Fat is considered to be the culprit of many troubles. Doctors and scientists advise cutting down on fat or eliminating it altogether. Of course, those who are obese or have chronic diseases are better off taking this advice. However, the rest would be foolish to give up fat. Let's find out more about them from the facts below.
1. Consumption of fats does not necessarily lead to their storage in the body
Many people think that fat consumption will definitely affect the figure in the form of deposits on the waist, hips and abdomen. If you eat more than your body requires, then yes, such a problem may arise. For example, if you consume an unlimited amount of starchy carbohydrates, then you can expect an increase in insulin levels, and then fat will be deposited. But if you eat, consuming fat and protein evenly, then this problem can be avoided. In everything you need to know when to stop.
2. No need to avoid the consumption of nuts
Nuts contain healthy forms of fat, monounsaturated fats, which help you feel full faster, but also raise your good cholesterol. Nuts do not affect weight gain in any way, because you cannot eat a lot of them due to their satiety, and besides, they are poorly digested by the body. Consequently, the cell walls of nuts are not easily destroyed when chewed. This means that they pass through the body in transit and do not excrete all of their fat.
3. It is not necessary to completely eliminate saturated fat from the body.
Saturated fats have always been thought to be the enemy of health, so they were advised to be eliminated from the diet. But today it has become clear that moderate consumption of saturated fat does no harm. And some of them even need to be included in a healthy eating program.
Extra virgin coconut oil is one of the healthy sources of saturated fat. It contains lauric acid which is found nowhere else except in breast milk. It is a powerful immune stimulant. It is advised to fry food in coconut oil.
4. If the product label says "no trans fats" does not mean that they are not there.
Many manufacturers believe that if a product contains a very small amount of an ingredient, then it is not necessary to indicate it on the label. It happens that a product contains only 0.5 g of trans fat, but you will not find it among the ingredients on the package. After eating several servings of such a product, you will not even know that you have eaten enough of this harmful ingredient.
5. Nutrients from vegetables without fat are absorbed worse
Studies have shown that lettuce seasoned with fat or a sauce with fats is significantly better absorbed by the body and receives more of the necessary nutrients - carotenoids. If you constantly eat salads without fats, then carotenoids will not be absorbed by the body at all. They are responsible for the colors red, yellow, orange and green and are important in the prevention of many diseases. To help your body absorb all the nutrients from vegetables, consume them with healthy fats.
6. Extra virgin olive oil is not suitable for frying.
Although it contains healthy monounsaturated fats, it loses its properties at high temperatures. Better to use it for dressing salads or marinating meat. Olive oil is very delicate and quickly deteriorates, so it should be stored in a dark glass container with a tightly closed lid to avoid oxidation and retain all its beneficial properties.
7. Fats have many functions in the body
Our body and our body cannot live without fats. There are several reasons for this:
The brain needs fats. About 60% of the dry weight of the human brain is fat. Healthy nerve cells contain fats - docosahexanoic acid;
Sex hormones are formed with the help of fats;
Fatty acids are essential for healthy skin and hair;
Fats are involved in metabolism, functions of the immune system, and help stabilize blood sugar.
Lipids are fat-like organic compounds, insoluble in water, but readily soluble in non-polar solvents (ether, gasoline, benzene, chloroform, etc.). Lipids are among the simplest biological molecules.Chemically, most lipids are esters of higher carboxylic acids and a number of alcohols. The best known among them are fats. Each fat molecule is formed by a molecule of a triatomic alcohol of glycerol and attached to it ether bonds of three molecules of higher carboxylic acids. According to the accepted nomenclature, fats are called triacylglcherols.
The carbon atoms in the molecules of higher carboxylic acids can be connected to each other by both single and double bonds. Of the limiting (saturated) higher carboxylic acids, palmitic, stearic, arachidic acids are most often included in the composition of fats; from unsaturated (unsaturated) - oleic and linoleic.
The degree of unsaturation and the chain length of higher carboxylic acids (i.e., the number of carbon atoms) determine the physical properties of a particular fat.
Fats with short and unsaturated acid chains have a low melting point. At room temperature, these are liquids (oils) or greasy substances (fats). Conversely, fats with long and saturated chains of higher carboxylic acids become solid at room temperature. That is why, during hydrogenation (saturation of acid chains with hydrogen atoms along double bonds), liquid peanut oil, for example, becomes buttery-like, and sunflower oil turns into solid margarine. Compared to inhabitants of southern latitudes, animals living in cold climates (for example, fish from the Arctic seas) usually contain more unsaturated triacylglycerols. For this reason, their body remains flexible even at low temperatures.
