What are Lipids?

Lipids, besides carbohydrates, proteins and nucleic acids, area unit altogether|one amongst|one in every of} the four major categories of biologically essential organic molecules found in all living organisms; their amounts and quality in diet area unit able to influence cell, tissue and body physiology.
Unlike carbohydrates, proteins and nucleic acids they aren’t polymers however little molecules, with a molecular weights that vary between one hundred and 5000, and additionally vary significantly in polarity, as well as hydrophobic molecules, like triglycerides or steroid esters, et al. a lot of soluble like phospholipids or terribly short-chain fatty acids, the latter fully mixable with water and insoluble in non polar solvents.
The little or absent water-solubility of the many of them implies that they’re subject to special treatments in the slightest degree stages of their utilization, that’s within the course of digestion, absorption, transport, storage and use.

Classification of lipids

They may be classified supported their physical properties at temperature (solid or liquid, severally fats and oils), on polarity, or on their importance for humans, however, the desirable classification relies on their structure.

Based on the structure, they will be classified into 3 major teams.



  • Simple lipids
    They contain 2 sorts of structural moieties.
    They include:
    glyceryl esters that are esters of glycerine and fatty acids: e.g. triacylglycerols, mono- and diacylglycerols;
    cholesteryl esters that are esters of cholesterin and fatty acids;
    waxes that are esters of long-chain alcohols and fatty acids, thus together with esters of vitamins A and D;
    ceramides that are amides of fatty acids with long-chain di- or radical bases containing 12–22 carbon atoms within the carbon chain: e.g. sphingosine.


  • complicated lipids
    They contain over 2 sorts of structural moieties.
    They include:
    phospholipids that are glycerine esters of fatty acids;
    phosphoric acid, and alternative teams containing nitrogen;
    the phosphatidic acid that’s diacylglycerol esterified to phosphorous acid;
    phosphatidylcholine that’s phosphatidic acid connected to B conjointly referred to as lecithin;
    phosphatidyl animal oil during which over one glycerine molecule is esterified to phosphorous acid: e.g. cardiolipin and diphosphatidyl acylglycerol;
    glycoglycerolipids that are one,2-diacylglycerol joined by a glycosidic linkage through position sn-3 with a sugar moiety;
    gangliosides that are glycolipids that are structurally the same as ceramide polyhexoside associate degreed conjointly contain 1-3 sialic acid residues; most contain an amino sugar additionally to the opposite sugars;
    sphingolipids, derivatives of ceramides;
    sphingomyelin that’s ceramide phosphorylcholine;
    cerebroside: they’re ceramide monohexoside that’s ceramide connected to one sugar moiety at the terminal chemical group of the base);
    ceramide di- and polyhexoside that’s connected severally to an oligosaccharide or a tri- or oligosaccharide;
    cerebroside salt that’s ceramide monohexoside esterified to a salt cluster.


  • Derived lipids They occur intrinsically or a free from the opposite 2 major teams as a result of the chemical reaction that’s are the building blocks for easy and sophisticated lipids.
    They include:
    fatty acids and alcohols;
    fat-soluble vitamins A, D, E and K;

Classification custom-made from: Bloor W.R. Proc Soc Exp Biol MEd, 17, 138, 1920; Christie W.W. in “Lipid Analysis” Pergamon Press, Oxford, 1982; Pomeranz Y. and Meloan C.L. in “Food Analysis; Theory and Practice” fourth erectile dysfunction., AVI, Westport, Connecticut, 1994; Akoh C.C. and Min D.B. “Food lipids: chemistry, nutrition, and biotechnology” 3th erectile dysfunction. 2008.

Functions of lipids

They area unit keep in animal tissue (triglycerides) and are one among the key energy supply. Lipids area unit the simplest energy supply for humans since at a parity of weight they supply the key a part of calories: if carbohydrates, on average, provides four kcal/g, as proteins, lipids offer, on average, 9 kcal/g. Moreover, they will be gift in foods while not there are fiber or water (for polysaccharides two g water/g) permitting to contain a good amount of energy in a very very little weight.
Mostly of Nutrition Organizations suggest that lipids should contribute up to half-hour (with saturated fatty acids solely but 10%) of the whole daily energy intake.
Some lipids area unit essential nutrients like fat-soluble vitamins A, (necessary for vision) and D (necessary for metal metabolism), gift in some fats and oils of animal origin, fat-soluble vitamin (prevention of autoxidation of unsaturated lipids), gift in vegetable oils, and vitamin K (normal coagulation of blood) gift in inexperienced leaves, essential fatty acids, specially linoleic and α-linolenic acids, founders of the family of omega-6 fatty acid and polyunsaturated fatty acid fatty acids severally.
During growth they’re used as “bricks” for construction of biological membranes (phospholipids, cholesterin and glycolipids beside proteins), thus tributary to construction of that barrier that separates intracellular surroundings from animate thing one and, within cell, circumscribes organelles like mitochondria, dictyosome or nucleus, and whose integrity is that the basis of life itself; furthermore they’re conjointly necessary for maintenance, physiochemical properties and repairing of cell membranes themselves.
Many hormones area unit lipids: steroid hormones, like estrogens, androgens and corticosteroid, area unit shaped from cholesterin (essential conjointly throughout embryogenesis), prostaglandins, prostacyclin, leukotrienes, thromboxanes, and alternative compounds (all eicosanoids) from polyunsaturated fatty acid and omega-6 fatty acid unsaturated fatty acids with twenty carbon atoms.
On plasmatic cell membranes they will act as receptors, antigens and membrane anchors for proteins and might modify the structure, and so the practicality, of membrane enzymes.
Many lipids, like diacylglycerol, ceramides, sphingosine and platelet-activating issue act as regulators of intracellular processes.
There area unit fat deposits not accessed throughout a quick, classified as structural fat, the operate of that is to carry organs and nerves within the right position protective they against traumatic injuries and shock; fat pads on the palms and buttocks shield the bones from mechanical pressure.
A connective tissue layer of fat is a gift in humans: it insulates the body reducing the loss of body heat and tributary to take care of blood heat.
On cuticle, they’re concerned about maintaining water barrier.
They area unit electrical material of nerve fibre of neurons that are lined over and all over again by plasmatic membranes of Swann cells, in peripheral systema nervosum, and of oligodendrocytes in the central nervous system; these plasmatic membranes have a lipid content larger than that of the opposite cells. This compound protein coating is named medullary sheath.
On alimentary tract, they facilitate the method|biological process} process depressing stomachic secretion, deceleration stomachic remotion and stimulating biliary and duct gland flow.
Bile salts (by-products of cholesterol) area unit natural detergents synthesized within the liver and secreted into digestive juice. They solubilize phospholipids and cholesterin within the digestive juice, allowing the secretion of cholesterin into the internal organ (the excretion of each cholesterin and digestive juice salts is that the major method by that cholesterin is aloof from the body). digestive juice salts conjointly aid within the digestion and absorption of fat and soluble-fat vitamins in the gut.
In several animals, some lipids area unit secreted into external surroundings and act as pheromones that attract or repel alternative organisms.
They have an effect on the feel and flavour of food so its taste property. Food makers use fat for its textural properties, e.g. in food fat increase the tenderness of the merchandise. Chefs recognize that fat addiction increases the taste property of meal and increase satiation when a meal.

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                                 Blaise Pascal