Thank you

The site provides background information for informational purposes only. Diagnosis and treatment of diseases should be carried out under the supervision of a specialist. All drugs have contraindications. Expert advice is required!

What are lipid substances?

Lipids are one of the groups organic compounds which is of great importance for living organisms. According to the chemical structure, all lipids are divided into simple and complex. A simple lipid molecule is composed of alcohol and bile acids, while a complex lipid contains other atoms or compounds.

In general, lipids are of great importance for humans. These substances are included in a significant part of food products, are used in medicine and pharmacy, and play an important role in many industries. In a living organism, lipids in one form or another are part of all cells. From a nutritional point of view, it is a very important source of energy.

What is the difference between lipids and fats?

In principle, the term "lipids" comes from the Greek root meaning "fat", however, these definitions still have some differences. Lipids are a broader group of substances, while only certain types of lipids are understood as fats. A synonym for "fats" are "triglycerides", which are obtained from the combination of glycerol alcohol and carboxylic acids. Both lipids in general and triglycerides in particular play a significant role in biological processes.

Lipids in the human body

Lipids are part of almost all tissues of the body. Their molecules are in any living cell, and life is simply impossible without these substances. There are many different lipids found in the human body. Each type or class of these compounds has its own functions. Many biological processes depend on the normal intake and formation of lipids.

From the point of view of biochemistry, lipids are involved in the following important processes:

• body's production of energy;

• cell division;
• transmission of nerve impulses;
• the formation of blood components, hormones and other important substances;
• protection and fixation of some internal organs;
• cell division, respiration, etc.

Thus, lipids are vital chemical compounds. A significant part of these substances enters the body with food. After that, the structural components of lipids are absorbed by the body, and cells produce new lipid molecules.

The biological role of lipids in a living cell

Lipid molecules perform a huge number of functions not only on the scale of the whole organism, but also in each living cell individually. In fact, a cell is a structural unit of a living organism. It is the assimilation and synthesis ( education) of certain substances. Some of these substances are used to maintain the life of the cell itself, some - for cell division, some - for the needs of other cells and tissues.

In a living organism, lipids perform following features:

• energy;
• reserve;
• structural;
• transport;
• enzymatic;
• storage;
• signal;
• regulatory.

energy function

The energy function of lipids is reduced to their breakdown in the body, during which a large amount of energy is released. Living cells need this energy to maintain various processes ( respiration, growth, division, synthesis of new substances). Lipids enter the cell with blood flow and are deposited inside ( in the cytoplasm) in the form of small drops of fat. If necessary, these molecules are broken down, and the cell receives energy.

Reserve ( storage) function

The reserve function is closely related to the energy function. In the form of fats inside cells, energy can be stored "in reserve" and released as needed. Special cells, adipocytes, are responsible for the accumulation of fats. Most of their volume is occupied by a large drop of fat. It is from adipocytes that adipose tissue in the body consists. The largest reserves of adipose tissue are in the subcutaneous fat, the greater and lesser omentum ( in the abdominal cavity). With prolonged starvation, adipose tissue gradually disintegrates, since lipid reserves are used for energy.

Also, adipose tissue deposited in the subcutaneous fat provides thermal insulation. Tissues rich in lipids generally conduct heat worse. This allows the body to maintain a constant body temperature and not cool or overheat so quickly in various conditions. external environment.

Structural and barrier functions ( membrane lipids)

Lipids play an important role in the structure of living cells. In the human body, these substances form a special double layer that forms the cell wall. Thanks to this, a living cell can perform its functions and regulate the metabolism with the external environment. The lipids that make up the cell membrane also help keep the shape of the cell.

Why do lipid monomers form a double layer ( bilayer)?

Monomers are chemical substances ( in this case, molecules), which are able, when combined, to form more complex compounds. The cell wall consists of a double layer ( bilayer) lipids. Each molecule forming this wall has two parts - hydrophobic ( not in contact with water) and hydrophilic ( in contact with water). The double layer is obtained due to the fact that lipid molecules are deployed by hydrophilic parts inside the cell and outward. The hydrophobic parts are practically in contact, as they are located between the two layers. Other molecules can also be located in the thickness of the lipid bilayer ( proteins, carbohydrates, complex molecular structures ), which regulate the passage of substances through the cell wall.

transport function

The transport function of lipids is of secondary importance in the body. It is performed only by some connections. For example, lipoproteins, consisting of lipids and proteins, carry certain substances in the blood from one organ to another. However, this function is rarely distinguished, not considering it the main one for these substances.

