, lipoprotein lipase, cholinesterase.
Take part in the formation of transport forms of other lipids
Can perform an energetic function
They are a component of lung surfactant (see below)
The main subclasses of plasmalogens are phosphatidalcholines, phosphatidal ethanolamines and phosphatidalserines. In dilute acids, they are hydrolyzed to form the aldehyde of the corresponding α,β-unsaturated alcohol, that is, during the acid hydrolysis of plasmalogens, “fatty” aldehydes are formed, called plasmals, which formed the basis of the term “plasmalogen”. Plasmalogens are also part of the membranes of muscles, nerve cells, and red blood cells.
Some phosphatides, discovered relatively recently, do not contain a nitrogenous base, the place of which in the molecule in this case is occupied by glycerol and its derivatives:
Phosphatidylglycerol is an obligatory component of chloroplasts and is present in small quantities in bacterial cells and animal tissues.
Cardiolipin- one of the essential compounds in the mitochondrial membranes, especially in the mitochondria of the heart muscle.
Sphingolipids
Another group of phospholipids are sphingolipids. Instead of glycerol, they contain the higher diatomic unsaturated amino alcohol sphingosine (the number of carbon atoms is 18, the double bond has a trans configuration). Hydroxyl groups are located at the first and third carbon atoms, the amino group is located at the second carbon atom of the chain, and the double bond is at the fourth carbon atom:
Sphingosine
The difference between sphingolipids and glycerophospholipids is that fatty acids combine in them not with hydroxyl groups, but with the amino groups of the amino alcohol, forming amide bonds (-CO-NH-). This bond is formed between the carboxyl group of the fatty acid and the amino group of the alcohol. Found in sphingolipids in significant quantities lignoceric and nervonic acids.
With a hydroxyl group in position 1, sphingolipids contain a phosphoric acid residue, which in turn is esterified with a molecule of a nitrogenous compound - most often with choline. The general structure of sphingomyelins looks like this:
Cphingomyelin
The general plan for the construction of the sphingomyelin molecule in a certain respect resembles the structure of glycerophospholipids. The sphingomyelin molecule contains a polar “head”, which carries both positive (choline residue) and negative (phosphoric acid residue) charges, and two non-polar “tails” (a long aliphatic chain of sphingosine and a fatty acid acyl radical).
Sphingomyelins are the most abundant sphingolipids. They are found mainly in the membranes of animal and plant cells. Nervous tissue is especially rich in them. The actual name sphingomyelins reflects their function in living tissues, where they form the myelin sheath around nerve fibers in the tissues of the liver, kidneys and other organs.
In some sphingomyelins, for example those isolated from the brain and spleen, instead of sphingosine, the alcohol dihydrosphingosine (reduced sphingosine) was found:
CH 3 -(CH 2) 14 -CH-CH-CH 2 -CH 2 OH
Dehydrosphingosine
An amino alcohol very similar to sphingosine was isolated from phospholipids of plant origin (from corn grain):
Phytosphingosine
The same alcohol is found in yeast and fungi, and recently in the human brain and kidneys, indicating the possibility of the existence of similar phospholipids in plant and animal matter.
Sphingophospholipids are insoluble in sulfuric ether, which is used in their separation from phosphatides. They are also characterized by difficult solubility in acetone and greater resistance to oxidizing agents than phosphatides.
Sphingolipids are characterized by very complex spatial configurations associated with the possibility of optical isomerism (two asymmetric carbon atoms in the molecule) and cis-trans isomerism at the site of the double bond. This explains their organ and species specificity. In addition, it has been established that the organ specificity of sphingolipids depends on the qualitative composition of higher fatty acids: for example, brain sphingolipids are characterized by the presence of nervonic acid.
Glycolipids
The second group of complex lipids is formed by glycolipids (from the Greek glykys - sweet and lipids). They are characterized by the fact that the polar mono- or oligosaccharide component (glucose, galactose, glucosamine, galactosamine, their N-acetyl derivatives, etc.) through a polyhydric alcohol residue (glycerol, sphingosine) combines with non-polar radicals of higher fatty acids (palmitic, stearic, oleic, lignoceric, nervonic, cerebronic, etc.) glycosidic and ester bonds.
