What is the regulatory function of lipids. Lipid chemistry

Lipids (Fats).
Lipids- called a complex mixture of organic compounds (compounds with carbon C), with similar physicochemical properties:
- insoluble in water.
- good solubility in organic solvents (gasoline, chloroform)
Lipids are widely distributed in nature. Together with proteins and carbohydrates, they make up the bulk of the organic substances of all living organisms, being an essential component of every cell. Lipids are the most important component of food, largely determining its nutritional value and taste.
In plants they accumulate mainly in seeds and fruits. In animals and fish, lipids are concentrated in subcutaneous adipose tissues, in the abdominal cavity and tissues surrounding many important organs (heart, kidneys), as well as in brain and nervous tissues. There are especially many lipids in the subcutaneous adipose tissue of whales (25-30% of their mass), seals and other marine animals. In humans, lipid content ranges from 10-20% on average.
Types of lipids.
There are many types of classifications of fats, we will analyze the simplest one, it divides them into three large groups:
- Simple lipids
- Complex lipids
- Lipid derivatives.
Let's look at each group of lipids separately, what they contain, and what they are needed for.
Simple Lipids.
1) Neutral fats (or just fats).
Neutral fats consist of triglycerides.
Triglyceride - a lipid or neutral fat that contains glycerol combined with three molecules of fatty acids.
Glycerol- chemical compound with the formula C3H5(OH)3, (colorless, viscous, odorless, sweetish liquid.)

Fatty acid– natural or created compounds with one or more groups - COOH (carboxyl) that do not create cyclic bonds (aromatic), with the number of carbon atoms (C) in the chain of at least 6.
Triglycerides are produced from the breakdown of dietary fats and are a form of fat storage in the human body. The bulk of dietary fats (98%) are triglycerides. Fat is also stored in the body in the form of triglycerides.
Types of fatty acids:
- Saturated fatty acids- contain only single bonds between carbon atoms with all other bonds attached to hydrogen atoms. The molecule combines with as many hydrogen atoms as possible, which is why the acid is called saturated. They differ from unsaturated acids in that they remain solid at room temperature.

Foods that contain the most saturated fat are lard and lard, chicken, beef and lamb fat, butter and margarine. Foods rich in such fats include sausage, sausages and other sausages, bacon, regular lean beef; varieties of meat called “marbled”; chicken skin, bacon; ice cream, creams, cheeses; most 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 bond with the fatty acid. Double bonds also result in a "bend" in the fatty acids, which prevents bonding between them.

Unsaturated fatty acids are found in plant sources.
They can be divided into two types:
1) monounsaturated – unsaturated fatty acids with one double bond. (for example - olive oil)
2) polyunsaturated - unsaturated fatty acids with two or more double bonds. (for example - linseed oil)
There will be a separate large topic about dietary fats, examining in detail all their properties.
2) Waxes.
Waxes are fat-like substances of animal or plant origin, consisting of esters of monohydric alcohols and fatty acids.
Esters– compounds – COOH (carboxyl) in which the hydrogen atom in the HO group is replaced by an organic group.
Alcohols– –OH compounds bonded to a carbon atom.
In simple words, waxes are shapeless, plastic substances that soften easily when heated, melting in the temperature range from 40 to 90 degrees Celsius.

Beeswax is secreted by special glands of honey bees, from which bees build honeycombs.
Complex lipids.
A complex lipid is a combination of a triglyceride with other chemicals.
There are three types in total.
Phospholipids– glycerol combined with one or two fatty acids as well as phosphoric acid.

The cell membrane is made up of phospholipids. The most popular in food products is lecithin.
Glycolipids – compounds of fatty and carbohydrate components. (Contained in all tissues, mainly in the outer lipid layer of plasma membranes.)
Lipoproteins– complexes of fats and proteins. (Blood plasma)
Lipid derivatives.
Cholesterol- a fatty, wax-like substance found in every cell of the body and in many foods. Some cholesterol in the blood is necessary, but high levels can lead to heart disease.