Enzymatic function

In principle, lipids are not part of the enzymes involved in the breakdown of other substances. However, without lipids, organ cells will not be able to synthesize enzymes, the end product of life. In addition, certain lipids play a significant role in the absorption of dietary fats. Bile contains significant amounts of phospholipids and cholesterol. They neutralize excess pancreatic enzymes and prevent them from damaging intestinal cells. It also dissolves in bile emulsification) exogenous lipids from food. Thus, lipids play a huge role in digestion and help in the work of other enzymes, although they are not enzymes themselves.

Signal function

Some of the complex lipids perform a signaling function in the body. It consists in maintaining various processes. For example, glycolipids in nerve cells are involved in the transmission of a nerve impulse from one nerve cell to another. Besides, great importance have signals within the cell itself. She needs to "recognize" the substances coming from the blood in order to transport them inside.

Regulatory function

The regulatory function of lipids in the body is secondary. Blood lipids themselves have little effect on the course of various processes. However, they are part of other substances that are of great importance in the regulation of these processes. First of all, these are steroid hormones ( adrenal and sex hormones). They play an important role in metabolism, growth and development of the body, reproductive function, and affect the functioning of the immune system. Lipids are also part of prostaglandins. These substances are produced during inflammatory processes and affect some processes in nervous system (e.g. perception of pain).

Thus, lipids themselves do not perform a regulatory function, but their deficiency can affect many processes in the body.

Biochemistry of lipids and their relationship with other substances ( proteins, carbohydrates, ATP, nucleic acids, amino acids, steroids)

Lipid metabolism is closely related to the metabolism of other substances in the body. First of all, this connection can be traced in human nutrition. Any food consists of proteins, carbohydrates and lipids, which must be ingested in certain proportions. In this case, a person will receive both enough energy and enough structural elements. Otherwise ( for example, with a lack of lipids) proteins and carbohydrates will be broken down to produce energy.

Lipids are also to some extent associated with the metabolism of the following substances:

• Adenosine triphosphoric acid ( ATP). ATP is a kind of unit of energy within the cell. When lipids are broken down, part of the energy goes to the production of ATP molecules, and these molecules take part in all intracellular processes ( transport of substances, cell division, neutralization of toxins, etc.).
• Nucleic acids. Nucleic acids are the building blocks of DNA and are found in the nuclei of living cells. The energy generated during the breakdown of fats goes partly into cell division. During division, new strands of DNA are formed from nucleic acids.
• Amino acids. Amino acids are the structural components of proteins. In combination with lipids, they form complex complexes, lipoproteins, which are responsible for the transport of substances in the body.
• Steroids. Steroids are a type of hormone containing a significant amount of lipids. With poor absorption of lipids from food, the patient may begin problems with the endocrine system.

Thus, the metabolism of lipids in the body, in any case, must be considered in combination, from the point of view of the relationship with other substances.

Digestion and absorption of lipids ( metabolism, metabolism)

Digestion and absorption of lipids is the first step in the metabolism of these substances. The main part of lipids enters the body with food. IN oral cavity food is crushed and mixed with saliva. Next, the lump enters the stomach, where the chemical bonds are partially destroyed under the action of of hydrochloric acid. Also, some chemical bonds in lipids are destroyed by the action of the enzyme lipase, contained in saliva.

Lipids are insoluble in water, so they are not immediately digested by enzymes in the duodenum. First, the so-called emulsification of fats occurs. After that, chemical bonds are cleaved under the action of lipase coming from the pancreas. In principle, for each type of lipid, its own enzyme is now defined, which is responsible for the breakdown and assimilation of this substance. For example, phospholipase breaks down phospholipids, cholesterol esterase breaks down cholesterol compounds, etc. All these enzymes are contained in pancreatic juice in one quantity or another.

The split fragments of lipids are individually absorbed by the cells of the small intestine. In general, the digestion of fats is a very complex process, which is regulated by many hormones and hormone-like substances.

What is lipid emulsification?

Emulsification is the incomplete dissolution of fatty substances in water. In the food bolus that enters the duodenum, fats are contained in the form of large drops. This prevents their interaction with enzymes. In the process of emulsification, large fat droplets are "crushed" into smaller droplets. As a result, the area of ​​contact between the fat droplets and the surrounding water-soluble substances increases, and the breakdown of lipids becomes possible.

