Lipids- Substances 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 stress.
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 animal or plant tissue is treated with one or more (more often sequentially) organic solvents, for example 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 from 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 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 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 glycerol 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. 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 21-35 carbon atoms.
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 connected 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 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 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 amounts.
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 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 special enzymes , for example, in cobra venom, which are 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 with 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, nervonic 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 nervonic 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.
Lipids (Fats).Lipids- called a complex mixture of organic compounds (compounds with carbon C), with similar physical and chemical properties:
- insolubility in water.
- good solubility in organic solvents (gasoline, chloroform)Lipids are widespread in nature. Together with proteins and carbohydrates, they constitute the bulk of the organic matter of all living organisms, being an indispensable component of every cell. Lipids - the most important component of food, largely determines its nutritional value and taste.
In plants, they accumulate mainly in seeds and fruits. In animals and fish, lipids are concentrated in the subcutaneous fatty tissues, in the abdominal cavity and tissues surrounding many important organs (heart, kidneys), as well as in the 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, the lipid content ranges from 10-20% on average.Types of lipids.
There are many types of fat classifications, we will analyze the simplest one, it divides them into three large groups:
- Simple lipids
- Complex lipids
- Derivatives of lipids.Let's analyze each group of lipids separately, what they include, and what they are for.
Simple Lipids.
1) Neutral fats (or just fats).
Neutral fats are made up of triglycerides.
Triglyceride - lipid or neutral fat, which contains glycerin combined with three fatty acid molecules.
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 at least 6.Triglycerides are produced from the breakdown of dietary fats and are a form of fat storage in the human body. The majority of dietary fats (98%) are triglycerides. Fat is also stored in the body as 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, therefore this acid is called saturated. They differ from unsaturated ones in that they remain solid at 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, small sausages and other sausages, bacon, ordinary lean beef; sorts of meat called "marble"; chicken skin, bacon; ice cream, creams, cheeses; most of the 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 bind to the fatty acid. Double bonds also lead to a "bend" in 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)There will be a separate big topic about edible fats, which examines in detail all their properties.
2) Waxes.
Waxes are fat-like substances of animal or vegetable 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 the carbon atom.
In simple words, waxes are shapeless, plastic, easily softened 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 of them.Phospholipids- glycerin combined with one or two fatty acids as well as phosphoric acid.
The cell membrane is composed of phospholipids. The most popular in food is lecithin.Glycolipids - compounds of fat and carbohydrate components. (Contained in all tissues, mainly in the outer lipid layer of plasma membranes.)
Lipoproteins- complexes of fats and proteins. (Blood plasma)
Derivatives of lipids.
Cholesterol is a wax-like fatty substance found in every cell of the body and in many foods. Some blood cholesterol is needed, but high levels can lead to heart disease.
A lot of cholesterol is found in eggs, fatty meats, sausages, fatty dairy products.With the general classification figured out, what functions do lipids perform?
Functions.
- Structural function.
Phospholipids are involved in the construction of cell membranes in all organs and tissues. They are involved in the formation of many biologically important compounds.
- Energy function.
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 in an industrial way. carbohydrates and proteins.
- 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.
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 derived from cholesterol, such as sex hormones (testosterone at men and progesterone in women) and corticosteroids. Derivatives of cholesterol, vitamin D play a key role in the metabolism of calcium and phosphorus. Bile acids are involved in digestion processes. In the myelinated (non-conductive charge) sheaths of the axons of nerve cells, lipids are insulators during the conduction of nerve impulses.
- Source of metabolic water.
Oxidation of 100 g of fat gives approximately 105-107 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.
Lipids are the most important source of the body's energy reserves. The fact is obvious even at the nomenclature level: the Greek "lipos" is translated as fat. Accordingly, the category of lipids unites fat-like substances of biological origin. The functional of the compounds is quite diverse, due to the heterogeneity of the composition of this category of bio-objects.
What functions do lipids perform?
List the main functions of lipids in the body, which are the main ones. At the introductory stage, it is advisable to highlight the key roles of fat-like substances in the cells of the human body. The basic list is the five functions of lipids:
- reserve energy;
- structure-forming;
- transport;
- insulating;
- signal.
The secondary tasks that lipids perform in combination with other compounds include a regulatory and enzymatic role.
