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Lipids

This document provides information about lipids and fatty acids. It begins with an outline of chapter topics on the chemistry and classification of lipids. It then defines lipids and lists their main functions in the body. Lipids are classified as simple, complex, or derived, and as saponifiable or non-saponifiable. Key reactions for lipids include hydrolysis. Fatty acids are classified based on saturation and chain length. Essential fatty acids, which must be obtained through diet, are discussed. Neutral fats are described as triacylglycerols composed of glycerol and fatty acids.

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LIPIDS In pursuit of quality education DR. USMAN SALEEM Pharm.D, M.Phil. Scholar, R.Ph, Lecturer Pharmaceutical Biochemistry Rashid Latif College of Pharmacy
CHAPTER OUTLINES  Chemistry of Fatty acids and Lipids  Classification  Saponifiable and non-saponifiable lipids  Simple, Complex and Derived lipids  Reactions of Fatty acids and other Lipids,  Essential fatty acids,  Biological and pharmaceutical importance of lipids.
1. Define and List the Functions of Lipids Learning Objective
DEFINITION  The lipids are a heterogeneous group of compounds related to fatty acids and include fats, oils, waxes and other related substances.  These are oily or greasy organic substances, relatively insoluble in water, and considerably soluble in organic solvents like ether, chloroform and benzene.  The term ‘lipid’ was first used by the German biochemist Bloor in 1943 for a major class of tissue components and foodstuffs.
FUNCTIONS OR BIOLOGICAL IMPORTANCE 1. Storage form of energy (triacylglycerol) 2. Structural components of biomembranes (phospholipids and cholesterol) 3. Metabolic regulators (steroid hormones and prostaglandins) 4. Act as surfactants, detergents and emulsifying agents (amphipathic lipids) 5. Act as electric insulators in neurons
FUNCTIONS OR BIOLOGICAL IMPORTANCE 6. Provide insulation against changes in external temperature (subcutaneous fat) 7. Give shape and contour to the body 8. Protect internal organs by providing a cushioning effect (pads of fat) 9. Help in absorption of fat soluble vitamins (A, D, E and K) 10. Improve taste and palatability of food.
2. Classify Lipids as Simple, Complex and Derived, and as Saponifiable or Nonsaponifiable. Learning Objective
CLASSIFICATION OF LIPIDS  Two commonly used classification systems exist for lipids:  A system based on chemical composition of lipids (Bloor’s Classification), and  A system based on particular chemical reaction (Saponification) that lipids undergo.
CLASSIFICATION OF LIPIDS  Bloor has proposed the following classification of lipids based on their chemical composition. 1. Simple lipids: These are esters of fatty acids with various alcohols. a) Neutral Fats (Triacylglycerol, TAG):  These are esters of fatty acids with trihydroxy alcohol, glycerol. Oils are fats in the liquid state. b) Waxes:  These are esters of fatty acids with higher molecular weight monohydric alcohols.
CLASSIFICATION OF LIPIDS 2. Compound lipids: These are esters of fatty acids with alcohol and possess additional group(s) also. a) Phospholipids:  These are lipids containing, in addition to fatty acids and glycerol, a phosphoric acid, a nitrogen base and other substituents. For example, in glycerophospholipids the alcohol is glycerol and in sphingophospholipids, the alcohol is sphingosine. b) Glycolipids:  These are lipids containing a fatty acid, sphingosine, and carbohydrate.
CLASSIFICATION OF LIPIDS 3. Derived Lipids: These are compounds obtained by hydrolysis of simple of compound lipids. These include fatty acids, alcohols, mono- and diglycerides, steroids, terpenes and carotenoids.  Glycerides and cholesterol esters, because of their uncharged nature, are also called neutral lipids.
CLASSIFICATION OF LIPIDS  Lipids are grouped into two main classes in the chemical reaction (saponification) classification system: 1) Saponifiable lipids 2) Nonsaponifiable lipids.  Saponification refers to the process in which esters are hydrolyzed under basic conditions.
CLASSIFICATION OF LIPIDS Saponifiable Lipids  Saponifiable lipids are esters that undergo hydrolysis in basic solution to yield two or more smaller product molecules.  Triglycerides, waxes, phospholipids, and sphingolipids are all belong to this class. Non-Saponifiable Lipids  Nonsaponifiable lipids are not esters and cannot be hydrolyzed into smaller components.  Steroids and prostaglandins belong to this class.