Depending on the nature of the lipid part, glycolipids can be divided into four groups:
1) glycosyl diglycerides, the lipid part of which is a glycerol residue acylated at positions 1 and 2 with higher fatty acids;
2) glycosphingolipids, in which the lipid fragment is ceramide - the residue of a higher amino alcohol (sphingosine base), N-acylated with a higher fatty acid;
3) polyprenyl phosphate sugars, in which the lipid part of the molecule is a polyprenol residue H(CH 2 C(CH 3) = CHCH 2) n OH;
4) glycolipids of microorganisms, which contain residues of higher fatty acids that acylate sugar residues or non-carbohydrate components of the molecule.
The vast majority of glycolipids belong to the first two groups and are important components of membranes.
Ceramides- the basis of glycolipids. The hydrogen in the hydroxyl group of ceramide can be replaced by different carbohydrate fragments, which determines whether the glycolipid belongs to a certain class.
Lipid chemistry
Lipids are a large group of compounds that vary significantly in their chemical structure and functions. Therefore, it is difficult to give a single definition that would be suitable for all compounds belonging to this class.
We can say that lipids are a group of substances that are characterized by the following characteristics: insolubility in water; solubility in non-polar solvents such as ether, chloroform or benzene; content of higher alkyl radicals; prevalence in living organisms.
A large number of substances fall under this definition, including those that are usually classified as other classes of compounds: for example, fat-soluble vitamins and their derivatives, carotenoids, higher hydrocarbons and alcohols. The inclusion of all these substances in the number of lipids is to a certain extent justified, because in living organisms they are found together with lipids and, together with them, are extracted with non-polar solvents. On the other hand, there are representatives of lipids that are quite soluble in water (for example, lysolecithins). The term "lipids" is more general than the term "lipoids", which combines a group of fat-like substances such as phospholipids, sterols, sphingolipids, etc.
Biological role and classification of lipids
Lipids play a vital role in life processes. Being one of the main components of biological membranes, lipids affect their permeability, participate in the transmission of nerve impulses, and the creation of intercellular contacts. Fat serves as a very efficient source of energy in the body, either when used directly or potentially in the form of stored adipose tissue. Natural dietary fats contain fat-soluble vitamins and “essential” fatty acids. An important function of lipids is the creation of thermal insulation covers in animals and plants, the protection of organs and tissues from mechanical influences.
There are several classifications of lipids. The most widespread classification is based on the structural characteristics of lipids. According to this classification, the following main classes of lipids are distinguished.
A. Simple lipids: esters of fatty acids with various alcohols.
1. Glycerides (acylglycerols, or acylglycerols - according to the international nomenclature) are esters of the trihydric alcohol glycerol and higher fatty acids.
2. Wax: esters of higher fatty acids and monohydric or dihydric alcohols.
B. Complex lipids: esters of fatty acids with alcohols, additionally containing other groups.
1. Phospholipids: lipids containing, in addition to fatty acids and alcohol, a phosphoric acid residue. They often contain nitrogenous bases and other components:
a) glycerophospholipids (glycerol acts as an alcohol);
b) sphingolipids (sphingosine in the role of alcohol).
2. Glycolipids (glycosphingolipids).
3. Steroids.
4. Other complex lipids: sulfolipids, aminolipids. Lipoproteins can also be included in this class.
5. Lipid precursors and derivatives: fatty acids, glycerol, sterols and other alcohols (other than glycerol and sterols), fatty acid aldehydes, hydrocarbons, fat-soluble vitamins and hormones.
Fatty acid
Fatty acids - aliphatic carboxylic acids - can be found in the body in a free state (trace amounts in cells and tissues) or act as building blocks for most classes of lipids.