Energy reserve of the body
This is not only one of the important, but the priority role of fat-like compounds. In fact, part of the lipids is the energy source of the entire cell mass. Indeed, fat for cells is analogous to fuel in a car's tank. The energy function is realized by lipids as follows. Fats and similar substances are oxidized in the mitochondria, breaking down to the level of water and carbon dioxide. The process is accompanied by the release of a significant amount of ATP - high-energy metabolites. Their supply allows the cell to participate in energy-dependent reactions.
Structural blocks
At the same time, lipids carry out a building function: with their help, the cell membrane is formed. The process involves the following groups of fat-like substances:
- cholesterol - lipophilic alcohol;
- glycolipids - compounds of lipids with carbohydrates;
- phospholipids are esters of complex alcohols and higher carboxylic acids.
It should be noted that the formed membrane does not contain fats directly. The formed wall between the cell and the external environment turns out to be two-layer. This is achieved due to the biphilicity. A similar characteristic of lipids indicates that one part of the molecule is hydrophobic, that is, insoluble in water, while the other, on the contrary, is hydrophilic. As a result, a cell wall bilayer is formed due to the ordered arrangement of simple lipids. Molecules unfold in hydrophobic regions towards each other, while hydrophilic tails are directed inward and outward of the cell.
This determines the protective functions of membrane lipids. First, the membrane gives the cell its shape and even preserves it. Secondly, the double wall is a kind of passport control point that does not allow unwanted visitors to pass through.
Autonomous heating system
Of course, this name is rather arbitrary, but it is quite applicable if we consider what functions lipids perform. The compounds do not so much heat the body as they keep the heat inside. A similar role is assigned to fatty deposits that form around various organs and in the subcutaneous tissue. This class of lipids is characterized by high heat-insulating properties, which protects vital organs from hypothermia.
Did you order a taxi?
The transport role of lipids is referred to as a secondary function. Indeed, the transfer of substances (mainly triglycerides and cholesterol) is carried out by separate structures. These are bound complexes of lipids and proteins called lipoproteins. As you know, fat-like substances are insoluble in water, respectively, in blood plasma. In contrast, the functions of proteins include hydrophilicity. As a result, the lipoprotein core is an accumulation of triglycerides and cholesterol esters, while the shell is a mixture of protein and free cholesterol molecules. In this form, lipids are delivered to the tissues or back to the liver for elimination from the body.
Secondary factors
The list of already listed 5 functions of lipids complements a number of equally important roles:
- enzymatic;
- signal;
- regulatory
Signal function
Some complex lipids, in particular their structure, allow the transmission of nerve impulses between cells. Glycolipids act as mediators in this process. No less important is the ability to recognize intracellular impulses, which is also realized by fat-like structures. This allows for the selection of substances necessary for the cell from the blood.
Enzymatic function
Lipids, regardless of their location in the membrane or outside it, are not part of the enzymes. However, their biosynthesis occurs with the presence of fat-like compounds. Additionally, lipids are involved in protecting the intestinal wall from pancreatic enzymes. The excess of the latter is neutralized by bile, where cholesterol and phospholipids are included in significant quantities.
One of the biggest myths of modern mankind is the harmfulness of fats. Fat has become enemy number one. People spend dollars, rubles, euros and so on to buy fat-free cookies, fat-free cola, pills that can inhibit the absorption of fat, pills that dissolve fat. People are on all kinds of fat-free diets.
But ... In countries that are prosperous in all respects, the number of obese people is steadily growing. A growing number of people suffering from cardiovascular diseases and diabetes mellitus, that is, diseases that are largely associated with overweight. The war on fats continues ...
So what's wrong?
Fact 1: fats are good for you
The first and main mistake is to assume that all fats are the same, rejecting all fats is a blessing. However, the education of the population is quite high, now many people know that unsaturated fats (mainly vegetable) are useful. And saturated (mainly animals) are harmful.
Let's figure it out.
Saturated fats are structural components of cell membranes and are involved in the biochemistry of the body. Therefore, a complete rejection of them will lead to irreversible changes in health. Another thing is that their consumption should correspond to age indicators. Children and adolescents need them in sufficient quantities, their consumption can be reduced with age.
Unsaturated fats - reduce the level of "bad" cholesterol, are necessary for the assimilation of certain vitamins (fat-soluble) by the organisms, and are involved in metabolism. That is, these fats are also necessary for the body.