3. Describe chemistry and classification of fatty acids. Learning Objective
FATTY ACIDS  Fatty acids are long, unbranched hydrocarbon chains with a carboxylic acid group at one end.  It is represented by a chemical formula R-COOH, where R stands for hydrocarbon chain.  Fatty acids are amphipathic compounds because the carboxyl group is hydrophilic and the hydrocarbon tail is hydrophobic.  The carboxyl group can ionize as the carboxylate anion (–COO- ) under the proper conditions of physiological pH.
FIGURE: The molecular structure of fatty acid. A. Lauric acid and B. a simplified diagram of a fatty acid with a nonpolar tail and a polar head.
FATTY ACIDS • In aqueous solution, the ions of fatty acids associate to form spherical clusters, called micelles. • In micelles, the nonpolar chains extend toward the interior of the structure away from water, and the polar carboxylate groups face outward in contact with the water.
FATTY ACIDS  The fatty acids found in natural lipids have several characteristics in common: 1. They are usually straight-chain carboxylic acids (no branching). 2. The sizes of most common fatty acids range from 10 to 20 carbons. 3. Fatty acids usually have an even number of carbon atoms (including the carboxyl group carbon). 4. Fatty acids can be saturated (containing no double bonds between carbons) or unsaturated (containing one or more double bonds between carbons).
FATTY ACIDS 5. In terms of carbon chain length, fatty acids are characterized as:  Long-chain fatty acids (C12 to C26),  Medium chain fatty acids (C8 and C10), or  Short-chain fatty acids (C4 and C6). 6. Fatty acids are rarely found free in nature but rather occur as part of the structure of more complex lipid molecules.
CLASSIFICATION OF FATTY ACIDS  The hydrocarbon chain of a fatty acid may or may not contain carbon–carbon double bonds.  On the basis of this consideration, fatty acids are classified as: 1. Saturated fatty acids (SFAs), 2. Unsaturated Fatty Acids 3. Monounsaturated fatty acids (MUFAs), and 4. Polyunsaturated fatty acids (PUFAs).
CLASSIFICATION OF FATTY ACIDS 1. Saturated Fatty Acids  A saturated fatty acid is a fatty acid with a carbon chain in which all carbon– carbon bonds are single bonds.  Examples include:  Propionic acid  Palmitic acid  Stearic acid
CLASSIFICATION OF FATTY ACIDS 2. Unsaturated Fatty Acids  They are classified further according to degree of unsaturation. a) Monounsaturated Fatty Acids (MUFA’s) b) Polyunsaturated Fatty Acids (PUFA’s)
CLASSIFICATION OF FATTY ACIDS a) Monounsaturated Fatty Acids  A monounsaturated fatty acid is a fatty acid with a carbon chain in which one carbon–carbon double bond is present.  For example, Oleic acid is a monounsaturated fatty acid, that is found in nearly all fats.
CLASSIFICATION OF FATTY ACIDS b) Polyunsaturated Fatty Acids  A polyunsaturated fatty acid is a fatty acid with a carbon chain in which two or more carbon–carbon double bonds are present.  Up to six double bonds are found in biochemically important PUFAs; they include: • Dienoic acids series have two double bonds, e.g. linoleic acid • Trienoic acids series have three double bonds, e.g. linolenic acid • Tetraenoic acid series with four double bonds, e.g. arachidonic acid
NOMENCLATURE OF FATTY ACIDS  The systematic nomenclature of the fatty acids is based on the Genevan system.  According to this system, the fatty acid is named after the hydrocarbon with the same number of carbon atoms.  The suffix -oic is written in place of the final letter e in the name of the hydrocarbon. The names of saturated fatty acids end with the suffix –anoic e.g., Octadecanoic acid. The names of unsaturated fatty acids end with the suffix –enoic e.g., Octadecenoic acid (Oleic acid).
NOMENCLATURE OF FATTY ACIDS  The position of carbon atoms in the fatty acid chain is indicated either:  By numbering - in which case the carboxyl carbon is numbered as C1, the carbon adjacent to C1 as C2 and so on; or  By the use of Greek letters - in which case C2 is denoted as a-carbon, C3 as b-carbon and so on, while the terminal methyl (-CH3) carbon is known as w-carbon.
NOMENCLATURE OF FATTY ACIDS  The notation most commonly used for fatty acids indicates the: • Number of carbon atoms, and • Number of double bonds.  The notation 18:0 denotes an C18 fatty acid with no double bonds, while 18:1 signifies an C18 fatty acid with one double bond.