In phospholipids, one of the extreme chains of the higher carboxylic acids of triacylglycerol is replaced by a group containing phosphate. Phospholipids have polar heads and non-polar tails. The groups forming the polar head are hydrophilic, while the non-polar tail groups are hydrophobic. The dual nature of these lipids determines their key role in the organization of biological membranes.
Another group of lipids is made up of steroids (sterols). These substances are based on cholesterol alcohol. Sterols are poorly soluble in water and do not contain higher carboxylic acids. These include bile acids, cholesterol, sex hormones, vitamin D, etc.
Lipids also include terpenes (plant growth substances - gibberellins; carotenoids - photosynthetic pigments; essential oils of plants, as well as waxes).
Lipids can form complexes with other biological molecules - proteins and sugars.
The functions of lipids are as follows:
Structural. Phospholipids, together with proteins, form biological membranes. The membranes also contain sterols.
Energy. When fat is oxidized, a large amount of energy is released, which goes into the formation of ATP. A significant part of the body's energy reserves is stored in the form of lipids, which are consumed when there is a lack of nutrients. Hibernating animals and plants accumulate fats and oils and use them to maintain vital processes. The high content of lipids in plant seeds ensures the development of the embryo and seedling before their transition to independent feeding. The seeds of many plants (coconut palm, castor oil plant, sunflower, soybean, rapeseed, etc.) are used as raw materials for the production of vegetable oil industrially.
Protective and heat-insulating. Accumulating in the subcutaneous tissue and around some organs (kidneys, intestines), the fat layer protects the animal body and its individual organs from mechanical damage. In addition, due to its low thermal conductivity, the layer of subcutaneous fat helps to retain heat, which allows, for example, many animals to live in cold climates. In whales, in addition, it plays another role - it contributes to buoyancy.
Lubricating and water repellent. The wax covers the skin, wool, feathers, makes them more elastic and protects them from moisture. Leaves and fruits of many plants have a waxy coating.
Regulatory. Many hormones are derivatives of cholesterol, such as sex hormones (testosterone in men and progesterone in women) and corticosteroids (aldosterone). Derivatives of cholesterol, vitamin D play a key role in the metabolism of calcium and phosphorus. Bile acids are involved in the processes of digestion (emulsification of fats) and absorption of higher carboxylic acids.
Lipids are also the source of metabolic water formation. Oxidation of 100 g of fat gives about 105 g of water. This water is very important for some desert inhabitants, in particular for camels, which can go without water for 10-12 days: the fat stored in the hump is used for this very purpose. Bears, marmots and other hibernating animals receive the water necessary for life as a result of fat oxidation.
In the myelin sheaths of the axons of nerve cells, lipids are insulators during the conduction of nerve impulses.
The wax is used by bees to build honeycombs.
The body produces most of the lipids on its own, only essential fatty acids and soluble vitamins come with food.
Lipids are a large group of organic substances, consisting of fats and their analogs. Lipids are similar in characteristics to proteins. In plasma, they are in the form of lipoproteins, completely insoluble in water, but perfectly soluble in ether. The exchange process between lipids is important for all active cells, since these substances are one of the most important components of biological membranes.
There are three classes of lipids: cholesterol, phospholipids, triglycerides. The best known among these classes is cholesterol. The determination of this indicator, of course, has the maximum value, but nevertheless, the content of cholesterol, lipoproteins, triglycerides in the cell membrane should be considered only in a complex manner.
The norm is the content of LDL in the range of 4-6.6 mmol / l. It is worth noting that in healthy people this indicator can change taking into account a number of factors: age, seasonality, mental and physical activity.
Peculiarities
The human body independently produces all the major groups of lipids. The cell membrane does not form only polyunsaturated fatty acids, which are irreplaceable substances and fat-soluble vitamins.
The bulk of lipids are synthesized by epithelial cells of the small intestine and liver. For individual lipids, communication with specific organs and tissues is characteristic, and the rest are in all cells and tissues. Most of the lipids are contained in the nervous and adipose tissue.
The liver contains from 7 to 14% of this substance. In diseases of this organ, the amount of lipids increases to 45%, mainly due to an increase in the number of triglycerides. Plasma contains lipids combined with proteins, this is how they enter organs, cells, tissues.