The process of lipid emulsification in the digestive system takes place in several stages:

• At the first stage, the liver produces bile, which will emulsify fats. It contains salts of cholesterol and phospholipids, which interact with lipids and contribute to their "crushing" into small drops.
• Bile secreted from the liver accumulates in the gallbladder. Here it is concentrated and released as needed.
• When fatty foods are consumed, the smooth muscles of the gallbladder receive a signal to contract. As a result, a portion of bile is secreted through the bile ducts into the duodenum.
• In the duodenum, fats are actually emulsified and interact with pancreatic enzymes. The contractions of the walls of the small intestine contribute to this process by "mixing" the contents.

Some people may have trouble absorbing fats after having their gallbladder removed. Bile enters the duodenum continuously, directly from the liver, and is not enough to emulsify all the lipids if too much is eaten.

Enzymes for splitting lipids

For the digestion of each substance in the body there are enzymes. Their mission is to destroy chemical bonds between molecules ( or between atoms in molecules) so that nutrients can be properly absorbed by the body. Different enzymes are responsible for the breakdown of different lipids. Most of them are found in the juice secreted by the pancreas.

The following groups of enzymes are responsible for the breakdown of lipids:

• lipases;
• phospholipases;
• cholesterol esterase, etc.

What vitamins and hormones are involved in lipid regulation?

The level of most lipids in human blood is relatively constant. It can fluctuate within certain limits. It depends on the biological processes occurring in the body itself, and on a number of external factors. The regulation of blood lipid levels is a complex biological process involving many different organs and substances.

The following substances play the greatest role in the assimilation and maintenance of a constant level of lipids:

• Enzymes. A number of pancreatic enzymes are involved in the breakdown of lipids that enter the body with food. With a lack of these enzymes, the level of lipids in the blood may decrease, since these substances simply will not be absorbed in the intestines.
• Bile acids and their salts. Bile contains bile acids and a number of their compounds, which contribute to the emulsification of lipids. Without these substances, normal absorption of lipids is also impossible.
• Vitamins. Vitamins have a complex strengthening effect on the body and directly or indirectly also affect lipid metabolism. For example, with a lack of vitamin A, cell regeneration in the mucous membranes deteriorates, and the digestion of substances in the intestine also slows down.
• intracellular enzymes. The cells of the intestinal epithelium contain enzymes that, after absorption of fatty acids, convert them into transport forms and direct them into the bloodstream.
• Hormones. A number of hormones affect the metabolism in general. For example, high level insulin can greatly affect blood lipid levels. That is why for patients with diabetes, some norms have been revised. Thyroid hormones, glucocorticoid hormones, or norepinephrine can stimulate the breakdown of adipose tissue to release energy.

Thus, maintaining a normal level of lipids in the blood is a very complex process, which is directly or indirectly affected by various hormones, vitamins and other substances. In the process of diagnosis, the doctor needs to determine at what stage this process was violated.

Biosynthesis ( education) and hydrolysis ( decay) lipids in the body ( anabolism and catabolism)

Metabolism is the totality of metabolic processes in the body. All metabolic processes can be divided into catabolic and anabolic. Catabolic processes include the breakdown and breakdown of substances. With respect to lipids, this is characterized by their hydrolysis ( breakup into more simple substances ) V gastrointestinal tract. Anabolism combines biochemical reactions aimed at the formation of new, more complex substances.

Lipid biosynthesis occurs in the following tissues and cells:

• Cells of the intestinal epithelium. Absorption of fatty acids, cholesterol and other lipids occurs in the intestinal wall. Immediately after this, new, transport forms of lipids are formed in the same cells, which enter the venous blood and are sent to the liver.
• Liver cells. In the liver cells, some of the transport forms of lipids will break down, and new substances are synthesized from them. For example, cholesterol compounds and phospholipids are formed here, which are then excreted in the bile and contribute to normal digestion.
• Cells of other organs. Part of the lipids enters with the blood into other organs and tissues. Depending on the type of cells, lipids are converted into certain types of compounds. All cells, one way or another, synthesize lipids to form a cell wall ( lipid bilayer). In the adrenal glands and gonads, steroid hormones are synthesized from a part of lipids.

The combination of the above processes is the lipid metabolism in the human body.

Resynthesis of lipids in the liver and other organs

Resynthesis is the process of formation of certain substances from simpler ones that were assimilated earlier. In the body, this process takes place in the internal environment of some cells. Resynthesis is necessary in order for tissues and organs to receive all the necessary types of lipids, and not just those that were consumed with food. Resynthesized lipids are called endogenous. For their formation, the body expends energy.