NOMENCLATURE OF FATTY ACIDS  To specify double-bond positioning within the carbon chain of an unsaturated fatty acid, the preceding notation is expanded by adding the Greek capital letter delta (D) followed by one or more superscript numbers.  The notation 18:3(D9,12,15) denotes a C18 PUFA with three double bonds at locations between carbons 9 and 10, 12 and 13, and 15 and 16.
SELECTED FATTY ACIDS OF BIOLOGICAL IMPORTANCE Saturated Fatty Acids Common Name Structural Notation Formula Common Sources Lauric Acid 12:0 CH3(CH2)10COOH Laurel oil, Spermaceti Myristic Acid 14:0 CH3(CH2)12COOH Butter and wool fat Palmitic Acid 16:0 CH3(CH2)14COOH Palm Oil Stearic Acid 18:0 CH3(CH2)16COOH Animal and plant fats Arachidic Acid 20:0 CH3(CH2)18COOH Peanut Oil
SELECTED FATTY ACIDS OF BIOLOGICAL IMPORTANCE Unsaturated Fatty Acids Common Name Structural Notation Formula Common Sources Oleic Acid 18:1 – D9 CH3(CH2)7CH=CH(CH2)7COOH Animal and plant fats Linoleic Acid 18:2 – D9,12 CH3(CH2)4CH=CH(CH2)CH=CH(CH2)7COOH Peanut & cottonseed Oil Linolenic Acid 18:3 – D9,12,15 CH3(CH2CH=CH)3(CH2)7COOH Linseed Oil Arachidonic Acid 20:4 – D5,8,11,14 CH3 (CH2)4(CH=CHCH2) 4(CH2)2COOH Animal fats
ISOMERISM IN FATTY ACIDS  The unsaturated fatty acids exhibit geometric (or cis-trans) isomerism at the double bonds.  In biochemically important MUFAs, the configuration about the double bond is nearly always cis rather than trans.  ‘Cis’ form is comparatively unstable and is more reactive.  For example, Oleic acid can exist in two forms: cis-oleic acid and trans-oleic acid which is also called elaidic acid.
ISOMERISM IN FATTY ACIDS
ISOMERISM IN FATTY ACIDS  ‘Cis’ configuration creates a rigid 30o bend, or kink, in the fatty acid chain that is not found in saturated fatty acids.  Such a bend affects the physical properties of a fatty acid.
ESSENTIAL FATTY ACIDS  Essential fatty acids are those polyunsaturated fatty acids that cannot be synthesized by our cells and we should obtain them from plants through diet.  Linoleic acid and linolenic acid are the only essential fatty acids for animals.  Other polyunsaturated fatty acids can be synthesized from these essential fatty acids.  For example, arachidonic acid can be synthesized only from linoleic acid.  Therefore, in deficiency of linoleic acid, arachidonic acid also becomes an essential fatty acids.
IMPORTANCE OF ESSENTIAL FATTY ACIDS  Linoleic acid is the starting material for the biosynthesis of arachidonic acid.  Arachidonic acid is the major starting material for eicosanoids, substances that help regulate blood pressure, clotting, and several other important body functions.  Linolenic acid is the starting material for the biosynthesis of two additional omega-3 fatty acids. Linolenic acid (18:3) → EPA (20:5) → DHA (22:6)
IMPORTANCE OF ESSENTIAL FATTY ACIDS  EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are important constituents of the communication membranes of the brain and are necessary for normal brain development.  EPA and DHA are also active in the retina of the eye.
NEUTRAL FATS (TRIACYLGLYCEROLS (TAG) OR TRIGLYCERIDES)  Triacylglycerol, also called triglycerides, are composed of three fatty acids bonded by an ester linkage to glycerol.
TYPES OF NEUTRAL FATS  Triacylglycerol are of two types: 1. Simple Triacylglycerol 2. Mixed Triacylglycerol  Naturally occurring simple triacylglycerols are rare.  Most biochemically important triacylglycerols are mixed triacylglycerols.
TYPES OF NEUTRAL FATS 1. Simple Triacylglycerol  These types of triacylglycerol contain the same types of fatty acids at the three carbon atoms.  The triacylglycerol produced from glycerol and three molecules of stearic acid is an example of a simple triacylglycerol.
ACTIVITY Draw the structural formula of the triacylglycerol produced from the reaction between glycerol and three molecules of Lauric acid.
TYPES OF NEUTRAL FATS 2. Mixed Triacylglycerol  These types of triacylglycerol contain more than one kind of fatty acid molecule.  Figure shows the structure of a mixed triacylglycerol in which one fatty acid is saturated, another monounsaturated, and the third polyunsaturated.