A lot of cholesterol is found in eggs, fatty meats, sausages, and fatty dairy products.
With the general classification figured out, what functions do lipids perform?
Functions.
- Structural function.
Phospholipids take part in the construction of cell membranes of all organs and tissues. They are involved in the formation of many biologically important compounds.
- Energy function.
When fats are oxidized, a large amount of energy is released, which goes towards the formation of ATP. A significant portion of the body's energy reserves are 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 lipid content in plant seeds ensures the development of the embryo and seedling before they transition to independent nutrition. The seeds of many plants (coconut palm, castor oil, sunflower, soybean, rapeseed, etc.) serve as raw materials for the production of vegetable oil industrially. With the complete breakdown of 1 g of fat, 38.9 kJ of energy is released, which is approximately 2 times more compared to carbohydrates and proteins.
- Protective and thermal insulation
Accumulating in the subcutaneous tissue and around some organs (kidneys, intestines), the fat layer protects the animal’s body and its individual organs from mechanical damage. In addition, due to low thermal conductivity, the layer of subcutaneous fat helps retain heat, which allows, for example, many animals to live in cold climates.
Lubricating and water repellent.
Wax covers the skin, wool, feathers, makes them more elastic and protects them from moisture. The leaves and fruits of many plants have a waxy coating.
- Regulatory.
Many hormones are derivatives of cholesterol, for example sex hormones (testosterone at men and progesterone in women) and corticosteroids. Cholesterol derivatives, vitamin D play a key role in the metabolism of calcium and phosphorus. Bile acids are involved in digestion processes. In the myelin (non-conductive charge) sheaths of the axons of nerve cells, lipids are insulators during the conduction of nerve impulses.
- Source of metabolic water.
Oxidation of 100 g of fat produces approximately 105-107 g of water. This water is very important for some desert inhabitants, in particular for camels, which can do without water for 10-12 days: the fat stored in the hump is used precisely for these purposes. Bears, marmots and other hibernating animals obtain the water they need for life as a result of fat oxidation.

It is usually believed that fats in the human body act as energy (calorie) suppliers. But this is not entirely correct. Of course, a significant part of fat is consumed as energy material. Moreover, fat serves as a source of energy in the body, either through direct use, or potentially in the form of reserves in adipose tissue. However, to a certain extent, fats are a plastic material, since they are part of cellular components (in the form of complexes with proteins - lipoproteins), in particular, membranes, i.e. are an essential nutritional factor. In addition, body fat provides insulation by accumulating in the subcutaneous layer and around certain organs. In addition, fats act as food solvents for fat-soluble vitamins and serve as a source of essential polyunsaturated fatty acids (linolenic, arachidonic).

With prolonged restriction of fats in the diet, disturbances in the physiological state of the body are observed: the activity of the central nervous system is disrupted, the immune system is weakened and life expectancy is reduced. However, excessive consumption of saturated fats leads to disruption of cholesterol metabolism, increased blood clotting properties, kidney and liver diseases, and contributes to the development of atherosclerosis and obesity with all the ensuing consequences.

The definition of lipids given in the literature is ambiguous. Fats (more correctly termed lipids) are organic compounds that are soluble in a number of organic solvents and insoluble in water. The main components of fats are trigcerides and lipoid substances, which include phospholipids, sterols, waxes, etc. In food technology, the term “fat” is used, which means the sum of substances extracted by organic solvents. When fat is almost completely extracted from food products, the term “fat” is equivalent to the term “lipids”.

It seems more preferable to define lipids as natural derivatives of fatty acids and related compounds that are part of all living cells and are extracted from organisms and tissues with non-polar solvents.

According to Blore's classification, lipids are divided into three groups:

Simple,

Complex,

Precursors and derivatives of lipids.

Simple lipids. Simple lipids are esters of fatty acids with various alcohols. These include, for example, fats and waxes.

