What is called a lipid solution. Lipids: their structure, composition and role in the human body. Structural function of lipids

Lipids (Fats).

Lipids- called a complex mixture of organic compounds (compounds with carbon C), with similar physicochemical properties:

- insoluble in water.
- good solubility in organic solvents (gasoline, chloroform)

Lipids are widely distributed in nature. Together with proteins and carbohydrates, they make up the bulk of the organic substances of all living organisms, being an essential component of every cell. Lipids are the most important component of food and largely determine it nutritional value and taste value.
In plants they accumulate mainly in seeds and fruits. In animals and fish, lipids are concentrated in subcutaneous adipose tissues, in abdominal cavity and tissues surrounding many important organs(heart, kidneys), as well as in brain and nervous tissues. There are especially many lipids in the subcutaneous adipose tissue of whales (25-30% of their mass), seals and other marine animals. In humans, lipid content ranges from 10-20% on average.

Types of lipids.

There are many types of classifications of fats, we will analyze the simplest one, it divides them into three large groups:

- Simple lipids
- Complex lipids
- Lipid derivatives.

Let's look at each group of lipids separately, what they contain, and what they are needed for.

Simple Lipids.

1) Neutral fats (or just fats).

Neutral fats consist of triglycerides.

Triglyceride - lipid or neutral fat, which contains glycerol combined with three molecules fatty acids.

Glycerol- chemical compound with the formula C3H5(OH)3, (colorless, viscous, odorless, sweetish liquid.)

Fatty acid– natural or created compounds with one or more groups - COOH (carboxyl) that do not create cyclic bonds (aromatic), with the number of carbon atoms (C) in the chain of at least 6.

Triglycerides are produced from the breakdown of dietary fats and are a form of fat storage in the human body. The bulk of dietary fats (98%) are triglycerides. Fat is also stored in the body in the form of triglycerides.

Types of fatty acids:

- Saturated fatty acids- contain only single bonds between carbon atoms with all other bonds attached to hydrogen atoms. The molecule combines with the maximum possible number of hydrogen atoms, so this acid is called saturated. They differ from unsaturated ones in that they remain solid when room temperature.

Foods that contain the most saturated fat are lard and fat, chicken, beef and lamb fat, butter and margarine. Foods rich in such fats include sausage, sausages and other sausages, bacon, regular lean beef; varieties of meat called “marbled”; chicken skin, bacon; ice cream, creams, cheeses; most flour and other confectionery products.

- unsaturated fatty acids - contain one or more double bonds along the main carbon chain. Each double bond reduces the number of hydrogen atoms that can bond with the fatty acid. Double bonds also result in a "bend" in the fatty acids, which prevents bonding between them.

Unsaturated fatty acids are found in plant sources.

They can be divided into two types:
1) monounsaturated – unsaturated fatty acids with one double bond. (for example - olive oil)
2) polyunsaturated - unsaturated fatty acids with two or more double bonds. (for example - linseed oil)

ABOUT dietary fats There will be a separate large topic examining in detail all their properties.

2) Waxes.

Waxes are fat-like substances of animal or plant origin, consisting of esters of monohydric alcohols and fatty acids.

Esters– compounds – COOH (carboxyl) in which the hydrogen atom in the HO group is replaced by an organic group.

Alcohols– –OH compounds bonded to a carbon atom.

In simple words, waxes are shapeless, plastic substances that soften easily when heated, melting in the temperature range from 40 to 90 degrees Celsius.

Beeswax is secreted by special glands of honey bees, from which bees build honeycombs.

Complex lipids.

A complex lipid is a combination of a triglyceride with other chemicals.
There are three types in total.

Phospholipids– glycerol combined with one or two fatty acids as well as phosphoric acid.

The cell membrane is made up of phospholipids. The most popular in food products is lecithin.

Glycolipids – compounds of fatty and carbohydrate components. (Contained in all tissues, mainly in the outer lipid layer of plasma membranes.)

Lipoproteins– complexes of fats and proteins. (Blood plasma)

Lipid derivatives.

Cholesterol- a fatty, wax-like substance found in every cell of the body and in many foods. Some cholesterol in the blood is necessary, but high levels can lead to heart disease.

Eggs contain a lot of cholesterol fatty varieties meat, sausage, fatty dairy products.

WITH general classification Have you figured out what functions lipids perform?

Functions.

- Structural function.

Phospholipids take part in the construction of cell membranes of all organs and tissues. They are involved in the formation of many biologically important compounds.

- Energy function.

When fats are oxidized, they are released a large number of energy that goes into the formation of ATP. A significant portion is stored in the form of lipids energy reserves organism, which are consumed due to lack of nutrients. Hibernating animals and plants accumulate fats and oils and use them to maintain vital processes. High content Lipids in plant seeds ensure the development of the embryo and seedling before they transition to independent nutrition. The seeds of many plants (coconut palm, castor bean, sunflower, soybean, rapeseed, etc.) serve as raw materials for obtaining vegetable oil industrially.. With the complete breakdown of 1 g of fat, 38.9 kJ of energy is released, which is approximately 2 times more compared to carbohydrates and proteins.