FATS AND OILS FATS  A fat is a triacylglycerol mixture that is a solid or a semi-solid at room temperature (25◦C).  Generally, fats are obtained from animal sources.  All fats, even highly saturated fats, contain some unsaturated fatty acids. OILS  An oil is a triacylglycerol mixture that is a liquid at room temperature (25 ◦C).  Generally, oils are obtained from plant sources.  All oils, even polyunsaturated oils, contain some saturated fatty acids.
5. Write key reactions for fats and oils. Learning Objective
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS 1. Hydrolysis  Fats can be hydrolyzed in the presence of an acid or a base.  Under acidic conditions, the hydrolysis products are glycerol and fatty acids.  Under basic conditions, the hydrolysis products are glycerol and fatty acid salts.  Within the human body, triacylglycerol hydrolysis occurs during the process of digestion by the specific fat-splitting enzymes called lipases, for example pancreatic lipase.
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS  Triacylglycerol is sequentially hydrolyzed to diacylglycerol and monoacylglycerol and finally glycerol plus 3 fatty acids.
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS 2. Saponification  Hydrolysis of a fat by an alkali such as sodium hydroxide or potassium hydroxide is called saponification.  For fats and oils, the products of saponification are glycerol and fatty acid salts.
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS 3. Hydrogenation  Hydrogenation involves hydrogen addition across carbon–carbon double bonds, which increases the degree of saturation as some double bonds are converted to single bonds.
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS  Many food products are produced via partial hydrogenation.  In partial hydrogenation some, but not all, of the double bonds present are converted into single bonds.  In this manner, liquids (usually plant oils) are converted into semi-solid materials.  This is the basis of Banaspati (Dalda) manufacture, where inedible and cheap oils like cotton seed oil are hydrogenated and converted to edible solid fat.
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS 4. Oxidation  Fats very rich in unsaturated fatty acids such as linseed oil undergo spontaneous oxidation at the double bond forming aldehyde and carboxylic acid products.  The short-chain aldehydes and carboxylic acids so produced often have objectionable odors, and fats and oils containing them are said to have become rancid.  To avoid this unwanted oxidation process, commercially prepared foods containing fats and oils always contain antioxidants.  Two naturally occurring antioxidants are vitamin C and vitamin E.
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS 5. Rancidity  The unpleasant taste and odor developed by most natural fats on aging is refereed to as rancidity.  Hydrolytic rancidity is due to partial hydrolysis of the fats due to traces of hydrolytic enzymes present in naturally occurring fats and oils.  Oxidative rancidity is the result of partial oxidation of unsaturated fatty acids with resultant formation of epoxides and peroxides of small molecular weight fatty acids by peroxides and free radicals.  The same process, if it occurs in vivo will affect the integrity of biomembranes, leading to cell death.
CHEMICAL REACTIONS OF TRIACYLGLYCEROLS  Many natural vegetable fats and oils may contain antioxidants like vitamin E which prevent onset of rancidity. Therefore, vegetable fats can be preserved for a longer time than animal fats.
CHARACTERIZATION OF FAT OR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS)  Fat constants or numbers are test necessary to:  Identify a pure fat  Assess the degree of adulteration  Determine the proportions of different types of fat in a mixture
CHARACTERIZATION OF FAT OR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 1. Saponification Number  Saponification number is defined as the number of milligrams of potassium hydroxide required to saponify one gram of fat.  It is inversely proportional to the molecular weight of fat.  This value is high in fats containing a short chain fatty acids.  For example, the saponification number of:  Butter = 220  Coconut oil = 260
CHARACTERIZATION OF FAT OR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 2. Acid Number  Acid number is the number of milligrams of KOH required to neutralize the free fatty acids present in one gram of fat.  It is used for the detection of hydrolytic rancidity because it measures the amount of free fatty acids present.  Acid number is directly proportional to the rancidity.
CHARACTERIZATION OF FAT OR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 3. Iodine Number  Iodine number is the number of grams of iodine absorbed by 100 grams of fat.  It is an index of the degree of unsaturation and is directly proportional to the content of unsaturated fatty acids.  Higher the iodine number, higher is the degree of unsaturation, e.g.  Butter = 28,  Sunflower oil = 130
CHARACTERIZATION OF FAT OR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 4. Acetyl Number  Acetyl number is the number of milligrams of KOH needed to neutralize the acetic acid liberated from hydrolysis of 1gm of acetylated fat.  The natural fat that contains fatty acids with free hydroxyl groups are converted into acetylated fat by reaction with acetic anhydride.  Thus, acetyl number is a measure of the amount of hydroxy fatty acids in fat content.
