Unsaponifiable fats function. Biological functions of lipids. Protective and lubricating function
The classification of lipids allows you to understand the nuances of the participation of these microelements in a variety of biological processes of human life. The biochemistry and structure of each such substance that is part of cells still cause a lot of controversy among scientists and experimenters.
General description of lipids
Lipids, as you know, are natural compounds that include various fats in their composition. The difference between these substances and other representatives of this organic group is that they are practically not utilized in water. Being active esters of acids with a high level of fat content, they are not able to completely eliminate themselves with the help of inorganic type solvents.
Lipids are present in the human body. Their share reaches an average of 10-15% of the total body. The importance of lipids cannot be underestimated: they serve as a direct supplier of unsaturated fatty acids. From the outside, substances enter the body with vitamin F, which is extremely important for the proper functioning of the digestive system.
In addition, lipid is a hidden fluid resource in the human body. Oxidized, 100 g of fats are able to form 106 g of water. One of the main purposes of these elements is to perform the function of a natural solvent. It is thanks to her that in the intestines there is a continuous absorption of valuable fatty acids and vitamins that dissolve in organic solvents. Almost half of the entire mass of the brain belongs to lipids. In the composition of other tissues and organs, their number is also large. In the layers of subcutaneous fat can be up to 90% of all lipids.
The main types of lipid compounds
The biochemistry of fatty organic substances and their structure predetermine class differences. The table allows you to visually demonstrate what lipids are.
Each fat-containing substance belongs to one of two categories of lipids:
- saponifiable;
- unsaponifiable.
If salts of high fat acids have been formed by hydrolysis using alkali, saponification may occur. In this case, potassium and sodium salts are called soaps. Saponifiable substances are the largest group of lipids.
In turn, the group of saponifiable elements can be conditionally divided into two groups:
- simple (consisting only of oxygen, carbon dioxide and hydrogen atoms);
- complex (they are simple compounds in combination with phosphorus bases, glycerol residues or two-volume unsaturated sphingosine).
Simple lipids
Biochemistry classifies various fatty acids and alcohol esters as simple lipids. Among the latter substances, the most common are cholesterol (the so-called cyclic alcohol), glycerol and oleic alcohol.
One of the esters of glycerol can be called triaciglycerol, which consists of several molecules of high fat acids. In fact, simple compounds are part of the apodocytes of adipose tissues. It should also be noted that ester contacts with fatty acids can occur at three points at once, since glycerol is a trihydric alcohol. In this case, compounds formed from the above-mentioned bond arise:
- triacylglycerides;
- diacylglycerides;
- monoacylglycerides.
The predominant part of these neutral-type fats is present in the body of warm-blooded animals. Their structure contains most of the residues of palmitic, stearic acids of high fat content. In addition, neutral fats in some tissues can differ significantly in content from fats in other organs within the same organism. For example, human subcutaneous tissue is enriched with such acids by an order of magnitude higher than the liver, which consists of unsaturated fats.
Neutral Fats
Both types of acids, regardless of saturation, belong to the type of aliphatic carboxylic acids. Biochemistry makes it possible to understand how important these substances are for lipids by comparing micronutrients with building blocks. Thanks to them, each lipid is built.
If we talk about the first type, about saturated acids, then in the human body you can most often find palmitic and stearic acids. Much less often, lignocerine is involved in biochemical processes, the structure of which is more complex (24 carbon atoms). At the same time, saturated acids, having less than 10 atoms in their composition, are practically absent in animal lipids.
The most common atomic set of unsaturated acids are compounds consisting of 18 carbon atoms. The following types of unsaturated acids are considered indispensable, having from 1 to 4 double bonds: 
- oleic;
- linoleic;
- linolenic;
- arachidonic.
Prostaglandids and waxes
To a greater or lesser extent, they all possess in the body of mammals. Derivatives of unsaturated acids, which are prostaglandids, are of great importance. Synthesized by all cells and tissues, except for erythrocytes, they have a tremendous effect on the functioning of the main structures and processes of the human body:
- circulatory system and heart;
- metabolism and electrolyte exchange;
- central and peripheral nervous systems;
- digestive organs;
- reproductive function.
