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PHOSPHOLIPIDS. PHYSICOCHEMICAL PROPERTIES OF PHOSPHOLIPIDS
Tashmukhamedova Shohista Sabirovna
Uzbekistan National University, Doctor of Biological Sciences (B.F.D.), professor.
Nazokat Gulomova
Uzbekistan National University, master’s program in biotechnology specialist.
https://doi.org/10.5281/zenodo.14557842
Abstract.
The article discusses the composition and physical and chemical properties of
phospholipids and the study of the chemical composition of phospholipids. It also discusses
the development of methods for identifying and establishing the chemical composition of
phospholipids.
Key words:
Phospholipids, lipids, esters, lecithin, living cells, cell membranes,
amphiphilic substances, hydrophilic, liposomes, cholesterol.
Introduction.
There are several classes of membrane lipids. They differ from
triacylglycerols in that, along with hydrocarbon chains, they contain one or more highly polar
"heads". For this reason, membrane lipids are often also called polar lipids. Polar lipids,
represented by phospholipids, are present in the greatest quantity in membranes.
Phospholipids are derivatives of either the trihydric alcohol glycerol or the more
complex amino alcohol sphingosine. Phospholipids that are derivatives of glycerol are called
phosphoacylglycerols. These compounds consist of glycerol (as the basis of the entire
structure), two fatty acid residues, and a phosphorylated alcohol. In phosphoacylglycerols, the
hydroxyl groups at the C1 and C2 atoms in glycerol esterified with carboxyl groups of two
fatty acids. The third hydroxyl group of glycerol esterified with phosphoric acid. The resulting
compound is the simplest phosphoacylglycerol and is called diacylglycerol-3-phosphate or
phosphatidic acid. This compound is a key intermediate in the biosynthesis of other more
complex phospholipids. All major membrane phospholipids are formed by esterification of the
phosphate group of phosphatidic acid with the hydroxyl groups of alcohols such as serine,
ethanolamine, choline, glycerol, and inositol. Thus, the phospholipids include phosphatidic
acid,
phosphatidylserine,
phosphatidylethanolamine,
phosphatidylcholine,
phosphatidylglycerols, and phosphatidylinositol, respectively. The only membrane
phospholipid that is not a derivative of glycerol is sphingomyelin.
Discussion.
Phosphatidic acid and phosphatidylglycerols. The starting compound for all
phosphoacylglycerols ( phospho -lipids) is, as already mentioned, phosphatidic acid (Fig. 1).
In free form, this compound is found in extremely small quantities. On the other hand,
phosphatidic acid is the most important intermediate compound in the processes of bio -
synthesis triacylglycerols and many phospholipids.
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Fig. 1. Structural
formula of phosphatidic acid.
Extremely interesting phospholipids are the so-called cardiolipins, which are “double”
phosphatidylglycerols. lycerols (Fig. 2). The main feature of cardiolipins is that these
compounds are localized mainly in the inner membrane of mitochondria.
Fig. 2. Cardiolipin (“double” phosphoglyceride ) is found in large quantities in
mitochondrial membranes.
Cardiolipin is a phospholipid that is part of mitochondrial membranes. It is formed from
two molecules of phosphatidic acid that are connected to each other by a “bridge” represented
by a glycerol residue.
Phosphatidylcholine (lecithin
). Lecithins, like neutral fats, contain glycerol and fatty
acid residues, but they also contain phosphoric acid and a nitrogenous base, choline. Lecithins
are widely present in the cells of various tissues, and they perform both metabolic and
structural functions. Most of these phospholipids, as a rule, contain a saturated acyl radical in
position C1 and an unsaturated radical in position C2 of glycerol .
At pH 7.0, the phosphoric acid residue in lecithins, as well as in all other phospholipids,
carries a negative charge. In addition, at pH close to neutral, the nitrogenous bases in
phospholipids can carry one or more electrical charges. Thus, phospholipids contain two
different types of groupings: polar hydrophilic "heads" and non-polar hydrophobic tails. Such
compounds are called amphipathic substances.
Phosphatidylinositol. In addition to glycerol , two fatty acid residues and a phosphoric
acid residue, phosphatidylinositol also contains the hexatomic cyclic alcohol inositol . Inositol
in this compound is represented by one of its stereoisomers – myoinositol .
This compound has pronounced physiological effects.
Fig. 3. Structural formula of phosphatidylcholine.
Phosphatidylethanolamine ( cephalin ).
Cephalins differ from lecithins only in that
their nitrogenous base choline is represented by another nitrogenous base -
ethanolamine.
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Rice. 4. Structural formula of phosphatidylethanolamine.
phosphatidylinositol
itself,
its
phosphorylated
form,
represented
by
phosphatidylinositol-4,5 -diphosphate, is present in cells , which is also an important
component of cell membranes. Thus, phosphatidylinositol-4,5-diphosphate takes part in the
physiological regulation of secretion processes, carried out with the help of secretogenic
compounds that interact with the corresponding receptors on the basal side of exocrine cells.
For example, as a result of the binding of acetylcholine or cholecystokinin to their receptors
on the basal side of exocrine cells, activation of intracellular phosphatidylinositol -specific
phospholipase C occurs, which breaks down phosphatidylinositol -4,5-diphosphate with the
formation of inositol-1,4,5-triphosphate and diacylglycerol . The latter initiate the release of
Ca2+ from the endoplasmic reticulum into the cytosol (inositol-1,4,5-triphosphate) or activate
protein kinase C ( diacylglycerol ), which ensures the release of protein products from
exocrine cells. Thus , both of these compounds act as intracellular second messengers of signal
transduction.
Fig. 5. Structural formula of phosphatidylinositol
Conclusions.
1. Precipitation of phospholipids with acetone. Phospholipids, being
amphipathic compounds, are poorly soluble in many organic solvents, for example, in acetone.
2.Emulsification of phospholipids. Emulsification of phospholipids is due to their ability to
form micelles and other structures in an aqueous solution. 3. Precipitation of lecithin (
phosphatidylcholine ) with cadmium chloride. When cadmium chloride is added to an alcohol
solution of phosphatidylcholine, the latter falls out as a white flocculent precipitate, as a
complex compound of phospholipid with cadmium chloride is formed, in which there are 4
molecules of salt for every 3 molecules of phosphatidylcholine. This compound is poorly
soluble in water.
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