CHARACTERIZATION OF FAT OR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS)  Castor oil because of its high content of ricinoleic acid has a high acetyl number.  Acetyl number of some oils are:  Castor oil = 146-150  Cod Liver oil = 1.1  Cotton Seed oil = 21-25  Olive oil = 10.5
CHARACTERIZATION OF FAT OR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 4. Reichert Meissl Number  Reichert-Meissl number is the numbers of milliliters of 0.1N alkali required to neutralize the volatile acid obtained from 5g of a fat, which has been saponified then acidified to liberate the fatty acids and then steam distilled.  It is also known as volatile fatty acid number.  Reichert Meissl value for:  Butter = 26  Coconut oil = 7.
CHARACTERIZATION OF FAT OR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS)  It is less than one for other edible oils.  The admixture of certain fats may be used to prepare synthetic butter which may simulate butter in most of the constants except RM value and hence, can be detected.
WAXES  Waxes are esters of long-chain saturated and unsaturated fatty acids with long-chain monohydroxy alcohols.  The fatty acids range in between C14 and C36 and the alcohols range from C16 to C36.
WAXES  Beeswax, for example, contains a wax (1-triacontyl palmitate) with the following structure:
WAXES  Waxes generally have higher melting points than fats (60 to 100°C) and are harder.  Animals and plants often use them for protective coatings.  In plants, waxes are secreted as surface coating to prevent excessive evaporation and to protect against parasites.  In animals, waxes are secreted by cutaneous glands as a protective coating to keep the skin pliable, lubricated and water-proof.
WAXES  Important waxes include carnauba wax (from a Brazilian palm tree), lanolin (from lamb’s wool), beeswax, and spermaceti (from whales).  These substances are used to make cosmetics, polishes, candles, and ointments.  Sperm whale wax (spermaceti) and beeswax are composed mainly of palmitic acid esterified with either hexacosanol, CH3(CH2)24.CH2OH or triacontanol, CH3(CH2)28.CH2OH.
6. What are Complex or Compound Lipids? Learning Objective
7. Describe chemistry and classification of Phospholipids. Learning Objective
PHOSPHOLIPIDS  Phospholipids are the most abundant membrane lipids.  They serve primarily as structural components of membranes and are never stored in large quantities.  They differ from triglycerides in possessing usually one hydrophilic polar “head” group and usually two hydrophobic nonpolar “tails”.  For this reason, they are often called polar lipids.
 There are two classes of phospholipids: A. Glycerophospholipids or Phosphoglycerides B. Sphingophospholipids or Phosphosphingosides
PHOSPHOLIPIDS A. Glycerophospholipids  In these compounds, glycerol is linked by ester bonds to two fatty acids and one phosphate, which in turn is linked by ester bond to another alcohol (usually amino alcohol).  Phosphoglycerides serve as a major component of cell membranes.
PHOSPHOLIPIDS
PHOSPHOLIPIDS  The alcohol attached to the phosphate group in a phosphoglyceride is usually one of three amino alcohols: choline, ethanolamine, or serine.
PHOSPHOLIPIDS  Phosphoglycerides containing these three amino alcohols are respectively known as phosphatidylcholines, phosphatidylethanolamines, and phosphatidylserines.  Phosphatidylcholines are also known as lecithins.  Phosphatidylethanolamines and phosphatidylserines are also known as cephalins.  Another important group of glycerophospholipids is the phosphatidylinositols (PI), in which the alcohol is inositol.  In phosphatidylinositol, inositol is present as the stereoisomer myoinositol.
PHOSPHOLIPIDS a) Lecithins  Various oil seeds like soybean and the yeasts are important sources from plant world.  In animals, they are distributed in liver, brain, nerve tissues, sperm and egg yolk.  Dipalmitoyl lecithin is an important phosphatidylcholine found in lungs, secreted by pulmonary type II epithelial cell.  It acts as a lung surfactant and is necessary for normal lung function.  It reduces surface tension in the alveoli, thereby prevents alveolar collapse.
ACTIVITY  Draw the structural formula for the glycerophospholipid that produces, upon hydrolysis, equimolar amounts of glycerol, phosphoric acid, and choline, and twice that molar amount of palmitic acid, the 16:0 fatty acid.
PHOSPHOLIPIDS b) Cephalins  Phosphoglycerides in which the alcohol is ethanolamine or serine, rather than choline, are called cephalins.  These compounds are found in heart and liver tissue and in high concentrations in the brain.  They are also found in blood platelets, where they play an important role in the blood-clotting process.