In a separate group are esters of complex acids and alcohols with one or two atoms in the chain - waxes. The total number of carbon particles in them can reach 22. Due to the solid texture, these substances are perceived by lipids as protectors. Among the natural waxes synthesized by organisms, the most common are beeswax, lanolin and an element that covers the surface of the leaves.
Complex lipids
Lipid classes are represented by groups of complex compounds. Biochemistry includes:
- phospholipids;
- glycolipids;
- sulfolipids.
Phospholipids are biological constructs with a complex structure. They necessarily include phosphorus, nitrogenous compounds, alcohols and much more. For the body, they play a significant role, being a fundamental component of the construction process of biological membranes. Phospholipids are present in the heart, liver, and brain.
The subclass of complex lipids also includes glycolipids - these are compounds that contain sphingosine alcohol, and hence carbohydrates. More than any other tissue in the body, nerve sheaths are rich in glycolipids.
A variety of glycolipids containing sulfuric acid residues are considered sulfolipids. Meanwhile, 
the classification of lipids always implies the allocation of these substances to a separate group. The main difference between the two complex compounds lies in the features of their structure. In place of the galactose of the third carbon atom of the glycolipid, there is a sulfuric acid residue.
Group of unsaponifiable lipids
Unlike the group of saponifiable lipids, which is impressive in terms of the number of varieties, unsaponifiable lipids completely release fatty acids and do not undergo hydrolysis by alkaline action. These substances are of two types:
- higher alcohols;
- higher hydrocarbons.
The first category includes vitamins that differ in fat-soluble qualities - A, E, D. The most famous representative of the second type of sterols - higher alcohols - is cholesterol. Scientists managed to isolate the element from gallstones by isolating monohydric alcohol several centuries ago.
Cholesterol cannot be found in plants, while in mammals it is present in absolutely all cells. Its presence is an important condition for the full functioning of the digestive, hormonal and genitourinary systems.
When considering higher hydrocarbons, which are also unsaponifiables, it is important to refer to the definition given by biochemistry. These elements are scientifically the components produced by isoprene. The molecular structure of hydrocarbons is based on the combination of isoprene particles.
As a rule, these elements are present in plant cells of especially fragrant species. In addition, the well-known natural rubber - polyterpene - belongs to the group of unsaponifiable higher hydrocarbons.
Unsaponifiables are lipids that, when hydrolyzed, do not form carboxylic acids or their salts. The unsaponifiable lipid fraction contains two main types of substances: steroids and terpenes. The former predominate in lipids of animal origin, the latter in plant lipids. For example, essential oils of plants are rich in terpenes: geraniums, roses, lavender, etc., as well as the resin of coniferous trees.
3.3.1. Terpenes.
Under this name, hydrocarbons are combined, the carbon skeleton of which is built from two or more links. isoprene(2-methylbutadiene-1,3):
and their derivatives - alcohols, aldehydes and ketones.
The general formula of terpene hydrocarbons is (C 5 H 8) n. They can have a cyclic or acyclic structure and be both limiting and non-limiting.
The basis of many terpenes is squalene C 30 H 50:
Examples of substituted acyclic terpenes are alcohol geraniol:
and the product of its mild oxidation geranial:
Most cyclic terpenes are mono- and bicyclic. The most common of these are:
The functional derivative of menthane is menthol found in peppermint essential oil:
It has an antiseptic and soothing effect, and is also part of validol and ointments used for the common cold.
An example of an unsaturated monocyclic terpene is limonene:
It is found in lemon oil and turpentine.
When limonene is reduced, menthane is obtained, and as a result of acid hydrolysis, a dihydric alcohol turpin, which is used as an expectorant:
A special group of terpenes are carotenoids. Some of them are vitamins or their precursors. The best known member of this group is carotene, found in large quantities in carrots. Three of its isomers are known: -, - and -carotene. They are precursors of the A vitamins.
3.3.2. Steroids.
Steroids are widely distributed in nature and perform a variety of functions in biological systems. The basis of their structure is sterane, the parts of which are three cyclohexane rings (denoted A, B and C) and one cyclopentane (D):
The general structure of steroids can be represented as follows:
Typical fragments of steroids are methyl groups (С-18 and С-19), hydrocarbon radical R at С-17 and functional group X at С-3 (OH, OR, etc.).