More than 200 fatty acids are found in nature, however, about 70 fatty acids are found in human and animal tissues as part of simple and complex lipids, more than half of them in trace quantities. In practice, a little more than 20 fatty acids are widely distributed. All of them contain an even number of carbon atoms, mainly from 12 to 24. Among them, acids with C 16 and C 18 (palmitic, stearic, oleic and linoleic) predominate. The numbering of carbon atoms in the fatty acid chain begins with the carbon atom of the carboxyl group. Approximately 3/4 of all fatty acids are unsaturated (unsaturated), i.e. contain double bonds. Unsaturated fatty acids of humans and animals involved in the construction of lipids usually contain a double bond between (9th and 10th hydrocarbon atoms); additional double bonds are often found in the area between the 11th carbon atom and the methyl end of the chain. The peculiarity of double bonds of natural unsaturated fatty acids is that they are always separated by two simple bonds, i.e. between them there is always at least one methylene group (-CH=CH-CH 2 -CH=CH-). Such double bonds are referred to as “isolated.”
Table 1 - Some physiologically important saturated fatty acids
| Number of C atoms | Trivial name | Systematic name | |
| 6 | Nylon | Hexane | CH 3 − (CH 2) 4 − COOH |
| 8 | Caprylic | Octane | CH 3 − (CH 2) 6 − COOH |
| 10 | Kaprinovaya | Dean's | CH 3 − (CH 2) 8 − COOH |
| 12 | Lauric | Dodecane | CH 3 −(CH 2) 10 COOH |
| 14 | Myristic | Tetradecane | CH 3 -(CH 2) 12 -COOH |
| 16 | Palmitic | Hexadeconic | CH 3 -(CH 2) 14 -COOH |
| 18 | Stearic | Octadecane | CH 3 -(CH 2) 16 -COOH |
| 20 | Arachinova | Eicosan | CH 3 -(CH 2) 18 -COOH |
| 22 | Begenovaya | Docosanova | CH 3 -(CH 2) 20 -COOH |
| 24 | Lignocyrinova | Tetracosane | CH 3 -(CH 2) 22 -COOH |
In solutions, a fatty acid chain can form an infinite number of conformations up to a coil, which also contains linear sections of varying lengths depending on the number of double bonds. The balls can stick together, forming so-called micelles. In the latter, the negatively charged carboxyl groups of fatty acids face the aqueous phase, and the nonpolar hydrocarbon chains are hidden inside the micellar structure. Such micelles have a net negative charge and remain suspended in solution due to mutual repulsion.
It is also known that in the presence of a double bond in the fatty acid chain, the rotation of carbon atoms relative to each other is limited. This ensures the existence of unsaturated fatty acids in the form of geometric isomers, and natural unsaturated fatty acids have cis- configuration and extremely rarely trance-configurations.
Table 11 - Some physiologically important unsaturated fatty acids
| Number of C atoms | Trivial name | Systematic name | Chemical formula of the compound |
| Monoenoic acids | |||
| 16 | Palmitic | 9-hexadecene | CH 3 −(CH 2) 5 −CH=CH−(CH 2) 5 COOH |
| 18 | Oleic | 9-octadecene | CH 3 −(CH 2) 7 −CH=CH−(CH 2) 7 COOH |
| Dienoic acids | |||
| 18 | Linoleic | 9,12-octadecene | CH 3 −(CH 2) 4 −CH=CH−CH 2 − −CH=CH− (CH2) 7 COOH |
| Trienoic acid | |||
| 18 | Linolenic | 9,12,15-octadecatriene | CH 3 −CH 2 −CH=CH−CH 2 − −CH=CH− CH 2 − CH=CH (CH 2) 7 −COOH |
| Tetraenoic acids | |||
| 20 | Arachidonic | 5,8,11,14-eicosatetraenoic | CH 3 −CH 2 −CH=CH−CH 2 − CH=CH−CH 2 − CH=CH−CH 2 − CH=CH−CH 2 − CH= − (CH 2) 5 −COOH |
A fatty acid with several double bonds is considered cis- the configuration gives the hydrocarbon chain a bent and shortened appearance. For this reason, the molecules of these acids occupy a larger volume, and when crystals form, they are not packed as tightly as trance- isomers. Consequently cis- isomers have a lower melting point (oleic acid, for example, is in a liquid state at room temperature, while elaidic acid is in a crystalline state). Cis- configuration makes the unsaturated acid less stable and more susceptible to catabolism.