- Protective and thermal insulation

Accumulating in subcutaneous tissue and around some organs (kidneys, intestines), the fat layer protects the animal’s body and its individual organs from mechanical damage. In addition, due to low thermal conductivity, the layer of subcutaneous fat helps retain heat, which allows, for example, many animals to live in cold climates.
Lubricating and water repellent.
Wax covers the skin, wool, feathers, makes them more elastic and protects them from moisture. The leaves and fruits of many plants have a waxy coating.

- Regulatory.

Many hormones are derivatives of cholesterol, for example sex hormones (testosterone at men and progesterone in women) and corticosteroids. Cholesterol derivatives, vitamin D play a key role in the metabolism of calcium and phosphorus. Bile acids are involved in digestion processes. In the myelin (non-conductive charge) sheaths of axons nerve cells Lipids are insulators during the conduction of nerve impulses.

- Source of metabolic water.

Oxidation of 100 g of fat produces approximately 105-107 g of water. This water is very important for some desert inhabitants, in particular for camels, which can do without water for 10-12 days: the fat stored in the hump is used precisely for these purposes. Bears, marmots and other hibernating animals obtain the water they need for life as a result of fat oxidation.

LIPIDS - this is a heterogeneous group of natural compounds, completely or almost completely insoluble in water, but soluble in organic solvents and in each other, yielding high molecular weight fatty acids upon hydrolysis.

In a living organism, lipids perform various functions.

Biological functions of lipids:

1) Structural

Structural lipids form complex complexes with proteins and carbohydrates, from which the membranes of cells and cellular structures are built, and participate in a variety of processes occurring in the cell.

2) Spare (energy)

Reserve lipids (mainly fats) are the body's energy reserve and participate in metabolic processes. In plants they accumulate mainly in fruits and seeds, in animals and fish - in subcutaneous fatty tissues and tissues surrounding internal organs, as well as liver, brain and nervous tissues. Their content depends on many factors (type, age, nutrition, etc.) and in some cases accounts for 95-97% of all secreted lipids.

Calorie content of carbohydrates and proteins: ~ 4 kcal/gram.

Caloric content of fat: ~ 9 kcal/gram.

The advantage of fat as an energy reserve, unlike carbohydrates, is its hydrophobicity - it is not associated with water. This ensures compactness of fat reserves - they are stored in anhydrous form, occupying a small volume. The average person's supply of pure triacylglycerols is approximately 13 kg. These reserves could be enough for 40 days of fasting in moderate conditions. physical activity. For comparison: total reserves glycogen in the body - approximately 400 g; when fasting, this amount is not enough even for one day.

3) Protective

Subcutaneous adipose tissue protects animals from cooling, and internal organs from mechanical damage.

The formation of fat reserves in the body of humans and some animals is considered an adaptation to irregular nutrition and living in a cold environment. Animals that hibernate for a long time (bears, marmots) and are adapted to living in cold conditions (walruses, seals) have a particularly large reserve of fat. The fetus has virtually no fat and appears only before birth.

A special group in terms of their functions in a living organism are the protective lipids of plants - waxes and their derivatives, covering the surface of leaves, seeds and fruits.

4) An important component of food raw materials

Lipids are an important component food, largely determining its nutritional value and taste. The role of lipids in various food technology processes is extremely important. Spoilage of grain and its processed products during storage (rancidity) is primarily associated with changes in its lipid complex. Lipids isolated from a number of plants and animals are the main raw materials for obtaining the most important food and technical products (vegetable oil, animal fats, including butter, margarine, glycerin, fatty acids, etc.).

2 Classification of lipids

There is no generally accepted classification of lipids.

It is most appropriate to classify lipids depending on their chemical nature, biological functions, as well as in relation to some reagents, for example, alkalis.

Based on their chemical composition, lipids are usually divided into two groups: simple and complex.

Simple lipids – esters of fatty acids and alcohols. These include fats , waxes And steroids .

Fats – esters of glycerol and higher fatty acids.

Waxes – esters of higher alcohols of the aliphatic series (with a long carbohydrate chain of 16-30 C atoms) and higher fatty acids.

Steroids – esters of polycyclic alcohols and higher fatty acids.

Complex lipids – in addition to fatty acids and alcohols, they contain other components of various chemical natures. These include phospholipids and glycolipids .

Phospholipids - This complex lipids, in which one of the alcohol groups is connected not to FA, but to phosphoric acid (phosphoric acid can be connected to an additional compound). Depending on which alcohol is included in the phospholipids, they are divided into glycerophospholipids (contain the alcohol glycerol) and sphingophospholipids (contain the alcohol sphingosine).