At the first stage, lipid resynthesis occurs in the intestinal walls. Here, the fatty acids that come with food are converted into transport forms that will go with the blood to the liver and other organs. Part of the resynthesized lipids will be delivered to the tissues, while the other part will form the substances necessary for vital activity ( lipoproteins, bile, hormones, etc.), the excess is converted into adipose tissue and stored "in reserve".

Are lipids part of the brain?

Lipids are a very important component of nerve cells not only in the brain, but throughout the nervous system. As you know, nerve cells control various processes in the body through the transmission of nerve impulses. At the same time, all nerve pathways are “isolated” from each other so that the impulse comes to certain cells and does not affect other nerve pathways. This "isolation" is possible due to the myelin sheath of nerve cells. Myelin, which prevents the chaotic propagation of impulses, is approximately 75% lipid. As in cell membranes, here they form a double layer ( bilayer), which is wrapped several times around the nerve cell.

The composition of the myelin sheath in the nervous system includes the following lipids:

• phospholipids;
• cholesterol;
• galactolipids;
• glycolipids.

Neurological problems are possible in some congenital disorders of lipid formation. This is due precisely to the thinning or interruption of the myelin sheath.

lipid hormones

Lipids play an important structural role, including being present in the structure of many hormones. Hormones that contain fatty acids are called steroid hormones. In the body, they are produced by the gonads and adrenal glands. Some of them are also present in adipose tissue cells. Steroid hormones are involved in the regulation of many vital important processes. Their imbalance can affect body weight, the ability to conceive a child, the development of any inflammatory processes, and the functioning of the immune system. The key to normal production of steroid hormones is a balanced intake of lipids.

Lipids are part of the following vital hormones:

• corticosteroids ( cortisol, aldosterone, hydrocortisone, etc.);
• male sex hormones - androgens ( androstenedione, dihydrotestosterone, etc.);
• female sex hormones - estrogen estriol, estradiol, etc.).

Thus, the lack of certain fatty acids in food can seriously affect the functioning of the endocrine system.

The role of lipids for skin and hair

Lipids are of great importance for the health of the skin and its appendages ( hair and nails). The skin contains the so-called sebaceous glands, which secrete a certain amount of secretion rich in fats to the surface. This substance performs many useful functions.

For hair and skin, lipids are important for the following reasons:

• a significant part of the substance of the hair consists of complex lipids;
• skin cells are rapidly changing, and lipids are important as an energy resource;
• secret ( excreted substance a) sebaceous glands moisturizes the skin;
• thanks to fats, elasticity, elasticity and smoothness of the skin are maintained;
• a small amount of lipids on the surface of the hair give them a healthy shine;
• lipid layer on the surface of the skin protects it from the aggressive effects of external factors ( cold, sun rays, microbes on the surface of the skin, etc.).

In skin cells, as well as in hair follicles, lipids come with blood. Thus, normal nutrition ensures healthy skin and hair. Use of shampoos and creams containing lipids ( especially essential fatty acids) is also important, because some of these substances will be absorbed from the surface of the cells.

Lipid classification

In biology and chemistry, there are quite a few different classifications of lipids. The main one is the chemical classification, according to which lipids are divided depending on their structure. From this point of view, all lipids can be divided into simple ( consisting only of oxygen, hydrogen and carbon atoms) and complex ( containing at least one atom of other elements). Each of these groups has corresponding subgroups. This classification is the most convenient, since it reflects not only the chemical structure of substances, but also partially determines the chemical properties.

Biology and medicine have their own additional classifications using other criteria.

Exogenous and endogenous lipids

All lipids in the human body can be divided into two large groups - exogenous and endogenous. The first group includes all substances that enter the body from the external environment. The greatest amount of exogenous lipids enters the body with food, but there are other ways. For example, when using various cosmetics or medicines the body can also receive some lipids. Their action will be predominantly local.

After entering the body, all exogenous lipids are broken down and absorbed by living cells. Here, from their structural components, other lipid compounds that the body needs will be formed. These lipids, synthesized by one's own cells, are called endogenous. They may have a completely different structure and function, but they consist of the same "structural components" that entered the body with exogenous lipids. That is why, with a lack of certain types of fats in food, various diseases. Part of the components of complex lipids cannot be synthesized by the body on its own, which affects the course of certain biological processes.

Fatty acid

Fatty acids are a class of organic compounds that are the structural part of lipids. Depending on which fatty acids are included in the composition of the lipid, the properties of this substance may change. For example, triglycerides, the most important source of energy for the human body, are derivatives of the alcohol glycerol and several fatty acids.

