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Lipids and Membranes Moshtaghi-Kashanian Pathological Biochemist Kerman University of Medical Sciences.

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Presentation on theme: "Lipids and Membranes Moshtaghi-Kashanian Pathological Biochemist Kerman University of Medical Sciences."— Presentation transcript:

1 Lipids and Membranes Moshtaghi-Kashanian Pathological Biochemist Kerman University of Medical Sciences

2 Lipids Lipids: a heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility propertiesLipids: a heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties They are insoluble in water, but soluble in aprotic organic solvents, including diethyl ether, chloroform, methylene chloride, and acetoneThey are insoluble in water, but soluble in aprotic organic solvents, including diethyl ether, chloroform, methylene chloride, and acetone Lipids includeLipids include triacylglycerols, phosphodiacylglycerols, sphingolipids, glycolipids, lipid-soluble vitamins, and prostaglandinstriacylglycerols, phosphodiacylglycerols, sphingolipids, glycolipids, lipid-soluble vitamins, and prostaglandins cholesterol, steroid hormones, and bile acidscholesterol, steroid hormones, and bile acids

3 Fatty Acids Fatty acid: a long, un-branched chain carboxylic acid, most commonly of 12 - 20 carbons, derived from hydrolysis of animal fats, vegetable oils, or phosphodiacylglycerols of biological membranesFatty acid: a long, un-branched chain carboxylic acid, most commonly of 12 - 20 carbons, derived from hydrolysis of animal fats, vegetable oils, or phosphodiacylglycerols of biological membranes In the shorthand notation for fatty acidsIn the shorthand notation for fatty acids the number of carbons and the number of double bonds in the chain are shown by two numbers, separated by a colonthe number of carbons and the number of double bonds in the chain are shown by two numbers, separated by a colon

4 Fatty Acids

5 Among the fatty acids most abundant in plants and animals Nearly all have an even number of carbon atoms, most between 12 and 20, in an un-branched chainNearly all have an even number of carbon atoms, most between 12 and 20, in an un-branched chain The three most abundant are palmitic (16:0), stearic acid (18:0), and oleic acid (18:1)The three most abundant are palmitic (16:0), stearic acid (18:0), and oleic acid (18:1) In most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rareIn most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare unsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting pointunsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting point

6 Triacylglycerols Triacylglycerol (triglyceride): an ester of glycerol with three fatty acidsTriacylglycerol (triglyceride): an ester of glycerol with three fatty acids natural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH, in a reaction called saponification (Latin, sapo, soapnatural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH, in a reaction called saponification (Latin, sapo, soap

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8 Soaps Soaps form water-insoluble salts when used in water containing Ca(II), Mg(II), and Fe(III) ions (hard water)Soaps form water-insoluble salts when used in water containing Ca(II), Mg(II), and Fe(III) ions (hard water)

9 Phosphoacylglycerols Phosphoacylglycerols (phosphoglycerides) are the second most abundant group of naturally occurring lipidsPhosphoacylglycerols (phosphoglycerides) are the second most abundant group of naturally occurring lipids found almost exclusively in plant and animal membranes, which typically consist of 40% -50% phosphoacylglycerols and 50% - 60% proteinsfound almost exclusively in plant and animal membranes, which typically consist of 40% -50% phosphoacylglycerols and 50% - 60% proteins the most abundant phosphoacylglycerols are derived from phosphatidic acid, a molecule in which glycerol is esterified with two molecules of fatty acid and one of phosphoric acidthe most abundant phosphoacylglycerols are derived from phosphatidic acid, a molecule in which glycerol is esterified with two molecules of fatty acid and one of phosphoric acid the three most abundant fatty acids in phosphatidic acids are palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1)the three most abundant fatty acids in phosphatidic acids are palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1)

10 Phosphoacylglycerols A phosphatidic acidA phosphatidic acid further esterification with a low-molecular weight alcohol gives a phosphoacylglycerolfurther esterification with a low-molecular weight alcohol gives a phosphoacylglycerol among the most common of these low-molecularamong the most common of these low-molecular

11 Phosphoacylglycerols

12 Phosphoacylglycerols

13 A lecithin A lecithin Phosphoacylglycerols

14 Waxe Esters of long-chain fatty acids and alcoholsEsters of long-chain fatty acids and alcohols from the Old English word weax = honeycomfrom the Old English word weax = honeycom

15 Sphingolipids

16 Glycolipids Glycolipid: a compound in which a carbohydrate is bound to an -OH of the lipid many glycolipids are derived from ceramidesGlycolipid: a compound in which a carbohydrate is bound to an -OH of the lipid many glycolipids are derived from ceramides

17 Steroids Steroids: a group of plant and animal lipids that have this tetracyclic ring structureSteroids: a group of plant and animal lipids that have this tetracyclic ring structure The features common to the ring system of most naturally occurring steroids are illustrated on the next screenThe features common to the ring system of most naturally occurring steroids are illustrated on the next screen

18 Steroids

19 Cholesterol

20 Androgens Androgens - male sex hormonesAndrogens - male sex hormones synthesized in the testessynthesized in the testes responsible for the development of male secondary sex characteristicsresponsible for the development of male secondary sex characteristics

21 Androgens

22 Estrogens Estrogens - female sex hormonesEstrogens - female sex hormones synthesized in the ovariessynthesized in the ovaries responsible for the development of female secondary sex characteristics and control of the menstrual cycleresponsible for the development of female secondary sex characteristics and control of the menstrual cycle