PHOSPHOLIPIDS c) Phosphatidylinositol  Another important group of glycerophospholipids is the phosphatidylinositols (PI), in which the alcohol is inositol.  In phosphatidylinositol, inositol is present as the stereoisomer myoinositol.  Phosphatidylinositols in their higher phosphorylated form, such as phosphatidylinositol 4,5-bisphosphates (PIP2), serve as signaling molecules in chemical communication.
PHOSPHOLIPIDS  Two less common phosphoglycerides are: i. Plasmalogens ii. Cardiolipins
PHOSPHOLIPIDS d) Plasmalogens  Plasmalogens constitute about 10% of the phospholipids of the brain and muscle.  Structurally, these resemble lecithins and cephalins but have one of the fatty acids replaced by an unsaturated ether.  These are found in myelin and in cardiac muscle.  Plasmalogen is a platelet activating factor (PAF) and involved in platelet aggregation and degranulation.
PHOSPHOLIPIDS e) Cardiolipin  Cardiolipins are present in abundance in inner mitochondrial membranes, and their complete hydrolysis yields:  Four molecules of fatty acids  Three glycerol molecules  Two phosphate ions
PHOSPHOLIPIDS B. Phosphosphingosides  A phosphosphingosides is a lipid that contains one fatty acid and one phosphate group attached to a sphingosine molecule and an alcohol attached to the phosphate group.  All phospholipids derived from sphingosine have: 1. the fatty acid attached to the sphingosine —NH2 group via an amide linkage, 2. the phosphate group attached to the sphingosine terminal —OH group via an ester linkage, and 3. an additional alcohol esterified to the phosphate group.
PHOSPHOLIPIDS B. Phosphosphingosides  Sphingophospholipids in which the alcohol esterified to the phosphate group is choline are called sphingomyelins.  Sphingomyelins are found in all cell membranes and are important structural components of the myelin sheath.
GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS  A glycolipid is a complex lipid that contains both a fatty acid and a carbohydrate component attached to a sphingosine molecule.
GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS a. Cerebrosides  Cerebrosides are the simplest sphingoglycolipid that contain a single monosaccharide unit—either glucose or galactose and named as glucocerebrosides and galactocerebrosides.  Cerebrosides are present in high concentrations in the white matter of the brain as well as in myelin sheathes.
GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS a. Cerebrosides  Four types of cerebrosides have been characterized, depending upon the type of fatty acids they contain.  Kerasin−contains saturated C 24 lignoceric acid.  Phrenosin (cerebron)−contains a 2-hydroxy derivative of lignoceric acid called cerebronic acid.  Nervon−contains an unsaturated homologue of lignoceric acid called nervonic acid,  Oxynervon−contains a 2-hydroxy derivative of nervonic acid called oxynervonic acid.
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GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS b. Gangliosides  Gangliosides are more complex glycolipids that contain a branched chain of up to seven monosaccharide residues.  Gangliosides also generally contain sialic acid, which is usually N- acetylneuraminic acid (NANA) attached to ceramide (N-acylsphingosine).  These substances occur in the gray matter of the brain as well as in the myelin sheath.
GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS b) Gangliosides  Several types of gangliosides such as GM1, GM2, GM3, etc. have been isolated from brain and other tissues.  The simplest ganglioside found in tissues is GM3.
GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS
7. What are Derived Lipids? Learning Objective
DERIVED LIPIDS  Unsponifiable compounds obtained by hydrolysis of simple or compound lipids are called derived lipids.  Derived lipids include prostaglandins and related compounds, fat soluble vitamins and steroids.
EICOSANOIDS  Eicosanoids are the compounds derived from arachidonic acid that function as messenger lipids.  There are three principal types of eicosanoids: 1. Prostaglandins 2. Leukotrienes 3. Thromboxanes
PROSTAGLANDINS  Prostaglandins were first detected in the seminal fluid, which is produced by the prostate gland and hence the name.  Chemically, they are considered to be derived from 20C cyclic saturated fatty acid, prostanoic acid.
PROSTAGLANDINS  Some of the functions of prostaglandins are: • Control of blood pressure • Stimulation of smooth muscle contraction • Induction of inflammation • Inhibition of platelet aggregation
LEUKOTRIENES  Leukotrienes are compounds that, like prostaglandins, are derived from arachidonic acid.  They are found in leukocytes (white blood cells) and have three conjugated double bonds; these two facts account for the name.