Figure 23 - Configuration of 18-carbon saturated (a) and monounsaturated (b) fatty acids
Biological functions of PUFAs:
1. structural. PUFAs are part of nerve fibers, cell membranes, and connective tissue.
2. protective (increases the body’s resistance to infections and radiation).
3. increase the elasticity of blood vessels, promote the removal of excess cholesterol.
4. Arachidonic acid is a precursor to prostaglandin hormones.
Glycerides (acylglycerols)
Glycerides (acylglycerols, or acylglycerols) are esters of the trihydric alcohol glycerol and higher fatty acids. If all three hydroxyl groups of glycerol are esterified with fatty acids (the acyl radicals R1, R2 and R3 can be the same or different), then such a compound is called a triglyceride (triacylglycerol), if two - diglyceride (diacylglycerol) and, finally, if one group is esterified with monoglyceride (monoacylglycerol):
The most common are triglycerides, often called neutral fats or simply fats. Neutral fats are found in the body either in the form of protoplasmic fat, which is a structural component of cells, or in the form of storage fat. The role of these two forms of fat in the body is not the same. Protoplasmic fat has a constant chemical composition and is contained in tissues in a certain amount, which does not change even with morbid obesity, while the amount of reserve fat undergoes large fluctuations.
As noted, the bulk of natural neutral fats are triglycerides. The fatty acids in triglycerides can be saturated or unsaturated. The most common fatty acids are palmitic, stearic and oleic acids. If all three acid radicals belong to the same fatty acid, then such triglycerides are called simple (for example, tripalmitin, tristearin, triolein, etc.), if different fatty acids, then mixed. The names of mixed triglycerides are formed depending on the fatty acids they contain, with the numbers 1, 2 and 3 indicating the connection of the fatty acid residue with the corresponding alcohol group in the glycerol molecule (for example, 1-oleo-2-palmitostearin). It should be noted that the position of the extreme atoms in the glycerol molecule at first glance is equivalent, however, they are designated from top to bottom - 1 and 3. This is explained, first of all, by the fact that in the structure of the triglyceride, when viewed spatially, the extreme “glycerol” carbon atoms become no longer equivalent if hydroxyls 1 and 3 are acylated by different fatty acids.
The fatty acids that make up triglycerides practically determine their physicochemical properties. Thus, the melting point of triglycerides increases with increasing number and length of saturated fatty acid residues. In contrast, the higher the content of unsaturated fatty acids, or short-chain fatty acids, the lower the melting point.
Animal fats (lard) usually contain a significant amount of saturated fatty acids (palmitic, stearic, etc.), due to which they are solid at room temperature. Fats, which contain many unsaturated acids, are liquid at ordinary temperatures and are called oils. Thus, in hemp oil, 95% of all fatty acids are oleic, linoleic and linolenic acids, and only 5% are stearic and palmitic acids. Human fat, which melts at 15°C (it is liquid at body temperature), contains 70% oleic acid.
Glycerides are capable of entering into all chemical reactions characteristic of esters. The most important reaction is the saponification reaction, which results in the formation of glycerol and fatty acids from triglycerides. Saponification of fat can occur either through enzymatic hydrolysis or through the action of acids or alkalis.
Phospholipids
Phospholipids are esters of polyhydric alcohols glycerol or sphingosine with higher fatty acids and phosphoric acid. Phospholipids also include nitrogen-containing compounds: choline, ethanolamine or serine. Depending on which polyhydric alcohol is involved in the formation of the phospholipid (glycerol or sphingosine), the latter are divided into 2 groups: glycerophospholipids and sphingophospholipids. It should be noted that in glycerophospholipids, either choline, ethanolamine or serine are connected by an ester bond to a phosphoric acid residue; Only choline was found in sphingolipids. The most common in animal tissues are glycerophospholipids.