Glycolipids – these are complex lipids in which one of the alcohol groups is associated not with FA, but with a carbohydrate component. Depending on which carbohydrate component is part of the glycolipids, they are divided into cerebrosides (they contain a monosaccharide, disaccharide or a small neutral homooligosaccharide as a carbohydrate component) and gangliosides (they contain an acidic heterooligosaccharide as a carbohydrate component).

Sometimes into an independent group of lipids ( minor lipids ) secrete fat-soluble pigments, sterols, and fat-soluble vitamins. Some of these compounds can be classified as simple (neutral) lipids, others - complex.

According to another classification, lipids, depending on their relationship to alkalis, are divided into two large groups: saponifiable and unsaponifiable. The group of saponified lipids includes simple and complex lipids, which, when interacting with alkalis, hydrolyze to form salts of high molecular weight acids, called “soaps”. The group of unsaponifiable lipids includes compounds that are not subject to alkaline hydrolysis (sterols, fat-soluble vitamins, ethers, etc.).

According to their functions in a living organism, lipids are divided into structural, storage and protective.

Structural lipids are mainly phospholipids.

Storage lipids are mainly fats.

Protective lipids of plants - waxes and their derivatives, covering the surface of leaves, seeds and fruits, animals - fats.

FATS

The chemical name of fats is acylglycerols. These are esters of glycerol and higher fatty acids. "Acyl" means "fatty acid residue".

Depending on the number of acyl radicals, fats are divided into mono-, di- and triglycerides. If the molecule contains 1 fatty acid radical, then the fat is called MONOACYLGLYCEROL. If the molecule contains 2 fatty acid radicals, then the fat is called DIACYLGLYCEROL. In the human and animal body, TRIACYLGLYCEROLS predominate (contain three fatty acid radicals).

The three hydroxyls of glycerol can be esterified either with only one acid, such as palmitic or oleic, or with two or three different acids:

Natural fats contain mainly mixed triglycerides, including residues of various acids.

Since the alcohol in all natural fats is the same - glycerol, the differences observed between fats are due solely to the composition of fatty acids.

Over four hundred carboxylic acids of various structures have been found in fats. However, most of them are present only in small quantities.

The acids contained in natural fats are monocarboxylic acids, built from unbranched carbon chains containing an even number of carbon atoms. Acids containing an odd number of carbon atoms, having a branched carbon chain, or containing cyclic moieties are present in small quantities. The exceptions are isovaleric acid and a number of cyclic acids found in some very rare fats.

The most common acids in fats contain 12 to 18 carbon atoms and are often called fatty acids. Many fats contain small amounts of low molecular weight acids (C 2 -C 10). Acids with more than 24 carbon atoms are present in waxes.

The glycerides of the most common fats contain significant quantities of unsaturated acids containing 1-3 double bonds: oleic, linoleic and linolenic. Arachidonic acid containing four double bonds is present in animal fats; acids with five, six or more double bonds are found in fats of fish and marine animals. Majority unsaturated acids lipids have a cis configuration, their double bonds are isolated or separated by a methylene (-CH 2 -) group.

Of all the unsaturated acids contained in natural fats, oleic acid is the most common. In many fats, oleic acid makes up more than half of the total mass of acids, and only a few fats contain less than 10%. Two other unsaturated acids - linoleic and linolenic acid - are also very widespread, although they are present in much smaller quantities than oleic acid. Linoleic and linolenic acids are found in noticeable quantities in vegetable oils; For animal organisms they are essential acids.

Of the saturated acids, palmitic acid is almost as widespread as oleic acid. It is present in all fats, with some containing 15-50% of the total acid content. Stearic and myristic acids are widely used. Stearic acid is found in large quantities (25% or more) only in the storage fats of some mammals (for example, in sheep fat) and in the fats of some tropical plants, such as cocoa butter.

It is advisable to divide the acids contained in fats into two categories: major and minor acids. The main acids of fat are acids whose content in fat exceeds 10%.

Physical properties of fats

As a rule, fats do not withstand distillation and decompose even if they are distilled under reduced pressure.

The melting point, and therefore the consistency of fats, depends on the structure of the acids that make up them. Solid fats, i.e. fats that melt at a relatively high temperature, consist predominantly of glycerides of saturated acids (stearic, palmitic), and oils that melt at a lower temperature and are thick liquids contain significant amounts of glycerides of unsaturated acids (oleic , linoleic, linolenic).

Since natural fats are complex mixtures of mixed glycerides, they do not melt at a certain temperature, but in a certain temperature range, and they are first softened. To characterize fats, it is usually used solidification temperature, which does not coincide with the melting point - it is slightly lower. Some natural fats are solids; others are liquids (oils). The solidification temperature varies widely: -27 °C for linseed oil, -18 °C for sunflower oil, 19-24 °C for cow lard and 30-38 °C for beef lard.

The solidification temperature of fat is determined by the nature of its constituent acids: the higher the content of saturated acids, the higher it is.