Biological purpose
Lipid classes serve a number of important functions.
- Construction. Phospholipids combine with proteins to form membranes.
- Accumulative. When fat is oxidized, a huge amount of energy is generated, which is subsequently spent on the creation of ATP. The body accumulates energy reserves mainly by lipid groups. For example, when animals fall asleep for the whole winter, their body receives all the necessary substances from the previously accumulated oils, fats, bacteria.
- Protective, heat-insulating. Most of the fat is deposited in the subcutaneous tissue, around the kidneys, and intestines. Thanks to the accumulated layer of fat, the body is protected from cold, as well as mechanical damage.
- Water-repellent, lubricating. The lipid layer on the skin retains the elasticity of cell membranes and protects them from moisture and bacteria.
- Regulatory. There is a link between lipid content and hormonal levels. Almost all hormones are produced from cholesterol. Vitamins and other cholesterol derivatives are involved in the metabolism of phosphorus and calcium. Bile acids are responsible for the absorption and digestion of food, as well as for the absorption of carboxylic acids.
Exchange processes
- Triglycerides protect soft subcutaneous tissues, as well as organs from damage, bacteria. There is a direct connection between their quantity and energy conservation.
- Phospholipids are responsible for metabolic processes.
- Cholesterol, steroids are substances needed to strengthen cell membranes, as well as to normalize the activity of the glands, in particular, the regulation of the reproductive system.
All types of lipids form compounds that support the body's vital activity, its ability to resist negative factors, including the reproduction of bacteria. There is a connection between lipids and the formation of many extremely important protein compounds. The work of the genitourinary system is impossible without these substances. A person's reproductive capacity can also fail.
Lipid metabolism involves the relationship between all of the above components and their complex effect on the body. During the delivery of nutrients, vitamins and bacteria to membrane cells, they are transformed into other elements. This situation contributes to the acceleration of blood supply and, due to this, the rapid intake, distribution and assimilation of vitamins supplied with food.
If at least one of the links stops, then the connection is disrupted and the person feels problems with the intake of vital substances, beneficial bacteria and their spread throughout the body. Such a violation directly affects the process of lipid metabolism.
Disruption of exchange
Each functioning cell membrane contains lipids. The composition of molecules of this kind has one unifying property - hydrophobicity, that is, they are insoluble in water. The chemical composition of lipids includes many elements, but the largest part is occupied by fats, which the body is able to produce on its own. But irreplaceable fatty acids get into it, as a rule, with food.
Lipid metabolism is carried out at the cellular level. This process protects the body, including against bacteria, occurs in several stages. First, lipids are broken down, then they are absorbed, and only after that an intermediate and final exchange occurs.
Any disruptions in the process of assimilating fats indicate a violation of the metabolism of lipid groups. The reason for this may be an insufficient amount of pancreatic lipase and bile entering the intestine. And also with:
- obesity;
- hypovitaminosis;
- atherosclerosis;
- diseases of the stomach;
- intestines and other painful conditions.
If the epithelial tissue of the villi is damaged in the intestine, fatty acids are not fully absorbed. As a result, a large amount of fat accumulates in the feces, which has not passed the breakdown stage. The feces become a specific grayish-white color due to the accumulation of fats and bacteria.
Lipid metabolism can be corrected with a dietary regimen and medication prescribed to lower the LDL value. It is necessary to systematically check the content of triglycerides in the blood. Also, do not forget that the human body does not need a large accumulation of fat.
In order to prevent disruptions in lipid metabolism, it is necessary to limit the use of oil, meat products, offal and enrich the diet with low-fat fish and seafood. As a preventive measure, a change in lifestyle will help - an increase in physical activity, sports training, and rejection of bad habits.
Lipids (from the 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 common properties. These organic substances do not dissolve in water, but they dissolve well in organic solvents: ether, benzene, gasoline, chloroform, etc. This property is due to the fact that non-polar and hydrophobic structures prevail in lipid molecules. All lipids can be roughly divided into fats and lipoids.
Fats
The most common are fats(neutral fats, triglycerides), which are complex compounds of a trihydric alcohol of glycerol and high molecular weight fatty acids. The remainder of glycerin 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 the water, the glycerol part of the molecules turns to it, and the chains of fatty acids protrude from the water. The fatty acids contain a carboxyl group (-COOH). It ionizes easily. With its help, fatty acid molecules combine with other molecules.