Glycerophospholipids. Glycerophospholipids are derivatives of phosphatidic acid. They contain glycerol, fatty acids, phosphoric acid and usually nitrogen-containing compounds. The general formula of glycerophospholipids looks like this:
In these formulas, R 1 and R 2 are radicals of higher fatty acids, and R 3 is often a radical of a nitrogenous compound. It is characteristic of all glycerophospholipids that one part of their molecules (radicals R 1 and R 2) exhibits pronounced hydrophobicity, while the other part is hydrophilic due to the negative charge of phosphoric acid and the positive charge of the R 3 radical.
Of all lipids, glycerophospholipids have the most pronounced polar properties. When glycerophospholipids are placed in water, only a small part of them passes into the true solution, while the bulk of the lipids are in the form of micelles. There are several groups (subclasses) of glycerophospholipids. Depending on the nature of the nitrogenous base attached to phosphoric acid, Glycerophospholipids are divided into phosphatidylcholines (lecithins), phosphatidylethanolamines (cephalins) and phosphatidylserines. Some glycerophospholipids contain the nitrogen-free six-carbon cyclic alcohol inositol, also called inositol, instead of nitrogen-containing compounds. These lipids are called phosphatidylinositols.
Phosphatidylcholines (lecithins). Unlike triglycerides, in the phosphatidylcholine molecule, one of the three hydroxyl groups of glycerol is associated not with fatty acid, but with phosphoric acid. In addition, phosphoric acid, in turn, is connected by an ester bond to a nitrogenous base - choline [HO-CH 2 -CH 2 -N + (CH 3) 3]. Thus, the phosphatidylcholine molecule contains glycerol, higher fatty acids, phosphoric acid and choline:
Phosphatidylethanolamines. The main difference between phosphatidylcholines and phosphatidylethanolamines is the presence of the nitrogenous base ethanolamine (HO-CH 2 -CH 2 -N + H 3) in the latter: 
Of the glycerophospholipids in the body of animals and higher plants, phosphatidylcholines and phosphatidylethanolamines are found in the largest quantities. These 2 groups of glycerophospholipids are metabolically related to each other and are the main lipid components of cell membranes.
Phosphatidylserines. In the phosphatidylserine molecule, the nitrogenous compound is the amino acid residue serine
Phosphatidylserines are much less widespread than phosphatidylcholines and phosphoethanolamines, and their importance is determined mainly by the fact that they participate in the synthesis of phosphatidylethanolamines.
Phosphatidylinositols. These lipids belong to the group of phosphatidic acid derivatives, but do not contain nitrogen. The radical (R 3) in this subclass of glycerophospholipids is the six-carbon cyclic alcohol inositol:
Phosphatidylinositols are quite widespread in nature. They are found in animals, plants and microorganisms. In animals, they are found in the brain, liver and lungs.
Plasmalogens. Plasmalogens differ from the glycerolipids considered in that instead of one higher fatty acid residue they contain an α,β-unsaturated alcohol residue, which forms a simple bond (in contrast to the ester bond formed by the fatty acid residue) with the hydroxyl group of glycerol at position C-1: 
Phosphatidalcholine (plasmalogen)
The main subclasses of plasmalogens are phosphatidalcholines, phosphatidal ethanolamines and phosphatidalserines. Acid hydrolysis of plasmalogens produces “fatty” aldehydes called plasmals, which formed the basis of the term “plasmalogen.”
Cardiolipin. A unique representative of glycerophospholipids is cardiolipin, which was first isolated from cardiac muscle. In terms of its chemical structure, cardiolipin can be considered a compound in which 2 molecules of phosphatidic acid are linked by one molecule of glycerol. Unlike other glycerophospholipids, cardiolipin is a “double” glycerophospholipid. Cardiolipin is localized in the inner membrane of mitochondria. Its function is still unclear, although it is known that, unlike other phospholipids, cardiolipin has immune properties. 
Cardiolipin
In this formula, R1, R2, R3, R4 are radicals of higher fatty acids.
It should be noted that free phosphatidic acid occurs in nature, but in relatively small quantities compared to glycerophospholipids. Among the fatty acids that make up glycerophospholipids, both saturated and unsaturated ones are found (usually stearic, palmitic, oleic and linoleic).