Steroids in which the hydrocarbon radical at C-17 contains 8 carbon atoms are called sterols. The best known representative of sterols is cholesterol:
3.3.3. Low molecular weight lipid bioregulators.
3.3.3.1. Vitamins.
Vitamins are called low molecular weight organic compounds of various nature, necessary for the implementation of important biochemical and physiological processes. The human and animal body is not able to synthesize most vitamins, so it must receive them from the outside.
About 20 vitamins are known. They are divided into water soluble and fat-soluble.
Water-soluble vitamins include B vitamins (thiamine (B 1), riboflavin (B 2), cobalamin (B 12), etc.), C (ascorbic acid), PP (nicotinamide, nicotinic acid) and some others.
Fat-soluble vitamins are A (retinol), D (calciferol), E (tocopherol) and K (phylloquinone).
Vitamin formulas are presented in Appendix 3.
unsaponifiable lipids. Terpenes.
Unsaponifiable lipids are the second major class of lipids.
The substances of this class of lipids are united by the fact that they not hydrolyzed in alkaline or acidic environment.
Earlier we considered the class saponifiable lipids. Substances belonging to this class, unlike unsaponifiable lipids, subject to hydrolysis. As a result of hydrolysis, salts of higher carboxylic acids are formed from saponifiable lipids, i.e. soap. That's where the name comes from.
Unsaponifiable lipid fraction contains two main types of substances:
- Terpenes and
- Steroids.
The former predominate plant lipids, second lipids of animal origin. There is much in common between them - terpenes and steroids are built from the same isoprene pentagonal fragments, and their biosynthesis includes the same initial and intermediate substances.
Connections built from fragments isoprene, have a common name isoprenoids.
One of the most common isoprenoids natural rubber- represents isoprene polymer.
Terpenes
Under this name they unite a number of hydrocarbons and their oxygen-containing derivatives - alcohols, aldehydes, ketones, the carbon skeleton of which is built of two, three or more links isoprene.
On the right side of the figure, isoprene is depicted in a form where carbon atoms are not shown, but only the bonds between them are shown.
The hydrocarbons themselves are called terpene hydrocarbons, and their oxygen-containing derivatives (alcohols, aldehydes, ketones) - terpenoids.
The name "Terpenes" comes from lat. Oleum Terebinthinae - turpentine.
Rich in terpenoids essential oils of plants(geranium, rose, lavender, lemon, peppermint, etc.), resin of coniferous trees and rubber-bearing.
To terpenes include various vegetable pigments and fat-soluble vitamins.
Terpene type grouping ( isoprenoid chain) is included in the structure of many biologically active compounds.
In most terpenes isoprene fragments connected to each other in a head-to-tail manner, as shown in the example myrcene.
Terpene hydrocarbons and terpenoids.
The general formula for most terpene hydrocarbons is (C 5 H 8) n.
They can have an acyclic and cyclic (bi-, tri-, polycyclic) structure.
Taking into account the number of isoprene groups in the molecule, there are:
- monoterpenes(two isoprene groups);
- sesquiterpenes(three isoprene groups);
- diterpenes(four isoprene groups);
- triterpenes(six isoprene groups);
- tetraterpenes(eight isoprene groups).
Examples of terpenes
An example of acyclic terpenes is the previously mentioned myricene- monoterpene contained in the essential oils of hops and noble laurel.
Another example is the alcohol related to myricene.
geraniol, which is part of the essential oils of geranium and rose.
Upon mild oxidation, geraniol forms citral aldehyde a.
triterpene squalene C 30 H 50 is an intermediate in cholesterol biosynthesis.
In recent years, it has been found that citral and geraniol secreted in small amounts by worker bees when looking for food. The smell of these substances attracts other bees. Compounds of this kind are called pheromones. They are secreted by animals and in a certain way affect the behavior of other individuals of the same or close species.
Among terpenes most common mono- and bicyclic terpenes. Many of them are used in medicine or serve as initial products for the synthesis of drugs.
The saturated cyclic hydrocarbons corresponding to mono- and bicyclic terpenes are called mentane, carane, pian and bornan.