Fats (triglycerides). Fats (triglycerides) are esters of fatty acids with glycerol. If they are in a liquid state, they are called oils. The composition of triglycerides includes glycerol (about 9%) and fatty acids with different lengths of hydrocarbon chains and degrees of saturation, the structure of which determines the properties of triglycerides.

Animal and vegetable fats have different physical properties and composition. Animal fats are solid substances that contain large amounts of saturated fatty acids that have a high melting point. Vegetable fats are usually liquid substances containing mainly unsaturated fatty acids with a low melting point. The source of vegetable fats is mainly vegetable oils (99.9% fat), nuts (53–65%), oat (6.1%) and buckwheat (3.3%) cereals. The source of animal fats is pork lard (90–92% fat), butter (72–82%), fatty pork (49%), sausages (20–40%), sour cream (30%), cheeses (15–30% ).

The main component of lipids are fatty acids. Naturally occurring trigcerides contain at least two different fatty acids.

1-Palmitoyl-2,3-distearoylgicerine

The chemical, biological and physical properties of fats are determined by the triglycerides included in its composition and, first of all, by the chain length and the degree of saturation of fatty acids. The composition of fats consists mainly of unbranched fatty acids containing an even number of carbon atoms (4–26), both saturated and mono- and polyunsaturated acids.

Saturated fatty acids (palmitic, stearic, etc.) are used by the body as a whole as energy material. Palmitic and stearic acids are found in all animal and vegetable fats. The largest amount of saturated fatty acids is found in animal fats: for example, in beef and pork fat - 25% palmitic, 20% and 13% stearic acids, respectively, in butter - 7% stearic, 25% palmitic and 8% myristic acids. They can be partially synthesized in the body from carbohydrates (and even from proteins).

Unsaturated fatty acids vary in their degree of “unsaturation.” Monounsaturated fatty acids contain one hydrogen-unsaturated bond between carbon atoms, polyunsaturated fatty acids contain several bonds (2–6). The most common monounsaturated fatty acids include oleic acid, which is abundant in olive oil (65%), margarines (43–47%), pork and beef fat, butter and goose meat (11–16%).

Most fatty acids that make up triglycerides contain 20 carbon atoms per molecule. There are 18 carbon atoms in the molecules of oleic, linoleic, and linolenic acid and they are dehydro derivatives of stearic acid, cis-isomers.

The most common saturated fatty acids in triglycerides are: stearic (C 17 H 35 COOH), palmitic (C 15 H 31 COOH), myristic (C 13 H 27 COOH), arachidic (C 19 H 39 COOH), lauric (C 11 H 23 COUN).

Of particular importance are polyunsaturated fatty acids, such as linoleic, linolenic and arachidonic acids, which are part of cell membranes and other structural elements of tissues and perform a number of important functions in the body, including ensuring normal growth and metabolism, vascular elasticity, etc. Most polyunsaturated acids cannot be synthesized in the human body and therefore these acids are essential, just as some amino acids and vitamins are essential. On the other hand, these acids, mainly linoleic and arachidonic, serve as precursors of hormone-like substances - prostaglandins, prevent the deposition of cholesterol in the walls of blood vessels (promote its removal from the body), and increase the elasticity of the walls of blood vessels. It should be noted that these functions are performed only by cis-isomers of unsaturated acids.

Saturated fatty acids perform mainly an energy function in the body and their excess in the diet often leads to impaired fat metabolism and increased blood cholesterol levels.

The composition of fats synthesized in different parts of the same body is different. Thus, in pigs, the outer layers of subcutaneous fat are more unsaturated than the inner ones. The acid composition of human fats is close to the composition of rendered beef lard.

