Lipids - what are they? Lipids: functions, characteristics. What are lipids and their functions? Are there essential lipids, and what are their most important sources?

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 substances 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 a low melting point. These fats are predominantly liquid. Vegetable fats run into liquid consistency oils . These fats include fish fat, sunflower, cottonseed, flaxseed, 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 is of great importance for the selective permeability of membranes.

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 important 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.

Most The body produces lipids on its own, only essential fatty acids and soluble vitamins come with food.

Lipids are a large group organic matter, consisting of fats and their analogues. Lipids have similar characteristics to proteins. In plasma they are found in the form of lipoproteins, completely insoluble in water, but highly 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, and triglycerides. The most famous among these classes is cholesterol. The determination of this indicator, of course, has the maximum value, but nevertheless, the content of cholesterol, lipoproteins, and triglycerides in the cell membrane must be considered only comprehensively.

The norm is the LDL content in the range of 4-6.6 mmol/l. It is worth noting that healthy people this indicator may change taking into account a number of factors: age, seasonality, mental and physical activity.

Peculiarities

The human body independently produces all the main groups of lipids. The cell membrane does not form only polyunsaturated fatty acids, which are essential substances and fat-soluble vitamins.

The bulk of lipids are synthesized by epithelial cells small intestine, liver. Individual lipids are characterized by association with specific bodies, tissues, and the rest are found in all cells and tissues. Most of the lipids are contained in 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, which is how they enter organs, cells, and tissues.

Biological purpose

Lipid classes perform a number of important functions.

  1. Construction. Phospholipids, combining with proteins, ensure the formation of membranes.
  2. Cumulative. During the oxidation of fats, it is produced great amount energy, which is subsequently used to create ATP. The body accumulates energy reserves mainly in lipid groups. For example, when animals fall asleep for the whole winter, their body receives all the necessary substances from previously accumulated oils, fats, and bacteria.
  3. Protective, heat-insulating. The main part of fats is stored in subcutaneous tissue, around the kidneys, intestines. Thanks to the accumulated layer of fat, the body is protected from the cold, as well as mechanical damage.
  4. Water-repellent, lubricating. The lipid layer on the skin maintains the elasticity of cell membranes and protects them from moisture and bacteria.
  5. Regulating. There is a connection 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 the absorption of carboxylic acids.

Exchange processes

The body contains lipids in the quantities determined by nature. Taking into account the structure, effects and conditions of accumulation in the body, all fat-like substances are divided into the following classes.

  1. Triglycerides protect soft subcutaneous tissue, as well as organs from damage and bacteria. There is a direct connection between their quantity and energy conservation.
  2. Phospholipids are responsible for metabolic processes.
  3. Cholesterol and 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 ensure the maintenance of the body’s vital processes and its ability to resist negative factors, including bacterial growth. There is a connection between lipids and the formation of many extremely important protein compounds. It is impossible to work without these substances genitourinary system. Failure of a person's reproductive capacity may also occur.

Lipid metabolism involves a connection between all of the above components and their complex effect on the body. During delivery useful substances, vitamins and bacteria into cell membranes they are transformed into other elements. This situation accelerates blood supply and, due to this, the rapid supply, distribution and absorption 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 flow of life. important substances, beneficial bacteria and spreading them throughout the body. This violation directly affects the process of lipid metabolism.

Metabolic disorder

Every 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 usually enter it with food products.

Lipid metabolism occurs at the cellular level. This process protects the body, including from bacteria, and occurs in several stages. First, lipids are broken down, then they are absorbed, and only after that the intermediate and final exchange occurs.

Any disruptions in the process of fat absorption indicate a disorder in the metabolism of lipid groups. The reason for this may be an insufficient amount of pancreatic lipase and bile entering the intestines. And also with:

  • obesity;
  • hypovitaminosis;
  • atherosclerosis;
  • stomach diseases;
  • intestines and other painful conditions.

When the villous epithelial tissue in the intestine is damaged, fatty acids are not fully absorbed. As a result, a large amount of fat accumulates in the stool, which has not gone through the breakdown stage. Feces become a specific grayish-white color due to the accumulation of fats and bacteria.

Adjust lipid metabolism possible with the help of a dietary regime and drug treatment, prescribed to lower LDL levels. 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 consumption of oil, meat products, offal and enrich the diet with fish and seafood of low fat content. As a preventive measure, changing your lifestyle will help - increasing physical activity, sports training, refusal bad habits.