It has also been established that most phosphatidylcholines and phosphatidylethanolamines contain one saturated higher fatty acid at the C-1 position and one unsaturated higher fatty acid at the C-2 position. Hydrolysis of phosphatidylcholines and phosphatidylethanolamines with the participation of special enzymes (these enzymes belong to phospholipases A2), contained, for example, in cobra venom, leads to the elimination of unsaturated fatty acids and the formation of lysophospholipids - lysophosphatidylcholines, or lysophosphatidylethanolamines, which have a strong hemolytic effect:
Sphingolipids (sphingophospholipids)
Sphingomyelins. These are the most common sphingolipids. They are mainly found in the membranes of animal and plant cells. Nervous tissue is especially rich in them. Sphingomyelins are also found in the tissue of the kidneys, liver and other organs. Upon hydrolysis, sphingomyelins form one molecule of fatty acid, one molecule of the dihydric unsaturated alcohol sphingosine, one molecule of a nitrogenous base (usually choline) and one molecule of phosphoric acid. The general formula of sphingomyelins can be represented as follows: 
The general plan for the construction of the sphingomyelin molecule in a certain respect resembles the structure of glycerophospholipids. The sphingomyelin molecule contains a polar “head”, which carries both positive (choline residue) and negative (phosphoric acid residue) charges, and two non-polar “tails” (a long aliphatic chain of sphingosine and a fatty acid acyl radical). In some sphingomyelins, for example those isolated from the brain and spleen, instead of sphingosine, the alcohol dihydrosphingosine (reduced sphingosine) was found:
Steroids
All lipids considered are usually called saponified, since their alkaline hydrolysis produces soaps. However, there are lipids that do not hydrolyze to release fatty acids. These lipids include steroids. Steroids are compounds widespread in nature. They are often found in association with fats. They can be separated from the fat by saponification (they end up in the unsaponifiable fraction). All steroids in their structure have a core formed by hydrogenated phenanthrene (rings A, B and C) and cyclopentane (ring D) (Fig. 1):
Figure 1 - Generalized steroid core
Steroids include, for example, hormones of the adrenal cortex, bile acids, vitamins D, cardiac glycosides and other compounds. In the human body, sterols (sterols) occupy an important place among steroids, i.e. steroid alcohols. The main representative of sterols is cholesterol (cholesterol).
Due to the complex structure and asymmetry of the molecule, steroids have many potential stereoisomers. Each of the six-carbon rings (rings A, B and C) of the steroid core can take on two different spatial conformations - the “chair” or “boat” conformation.
In natural steroids, including cholesterol, all rings are in the shape of a “chair”, which is a more stable conformation.
Cholesterol. As noted, among steroids there is a group of compounds called sterols (sterols). Sterols are characterized by the presence of a hydroxyl group at position 3, as well as a side chain at position 17. In the most important representative of sterols, cholesterol, all rings are located in trance- position; in addition, it has a double bond between the 5th and 6th carbon atoms. Therefore, cholesterol is an unsaturated alcohol:
The ring structure of cholesterol is characterized by significant rigidity, while the side chain is relatively flexible. So, cholesterol contains an alcohol hydroxyl group at C-3 and a branched aliphatic chain of 8 carbon atoms at C-17. The chemical name for cholesterol is 3-hydroxy-5,6-cholestene. The hydroxyl group at C-3 can be esterified with a higher fatty acid, resulting in the formation of cholesterol esters (cholesterides).
Every cell in the mammalian body contains cholesterol. Being part of cell membranes, non-esterified cholesterol, together with phospholipids and proteins, ensures selective permeability of the cell membrane and has a regulatory effect on the state of the membrane and the activity of enzymes associated with it. In the cytoplasm, cholesterol is found predominantly in the form of esters with fatty acids, forming small droplets - the so-called vacuoles. In blood plasma, both unesterified and esterified cholesterol are transported as part of lipoproteins.
Cholesterol is the source of formation in the body of mammals of bile acids, as well as steroid hormones (sex and corticoid). Cholesterol, or more precisely the product of its oxidation - 7-dehydrocholesterol, is converted into vitamin D 3 in the skin under the influence of UV rays. Thus, the physiological function of cholesterol is diverse.