Waxes. Waxes are esters of fatty acids with monohydric alcohols. Waxes are the historical name for products of different composition and origin, mostly natural, whose properties are close to beeswax. Most natural waxes contain esters of monobasic saturated carboxylic acids of normal structure and sterols with 12–46 carbon atoms per molecule. Such waxes are similar in chemical properties to fats (triglycerides), but are saponified only in an alkaline environment. Waxes differ from fats in that instead of glycerol, they contain sterols or higher aliphatic alcohols with an even number of carbon atoms (16–36). Vegetable waxes also contain paraffinic hydrocarbons.

Waxes are widely distributed in nature. In plants, they cover leaves, stems, and fruits with a thin layer, protecting them from wetting with water, drying out, and the action of microorganisms. The wax content in grains and fruits is low. The shells of sunflower seeds contain up to 0.2% of waxes by weight of the shell, soybean seeds - 0.01%, rice - 0.05%.

Complex lipids. Complex lipids are esters of fatty acids with alcohols, additionally containing other groups.

Phospholipids. The most important representatives of complex lipids are phospholipids. These are lipids containing, in addition to fatty acids and alcohol, a phosphoric acid residue. They contain nitrogenous bases (most often choline + OH - or ethanolamine HO-CH 2 -CH 2 -NH 2), amino acid residues and other components. Depending on the alcohol included in the molecule, a phospholipid is either a glycerophospholipid (glycerol acts as an alcohol) or a sphingophospholipid, which includes sphingosine. Phospholipid molecules contain non-polar hydrophobic hydrocarbon radicals - “tails” and a polar hydrophilic “head” (residues of phosphoric acid and nitrogenous base), which determines the ability of phospholipids to form biological membranes. As part of cell membranes, phospholipids play an essential role in their permeability and metabolism between cells and the intracellular space.

The most common group of phospholipids is phosphoglycerides. They contain glycerin, fatty acids, phosphoric acid and amino alcohols (for example, choline in lecithin, ethanolamine in cephalin). The amino alcohol included in the phospholipid determines the biological effect of the phospholipid. For example, lecithin is a glyceride esterified with two, usually different fatty acids (for example, stearic and oleic) and containing a phosphocholine group, which, when saponified, gives inorganic phosphate and a quaternary base - choline.

Lecithin exhibits a lipotropic effect, i.e. helps remove cholesterol from the body. Lecithin and choline prevent fatty liver and these drugs are used to prevent liver diseases. Choline, in addition, is part of the nervous tissue, in particular in the brain tissue. Acetylcholine plays an important role in the transmission of nerve impulses. In the human body, choline can be formed from serine, but choline biosynthesis is limited and choline must be supplied additionally from food. Thus, choline, like polyunsaturated fatty acids and a number of amino acids, is an essential nutrient.

Phospholipids in food products differ in their chemical composition and biological effects. The latter, as already mentioned, largely depends on the nature of the amino alcohol included in their composition. The foods found mainly include lecithin, which contains choline, an amino alcohol, and cephalin, which contains ethanolamine.

Phospholipids contained in food products promote better absorption of fats. Thus, the fat in milk is in a finely dispersed state, largely due to milk phospholipids. Milk fat is considered one of the most easily digestible fats. The largest amount of phospholipids is found in eggs (3.4%), relatively high (0.3–0.9%) in grains and legumes and unrefined oils. When storing unrefined vegetable oil, phospholipids precipitate. When refining vegetable oils, the content of phospholipids in them is reduced to 0.2–0.3%. It is believed that the optimal content of phospholipids in food should be 5–10 g per day.

In addition to phospholipids, complex lipids include g lycolipids(glycosphingolipids) containing a fatty acid, sphingosine and a carbohydrate component. Glycolipids are present in noticeable quantities in plant products (lipids from wheat, oats, corn, sunflower). They are also found in animals and microorganisms. Glycolipids perform structural functions, participate in the construction of membranes, and play an important role in the formation of wheat gluten proteins, which determine the baking properties of flour. Complex lipids are also sulfolipids and aminolipids. Lipoproteins also fall into this category.