Examples of cyclic terpenes
Limonene- representative monocyclic terpenes. It is contained in lemon oil and turpentine. Limonene included in oil cumin.
The racemic form of limonene(dipentene) can be obtained by a diene fusion reaction from isoprene by heating.
dienes- unsaturated hydrocarbons containing 2 double bonds in the molecule ( C=C), for example butadiene.
- a reaction, as a result of which a new six-membered ring is formed from two reacting molecules (dienes and dienophiles).
The racemic form of limonene(dipentene) is a stereoisomer of limonene, which is its mirror opposite.
When restoring optically active limonene or dipentene is obtained menthan, and when they are completely hydrated in an acidic medium, a dihydric alcohol is formed turpin. Terpine in the form of a hydrate is used as an expectorant in chronic bronchitis.
3-substituted dipentenes(for example, cannabidiol) - psychoactive beginning hashish(marijuana).
Like limonene, it has menthan skeleton. It is found in peppermint essential oil. It has an antiseptic, sedative and analgesic (distracting) effect, is part of validol, as well as ointments used for the common cold.
alpha pinene- bicyclic monoterpene of the series pinana. Its levorotatory enantiomer is an important constituent turpentine obtained from coniferous trees.
Camphor, a bicyclic ketone, is a rare example of a compound in which the six-membered ring has a bath conformation.
Camphor has long been used in medicine as a stimulant of cardiac activity. Its dextrorotatory stereoisomer is isolated from camphor essential oil.
Carotenoids.
A special group of terpenes are carotenoids - plant pigments.
Some of them play a role vitamins or precursors of vitamins, and are also involved in photosynthesis. Majority carotenoids refers to tetraterpenes. Their molecules contain a significant number of conjugated double bonds, therefore they have yellow-red color. Natural carotenoids are characterized by a trans-configuration of double bonds.
Carotene is a yellow-red plant pigment found in large quantities in carrots, as well as tomatoes and butter. There are three known isomers, called alpha, beta and gamma carotenes, differing in the number of cycles and the position of double bonds. All of them are precursors of vitamins of group A.
The molecule is symmetrical and consists of two identical parts:
Consider the features of the chemical structure and biochemical functions of the most important representatives of unsaponifiable lipids - steroids and terpenes.
Steroids.
Steroids include an extensive class of natural substances, the molecules of which are based on a condensed backbone called sterane. Cholesterol is the most common among numerous biological compounds of a steroid nature.
Cholesterol- monohydric alcohol (cholesterol); it exhibits the properties of a secondary alcohol and an alkene. About 30% of cholesterol in the body is found in free form, the rest is in the composition of acylcholesterols, i.e. esters with higher carboxylic acids, both saturated (palmitic and stearic) and unsaturated (linoleic, arachidonic, etc.), i.e. in the form of acylcholesterols. The total cholesterol content in the human body is 210-250 g. It is found in large quantities in the brain and spinal cord, and is a component of biomembranes.
The most important biochemical function of cholesterol is due to the fact that it plays the role of an intermediate product in the synthesis of many steroid compounds: in the placenta, testes, corpus luteum and adrenal glands, cholesterol is converted into the hormone progesterone, which is the initial substrate of a complex chain of biosynthesis of steroid sex hormones and corticosteroids.
Other ways of using cholesterol in the body are associated with the formation of vitamin D and the bile acids necessary for digestion - cholic and 7-deoxycholic.
In the body, cholic acid, forming amides at the carbonyl group with glycine and taurine, is converted into glycinecholic and taurocholic acids.
The anions of these acids are effective surfactants. In the intestines, they are involved in the emulsification of fats and thus contribute to their absorption and digestion.
Bile acids are used as drugs to prevent the formation and dissolution of existing gallstones, which are made up of cholesterol and bilirubin.
The transport of lipids insoluble in body fluids, including cholesterol, is carried out as part of special particles - lipoproteins, which are complex complexes with proteins.
Several forms of lipoproteins have been found in the blood, which differ in density: chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL). Lipoproteins can be separated using ultracentrifugation.
Lipoproteins are spherical particles, the hydrophilic surface of which is a layer of oriented phospholipids and proteins, and the core is formed by hydrophobic molecules of triacylglycerols and cholesterol esters.