All fatty acids are divided into two groups - saturated and unsaturated ... Unsaturated fatty acids do not have double (unsaturated) bonds, saturated ones do. Saturated fatty acids include palmitic, butyric, lauric, stearic, etc. Unsaturated - 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 a high melting point. They are generally hard in consistency. These are the fats of many animals, coconut oil. Fats that contain unsaturated fatty acids have a low melting point. These fats are predominantly liquid. Vegetable fats of a liquid consistency are bursting oils ... These fats include fish oil, sunflower, cotton, linseed, hemp oils, etc.
Lipoids
Lipoids can form complex complexes with proteins, carbohydrates and other substances. The following compounds can be distinguished:
- 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 non-polar tail formed by two fatty acid molecules. The main components of cell membranes.
- Waxes. These are complex lipids, composed of more complex alcohols than glycerol and fatty acids. They have a protective function. Animals and plants use them as water-repellent and drying-out agents. Waxes cover the surface of plant leaves, the surface of the body of arthropods living on land. Waxes secrete the sebaceous glands of mammals, the coccygeal gland of birds. Bees build honeycombs from wax.
- Steroids (from the Greek stereos - hard). These lipids are characterized by the presence of not carbohydrate, but more complex structures. Steroids include important substances in the body: vitamin D, hormones of the adrenal cortex, gonads, bile acids, cholesterol.
- Lipoproteins and glycolipids. Lipoproteins consist of proteins and lipids, glucoproteins - of lipids and carbohydrates. There are many glycolipids in the composition of brain tissues and nerve fibers. Lipoproteins are part of many cellular structures, provide their strength and stability.
Lipid functions
Fats are the main type storing substances. They are stored in semen, subcutaneous fatty tissue, adipose tissue, and the fatty body of insects. Fat stores significantly exceed carbohydrate stores.
Structural. Lipids are part of the cell membranes of all cells. The ordered arrangement of hydrophilic and hydrophobic ends of molecules is of great importance for the selective permeability of membranes.
Energy. Provide 25-30% of all energy required by the body. With the breakdown of 1 g of fat, 38.9 kJ of energy is released. This is almost twice as much compared to carbohydrates and proteins. In migratory birds and hibernating animals, lipids are the only source of energy.
Protective. A layer of fat protects delicate internal organs from shock, shock, 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 called brown fat. It has this color because it is rich in red-brown mitochondria, since they contain iron-containing proteins. This tissue generates heat energy, which is necessary for animals in low
temperatures. Brown fat surrounds vital organs (heart, brain, etc.) or lies in the path of 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, there are many desert animals: camels, jerboas, etc. Animals during hibernation also produce endogenous water from fats.
A fatty substance covers the surface of the leaves, 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.
Lipids- Substances that are very heterogeneous in their chemical structure, characterized by different solubility in organic solvents and, as a rule, insoluble in water. They play an important role in life processes. As 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 thermal insulating covers in animals and plants, the protection of organs and tissues from mechanical influences.
CLASSIFICATION OF LIPIDS
Depending on the chemical composition, lipids are divided into several classes.
- Simple lipids include substances whose molecules consist only of residues of fatty acids (or aldehydes) and alcohols. These include
- fats (triglycerides and other neutral glycerides)
- waxes
- Complex lipids
- derivatives of phosphoric acid (phospholipids)
- lipids containing sugar residues (glycolipids)
- sterols
- sterides
In this section, lipid chemistry will be considered only to the extent that is necessary for understanding lipid metabolism.
If an animal or plant tissue is treated with one or more (more often sequentially) organic solvents, such as chloroform, benzene or petroleum ether, then some of the material goes into solution. The components of this soluble fraction (extract) are called lipids. The lipid fraction contains substances of various types, most of which are shown in the diagram. Note that due to the heterogeneity of the components included in the lipid fraction, the term "lipid fraction" cannot be regarded as a structural characteristic; it is only a working laboratory name for the fraction obtained from the extraction of biological material with low-polarity solvents. Nevertheless, most lipids share some common structural features that determine their important biological properties and similar solubility.
Fatty acid
Fatty acids - aliphatic carboxylic acids - in the body can be in a free state (trace amounts in cells and tissues) or serve 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 a predominantly unbranched carbon chain. Below are the formulas for the most commonly found natural fatty acids.
Natural fatty acids, although somewhat conditionally, 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] .