Precursors and derivatives of lipids. This group includes fatty acids, glycerol, steroids and other alcohols, fatty acid aldehydes and ketone bodies, hydrocarbons, fat-soluble vitamins and hormones.

Sterols (sterols). Sterols (sterols) are alicyclic natural alcohols (monohydric secondary alcohols of the series, containing a hydroxyl group at the carbon atom in position 3 and methyl groups at the C 10 and C 13 atoms), related to steroids. Sterols are a component of the unsaponifiable fraction of animal and plant lipids. There are animal sterols (zoosterols), plant sterols (phytosterols) and fungal sterols (mycosterols). The main sterol of higher animals is cholesterol, and the main sterol of plants is b-sitosterol. Cholesterol is found in the tissues of all animals and is absent, or present in small quantities, in plants. Phytosterols, unlike cholesterol, are not absorbed by the body.

Sterols, along with lipids and phospholipids, are the main structural components of cell membranes. They are believed to affect cellular metabolism. Sterols carry out their functions in the body in the form of complexes with proteins (lipoproteins) and esters of higher fatty acids, being their carriers to all organs and tissues through the bloodstream system. Cholesterol is also involved in the metabolism of bile acids and hormones. Up to 80% of cholesterol in the human body is synthesized in the liver and other tissues. The cholesterol content in eggs reaches 0.57%, and in cheeses – 0.28–1.61%. Butter contains about 0.20%, and meat – 0.06–0.10%. It is believed that the daily intake of cholesterol from food should not exceed 0.5 g. Otherwise, the level of its content in the blood increases, which means the risk of the occurrence and development of atherosclerosis increases.

The importance of lipids. When discussing groups of lipids, mention was made of their various functions in the body. Summarizing the above, we can distinguish the following functions of lipids in a living organism.

Lipids, being part of cell walls, perform a plastic function in the body and are called structural. They are part of the cell membrane and participate in a variety of processes occurring in the cell.

Moreover, as already mentioned, lipids can serve as a source of energy in the body, either through direct use, or potentially in the form of reserves in adipose tissue. While body fat is composed primarily of glycerides, brain and spinal tissue contain complex structural units made of protein, cholesterol, and phospholipids such as lecithin.

The lipids found in special “fat” cells are called storage lipids and consist mainly of triglycerides. These lipids are an accumulator of chemical energy and are used when there is a lack of food. Lipids have a high calorie content: 1 g is 9 kcal - this is 2 times higher than the calorie content of proteins and carbohydrates. Most all plant species also contain storage lipids, mainly in the seeds. Lipids help the plant to withstand the adverse effects of the external environment, for example, low temperatures, i.e. perform a protective function.

In plants, lipids accumulate mainly in seeds and fruits, and their content depends on the variety, location and growing conditions. In animals and fish, lipids are concentrated in the subcutaneous, brain and nervous tissues and tissues surrounding important organs (heart, kidneys). The lipid content of animals is determined by the species, feed composition, housing conditions, etc.

The composition of food products includes so-called “invisible” fats (in meat, fish and milk) and “visible” - vegetable oils and animal fats specially added to food. In foods, lipids are contained in the form of individual fat cells, from where they are easily extracted by most organic solvents (often called “free lipids”) or are part of almost all vital cells. In the latter case, they are more tightly bound in cells (so-called tightly bound lipids). Lipid quantification methods take these features into account.

In addition to the fact that lipids are necessary in nutrition as energy and structural material, they participate in the metabolism of other nutrients, for example, they contribute to the absorption of vitamins A and D, and animal fats are a source of these vitamins. The only source of vitamin E and b-carotene is vegetable fats.

None of the fats, taken separately, can fully meet the body's needs for fatty substances. The recommended caloric content of lipids in the diet is 30–35%, which in weight units (on average 102 g) is slightly higher than the amount of proteins. Of the indicated 102 g, it is recommended to consume 45–50 g directly in the form of fat. When working in the cold, the amount of fat in the diet should be increased, since fat is involved in the processes of thermoregulation of the body. This increase should come from a quota of carbohydrates, not proteins, since proteins are necessary for the proper processing of fats.