A little observation: saturated fats are solid, unsaturated fats are liquid.
According to physiological indicators, for an average person, the ratio of saturated - unsaturated fats should be 1/3: 2/3. Eating healthy fats is essential!
Trans fats are definitely harmful. They are also found in nature (for example, in natural milk), but for the most part they are formed from other (vegetable) fats, by hydrogenation (a method of processing fats to give them a solid form).
Fact 2: body fat is not the result of eating fat
What?! Of course, if you simply increase your fat intake without reducing other foods, you will gain weight. The basis for maintaining a healthy weight is balance. You should be spending as many calories as you consume.
But diets with a sharp calorie restriction can lead to a sharp increase in weight after cancellation. Why? The body received the installation: hunger. Hence, it is necessary to accumulate fats in reserve. Therefore, all food is processed and goes to the "depot" - fat deposits. In this case, you can fall into hungry faints. Processed carbohydrates are stored in fat stores.
Studies show that if a person is on a low-calorie, fat-free diet, then with great difficulty shed a few pounds will return, even if you continue to "sit" on this diet.
In addition, people who eat a small amount of fat are prone to obesity.
And observation of patients in the United States revealed a picture that a decrease in the amount of fat from 40% (which is considered the norm) to 33% in the diet is accompanied by an increase in overweight people.
Remember that unsaturated fats are involved in the metabolism. The ratio of protein: fat: carbohydrates for an adult should be approximately 14%: 33%: 53%.
Output: an increase in unsaturated fats in food with a constant calorie content will not lead to weight gain, but will contribute to improving health through metabolism.
What are lipids, what is the classification of lipids, what is their structure and function? The answer to this and many other questions is given by biochemistry, which studies these and other substances that are of great importance for metabolism.
What it is
Lipids are organic substances that do not dissolve in water. The functions of lipids in the human body are diverse.
Lipids - this word means "small particles of fat"
This is primarily:
- Energy. Lipids serve as a substrate for storing and using energy. The breakdown of 1 gram of fat releases about 2 times more energy than the breakdown of protein or carbohydrates of the same weight.
- Structural function. The structure of lipids determines the structure of the cell membranes in our body. They are arranged in such a way that the hydrophilic part of the molecule is inside the cell, and the hydrophobic part is on its surface. Due to these properties of lipids, each cell, on the one hand, is an autonomous system, fenced off from the outside world, and on the other, each cell can exchange molecules with others and with the environment using special transport systems.
- Protective. The surface layer that we have on the skin and serves as a kind of barrier between us and the outside world is also composed of lipids. In addition, they, in the composition of adipose tissue, provide the function of thermal insulation and protection from harmful external influences.
- Regulatory. They are part of vitamins, hormones and other substances that regulate many processes in the body.
The general characteristics of lipids are based on structural features. They have two properties, since they have soluble and insoluble parts in the molecule.
Intake of the body
Lipids partly enter the human body with food, partly they are able to synthesize endogenously. The splitting of the main part of dietary lipids occurs in the duodenum under the influence of pancreatic juice secreted by the pancreas and bile acids in the bile. Having split, they are resynthesized again in the intestinal wall and, already in the composition of special transport particles ─ lipoproteins, ─ are ready to enter the lymphatic system and the general bloodstream.
With food, a person needs to get about 50-100 grams of fat every day, which depends on the state of the body and the level of physical activity.
Classification
The classification of lipids, depending on their ability to form soaps under certain conditions, divides them into the following classes of lipids:
- Saponified. This is the name of substances that, in an alkaline reaction medium, form salts of carboxylic acids (soaps). This group includes simple lipids, complex lipids. Both simple and complex lipids are important for the body, they have a different structure and, accordingly, lipids perform different functions.
- Unsaponifiables. They do not form carboxylic acid salts in an alkaline medium. This biological chemistry includes fatty acids, derivatives of polyunsaturated fatty acids ─ eicosanoids, cholesterol, as the most prominent representative of the main class of sterols-lipids, as well as its derivatives ─ steroids and some other substances, for example, vitamins A, E, etc.