Definition of indicators lipid profile blood is necessary for the diagnosis, treatment and prevention of cardiovascular diseases. The most important mechanism for the development of such a pathology is the formation of atherosclerotic plaques on the inner wall of blood vessels. Plaques are accumulations of fat-containing compounds (cholesterol and triglycerides) and fibrin. The higher the concentration of lipids in the blood, the probable occurrence atherosclerosis. Therefore, it is necessary to systematically take a blood test for lipids (lipid profile), this will help to identify abnormalities in a timely manner. fat metabolism from the norm.

Lipidogram - a study that determines the level of lipids of various fractions

Atherosclerosis is dangerous due to the high probability of complications - stroke, myocardial infarction, gangrene lower limbs. These diseases often result in disability of the patient, and in some cases, death.

The role of lipids

Functions of lipids:

  • Structural. Glycolipids, phospholipids, cholesterol are the most important components of cell membranes.
  • Thermal insulation and protective. Excess fat is deposited in subcutaneous fat, reducing heat loss and protecting internal organs. If necessary, the lipid supply is used by the body to obtain energy and simple compounds.
  • Regulatory. Cholesterol is necessary for the synthesis of adrenal steroid hormones, sex hormones, vitamin D, bile acids, is part of the myelin sheaths of the brain, is needed for normal functioning serotonin receptors.

Lipidogram

A lipidogram can be prescribed by a doctor both if an existing pathology is suspected and for preventive purposes, for example, during a medical examination. It includes several indicators that allow you to fully assess the state of fat metabolism in the body.

Lipid profile indicators:

  • Total cholesterol (TC). This the most important indicator lipid spectrum blood, includes free cholesterol, as well as cholesterol contained in lipoproteins and associated with fatty acids. A significant portion of cholesterol is synthesized by the liver, intestines, and gonads; only 1/5 of the TC comes from food. With normally functioning mechanisms of lipid metabolism, a slight deficiency or excess of cholesterol supplied from food is compensated by an increase or decrease in its synthesis in the body. Therefore, hypercholesterolemia is most often caused not by excess cholesterol intake from foods, but by a failure of the fat metabolism process.
  • Lipoproteins high density(HDL). This indicator has an inverse relationship with the likelihood of developing atherosclerosis - an increased level of HDL is considered an anti-atherogenic factor. HDL transports cholesterol to the liver, where it is utilized. Women have higher HDL levels than men.
  • Low density lipoproteins (LDL). LDL carries cholesterol from the liver to tissues, otherwise known as “bad” cholesterol. This is due to the fact that LDL is capable of forming atherosclerotic plaques, narrowing the lumen of blood vessels.

This is what an LDL particle looks like

  • Very low density lipoproteins (VLDL). The main function of this group of particles, heterogeneous in size and composition, is the transport of triglycerides from the liver to tissues. High concentration VLDL in the blood leads to clouding of the serum (chylosis), and the possibility of the appearance of atherosclerotic plaques also increases, especially in patients with diabetes mellitus and kidney pathologies.
  • Triglycerides (TG). Like cholesterol, triglycerides are transported through the bloodstream as part of lipoproteins. Therefore, an increase in the concentration of TG in the blood is always accompanied by an increase in cholesterol levels. Triglycerides are considered the main source of energy for cells.
  • Atherogenic coefficient. It allows you to assess the risk of developing vascular pathology and is a kind of summary of the lipid profile. To determine the indicator, you need to know the value of TC and HDL.

Atherogenic coefficient = (TC - HDL)/HDL

Optimal blood lipid profile values

Floor Indicator, mmol/l
OH HDL LDL VLDL TG CA
Male 3,21 — 6,32 0,78 — 1,63 1,71 — 4,27 0,26 — 1,4 0,5 — 2,81 2,2 — 3,5
Female 3,16 — 5,75 0,85 — 2,15 1,48 — 4,25 0,41 — 1,63

It should be taken into account that the value of the measured indicators may vary depending on the units of measurement and the analysis methodology. Normal values also vary depending on the age of the patient; the above indicators are averaged for persons 20 - 30 years old. The level of cholesterol and LDL in men after 30 years tends to increase. In women, indicators increase sharply with the onset of menopause, this is due to the cessation of the antiatherogenic activity of the ovaries. The interpretation of the lipid profile must be carried out by a specialist, taking into account the individual characteristics of the person.

A study of blood lipid levels may be prescribed by a doctor to diagnose dyslipidemia, assess the likelihood of developing atherosclerosis, and in some cases chronic diseases(diabetes mellitus, kidney and liver diseases, thyroid gland), and also as a screening study for early detection persons with lipid profile deviations from the norm.