In nature, fatty acids are found in a variety of substances - from oil to vegetable oils. They enter the human body mainly with food. Each acid is a structural component for certain cells, enzymes or compounds. After absorption, the body converts it and uses it in various biological processes.

The most important sources of fatty acids for humans are:

• animal fats;
• vegetable fats;
• tropical oils ( citrus, palm, etc.);
• fats for Food Industry (margarine, etc.).

In the human body, fatty acids can be stored in adipose tissue as triglycerides or circulate in the blood. They are found in the blood both in the free form and in the form of compounds ( various fractions of lipoproteins).

Saturated and unsaturated fatty acids

All fatty acids are divided into saturated and unsaturated according to their chemical structure. Saturated acids are less beneficial to the body, and some of them are even harmful. This is due to the fact that there are no double bonds in the molecule of these substances. These are chemically stable compounds, and they are less absorbed by the body. Some saturated fatty acids have now been shown to be associated with the development of atherosclerosis.

Unsaturated fatty acids are divided into two large groups:

• Monounsaturated. These acids have one double bond in their structure and are thus more active. It is believed that eating them can lower cholesterol levels and prevent the development of atherosclerosis. The largest amount of monounsaturated fatty acids is found in a number of plants ( avocado, olives, pistachios, hazelnuts) and, accordingly, in the oils obtained from these plants.
• Polyunsaturated. Polyunsaturated fatty acids have several double bonds in their structure. Distinctive feature of these substances is that the human body is not able to synthesize them. In other words, if polyunsaturated fatty acids are not supplied to the body with food, over time this will inevitably lead to certain disorders. The best sources of these acids are seafood, soy and linseed oil, sesame seeds, poppy seeds, germinated wheat, etc.

Phospholipids

Phospholipids are complex lipids containing a phosphoric acid residue in their composition. These substances, along with cholesterol, are the main component of cell membranes. Also, these substances are involved in the transport of other lipids in the body. WITH medical point of vision, phospholipids can also play a signaling role. For example, they are part of bile, as they contribute to emulsification ( dissolution) other fats. Depending on which substance is more in bile, cholesterol or phospholipids, it is possible to determine the risk of developing cholelithiasis.

Glycerin and triglycerides

Chemically, glycerol is not a lipid, but it is an important structural component of triglycerides. This is a group of lipids that play a huge role in the human body. The most important function of these substances is the supply of energy. Triglycerides that enter the body with food are broken down into glycerol and fatty acids. As a result, a very large amount of energy is released, which goes to the work of the muscles ( skeletal muscles, heart muscles, etc.).

Adipose tissue in the human body is represented mainly by triglycerides. Most of these substances, before being deposited in adipose tissue, undergo some chemical transformations in the liver.

Beta lipids

Beta lipids are sometimes referred to as beta lipoproteins. The duality of the name is explained by differences in classifications. This is one of the fractions of lipoproteins in the body, which plays an important role in the development of certain pathologies. First of all, we are talking about atherosclerosis. Beta-lipoproteins transport cholesterol from one cell to another, but due to the structural features of the molecules, this cholesterol often "gets stuck" in the walls of blood vessels, forming atherosclerotic plaques and preventing normal blood flow. Before use, you should consult with a specialist.

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 usefulness 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 milk various kinds animal lipid content ranges from 1.7% in mare's milk to 34.5% in the milk of female reindeer.

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

By chemical structure lipids are derivatives of fatty acids, alcohols, aldehydes built using ester, ether, phosphoester, 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. Molecules of complex lipids contain in their composition not only the remains of high-molecular carboxylic acids, but also phosphoric, sulfuric acids or nitrogen.

The most important and widespread group of simple neutral lipids are acylglycerols (or glycerides). This esters glycerol and higher carboxylic acids. They make up the bulk of lipids (sometimes up to 95%) and, in fact, 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- obligatory components of plants (0.3-1.7%). Their molecules are built from residues of alcohols (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 general principle. They include, on the one hand, hydrophobic, characterized by low affinity for water, 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 form an interface (membrane) between water and the hydrophobic phase in living organism systems and foods.