It is recommended to consume animal and vegetable fats in combination. The optimal ratio is 70% animal and 30% vegetable fats. This ratio ensures that the body receives the necessary amounts of polyunsaturated and saturated acids. As you age, it is recommended to reduce your consumption of animal fats.

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

Lipids are organic compounds that include fats and other fat-like substances. They actively participate in the process of cell structure and are part of membranes. They affect the permeability of cell membranes, as well as enzymatic activity. They influence the creation of intercellular connections and various chemical processes in the body. Insoluble in water, but they dissolve in organic solvents (such as gasoline or chloroform). In addition, there are types that are fat soluble.

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

Classification of lipids

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

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

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

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

Polar ones include:

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

Neutral ones include:

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

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

Cyclooxygenase pathway.
Lipoxygenase pathway.

Importance for membrane cells

increase

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

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

Part of a bacterial cell

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

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

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

What functions do they perform in the body?

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

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

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

What is lipid metabolism

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

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

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

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

In a living organism, lipids perform various functions.

Biological functions of lipids:

1) Structural

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

2) Spare (energy)

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

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

Caloric content of fat: ~ 9 kcal/gram.

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

3) Protective

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

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

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

4) An important component of food raw materials

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

2 Classification of lipids

There is no generally accepted classification of lipids.

It is most appropriate to classify lipids depending on their chemical nature, biological functions, and also in relation to certain reagents, for example, alkalis.

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

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

Fats – esters of glycerol and higher fatty acids.

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

Steroids – esters of polycyclic alcohols and higher fatty acids.

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

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

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

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

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

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

Structural lipids are mainly phospholipids.

Storage lipids are mainly fats.

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

FATS

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

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

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

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

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

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

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

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

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

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

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

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

Physical properties of fats

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

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

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

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

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

Chemical properties of fats

Fats enter into all chemical reactions characteristic of esters, but their chemical behavior has a number of features associated with the structure of fatty acids and glycerol.

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

Lipids - what are they? Translated from Greek, the word "lipids" means "small particles of fat." They are groups of natural organic compounds of a broad nature, including fats themselves, as well as fat-like substances. They are part of all living cells without exception and are divided into simple and complex categories. Simple lipids contain alcohol and fatty acids, while complex lipids contain high-molecular components. Both are associated with biological membranes, have an effect on active enzymes, and also participate in the formation of nerve impulses that stimulate muscle contractions.

Fats and hydrophobia

One of them is the creation of the body’s energy reserve and ensuring the water-repellent properties of the skin, coupled with thermal insulation protection. Some fat-containing substances that do not have fatty acids are also classified as lipids, for example, terpenes. Lipids are not susceptible to exposure to an aqueous environment, but are easily dissolved in organic liquids such as chloroform, benzene, and acetone.

Lipids, the presentation of which is periodically held at international seminars in connection with new discoveries, are an inexhaustible topic for research and scientific research. The question "Lipids - what are they?" never loses its relevance. However, scientific progress does not stand still. Recently, several new fatty acids have been identified that are biosynthetically related to lipids. Classification of organic compounds can be difficult due to similarity in certain characteristics, but significant differences in other parameters. Most often, a separate group is created, after which the overall picture of the harmonious interaction of related substances is restored.

Cell membranes

Lipids - what are they in terms of their functional purpose? First of all, they are an essential component of living cells and tissues of vertebrates. Most processes in the body occur with the participation of lipids; the formation of cell membranes, interconnection and exchange of signals in the intercellular environment cannot do without fatty acids.

Lipids - what are they if we consider them from the perspective of spontaneously occurring steroid hormones, phosphoinositides and prostaglandins? This is, first of all, the presence in the blood plasma of which, by definition, are individual components of lipid structures. Because of the latter, the body is forced to develop complex systems for their transportation. Fatty acids of lipids are mainly transported in complex with albumin, and lipoproteins, soluble in water, are transported in the usual manner.