Fats are soluble in ether, polyhalogen derivatives, carbon disulfide, aromatic hydrocarbons (benzene, toluene) and gasoline. Solid fats are poorly soluble in petroleum ether; insoluble in cold alcohol. Fats are insoluble in water, but they can form emulsions that are stabilized in the presence of surfactants (emulsifiers) such as proteins, soaps and some sulfonic acids, mainly in a slightly alkaline environment. Milk is a natural fat emulsion stabilized by proteins.

Chemical properties of fats

Fats go into everything chemical reactions, characteristic of esters, however, their chemical behavior has a number of features associated with the structure of fatty acids and glycerol.

Among the chemical reactions involving fats, several types of transformations are distinguished.

Lipids- very diverse in their own way chemical structure substances characterized by varying solubility in organic solvents and, as a rule, insoluble in water. They play an important 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.

Other functions of lipids are the formation of an energy reserve, the creation of protective water-repellent and thermally insulating covers in animals and plants, and the protection of organs and tissues from mechanical stress.

CLASSIFICATION OF LIPIDS

Depending on their chemical composition, lipids are divided into several classes.

1. Simple lipids include substances whose molecules consist only of fatty acid (or aldehyde) residues and alcohols. These include
   • fats (triglycerides and other neutral glycerides)
   • waxes
2. Complex lipids
   • orthophosphoric acid derivatives (phospholipids)
   • lipids containing sugar residues (glycolipids)
   • sterols
   • steroids

IN this section Lipid chemistry will be discussed only to the extent necessary to understand lipid metabolism.

If an animal or plant tissue treated with one or more (usually sequentially) organic solvents, for example chloroform, benzene or petroleum ether, then some of the material goes into solution. The components of such a soluble fraction (extract) are called lipids. The lipid fraction contains substances various types, most of which are presented in the diagram. Note that due to the heterogeneity of the components included in the lipid fraction, the term “lipid fraction” cannot be considered as a structural characteristic; it is only a working laboratory name for the fraction obtained during the extraction of biological material with low-polarity solvents. However, most lipids have some common structural features, determining their important biological properties and similar solubility.

Fatty acid

Fatty acids - aliphatic carboxylic acids- in the body they can be in a free state (trace amounts in cells and tissues) or act as building blocks for most classes of lipids. Over 70 different fatty acids have been isolated from the cells and tissues of living organisms.

Fatty acids found in natural lipids contain an even number of carbon atoms and have predominantly straight carbon chains. Below are the formulas for the most commonly found naturally occurring fatty acids.

Natural fatty acids, although somewhat arbitrarily, can be divided into three groups:

• saturated fatty acids [show]
• monounsaturated fatty acids [show]

  Monounsaturated (with one double bond) fatty acids:

• polyunsaturated fatty acids [show]

  Polyunsaturated (with two or more double bonds) fatty acids:

In addition to these main three groups, there is also a group of so-called unusual natural fatty acids [show] .

Fatty acids that are part of the lipids of animals and higher plants have many general properties. As already noted, almost all natural fatty acids contain an even number of carbon atoms, most often 16 or 18. Unsaturated fatty acids in animals and humans involved in the construction of lipids usually contain a double bond between the 9th and 10th carbons; additional double bonds, such as usually occur in the area between the 10th carbon and the methyl end of the chain. The counting starts from the carboxyl group: the C-atom closest to the COOH group is designated as α, the one next to it is designated as β, and the terminal carbon atom in the hydrocarbon radical is designated as ω.

The peculiarity of the double bonds of natural unsaturated fatty acids is that they are always separated by two simple bonds, that is, there is always at least one methylene group between them (-CH=CH-CH 2 -CH=CH-). Such double bonds are referred to as “isolated.” Natural unsaturated fatty acids have a cis configuration and trans configurations are extremely rare. It is believed that in unsaturated fatty acids with several double bonds, the cis configuration gives the hydrocarbon chain a bent and shortened appearance, which has biological meaning(especially considering that many lipids are part of membranes). In microbial cells, unsaturated fatty acids usually contain one double bond.

Long chain fatty acids are practically insoluble in water. Their sodium and potassium salts (soaps) form micelles in water. 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 total negative charge and remain suspended in solution due to mutual repulsion (Fig. 95).

Neutral fats (or glycerides)

Neutral fats are esters of glycerol and fatty acids. If all three hydroxyl groups of glycerol are esterified with fatty acids, then such a compound is called a triglyceride (triacylglycerol), if two are esterified, a diglyceride (diacylglycerol) and, finally, if one group is esterified, a monoglyceride (monoacylglycerol).

Neutral fats are found in the body either in the form of protoplasmic fat, which is structural component cells, or in the form of spare, reserve 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 is subject to large fluctuations.

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 acid. If all three acid radicals belong to the same fatty acid, then such triglycerides are called simple (for example, tripalmitin, tristearin, triolein, etc.), but if they belong to different fatty acids, then they are mixed. The names of mixed triglycerides are derived from the fatty acids they contain; in this case, numbers 1, 2 and 3 indicate the connection of the fatty acid residue with the corresponding alcohol group in a glycerol molecule (for example, 1-oleo-2-palmitostearin).