The doctor gives the patient a referral for a lipid profile

Preparing for the study

Lipid profile values ​​can fluctuate not only depending on the gender and age of the subject, but also on the impact on the body of various external and internal factors. To minimize the likelihood of an unreliable result, you must adhere to several rules:

  1. You should donate blood strictly in the morning on an empty stomach; in the evening of the previous day it is recommended light dietary dinner.
  2. Do not smoke or drink alcohol the night before the test.
  3. Avoid 2-3 days before donating blood stressful situations and intense physical activity.
  4. Stop using all medicines and dietary supplements, except for vital ones.

Methodology

There are several methods laboratory evaluation lipid profile. IN medical laboratories analysis can be carried out manually or using automatic analyzers. The advantage of an automated measurement system is the minimal risk of erroneous results, the speed of obtaining analysis, high accuracy research.

Serum is required for analysis. venous blood patient. Blood is drawn into a vacuum tube using a syringe or vacutainer. To avoid clot formation, the blood tube should be inverted several times and then centrifuged to obtain serum. The sample can be stored in the refrigerator for 5 days.

Taking blood for lipid profile

Nowadays, blood lipids can be measured without leaving home. To do this, you need to purchase a portable biochemical analyzer that allows you to assess the level of total cholesterol in the blood or several indicators at once in a matter of minutes. A drop is needed for research capillary blood, it is applied to the test strip. Test strip is saturated special composition, for each indicator it is different. The results are read automatically after inserting the strip into the device. Thanks to the small size of the analyzer and the ability to operate on batteries, it is convenient to use at home and take with you on a trip. Therefore, persons with a predisposition to cardiovascular diseases It is recommended to have it at home.

Interpretation of results

The most ideal result of the analysis for the patient will be a laboratory conclusion that there are no deviations from the norm. In this case, a person need not fear for the condition of his circulatory system- the risk of atherosclerosis is practically absent.

Unfortunately, this is not always the case. Sometimes the doctor, after reviewing the laboratory data, makes a conclusion about the presence of hypercholesterolemia. What it is? Hypercholesterolemia - an increase in the concentration of total cholesterol in the blood above normal values, with high risk development of atherosclerosis and related diseases. This condition may be due to a number of reasons:

  • Heredity. Science knows cases of familial hypercholesterolemia (FH), in such a situation the defective gene responsible for lipid metabolism is inherited. Patients experience constantly elevated levels of TC and LDL; the disease is especially severe in the homozygous form of FH. Such patients have an early onset of coronary artery disease (at the age of 5-10 years); in the absence of proper treatment, the prognosis is unfavorable and in most cases ends in death before reaching 30 years of age.
  • Chronic diseases. Increased level cholesterol is observed in diabetes mellitus, hypothyroidism, kidney and liver pathology, and is caused by lipid metabolism disorders due to these diseases.

For patients suffering from diabetes, it is important to constantly monitor cholesterol levels

  • Poor nutrition. Long-term abuse of fast food, fatty, salty foods leads to obesity, and, as a rule, there is a deviation in lipid levels from the norm.
  • Bad habits. Alcoholism and smoking lead to disruptions in the mechanism of fat metabolism, as a result of which lipid profile indicators increase.

With hypercholesterolemia, it is necessary to adhere to a diet with limited fat and salt, but in no case should you completely abandon all foods rich in cholesterol. Only mayonnaise, fast food and all products containing trans fats should be excluded from the diet. But eggs, cheese, meat, sour cream must be present on the table, you just need to choose products with a lower percentage of fat content. Also important in the diet is the presence of greens, vegetables, cereals, nuts, and seafood. The vitamins and minerals they contain perfectly help stabilize lipid metabolism.

An important condition for normalizing cholesterol is also giving up bad habits. Constant physical activity is also beneficial for the body.

In case if healthy image life in combination with diet did not lead to a decrease in cholesterol, it is necessary to prescribe appropriate drug treatment.

Drug treatment of hypercholesterolemia includes the prescription of statins

Sometimes specialists are faced with a decrease in cholesterol levels - hypocholesterolemia. Most often, this condition is caused by insufficient intake of cholesterol from food. Fat deficiency is especially dangerous for children; in such a situation, there will be a lag in physical and mental development, cholesterol is vital for a growing body. In adults, hypocholesteremia leads to disorders emotional state due to malfunctions nervous system, problems with reproductive function, decreased immunity, etc.

Changes in the blood lipid profile inevitably affect the functioning of the entire body, so it is important to systematically monitor fat metabolism indicators for timely treatment and prevention.

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 acids. 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 room temperature hard. 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 entering into all chemical reactions characteristic of esters. Highest value has a saponification reaction, as a result of which glycerol and fatty acids are formed 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

To this class complex lipids include 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 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.

    From glycerophospholipids in the body of animals and higher plants in the greatest number phosphatidylcholines and phosphatidylethanolamines are also found. 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 in membranes is especially high 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 compounds.

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 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.

Loading...Loading...