Classification of lipids

The categorization of compounds of biological origin is a process that involves some controversial issues. Lipids, due to their biochemical and structural properties, can be equally classified into different categories. The main classes of lipids include simple and complex compounds.

Simple ones include:

Glycerides are esters of glycerin alcohol and fatty acids of the highest category.
Waxes are an ester of a higher fatty acid and a 2-hydroxy alcohol.

Complex lipids:

Phospholipid compounds - with the inclusion of nitrogenous components, glycerophospholipids, ophingolipids.
Glycolipids - located in the outer biological layers of the body.
Steroids are highly active substances of the animal spectrum.
Complex fats - sterols, lipoproteins, sulfolipids, aminolipids, glycerol, hydrocarbons.

Operation

Lipid fats act as material for cell membranes. Participate in the transport of various substances around the periphery of the body. Fat layers based on lipid structures help protect the body from hypothermia. They have the function of energy accumulation “in reserve”.

Fat reserves are concentrated in the cytoplasm of cells in the form of droplets. Vertebrates, including humans, have special cells - adipocytes, which are capable of containing quite a lot of fat. The placement of fat accumulations in adipocytes occurs thanks to lipoid enzymes.

Biological functions

Fat is not only a reliable source of energy, it also has insulating properties, which biology contributes to. In this case, lipids allow you to achieve several useful functions, such as natural cooling of the body or, conversely, its thermal insulation. In northern regions characterized by low temperatures, all animals accumulate fat, which is deposited evenly throughout the body, and thus creates a natural protective layer that serves as heat protection. This is especially important for large marine animals: whales, walruses, seals.

Animals living in hot countries also accumulate fat deposits, but they are not distributed throughout the body, but are concentrated in certain places. For example, in camels, fat accumulates in the humps, in desert animals - in thick, short tails. Nature carefully monitors the correct placement of both fat and water in living organisms.

Structural function of lipids

All processes associated with the life of the body are subject to certain laws. Phospholipids are the basis of the biological layer of cell membranes, and cholesterol regulates the fluidity of these membranes. Thus, most living cells are surrounded by plasma membranes with a lipid bilayer. This concentration is necessary for normal cellular activity. One biomembrane microparticle contains more than a million lipid molecules, which have dual characteristics: they are both hydrophobic and hydrophilic. As a rule, these mutually exclusive properties are of a non-equilibrium nature, and therefore their functional purpose looks quite logical. Lipids in the cell are an effective natural regulator. The hydrophobic layer usually dominates and protects the cell membrane from the penetration of harmful ions.

Glycerophospholipids, phosphatidylethanolamine, phosphatidylcholine, and cholesterol also contribute to cell impermeability. Other membrane lipids are located in tissue structures, these are sphingomyelin and sphingoglycolipid. Each substance performs a specific function.

Lipids in the human diet

Triglycerides are an effective source of energy. Meat and dairy products have acids. And fatty acids, but unsaturated, are found in nuts, sunflower and olive oil, seeds and corn grains. To prevent cholesterol levels from increasing in the body, it is recommended to limit the daily intake of animal fats to 10 percent.

Lipids and carbohydrates

Many organisms of animal origin “store” fats at certain points, subcutaneous tissue, in the folds of the skin, and other places. The oxidation of lipids in such fat deposits occurs slowly, and therefore the process of their conversion into carbon dioxide and water allows you to obtain a significant amount of energy, almost twice as much as carbohydrates can provide. In addition, the hydrophobic properties of fats eliminate the need to use large amounts of water to promote hydration. The transition of fats into the energy phase occurs “dry”. However, fats act much more slowly in terms of energy release and are more suitable for hibernating animals. Lipids and carbohydrates seem to complement each other during the life of the body.