The fatty acids that make up triglycerides practically determine them physicochemical characteristics. 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 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 mono- and polyunsaturated 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 acid. Note that human fat, which melts at 15°C (it is liquid at body temperature), contains 70% oleic acid.

Glycerides are capable of participating in 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.

Alkaline breakdown of fat under the action of caustic soda or caustic potassium is carried out during the industrial production of soap. Let us remember that soap is sodium or potassium salts of higher fatty acids.

The following indicators are often used to characterize natural fats:

1. iodine number - the number of grams of iodine that is in certain conditions binds 100 g of fat; given number characterizes the degree of unsaturation of fatty acids present in fats, the iodine number of beef fat is 32-47, lamb fat 35-46, pork fat 46-66;
2. acid number - the number of milligrams of potassium hydroxide required to neutralize 1 g of fat. This number indicates the amount of free fatty acids present in the fat;
3. saponification number - the number of milligrams of potassium hydroxide used to neutralize all fatty acids (both those included in triglycerides and free ones) contained in 1 g of fat. This number depends on the relative molecular weight fatty acids that make up fat. The saponification number for the main animal fats (beef, lamb, pork) is almost the same.

Waxes are esters of higher fatty acids and higher monohydric or dihydric alcohols with the number of carbon atoms from 20 to 70. Their general formulas are presented in the diagram, where R, R" and R" are possible radicals.

Waxes can be part of the fat covering the skin, wool, and feathers. In plants, 80% of all lipids that form a film on the surface of leaves and trunks are waxes. Waxes are also known to be normal metabolites of certain microorganisms.

Natural waxes (eg. beeswax, spermaceti, lanolin) usually contain, in addition to the mentioned esters, a certain amount of free higher fatty acids, alcohols and hydrocarbons with a number of carbon atoms of 21-35.

Phospholipids

This class of complex lipids includes glycerophospholipids and sphingolipids.

Glycerophospholipids are derivatives of phosphatidic acid: they contain glycerol, fatty acids, phosphoric acid and usually nitrogen-containing compounds. General formula glycerophospholipids are presented in the diagram, where R 1 and R 2 are radicals of higher fatty acids, and R 3 is a radical of a nitrogenous compound.

A characteristic feature of all glycerophospholipids is that one part of their molecule (radicals R 1 and R 2) exhibits pronounced hydrophobicity, while the other part is hydrophilic due to the negative charge of the phosphoric acid residue 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 “dissolved” lipid is found in aqueous systems in the form of micelles. There are several groups (subclasses) of glycerophospholipids.

[show] .



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 the nitrogenous base [HO-CH 2 -CH 2 -N+=(CH 3) 3 ] - choline. Thus, the phosphatidylcholine molecule contains glycerol, higher fatty acids, phosphoric acid and choline

[show] .



The main difference between phosphatidylcholines and phosphatidylethanolamines is that the latter contain the nitrogenous base ethanolamine (HO-CH 2 -CH 2 -NH 3 +) instead of choline.

Of the glycerophospholipids in the body of animals and higher plants, phosphatidylcholines and phosphatidylethanolamines are found in the largest quantities. These two groups of glycerophospholipids are metabolically related to each other and are the main lipid components of cell membranes.

• Phosphatidylserines [show] .

  

  In the phosphatidylserine molecule, the nitrogenous compound is the amino acid residue serine.

  Phosphatidylserines are much less widespread than phosphatidylcholines and phosphatidylethanolamines, and their importance is determined mainly by the fact that they participate in the synthesis of phosphatidylethanolamines.

• Plasmalogens (acetal phosphatides) [show] .

  

  They differ from the glycerophospholipids discussed above in that instead of one higher fatty acid residue, they contain a fatty acid aldehyde residue, which is linked to the hydroxyl group of glycerol by an unsaturated ester bond:

  Thus, plasmalogen, upon hydrolysis, breaks down into glycerol, higher fatty acid aldehyde, fatty acid, phosphoric acid, choline or ethanolamine.

[show] .



The R3 radical in this group of glycerophospholipids is the six-carbon sugar alcohol - inositol:

Phosphatidylinositols are quite widespread in nature. They are found in animals, plants and microbes. In animals, they are found in the brain, liver and lungs.

[show] .



It should be noted that free phosphatidic acid occurs in nature, although in relatively small quantities compared to other glycerophospholipids.

Cardiolylin belongs to glycerophospholipids, more precisely to polyglycerol phosphates. The backbone of the cardiolipin molecule includes three glycerol residues connected to each other by two phosphodiester bridges through positions 1 and 3; the hydroxyl groups of the two outer glycerol residues are esterified with fatty acids. Cardiolipin is part of mitochondrial membranes. In table 29 summarizes data on the structure of the main glycerophospholipids.