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. In terms of mass, structural lipids make up a much smaller group of lipids (3-5% in oilseeds). These are hard-to-remove "bound" and "strongly bound" lipids.

	|	next lecture ==>

§ 4. CLASSIFICATION AND FUNCTIONS OF LIPIDS

Lipids are a heterogeneous group of chemical compounds that are insoluble in water, but highly soluble in non-polar organic solvents: chloroform, ether, acetone, benzene, etc., i.e. their common property is hydrophobicity (hydro - water, phobia - fear). Due to the wide variety of lipids, give more precise definition it is impossible for them. Lipids in most cases are esters of fatty acids and some kind of alcohol. The following classes of lipids are distinguished: triacylglycerols, or fats, phospholipids, glycolipids, steroids, waxes, terpenes. There are two categories of lipids - saponifiable and unsaponifiable. Saponifiables include substances containing an ester bond (waxes, triacylglycerols, phospholipids, etc.). Unsaponifiables include steroids and terpenes.

Triacylglycerols or fats

Triacylglycerols are esters of the trihydric alcohol glycerol

and fatty (higher carboxylic) acids. General formula fatty acids has the form: R-COOH, where R is a hydrocarbon radical. Natural fatty acids contain from 4 to 24 carbon atoms. As an example, we give the formula of one of the most common stearic acid in fats:

CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -COOH

IN general view The triacylglycerol molecule can be written as:

If triacioglycerol contains residues of various acids (R 1 R 2 R 3), then the central carbon atom in the glycerol residue becomes chiral.

Triacylglycerols are non-polar and therefore practically insoluble in water. The main function of triacylglycerols is energy storage. When 1 g fat is oxidized, 39 kJ of energy is released. Triacylglycerols accumulate in adipose tissue, which, in addition to storing fat, performs a thermal insulating function and protects organs from mechanical damage. More detailed information about fats and fatty acids, see the next paragraph.

Interesting to know! The fat with which the camel's hump is filled serves, first of all, not as a source of energy, but as a source of water formed during its oxidation.

Phospholipids

Phospholipids contain hydrophobic and hydrophilic regions and therefore have amphiphilic properties, i.e. they can dissolve in non-polar solvents and form stable emulsions with water.

Phospholipids, depending on the presence of glycerol and sphingosine alcohols in their composition, are divided into glycerophospholipids And sphingophospholipids.

Glycerophospholipids

The structure of the glycerophospholipid molecule is based on phosphatidic acid, formed by glycerol, two fatty acids and phosphoric acids:

In glycerophospholipid molecules, an HO-containing polar molecule is attached to phosphatidic acid by an ester bond. The formula of glycerophospholipids can be represented as follows:

where X is the residue of an HO-containing polar molecule (polar group). The names of phospholipids are formed depending on the presence of one or another polar group in their composition. Glycerophospholipids containing an ethanolamine residue as a polar group,

HO-CH 2 -CH 2 -NH 2

are called phosphatidylethanolamines, a choline residue

- phosphatidylcholines, serine

- phosphatidylserines.

The formula for phosphatidylethanolamine looks like this:

Glycerophospholipids differ from each other not only in polar groups, but also in fatty acid residues. They include both saturated (usually consisting of 16-18 carbon atoms) and unsaturated (more often containing 16-18 carbon atoms and 1-4 double bonds) fatty acids.

Sphingophospholipids

Sphingophospholipids are similar in composition to glycerophospholipids, but instead of glycerol they contain the amino alcohol sphingosine:

or dihydrosphingazine:

The most common sphingophospholipids are sphingomyelins. They are formed by sphingosine, choline, fatty acid and phosphoric acid:

The molecules of both glycerophospholipids and sphingophospholipids consist of a polar head (formed by phosphoric acid and a polar group) and two non-polar hydrocarbon tails (Fig. 1). In glycerophospholipids, both non-polar tails are fatty acid radicals, in sphingophospholipids, one tail is a fatty acid radical, the other is a hydrocarbon chain of sphingazine alcohol.

Rice. 1. Schematic representation of a phospholipid molecule.

When shaken in water, phospholipids spontaneously form micelles, in which nonpolar tails are collected inside the particle, and polar heads are located on its surface, interacting with water molecules (Fig. 2a). Phospholipids can also form bilayers(Fig. 2b) and liposomes– closed bubbles surrounded by a continuous bilayer (Fig. 2c).

Rice. 2. Structures formed by phospholipids.

The ability of phospholipids to form a bilayer underlies the formation of cell membranes.

Glycolipids

Glycolipids contain a carbohydrate component in their composition. These include glycosphingolipids containing, in addition to carbohydrates, alcohol, sphingosine and a fatty acid residue:

They, like phospholipids, consist of a polar head and two non-polar tails. Glycolipids are located on the outer layer of the membrane, are integral part receptors provide interaction between cells. They are especially numerous in the nervous tissue.