Cholesterol is found in animal fats, but not in vegetable fats. Plants and yeast contain compounds similar in structure to cholesterol, including ergosterol.
Ergosterol– a precursor of vitamin D. After exposure of ergosterol to UV rays, it acquires the property of having an antirachitic effect (when the B ring opens).
Restoration of the double bond in the cholesterol molecule leads to the formation of coprosterol (coprostanol). Coprosterol is found in feces and is formed as a result of the restoration by bacteria of the intestinal microflora of the double bond in cholesterol between the C 5 and C 6 atoms. 
These sterols, unlike cholesterol, are very poorly absorbed in the intestines and therefore are found in human tissues in trace amounts.
Waxes
Waxes– these are esters of fatty acids and higher monohydric alcohols (C 12 - C 46). Waxes are part of the protective coating of plant leaves and human and animal skin. They give the surface a characteristic shine and water-repellent properties, which is important for preserving water inside the body and creating a barrier between the body and the environment.
In appearance, physical properties and sources of origin, fats and waxes have much in common, but waxes are very resistant to chemical reagents and do not change during long-term storage.
There is a simple way to help distinguish them. When heated strongly, fat emits a sharp, unpleasant odor of acrolein, while wax has a pleasant odor.
Waxes can be plant, animal, fossil and synthetic.
Vegetable waxes
Carnauba wax coats the leaves of the Brazilian palm Copernicia cerifera. It is an ester of triacontanol CH 3 (CH 2) 29 OH and tetracosanoic acid CH 3 (CH 2) 22 COOH. To obtain carnauba wax, palm leaves are dried, a powder is beaten out, which is boiled in water and poured into molds. 2000 leaves yield about 16 kg of wax. Carnauba wax is used to make mastics and shoe polishes.
Palm wax is found in the recesses of the ringed trunk of the wax palm, from where it is scraped off. One tree produces 12 kg of wax.
Japanese wax is extracted from the lacquer tree, which grows in Japan and China.
Fruits, vegetables and berries (for example, blueberries) are coated with vegetable waxes.
Animal waxes
Beeswax, the best known of this type of wax, is a palmitinomyricyl ester.
Wool (wool) wax - lanolin - coats animal hair abundantly.
Spermaceti is found in the bony cranial sockets of some species of whales, especially sperm whales. 90% consists of palmitinocetyl ether:
Chinese wax is produced by a mealybug that lives on Chinese ash and forms a waxy covering on it. Contains the ester of hexacosanoic acid CH 3 (CH 2) 24 COOH and hexadecane alcohol CH 3 (CH 2) 15 OH.
Waxes include sebum and earwax.
Bacterial wax coats the surface of acid-resistant bacteria, such as tuberculosis, making them resistant to external influences. Contains esters of mycolic acid C 88 H 172 O 2 and octadecanol C 20 H 42 O.
Fossil waxes
Peat wax is obtained by extraction of high-moor bituminous peat with gasoline at 80°C.
Lignite wax (montan wax) is extracted from brown bituminous coal with gasoline.
Mountain wax – ozokerite – is a mineral from the group of petroleum bitumens.
Synthetic waxes are obtained on the basis of petroleum and resin paraffins and their derivatives.
Waxes are used in more than 200 sectors of the national economy. They are included in polishes, protective compositions for metals, fabrics, paper, leather, wood; as an insulating material; components of ointments in cosmetics and medicine.
Related information.