23 Estrogens

24 Biological Membranes In aqueous solution, phosphoglycerides spontaneously form into a lipid bilayer, with a back- to-back arrangement of lipid monolayersIn aqueous solution, phosphoglycerides spontaneously form into a lipid bilayer, with a back- to-back arrangement of lipid monolayers polar head are in contact with the aqueous environmentpolar head are in contact with the aqueous environment nonpolar tails are buried within the bilayernonpolar tails are buried within the bilayer the major force driving the formation of lipid bilayers is hydrophobic interactionthe major force driving the formation of lipid bilayers is hydrophobic interaction the arrangement of hydrocarbon tails in the interior can be rigid (if rich in saturated fatty acids) or fluid (if rich in unsaturated fatty acids)the arrangement of hydrocarbon tails in the interior can be rigid (if rich in saturated fatty acids) or fluid (if rich in unsaturated fatty acids)

25 Biological Membranes the presence of cholesterol increases rigiditythe presence of cholesterol increases rigidity with heat, membranes become more disordered; the transition temperature is higher for more rigid membranes; it is lower for less rigid membraneswith heat, membranes become more disordered; the transition temperature is higher for more rigid membranes; it is lower for less rigid membranes

26 Membrane Proteins Functions: transport substances across membranes, receptor sites, and sites of enzyme catalysisFunctions: transport substances across membranes, receptor sites, and sites of enzyme catalysis Peripheral proteinsPeripheral proteins bound by electrostatic interactionsbound by electrostatic interactions can be removed by raising the ionic strengthcan be removed by raising the ionic strength Integral proteinsIntegral proteins bound tightly to the interior of the membranebound tightly to the interior of the membrane removed by treatment with detergents or ultrasonificationremoved by treatment with detergents or ultrasonification removal generally denatures themremoval generally denatures them

27 Fluid Mosaic Model Fluid: there is lateral motion of components in the membrane;Fluid: there is lateral motion of components in the membrane; proteins, for example, “float” in the membrane and can move along its planeproteins, for example, “float” in the membrane and can move along its plane Mosaic:components in the membrane exist side-by-side as separate entitiesMosaic:components in the membrane exist side-by-side as separate entities the basic structure is that of a lipid bilayer with proteins, glycolipids, and steroids such as cholesterol embedded in itthe basic structure is that of a lipid bilayer with proteins, glycolipids, and steroids such as cholesterol embedded in it no complexes, as for example, lipid-protein complexes, are formedno complexes, as for example, lipid-protein complexes, are formed

28 Membrane Transport Passive transportPassive transport driven by a concentration gradientdriven by a concentration gradient simple diffusion: a molecule or ion moves through an opening created by a channel proteinsimple diffusion: a molecule or ion moves through an opening created by a channel protein facilitated diffusion: molecule or ion is carried across a membrane by a carrier proteinfacilitated diffusion: molecule or ion is carried across a membrane by a carrier protein Active transportActive transport a molecule or ion is moved against a concentration gradienta molecule or ion is moved against a concentration gradient see the Na+/K+ ion pumpsee the Na+/K+ ion pump

29 Membrane Receptors Membrane receptorsMembrane receptors generally oligomeric proteinsgenerally oligomeric proteins binding of a biologically active substance to a receptor initiates an action within the cellbinding of a biologically active substance to a receptor initiates an action within the cell

30 Lipid-Soluble Vitamins Vitamins are divided into two broad classes on the basis of their solubilityVitamins are divided into two broad classes on the basis of their solubility. Those that are water-soluble. Those that are water-soluble. Those that are lipid-soluble (and hence classified as lipids). Those that are lipid-soluble (and hence classified as lipids) The lipid-soluble vitamins include A, D, E, and K

31 Prostaglandins Prostaglandins: a family of compounds that have the 20-carbon skeleton of prostanoic acidProstaglandins: a family of compounds that have the 20-carbon skeleton of prostanoic acid

32 Prostaglandins Prostaglandins are not stored in tissues as such, but are synthesized from membrane- bound 20-carbon polyunsaturated fatty acids in response to specific physiological triggersProstaglandins are not stored in tissues as such, but are synthesized from membrane- bound 20-carbon polyunsaturated fatty acids in response to specific physiological triggers one such polyunsaturated fatty acid is arachidonic acidone such polyunsaturated fatty acid is arachidonic acid

33 Prostaglandins among those synthesized from arachidonic acid areamong those synthesized from arachidonic acid are

34 Prostaglandins Research on the involvement of PGs in reproductive physiology has produced several clinically useful derivativesResearch on the involvement of PGs in reproductive physiology has produced several clinically useful derivatives 15-Methyl-PGF2a is used as a therapeutic abortifacient15-Methyl-PGF2a is used as a therapeutic abortifacient

35 Prostaglandins the PGE1 analog, misoprostol, is used for prevention of ulceration associated with the use of aspirin-like non-steroidal antiinflammatory drugs (NSAIDs)the PGE1 analog, misoprostol, is used for prevention of ulceration associated with the use of aspirin-like non-steroidal antiinflammatory drugs (NSAIDs)

36 Leukotrienes Leukotrienes: derived from arachidonic acidLeukotrienes: derived from arachidonic acid found in white blood cells (leukocytes)found in white blood cells (leukocytes) an important property is constriction of smooth muscles, especially in the lungsan important property is constriction of smooth muscles, especially in the lungs

37 Thromboxanes derived from arachidonic acidderived from arachidonic acid contain a four-membered cyclic ether within a six-membered ring induce platelet aggregation and smooth muscle contractioncontain a four-membered cyclic ether within a six-membered ring induce platelet aggregation and smooth muscle contraction

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