LEUKOTRIENES  Various inflammatory and hypersensitivity (allergy) responses are associated with elevated levels of leukotrienes.  Leukotriene C produce long-lasting muscle contractions, especially in the lungs, and can cause asthma-like attacks.  One way to counteract the effects of leukotrienes is to inhibit their uptake by leukotriene receptors (LTRs) in the body.  A new antagonist of LTRs, zafirlukast, is used to treat and control chronic asthma.
THROMBOXANES  Thromboxanes contain cyclic ethers as part of their structures.  These compounds were called thromboxanes because they were first isolated from thrombocytes.  The most widely studied member of the group, thromboxane A2 (TxA2), is known to induce platelet aggregation and smooth-muscle contraction.
STEROIDS  Steroids are a group of compounds that contain cyclopentanoperhydrophenanthrene ring structure.  This ring is present in steroid hormones, bile acids, cholesterol etc.
CHOLESTEROL  Cholesterol is a C27 steroid molecule that is a component of cell membranes and a precursor for other steroid-based lipids.  Cholesterol is amphipathic, with a:  Polar head, the hydroxyl group at C3 and a  Nonpolar the steroid nucleus and hydrocarbon side chain at C17.  Most of the cholesterol in the body exists as a cholesterol ester, with a fatty acid attached to the hydroxyl group at C3.
CHOLESTEROL
CHOLESTEROL  Cholesterol is widely distributed in all the cells of the body but particularly in nervous tissue.  It is synthesized in our body as well as supplied in the diet.  Cholesterol serves as the precursor for a variety of biologically important products, including: steroid hormones, bile acids and fat soluble vitamins.  It is a major structural constituent of the cell membranes and plasma lipoproteins.
BILE ACIDS  A bile acid is a cholesterol derivative that functions as a lipid-emulsifying agent in the aqueous environment of the digestive tract.  Approximately one-third of the daily production of cholesterol by the liver is converted to bile acids.
BILE ACIDS  Obtained by oxidation of cholesterol, bile acids differ structurally from cholesterol in three respects: 1. They are tri- or dihydroxy cholesterol derivatives. 2. The carbon 17 side chain of cholesterol has been oxidized to a carboxylic acid. 3. The oxidized acid side chain is bonded to an amino acid (either glycine or taurine) through an amide linkage.  The presence of this amino acid attachment increases both the polarity of the bile acid and its water solubility.
BILE ACIDS  The three major types of bile acids produced from cholesterol by biochemical oxidation are:  Cholic acid,  7-deoxycholic acid, and  12-deoxycholic acid.

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Lipids

  • 1.
    LIPIDS In pursuit ofquality education DR. USMAN SALEEM Pharm.D, M.Phil. Scholar, R.Ph, Lecturer Pharmaceutical Biochemistry Rashid Latif College of Pharmacy
  • 2.
    CHAPTER OUTLINES  Chemistryof Fatty acids and Lipids  Classification  Saponifiable and non-saponifiable lipids  Simple, Complex and Derived lipids  Reactions of Fatty acids and other Lipids,  Essential fatty acids,  Biological and pharmaceutical importance of lipids.
  • 3.
    1. Define andList the Functions of Lipids Learning Objective
  • 4.
    DEFINITION  The lipidsare a heterogeneous group of compounds related to fatty acids and include fats, oils, waxes and other related substances.  These are oily or greasy organic substances, relatively insoluble in water, and considerably soluble in organic solvents like ether, chloroform and benzene.  The term ‘lipid’ was first used by the German biochemist Bloor in 1943 for a major class of tissue components and foodstuffs.
  • 5.
    FUNCTIONS OR BIOLOGICALIMPORTANCE 1. Storage form of energy (triacylglycerol) 2. Structural components of biomembranes (phospholipids and cholesterol) 3. Metabolic regulators (steroid hormones and prostaglandins) 4. Act as surfactants, detergents and emulsifying agents (amphipathic lipids) 5. Act as electric insulators in neurons
  • 6.
    FUNCTIONS OR BIOLOGICALIMPORTANCE 6. Provide insulation against changes in external temperature (subcutaneous fat) 7. Give shape and contour to the body 8. Protect internal organs by providing a cushioning effect (pads of fat) 9. Help in absorption of fat soluble vitamins (A, D, E and K) 10. Improve taste and palatability of food.
  • 7.
    2. Classify Lipidsas Simple, Complex and Derived, and as Saponifiable or Nonsaponifiable. Learning Objective
  • 8.