Steroids

Steroids are derivatives cyclopentanperhydrophenanthrene(Fig. 3). One of the most important representatives of steroids - cholesterol. In the body, it occurs both in the free state and in the bound state, forming esters with fatty acids (Fig. 3). In free form, cholesterol is part of the membranes and lipoproteins of the blood. Cholesterol esters are its reserve form. Cholesterol is the precursor of all other steroids: sex hormones (testosterone, estradiol, etc.), hormones of the adrenal cortex (corticosterone, etc.), bile acids (deoxycholic, etc.), vitamin D (Fig. 3).

Interesting to know! The body of an adult contains about 140 g of cholesterol, most of which is found in the nervous tissue and adrenal glands. Every day, 0.3-0.5 g of cholesterol enters the human body, and up to 1 g is synthesized.

Wax

Waxes are esters formed from long-chain fatty acids (14-36 carbon atoms) and long-chain monohydric alcohols (16-22 carbon atoms). As an example, consider the formula for wax formed by oleic alcohol and oleic acid:

Waxes perform mainly a protective function, being on the surface of leaves, stems, fruits, seeds, they protect tissues from drying out and penetration of microbes. They cover the wool and feathers of animals and birds, protecting them from getting wet. Beeswax serves as a building material for bees to create honeycombs. In plankton, wax is the main form of energy storage.

Terpenes

Terpene compounds are based on isoprene residues:

Terpenes are essential oils, resin acids, rubber, carotenes, vitamin A, squalene. As an example, here is the formula for squalene:

Squalene is the main component of the secretion of the sebaceous glands.

The structure of lipids, fatty acids

Lipids - enough large group 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.).

Remark 1

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

At 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, therefore esters are easily formed.

Sometimes fatty acids have 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 that do not have double bonds are called rich . 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 more low temperatures than saturated.

Example 1

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

Definition 1

Most lipids are esters of 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 the state in which they remain at room temperature: solid (fats), or liquid (oils).

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

Oils tend to have more unsaturated fatty acids than fats.

Example 2

In the body of animals living in cold climatic zones (fish of the Arctic seas) there are usually more unsaturated triacylglycerols than in the inhabitants of southern latitudes. Because their body remains flexible even at low temperatures. environment.

Functions of lipids

Important groups of lipids include

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

Remark 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 storage of spare 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. Spend them later in the process of life. Thanks to high content lipids, plant seeds provide energy for the development of the embryo and sprout until it passes to independent nutrition. Seeds of many plants (sunflower, soybean, flax, corn, mustard, coconut tree, castor beans, etc.) are raw materials for industrial production of oils.

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

I. LIPIDS - organic substances characteristic of living organisms, insoluble in water, but soluble in organic solvents (carbon disulfide, chloroform, ether, benzene), giving at hydrolysis of high molecular weight fatty acids. They are not unlike proteins, nucleic acids and polysaccharides, they are not high-molecular compounds, their structure is very diverse, they have only one common feature- hydrophobicity.

Lipids perform the following functions in the body:

1. energy - are reserve compounds, the main form of energy and carbon storage. The oxidation of 1 g of neutral fats (triacylglycerols) releases about 38 kJ of energy;

2. regulatory- lipids are fat-soluble vitamins and derivatives of certain fatty acids that are involved in metabolism.

3. structural - are the main structural components of cell membranes, form double layers of polar lipids, into which enzyme proteins are embedded;

4. protective function:

Ø protects organs from mechanical damage;

Ø is involved in thermoregulation.

The formation of fat reserves in the human body and some animals is considered as an adaptation to an irregular diet and to living in a cold environment. A particularly large supply of fat is in animals falling into long hibernation (bears, marmots) and adapted to living in cold conditions (walruses, seals). The fetus has practically no fat, and appears only before birth.

Lipids can be divided into three groups based on their structure:

Ø simple lipids - they include only esters of fatty acids and alcohols. These include: fats, waxes and sterides;

Ø complex lipids - they include fatty acids, alcohols and other components of various chemical structures. These include phospholipids, glycolipids, etc.;

Ø lipid derivatives are mainly fat-soluble vitamins and their precursors.

In animal tissues, fats are in a partially free state, to a greater extent they form a complex with proteins.

By chemical composition, structure and function performed in a living cell, lipids are divided into:

II. Simple lipads are compounds consisting only of fatty acids and alcohols. They are divided into neutral acylglycerides (fats) and waxes.