Among the fatty acids that make up glycerophospholipids, both saturated and unsaturated fatty acids are found (usually stearic, palmitic, oleic and linoleic).

It has also been established that most phosphatidylcholines and phosphatidylethanolamines contain one saturated higher fatty acid, esterified in position 1 (at the 1st carbon atom of glycerol), and one unsaturated higher fatty acid, esterified in position 2. Hydrolysis of phosphatidylcholines and phosphatidylethanolamines with the participation of special enzymes contained , for example, in cobra venom, which belong to phospholipases A 2, leads to the cleavage of unsaturated fatty acids and the formation of lysophosphatidylcholines or lysophosphatidylethanolamines, which have a strong hemolytic effect.

Sphingolipids

Glycolipids

Complex lipids containing carbohydrate groups in the molecule (usually a D-galactose residue). Glycolipids play an essential role in the functioning of biological membranes. They are found primarily in brain tissue, but are also found in blood cells and other tissues. There are three main groups of glycolipids:

• cerebrosides
• sulfatides
• gangliosides

Cerebrosides contain neither phosphoric acid nor choline. They contain a hexose (usually D-galactose), which is linked by an ester bond to the hydroxyl group of the amino alcohol sphingosine. In addition, Cerebroside contains a fatty acid. Among these fatty acids, the most common are lignoceric, nervonic and cerebronic acids, i.e. fatty acids having 24 carbon atoms. The structure of cerebrosides can be represented by a diagram. Cerebrosides can also be classified as sphingolipids, since they contain the alcohol sphingosine.

The most studied representatives of cerebrosides are nervon, containing nervonic acid, cerebron, which includes cerebronic acid, and kerazin, containing lignocyric acid. The content of cerebrosides is especially high in the membranes of nerve cells (in the myelin sheath).

Sulfatides differ from cerebrosides in that they contain a sulfuric acid residue in the molecule. In other words, the sulfatide is a cerebroside sulfate in which the sulfate is esterified at the third carbon atom of the hexose. In the mammalian brain, sulfatides, like n cerebrosides, are found in the white matter. However, their content in the brain is much lower than that of cerebrosides.

When hydrolyzing gangliosides, one can detect higher fatty acid, sphingosine alcohol, D-glucose and D-galactose, as well as amino sugar derivatives: N-acetylglucosamine and N-acetylneuraminic acid. The latter is synthesized in the body from glucosamine.

Structurally, gangliosides are largely similar to cerebrosides, the only difference being that instead of a single galactose residue they contain a complex oligosaccharide. One of the simplest gangliosides is hematoside, isolated from the stroma of erythrocytes (scheme)

Unlike cerebrosides and sulfatides, gangliosides are found predominantly in gray matter brain and are concentrated in the plasma membranes of nerve and glial cells.

All the lipids discussed above are usually called saponified, since their 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 derivatives of a core containing three fused cyclohexane rings and one cyclopentane ring. Steroids include numerous substances of a hormonal nature, as well as cholesterol, bile acids and other connections.

In the human body, the first place among steroids is occupied by sterols. The most important representative of sterols is cholesterol:

It contains an alcohol hydroxyl group at C3 and a branched aliphatic chain of eight carbon atoms at C17. The hydroxyl group at C 3 can be esterified with a higher fatty acid; in this case, cholesterol esters (cholesterides) are formed:

Cholesterol plays a role as a key intermediate in the synthesis of many other compounds. The plasma membranes of many animal cells are rich in cholesterol; it is found in significantly less quantity in mitochondrial membranes and in the endoplasmic reticulum. Note that there is no cholesterol in plants. Plants have other sterols, collectively known as phytosterols.

Lipids (from Greek lipos– fat) include fats and fat-like substances. Contained in almost all cells - from 3 to 15%, and in the cells of subcutaneous fatty tissue up to 50%.

There are especially many lipids in the liver, kidneys, nervous tissue (up to 25%), blood, seeds and fruits of some plants (29-57%). Lipids have different structures, but some properties are common. These organic matter do not dissolve in water, but dissolve well in organic solvents: ether, benzene, gasoline, chloroform, etc. This property is due to the fact that non-polar and hydrophobic structures predominate in lipid molecules. All lipids can be divided into fats and lipoids.

Fats

The most common are fats(neutral fats, triglycerides), which are complex compounds of trihydric alcohol glycerol and high molecular weight fatty acids. The glycerol residue is a substance that is highly soluble in water. Fatty acid residues are hydrocarbon chains that are almost insoluble in water. When a drop of fat enters water, the glycerol part of the molecules is exposed to it, and the chains of fatty acids protrude from the water. Fatty acids contain a carboxyl group (-COOH). It ionizes easily. With its help, fatty acid molecules connect with other molecules.

All fatty acids are divided into two groups - rich And unsaturated . Unsaturated fatty acids do not have double (unsaturated) bonds, saturated ones do. Saturated fatty acids include palmitic, butyric, lauric, stearic, etc. Unsaturated fatty acids include oleic, erucic, linoleic, linolenic, etc. The properties of fats are determined by the qualitative composition of fatty acids and their quantitative ratio.