Sphingolipids. They are mainly found in the membranes of animal and plant cells. Nervous tissue is especially rich in them. Sphingomyelins are also found in the tissue of the kidneys, liver and other organs. Upon hydrolysis, sphingomyelins form one molecule of fatty acid, one molecule of the dihydric unsaturated alcohol sphingosine, one molecule of a nitrogenous base (usually choline) and one molecule of phosphoric acid. The general formula of sphingomyelins can be represented as follows:
General plan for constructing the sphingomyelin molecule in in a certain way reminds structure of glycerophospholipids. The sphingomyelin molecule contains a polar “head”, which carries both positive (choline residue) and negative (phosphoric acid residue) charges, and two non-polar “tails” (a long aliphatic chain of sphingosine and a fatty acid acyl radical). In some sphingomyelins, for example those isolated from the brain and spleen, instead of sphingosine, the alcohol dihydrosphingosine (reduced sphingosine) was found:
7.6 Steroids
All lipids considered are usually called saponified, since their alkaline hydrolysis produces soaps. However, there are lipids that are not hydrolyzed with the release of fatty acids. These lipids include steroids. Steroids are compounds widespread in nature. They are often found in association with fats. They can be separated from the fat by saponification (they end up in the unsaponifiable fraction). All steroids in have a core in their structure, formed by hydrogenated phenanthrene (rings A, B and C) and cyclopentane (ring D) (Fig. 24):
Figure 24 - Generalized steroid core
Steroids include, for example, hormones of the adrenal cortex, bile acids, vitamins D, cardiac glycosides and other compounds. In the human body, sterols (sterols) occupy an important place among steroids, i.e. steroid alcohols. The main representative of sterols is cholesterol (cholesterol).
Due to the complex structure and asymmetry of the molecule, steroids have many potential stereoisomers. Each of the six-carbon rings (rings A, B and C) of the steroid core can take on two different spatial conformations - the “chair” or “boat” conformation.
Cholesterol is the source of formation in the body of mammals of bile acids, as well as steroid hormones (sex and corticoid). Cholesterol, or more precisely the product of its oxidation - 7-dehydrocholesterol, is converted into vitamin D 3 in the skin under the influence of UV rays. Thus, physiological The function of cholesterol is diverse.
Cholesterol is found in animal fats, but not in vegetable fats. IN plants and yeast contain compounds similar in structure to cholesterol, including ergosterol.
Ergosterol is a precursor of vitamin D. After exposure of ergosterol to UV rays, it acquires the property of having an antirachitic effect (when the B ring opens).
Restoration of the double bond in the cholesterol molecule leads to the formation of coprosterol (coprostanol). Coprosterol is found in composition of feces and is formed in as a result of the restoration by bacteria of the intestinal microflora of the double bond in cholesterol between the C 5 and C 6 atoms. 
These sterols, unlike cholesterol, are very poorly absorbed into intestines and are therefore found in human tissues in trace amounts.
8 Chemistry of carbohydrates
The term “carbohydrates” was first proposed by Professor of Dorpat (now Tartu) University K.G. Schmidt in 1844. At that time, it was assumed that all carbohydrates have the general formula C m (H 2 O) n, i.e. carbohydrate + water. Hence the name "carbohydrates". For example, glucose and fructose have the formula C(H2O)6, cane sugar (sucrose) C12(H2O)11, starch [C6(H2O)5]n, etc. IN later it turned out that a number of compounds, which in their properties belong to the class of carbohydrates, contain hydrogen and oxygen in a slightly different proportion than indicated in the general formula (for example, deoxyribose C 5 H 10 O 4). In 1927, the International Commission for the Reform of Chemical Nomenclature proposed replacing the term “carbohydrates” with the term “glycides,” but the old name “carbohydrates” has taken root and is generally accepted.
The chemistry of carbohydrates is one of the leading places in the history of development organic chemistry. Cane sugar can be considered the first organic compound isolated in a chemically pure form. Produced in 1861 by A.M. Butlerov's synthesis (outside the body) of carbohydrates from formaldehyde was the first synthesis of representatives of one of three main classes of substances(proteins, lipids, carbohydrates) that make up living organisms. The chemical structure of the simplest carbohydrates was elucidated at the end of the 19th century. V as a result of fundamental research by E. Fischer. A significant contribution to the study of carbohydrates was made by domestic scientists A.A. Colley, P.P. Shorygin, N.K. Kochetkov and others. In the 20s of this century, the foundations of the structural chemistry of polysaccharides were laid by the work of the English researcher W. Haworth. From the second half of the 20th century. There is a rapid development of the chemistry and biochemistry of carbohydrates, due to their important biological significance.