Fats- reserve substances that accumulate in very large quantities in the seeds and fruits of many plants are part of the human body, animals, microbes and even viruses.

According to the chemical structure, fats - a mixture of esters (glycerinodes) of the triatomic spire of glycerol and high molecular weight fatty acids - are built according to the type:

CH 2 -O-C-R 1

CH 2 -O-C-R 3

where R 1 , R 2 , R 3 are the radicals of high molecular weight fatty acids.

Fatty acids are long chain monocarboxylic acids (containing 12 to 20 carbon atoms).

Fatty acids that make up fats are divided into saturated (do not contain double carbon-carbon bonds) and unsaturated or unsaturated (contain one or more double carbon-carbon bonds). Unsaturated fatty acids are classified into:

1. monounsaturated - contain one bond:

2. polyunsaturated - contain more than one bond.

Of the saturated acids, the most important are:

palmitic (CH 3 - (CH 2) 14 - COOH)

stearic (CH 3 - (CH 2) 16 - COOH);

The most important unsaturated fatty acids are oleic, linoleic and linolenic.

CH 3 - (CH 2) 7 - CH \u003d CH - (CH 2) 7 - COOH - oleic acid

CH 3 - (CH 2) 4 -CH \u003d CH - CH 2 - CH \u003d CH - (CH 2) 7 - COOH - linoleic acid

CH 3 -CH 2 -CH \u003d CH -CH 2 -CH \u003d CH -CH 2 -CH \u003d CH - (CH 2) 7 - COOH - linolenic

The properties of fats are determined by the qualitative composition of fatty acids, their quantitative ratio, the percentage of free fatty acids unbound to glycerol, etc.

If saturated (limiting) fatty acids predominate in the composition of fat, then the fat has a solid consistency. In contrast, liquid fats are dominated by unsaturated (unsaturated) acids. Liquid fats are called oils.

An indicator of the saturation of fat is the iodine number - the number of milligrams of iodine that can join 100 g of fat at the site of the double bond rupture in the molecules of non-peroxide acids. The more double bonds in a fat molecule (the higher its unsaturation), the higher its iodine number.

Another important indicator- number of saponification of fat. Hydrolysis of fat produces glycerol and fatty acids. The latter with alkalis form layers called soaps, and the process of their formation is called saponification of fats.

The saponification number is the amount of KOH (mg) used to neutralize the acids formed during the hydrolysis of 1 g of fat.

A feature of fats is their ability to form aqueous emulsions under certain conditions, which is important for the nutrition of the body. An example of such an emulsion is milk - the secret of the mammary glands of mammals and humans. Milk is a thin emulsion of milk fat in its plasma. 1 mm 3 of milk contains up to 5-6 million milk fat globules with a diameter of about 3 microns. Milk lipids consist mainly of triglycerides, in which oleic and palmetic acids predominate.

Polyunsaturated fatty acids (oleic, linoleic, linolenic and arachidonic acids) are called essential (essential) acids. they are essential to man. Polyunsaturated fatty acids promote the release of cholesterol from the body, preventing and weakening atherosclerosis, increase the elasticity of blood vessels.

Due to the fact that unsaturated fatty acids have double bonds, they are very easily oxidized. The process of fat oxidation can proceed by itself due to the addition of atmospheric oxygen at the site of double bonds, however, it can be significantly accelerated under the influence of the lipoxygenase enzyme.

Waxes- esters of high molecular weight fatty acids and monohydric alcohols with a long carbon chain. These are solid compounds with pronounced hydrophobic properties. Fatty acids in them contain from 24 to 30 carbon atoms, and macromolecular alcohols - 16-30 carbon atoms.

R 1 - CH 2 - O - CO - R 2

The main function of natural waxes is the formation protective coatings on leaves, stems and fruits of plants, which protect the fruits from drying out and damage by microorganisms. under the cover of beeswax honey is stored and bee larvae develop. Lanolin - wax of animal origin protects hair and skin from the action of water

Sterids- esters of cyclic alcohols (sterols) and higher fatty acids. They form the saponifiable fraction of lipids.

The saponifiable fraction of lipids is formed by sterols.

II . Complex lipids

Phosphatides (phospholipids) - fats containing in their composition phosphoric acid associated with a nitrogenous base or other compound ( IN).

CH 2 -O-C-R 1

CH 2 -O- P \u003d O

If IN is a choline residue, the phosphatide is called lecithin; if colamine - cofalin. Lecithin predominates in grains and seeds; cephalin accompanies it in small quantities.