Triacylglycerols and cholesterol under the action of specific enzymes (lipoprotein lipase) are released from chylomicrons and then consumed by adipose tissue, liver, heart and other organs.
With some metabolic disorders or a high concentration of cholesterol in the blood, the concentration of VLDL and LDL increases, which leads to their deposition on the walls of blood vessels (atherosclerosis), including in the arteries of the heart muscle (ischemic heart disease and myocardial infarction).
Terpenes.
Terpenes are a series of biologically active hydrocarbons and their oxygen-containing derivatives, the carbon skeleton of which consists of several units of isoprene C 5 H 8 . Therefore, the general formula for most terpenes is (C 5 H 8) n. Terpenes can have an acyclic or cyclic (bi-, tri- and polycyclic) structure. Structures of terpenes with the general formula C 10 H 16 - myrcene and limonene:
The composition of essential oils includes derivatives of terpenes containing hydroxyl, aldehyde or keto groups - terpenoids. Among them, menthol is widely used (contained in mint oil, from which it got its name, from Latin menta - mint), linalool (a liquid with the smell of lily of the valley), citral, camphor.
Terpenes include resin acids, which have the general formula C 20 H 30 O 2 and make up 4/5 of the resin of coniferous plants (resin). During the processing of resin, a solid residue of resin acids is obtained - rosin, which serves as a raw material for many industries. In addition, terpene groups (isoprenoid chains) are included in the structure of many complex biologically active compounds, such as carotenoids, phytol, etc.
Phytol is not found in free form in nature, but is part of the molecules of chlorophyll, vitamins A and E and other biocompounds.
Rubber and gutta are polyterpenes in which isoprene residues are linked head-to-tail.
lipid catabolism
General characteristics of lipids, their classification. Biological functions of lipids.
Digestion, absorption and transport of food fats. Degradation of fats in cells.
General characteristics of lipids and their classification.
Lipids are substances of biological origin, highly soluble in organic solvents such as methanol, acetone, chloroform, benzene, etc., and insoluble or slightly soluble in water.
In relation to alkalis, lipids are divided into saponifiable and unsaponifiable.
Saponifiable lipids include compounds undergoing hydrolysis, i.e. carboxylic acid derivatives such as esters and lactones, amides and lactams.
Saponifiable lipids Examples
I. Esters
1. Fats (glycerin + 3 fatty acids)
2. Waxes (fatty alcohols + fatty acids)
3. Esters of sterols (sterol + fatty acid)
II. Phospholipids
1. Phosphatic acids
(glycerin + 2 fatty acids + phosphate)
2. Phosphatides
(glycerin + 2 fatty acids
Phosphate + amino alcohol)
3. Sphingophospholipids
(sphingosine + fatty kta +
phosphate + amino alcohol)
III. Sphingolipids
Unsaponifiable lipids
Unsaponifiable lipids do not contain ester bonds or amide bonds in their structure and therefore are not hydrolyzed, although they can react with alkali, showing acidic properties, for example, fatty acids, bile acids, etc. Therefore, lipids are also divided into neutral and acidic.
hydrocarbons
Isoprenoids
Structural element of isoprenoids
is isoprene
2.1. Linear isoprenoids
2.2. Steroids
2.2.1. Sterols
2.2.2. Steroid hormonesSex hormones and corticosteroids
2.3. Bile acids
Alcohols with a long aliphatic chain
carboxylic acids
4.1Fatty acids
4.2. Eicosanoids
In connection with the special importance of fats and carboxylic acids, we will consider them in more detail.
Fats.
fats Esters of glycerol and fatty acids are called. Compounds with one fatty acid residue belong to the group of monoacylglycerols. By subsequent esterification of these compounds, one can proceed to diacyl- and then to triacylglycerols. Since fat molecules do not carry a charge, this group of substances is called neutral fats. The three fatty acid residues can differ both in chain length and in the number of double bonds. Fats extracted from biological material are always a mixture of substances similar in properties, differing only in fatty acid residues. Dietary fats most often contain palmitic, stearic, oleic and linoleic acids. Unsaturated fatty acid residues are usually found in position 2 of glycerol. The more unsaturated acids in the composition of the fat, the lower the softening or solidification point they have. Liquid fats are often called oils, for example, sunflower fat - sunflower oil, cottonseed fat - cottonseed oil. The term "butter" is sometimes attributed to vegetable fats, such as cocoa butter, but it is solid.