The fatty acids that make up the lipids of animals and higher plants have many properties in common. As already noted, almost all natural fatty acids contain an even number of carbon atoms, most often 16 or 18. Unsaturated fatty acids of animals and humans, which are involved in the construction of lipids, usually contain a double bond between the 9th and 10th carbon, additional double bonds, such as usually occur between the 10th carbon and the methyl end of the chain. The count comes from the carboxyl group: the C-atom closest to the COOH group is designated as α, the adjacent one is β, and the terminal carbon atom in the hydrocarbon radical is ω.
The peculiarity of double bonds of natural unsaturated fatty acids lies in the fact 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". Naturally occurring unsaturated fatty acids have a cis configuration and are extremely rare in a trans configuration. It is believed that in unsaturated fatty acids with several double bonds, the cis configuration gives the hydrocarbon chain a curved and shortened appearance, which makes a biological sense (especially when you consider 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, negatively charged carboxyl groups of fatty acids face the aqueous phase, and non-polar 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 glycerin and fatty acids. If all three hydroxyl groups of glycerol are esterified with fatty acids, then such a compound is called triglyceride (triacylglycerol), if two - diglyceride (diacylglycerol) and, finally, if one group is esterified - monoglyceride (monoacylglycerol).
Neutral fats are found in the body either in the form of protoplasmic fat, which is a structural component of cells, or in the form of reserve, 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. Palmitic, stearic and oleic acids are more common among fatty acids. If all three acid radicals belong to the same fatty acid, then such triglycerides are called simple (for example, tripalmitin, tristearin, triolein, etc.), if they are different fatty acids, then they are called mixed. Mixed triglycerides are named from their constituent fatty acids; the numbers 1, 2 and 3 indicate the bond of the fatty acid residue with the corresponding alcohol group in the glycerol molecule (for example, 1-oleo-2-palmitostearin).
Fatty acids that make up triglycerides practically determine their physicochemical properties. Thus, the melting point of triglycerides increases with an increase in the number and length of saturated fatty acid residues. In contrast, the higher the content of unsaturated fatty acids or short-chain 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. So, in hemp oil, 95% of all fatty acids are oleic, linoleic and linolenic acids, and only 5% are stearic and palmitic acids. Note that human fat melting at 15 ° C (it is liquid at body temperature) contains 70% oleic acid.
Glycerides are able to enter into all chemical reactions inherent in esters. Of greatest importance is the saponification reaction, as a result of which glycerol and fatty acids are formed from triglycerides. Saponification of fat can occur both by enzymatic hydrolysis and by the action of acids or alkalis.
Alkaline cleavage of fat by the action of caustic soda or caustic potash is carried out in the industrial production of soap. Let us recall that soap is sodium or potassium salts of higher fatty acids.
The following indicators are often used to characterize natural fats:
- iodine number - the number of grams of iodine, which, under certain conditions, binds 100 g of fat; this number characterizes the degree of unsaturation of fatty acids present in fats, the iodine number of beef fat 32-47, lamb 35-46, pork 46-66;
- acid number - the number of milligrams of caustic potassium required to neutralize 1 g of fat. This number indicates the amount of free fatty acids present in the fat;
- saponification number - the number of milligrams of caustic potassium consumed to neutralize all fatty acids (both included in triglycerides and free) contained in 1 g of fat. This number depends on the relative molecular weight of the fatty acids that make up the fat. The saponification number for the main animal fats (beef, lamb, pork) is practically 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 shown in the diagram, where R, R "and R" are possible radicals.
Waxes can be part of the fat that covers the skin, wool, feathers. In plants, 80% of all lipids that form a film on the surface of leaves and trunks are waxes. It is also known that waxes are normal metabolites of some microorganisms.
Natural waxes (for example, beeswax, spermaceti, lanolin) usually contain, in addition to the aforementioned esters, a certain amount of free higher fatty acids, alcohols and hydrocarbons with a carbon number 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. The general formula of glycerophospholipids is shown 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.
It is characteristic of all glycerophospholipids 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 radical R 3.
Of all lipids, glycerophospholipids have the most pronounced polar properties. When glycerophospholipids are placed in water, only a small part of them passes into a true solution, while the bulk of the "dissolved" lipid is in aqueous systems in the form of micelles. There are several groups (subclasses) of glycerophospholipids.
- [show]
.
- Phosphatidylserines [show]
.
In the phosphatidylserine molecule, the nitrogenous compound is the serine amino acid residue.