Fats that contain saturated fatty acids have high temperature melting. They are usually hard in consistency. These are fats from many animals, coconut oil. Fats that contain unsaturated fatty acids have low temperature melting. These fats are predominantly liquid. Vegetable fats run into liquid consistency oils . These fats include fish fat, sunflower, cottonseed, linseed, hemp oils, etc.

Lipoids

Lipoids can form complex complexes with proteins, carbohydrates and other substances. The following connections can be distinguished:

1. Phospholipids. They are complex compounds of glycerol and fatty acids and contain a phosphoric acid residue. All phospholipid molecules have a polar head and a nonpolar tail formed by two fatty acid molecules. Main components of cell membranes.
2. Waxes. They are complex lipids, consisting of more complex alcohols than glycerol and fatty acids. Execute protective function. Animals and plants use them as water-repellent substances that protect against drying out. Waxes cover the surface of plant leaves and the surface of the body of arthropods living on land. Waxes are released sebaceous glands mammals, coccygeal gland of birds. Bees use wax to build honeycombs.
3. Steroids (from the Greek stereos - solid). These lipids are characterized by the presence of more complex structures rather than carbohydrate ones. Steroids include important body substances: vitamin D, hormones of the adrenal cortex, gonads, bile acids, cholesterol.
4. Lipoproteins And glycolipids. Lipoproteins consist of proteins and lipids, glucoproteins - of lipids and carbohydrates. There are many glycolipids in the composition of brain tissue and nerve fibers. Lipoproteins are part of many cellular structures and ensure their strength and stability.

Functions of lipids

Fats are the main type stockpiling substances. They are stored in the seed, subcutaneous fatty tissue, adipose tissue, fat body insects Fat reserves significantly exceed carbohydrate reserves.

Structural. Lipids are part of the cell membranes of all cells. The ordered arrangement of hydrophilic and hydrophobic ends of molecules has great importance for selective membrane permeability.

Energy. Provide 25-30% of all energy, necessary for the body. When 1 g of fat breaks down, 38.9 kJ of energy is released. This is almost twice as much as carbohydrates and proteins. In migratory birds and hibernating animals, lipids - the only source of energy.

Protective. A layer of fat protects delicate internal organs from shocks, shocks, and damage.

Thermal insulation. Fats do not conduct heat well. Under the skin of some animals (especially marine animals), they are deposited and form layers. For example, a whale has a layer of subcutaneous fat of about 1 m, which allows it to live in cold water.

Many mammals have a special adipose tissue, which is called brown fat. It has this color because it is rich in red-brown colored mitochondria, as they contain iron-containing proteins. This tissue produces thermal energy, necessary for animals in low conditions

temperatures Brown fat surrounds vital organs (heart, brain, etc.) or lies in the path of the blood that flows to them, and thus directs heat to them.

Endogenous water suppliers

When 100 g of fat is oxidized, 107 ml of water is released. Thanks to this water, many desert animals exist: camels, jerboas, etc. During hibernation, animals also produce endogenous water from fats.

A fatty substance covers the surface of the leaves and prevents them from getting wet during rains.

Some lipids have high biological activity: a number of vitamins (A, D, etc.), some hormones (estradiol, testosterone), prostaglandins.

Fat-like substances lipids are components that take part in vital processes in the human body. There are several groups that perform the main functions of the body, such as the formation hormonal levels or metabolism. In this article we will explain in detail what it is and what its role is in life processes.

Lipids are organic compound, which includes fats and other fat-like substances. They actively participate in the process of cell structure and are part of membranes. Affect throughput cell membranes, as well as enzyme activity. They influence the creation of intercellular connections and a variety of chemical processes in organism. Insoluble in water, but they dissolve in solvents organic origin(such as gasoline or chloroform). In addition, there are types that are fat soluble.

This substance can be of plant or animal origin. If we are talking about plants, then most of them are in nuts and seeds. Of animal origin are mainly located in subcutaneous tissue, nervous and cerebral.

Classification of lipids

Lipids are present in almost all tissues of the body and in the blood. There are several classifications; below we present the most common one, based on the characteristics of structure and composition. According to their structure, they are divided into 3 large groups, which are subdivided into smaller ones.

The first group is simple. They include oxygen, hydrogen and carbon. They are divided into the following types:

1. Fatty alcohols. Substances containing from 1 to 3 hydroxyl groups.
2. Fatty acid. Found in various oils and fats.
3. Fatty aldehydes. The molecule contains 12 carbon atoms.
4. Triglycerides. These are precisely the fats that are deposited in the subcutaneous tissues.
5. Sphingosine bases. They are located in the plasma, lungs, liver and kidneys, and are found in nerve tissues.
6. Waxes. These are esters of fatty acids and high molecular weight alcohols.
7. Saturated hydrocarbons. They have exclusively single bonds, with carbon atoms in a state of hybridization.