General classification of lipids
Fatty acid
Substances that belong to the group of so-called simple lipids and are of great importance for the body are fatty acids. Depending on the presence of double bonds in the non-polar (water-insoluble) carbon "tail", fatty acids are divided into saturated (do not have double bonds) and unsaturated (have one or even more double carbon-carbon bonds). Examples of the first: stearic, palmitic. Examples of unsaturated and polyunsaturated fatty acids: oleic, linoleic, etc.
It is the unsaturated fatty acids that are especially important for us and must be taken with food.
Why? Because they:
- They serve as a component for the synthesis of cell membranes, participate in the formation of many biologically active molecules.
- They help to maintain the normal functioning of the endocrine and reproductive systems.
- They help prevent or slow down the development of atherosclerosis and many of its consequences.
Fatty acids are divided into two large groups: unsaturated and saturated
Inflammatory mediators and more
Another type of simple lipids are such important mediators of internal regulation as eicosanoids. They have a unique (like almost everything in biology) chemical structure and, accordingly, unique chemical properties. The main basis for the synthesis of eicosanoids is arachidonic acid, which is one of the most important unsaturated fatty acids. It is eicosanoids that are responsible in the body for the course of inflammatory processes.
Their role in inflammation can be briefly described as follows:
- They change the permeability of the vascular wall (namely, increase its permeability).
- Stimulates the release of leukocytes and other cells of the immune system into the tissue.
- With the help of chemicals, they mediate the movement of immune cells, the release of enzymes and the absorption of particles foreign to the body.
But the role of eicosanoids in the human body does not end there, they are also responsible for the blood coagulation system. Depending on the developing situation, eicosanoids can dilate blood vessels, relax smooth muscles, reduce aggregation, or, if necessary, cause opposite effects: vasoconstriction, contraction of smooth muscle cells and thrombus formation.
Eicosanoids - a large group of physiologically and pharmacologically active compounds
Studies have been conducted according to which, people who received sufficient amounts of the main substrate for the synthesis of eicosanoids ─ arachidonic acid ─ with food (found in fish oil, fish, vegetable oils) suffered less from diseases of the cardiovascular system. Most likely, this is due to the fact that such people have a more perfect exchange of eicosanoids.
Substances of a complex structure
Complex lipids are a group of substances that are no less important for the body than simple lipids. The main properties of this group of fats:
- Participate in the formation of cell membranes, along with simple lipids, and also provide intercellular interactions.
- They are part of the myelin sheath of nerve fibers, which is necessary for the normal transmission of nerve impulses.
- They are one of the important components of a surfactant ─ a substance that ensures breathing processes, namely, prevents the alveoli from collapsing during exhalation.
- Many of them act as receptors on the cell surface.
- The significance of some complex fats secreted from cerebrospinal fluid, nervous tissue, and heart muscle is not fully understood.
The simplest representatives of this group of lipids are phospholipids, glyco- and sphingolipids.
Cholesterol
Cholesterol is a substance of a lipid nature with the most important value in medicine, since the violation of its metabolism negatively affects the state of the whole organism.
Some of the cholesterol is ingested with food, and some is synthesized in the liver, adrenal glands, gonads and skin.
It also participates in the formation of cell membranes, the synthesis of hormones and other chemically active substances, and also participates in the metabolism of lipids in the human body. Indicators of cholesterol in the blood are often studied by doctors, as they show the state of lipid metabolism in the human body as a whole.
Lipids have their own special transport forms ─ lipoproteins. With their help, they can be carried with the blood stream without causing embolism.
Disorders of fat metabolism are most rapidly and clearly manifested by disorders of cholesterol metabolism, the predominance of atherogenic carriers (the so-called low and very low density lipoproteins) over antiatherogenic (high density lipoproteins).
The main manifestation of lipid metabolism pathology is the development of atherosclerosis.
It manifests itself as a narrowing of the lumen of arterial vessels throughout the body. Depending on the prevalence in the vessels of various localizations, a narrowing of the lumen of the coronary vessels develops (accompanied by angina pectoris), cerebral vessels (with impaired memory, hearing, possible headaches, noise in the head), renal vessels, vessels of the lower extremities, vessels of the digestive system with corresponding symptoms ...
Thus, lipids are at the same time an indispensable substrate for many processes in the body and, at the same time, when fat metabolism is disturbed, they can cause many diseases and pathological conditions. Therefore, fat metabolism requires control and correction when such a need arises.
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