Phosphatidylserines are much less widespread than phosphatidylcholines and phosphatidylethanolamines, and their importance is determined mainly by the fact that they are involved 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, during hydrolysis, plasmalogen decomposes into glycerol, higher fatty acid aldehyde, fatty acid, phosphoric acid, choline, or ethanolamine.
[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 linked with an ether bond with a nitrogenous base [HO-CH 2 -CH 2 -N + = (CH 3) 3] - choline. Thus, glycerol, higher fatty acids, phosphoric acid and choline are combined in the phosphatidylcholine molecule.
[show] .
The main difference between phosphatidylcholines and phosphatidylethanolamines is that the latter include 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 greatest amount. These two groups of glycerophospholipids are metabolically linked to each other and are the main lipid components of cell membranes.
The R 3 -radical in this group of glycerophospholipids is a six-carbon sugar alcohol - inositol:
Phosphatidylinositols are quite widespread in nature. They are found in animals, plants and microbes. In the animal body, they are found in the brain, liver and lungs.
[show] . 
It should be noted that free phosphatidic acid is found in nature, although in comparison with other glycerophospholipids in relatively small quantities.
Cardiolilin 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 the mitochondrial membranes. Table 29 summarizes the data on the structure of the main glycerophospholipids.
Among the fatty acids that make up glycerophospholipids, both saturated and unsaturated fatty acids (more often stearic, palmitic, oleic and linoleic) are found.
It was also found that most phosphatidylcholines and phosphatidylethanolamines contain one saturated higher fatty acid esterified at position 1 (at the 1st carbon atom of glycerol), and one unsaturated higher fatty acid esterified at position 2. Hydrolysis of phosphatidylcholines and phosphatidylethanolamines with the participation of specific enzymes , for example, in the venom of cobra, which belong to phospholipases A 2, leads to the elimination of unsaturated fatty acids and the formation of lysophosphatidylcholines or lysophosphatidylethanolamines with a strong hemolytic effect.
Sphingolipids
Glycolipids
Complex lipids containing carbohydrate groups in the molecule (more often a D-galactose residue). Glycolipids play an essential role in the functioning of biological membranes. They are found predominantly in brain tissue, but they 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 include hexose (usually D-galactose), which is linked by an ether bond to the hydroxyl group of the amino alcohol sphingosine. In addition, a fatty acid is a part of cerebroside. Among these fatty acids, the most common are lignoceric, nervous and cerebronic acids, i.e. fatty acids having 24 carbon atoms. The structure of cerebrosides can be represented by the diagram. Cerebrosides can also be classified as sphingolipids, since they contain the alcohol sphingosine.
The most studied representatives of cerebrosides are the nerve containing neurotic acid, the cerebron, which contains cerebronic acid, and kerazine, which contains 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 cerebrosides, are found in the white matter. However, their content in the brain is much lower than that of cerebrosides.
During the hydrolysis of gangliosides, one can find higher fatty acid, sphingosine alcohol, D-glucose and D-galactose, as well as derivatives of amino sugars: N-acetylglucosamine and N-acetylneuraminic acid. The latter is synthesized in the body from glucosamine.
Structurally, gangliosides are largely similar to cerebrosides, with the only difference that instead of one 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 mainly in the gray matter of the brain and are concentrated in the plasma membranes of nerve and glial cells.
All the lipids considered above are usually called saponifiable, since soaps are formed during their hydrolysis. However, there are lipids that are not hydrolyzed to release fatty acids. These lipids include steroids.
Steroids are naturally occurring compounds. They are derivatives of the core containing three fused cyclohexane and one cyclopentane ring. Steroids include numerous substances of a hormonal nature, as well as cholesterol, bile acids and other compounds.
In the human body, sterols occupy the first place among steroids. The most important representative of sterols is cholesterol:
It contains an alcoholic hydroxyl group at C 3 and a branched aliphatic chain of eight carbon atoms at C 17. The hydroxyl group at C 3 can be esterified with a higher fatty acid; in this case, cholesterol esters (cholesterides) are formed:
Cholesterol plays the role of a key intermediate in the synthesis of many other compounds. Plasma membranes of many animal cells are rich in cholesterol; in a significantly smaller amount, it is contained in the membranes of mitochondria and in the endoplasmic reticulum. Note that there is no cholesterol in plants. Plants have other sterols known collectively as phytosterols.
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