The second group is complex. They, like simple ones, include oxygen, hydrogen and carbon. But, besides them, they also contain different additional components. In turn, they are divided into 2 subgroups: polar and neutral.

Polar ones include:

1. Glycolipids. They appear after combining carbohydrates with lipids.
2. Phospholipids. These are esters of fatty acids, as well as polyhydric alcohols.
3. Sphingolipids. They are derivatives of aliphatic amino alcohols.

Neutral ones include:

1. Acylglycerides. Includes monoglycerides and diglycerides.
2. N-acetylethanolamides. They are ethanolamides of fatty acids.
3. Ceramides. They contain fatty acids combined with sphingosine.
4. Sterol esters. They represent complex cyclic alcohols of high molecular weight. They contain fatty acids.

The third group is oxylipids. The substances appear as a result of oxygenation of polyunsaturated fatty acids. In turn, they are divided into 2 types:

1. Cyclooxygenase pathway.
2. Lipoxygenase pathway.

Importance for membrane cells

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The cell membrane is what separates the cell from the environment around it. In addition to protection, it performs quite a large number of necessary for normal life functions. The importance of lipids in the membrane cannot be overestimated.

In the cell wall, the substance forms a double layer. This helps cells interact normally with environment. Therefore, there are no problems with controlling and regulating metabolism. Membrane lipids maintain the shape of the cell.

Part of a bacterial cell

An integral part of the cell structure is bacterial lipids. As a rule, they contain waxes or phospholipids. But the amount of the substance directly varies between 5-40%. The content depends on the type of bacterium, for example, the diphtheria bacillus contains about 5%, but the tuberculosis pathogen already contains more than 30%.

A bacterial cell is different in that the substances in it are associated with other components, for example, proteins or polysaccharides. In bacteria they have many more varieties and perform many tasks:

• energy storage;
• participate in metabolic processes;
• are a component of membranes;
• cell resistance to acids depends on them;
• components of antigens.

What functions do they perform in the body?

Lipids component almost all fabrics human body. There are different subspecies, each of which is responsible for a specific function. Next, we will dwell in more detail on the importance of the substance for life:

1. Energy function. They tend to disintegrate and in the process a lot of energy appears. The body's cells need it to support processes such as air flow, substance formation, growth and respiration.
2. Backup function. In the body, fats are stored in reserve; they are what make up the fatty layer of the skin. If hunger sets in, the body uses these reserves.
3. Thermal insulation function. The fat layer conducts heat poorly, and therefore it is much easier for the body to maintain temperature.
4. Structural function. This applies to cell membranes because the substance is a permanent component of them.
5. Enzymatic function. One of the secondary functions. They help cells form enzymes and help with the absorption of certain microelements coming from outside.
6. Transport function. The side effect lies in the ability of some types of lipids to transport substances.
7. Signal function. It is also secondary and simply supports some body processes.
8. Regulatory function. This is another mechanism that has a secondary meaning. By themselves, they are almost not involved in the regulation of various processes, but are a component of substances that directly affect them.

Thus, we can say with confidence that the functional importance of lipids for the body is difficult to overestimate. Therefore, it is important that their level is always normal. Many biological and biochemical processes in the body are tied to them.

What is lipid metabolism

Lipid metabolism is a process of physiological or biochemical nature that occurs in cells. Let's look at them in more detail:

1. Triacyglycerol metabolism.
2. Phospholipid metabolism. They are distributed unevenly. There are many of them in the liver and plasma (up to 50%). The half-life is 1-200 days, depending on the type.
3. Cholesterol exchange. It is formed in the liver and comes with food. Excess is eliminated naturally.
4. Catabolism of fatty acids. Occurs during β-oxidation; α- or ω-oxidation is less commonly involved.
5. Included in the metabolic processes of the gastrointestinal tract. Namely, the breakdown, digestion and absorption of these substances coming from food. Digestion begins in the stomach with the help of an enzyme called lipase. Next, pancreatic juice and bile come into action in the intestines. The cause of malfunctions may be a violation of secretion gallbladder or pancreas.
6. Lipogenesis. Simply put - the synthesis of fatty acids. Occurs in the liver or adipose tissue.
7. This includes the transport of various fats from the intestines.
8. Lipolysis. Catabolism, which occurs with the participation of lipase and provokes the breakdown of fats.
9. Synthesis ketone bodies. Acetoacetyl-CoA gives rise to their formation.
10. Interconversion of fatty acids. From fatty acids found in the liver, acids characteristic of the body are formed.

Lipids are important substance, affecting almost all areas of life. The most common triglycerides and cholesterol in the human diet. Triglycerides are an excellent source of energy; it is this type that forms fat layer bodies. Cholesterol affects the body’s metabolic processes, as well as the formation of hormonal levels. It is important that the content is always within the normal range, neither exceeding nor underestimating it. An adult needs to consume 70-140 g of lipids.