Fatty acid
fatty acids are called carboxylic acids with a carbon chain of at least 4 carbon atoms. They are called fatty because they are found in fats. Free fatty acids are present in the body in small amounts, for example in the blood. They are mainly present in organisms of all kinds in the form of esters of various alcohols: higher aliphatic alcohols, glycerol, cholesterol, sphingosine, etc.
The following are the fatty acids found in plant and animal tissues.
Higher plants and animals contain mainly fatty acids with a long and unbranched chain of 16 and 18 carbon atoms, namely, palmitic and stearic. All long-chain natural fatty acids consist of an even number of carbon atoms, which is due to the biosynthesis of these compounds in the body from precursors.
Many fatty acids have one or more double bonds. The most common unsaturated acids are oleic and linoleic. Of the two possible cis- and trance-double bond configurations in natural lipids are present only cis- the form. Branched fatty acids are found only in bacteria. Abbreviated names are sometimes used to designate fatty acids, where the first number indicates the number of carbon atoms, the second number indicates the number of double bonds, and the subsequent ones indicate the position of these bonds. As usual, the numbering of carbon atoms begins with the carboxy group.
to essential fatty acids include those that are not synthesized in the body and must be supplied with food. We are talking about highly unsaturated acids, in particular arachidonic (20:4; 5,8,11,14), linoleic(18:2; 9.12) and linolenic(18:3; 9,12,15). Arachidonic acid is a precursor of zecosanoids (prostaglandins and leukotrienes) and therefore must be present in the diet. Linoleic and linolenic acids, which have a shorter carbon chain, can be converted to arachidonic acid by chain extension, and therefore are substitutes for it.
Eicosanoids
Eicosanoids are the products of oxidation of arachidonic acid in the body. They are divided into leukotrienes, prostaglandins and prostacyclins.
Leukotrienes do not have a cycle in their structure
Prostaglandins have one five-term cycle
Prostacyclins have a cyclopentatetrahydrofuran ring
Eicosanoids constitute a large group of mediators with a wide spectrum of biological activity. Eicosanoids are produced in almost all cells of the body.
They serve as secondary messengers of hydrophilic hormones, control the contraction of smooth muscle tissue of venous vessels, bronchi, uterus, take part in the release of products of intracellular synthesis, affect bone metabolism, peripheral nervous system, immune system, movement and aggregation of cells (leukocytes, platelets), are effective pain receptor ligands. Eicosanoids act as local bioregulators by binding to membrane receptors in close proximity to their site of synthesis. Acetylsalicylic acid and other antipyretic drugs are specific inhibitors of prostaglandin synthase.
Biological functions of lipids
Energy.
Lipids are the most important energy source of all nutrients. In quantitative terms, lipids are the main energy reserve of the body. Basically, fat is found in cells in the form of fat droplets, which serve as metabolic "fuel". Lipids are oxidized in mitochondria to water and carbon dioxide with the simultaneous formation of a large amount of ATP.
Structural.
A number of lipids take part in the formation of cell membranes. Typical membrane lipids are phospholipids, glycolipids and cholesterol. It should be noted that the membranes do not contain fats.
3 . insulating.
Fat deposits in the subcutaneous tissue and around various organs have high heat-insulating properties. As the main component of cell membranes, lipids isolate the cell from the environment and, due to their hydrophobic properties, ensure the formation of membrane potentials.
4. Special features:
Hormones. - male and female sex hormones, hormones of the adrenal cortex. - steroid compounds.
mediators. - substances that act on the synaptic receptors of membranes, resulting in transmembrane electron transfer - the occurrence of an electrical impulse.
Secondary messengers ( secondary signal carriers ) - "intracellular hormones" - prostaglandins and other eicosanoids.
anchor function. Some lipids hold proteins and other compounds on membranes.
Enzyme cofactors - retinal, vitamin K, ubiquinone.
Since some lipids are not synthesized in the human body, they must be supplied in the diet in the form of essential fatty acids and fat-soluble vitamins.
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