    CLASSIFICATION OF LIPIDS Two commonly used classification systems exist for lipids:  A system based on chemical composition of lipids (Bloor’s Classification), and  A system based on particular chemical reaction (Saponification) that lipids undergo.
  • 9.
    CLASSIFICATION OF LIPIDS Bloor has proposed the following classification of lipids based on their chemical composition. 1. Simple lipids: These are esters of fatty acids with various alcohols. a) Neutral Fats (Triacylglycerol, TAG):  These are esters of fatty acids with trihydroxy alcohol, glycerol. Oils are fats in the liquid state. b) Waxes:  These are esters of fatty acids with higher molecular weight monohydric alcohols.
  • 10.
    CLASSIFICATION OF LIPIDS 2.Compound lipids: These are esters of fatty acids with alcohol and possess additional group(s) also. a) Phospholipids:  These are lipids containing, in addition to fatty acids and glycerol, a phosphoric acid, a nitrogen base and other substituents. For example, in glycerophospholipids the alcohol is glycerol and in sphingophospholipids, the alcohol is sphingosine. b) Glycolipids:  These are lipids containing a fatty acid, sphingosine, and carbohydrate.
  • 11.
    CLASSIFICATION OF LIPIDS 3.Derived Lipids: These are compounds obtained by hydrolysis of simple of compound lipids. These include fatty acids, alcohols, mono- and diglycerides, steroids, terpenes and carotenoids.  Glycerides and cholesterol esters, because of their uncharged nature, are also called neutral lipids.
  • 12.
    CLASSIFICATION OF LIPIDS Lipids are grouped into two main classes in the chemical reaction (saponification) classification system: 1) Saponifiable lipids 2) Nonsaponifiable lipids.  Saponification refers to the process in which esters are hydrolyzed under basic conditions.
  • 13.
    CLASSIFICATION OF LIPIDS SaponifiableLipids  Saponifiable lipids are esters that undergo hydrolysis in basic solution to yield two or more smaller product molecules.  Triglycerides, waxes, phospholipids, and sphingolipids are all belong to this class. Non-Saponifiable Lipids  Nonsaponifiable lipids are not esters and cannot be hydrolyzed into smaller components.  Steroids and prostaglandins belong to this class.
  • 15.
    3. Describe chemistryand classification of fatty acids. Learning Objective
  • 16.
    FATTY ACIDS  Fattyacids are long, unbranched hydrocarbon chains with a carboxylic acid group at one end.  It is represented by a chemical formula R-COOH, where R stands for hydrocarbon chain.  Fatty acids are amphipathic compounds because the carboxyl group is hydrophilic and the hydrocarbon tail is hydrophobic.  The carboxyl group can ionize as the carboxylate anion (–COO- ) under the proper conditions of physiological pH.
  • 17.
    FIGURE: The molecularstructure of fatty acid. A. Lauric acid and B. a simplified diagram of a fatty acid with a nonpolar tail and a polar head.
  • 18.
    FATTY ACIDS • Inaqueous solution, the ions of fatty acids associate to form spherical clusters, called micelles. • In micelles, the nonpolar chains extend toward the interior of the structure away from water, and the polar carboxylate groups face outward in contact with the water.
  • 19.
    FATTY ACIDS  Thefatty acids found in natural lipids have several characteristics in common: 1. They are usually straight-chain carboxylic acids (no branching). 2. The sizes of most common fatty acids range from 10 to 20 carbons. 3. Fatty acids usually have an even number of carbon atoms (including the carboxyl group carbon). 4. Fatty acids can be saturated (containing no double bonds between carbons) or unsaturated (containing one or more double bonds between carbons).
  • 20.
    FATTY ACIDS 5. Interms of carbon chain length, fatty acids are characterized as:  Long-chain fatty acids (C12 to C26),  Medium chain fatty acids (C8 and C10), or  Short-chain fatty acids (C4 and C6). 6. Fatty acids are rarely found free in nature but rather occur as part of the structure of more complex lipid molecules.
  • 21.
    CLASSIFICATION OF FATTYACIDS  The hydrocarbon chain of a fatty acid may or may not contain carbon–carbon double bonds.  On the basis of this consideration, fatty acids are classified as: 1. Saturated fatty acids (SFAs), 2. Unsaturated Fatty Acids 3. Monounsaturated fatty acids (MUFAs), and 4. Polyunsaturated fatty acids (PUFAs).
  • 22.
    CLASSIFICATION OF FATTYACIDS 1. Saturated Fatty Acids  A saturated fatty acid is a fatty acid with a carbon chain in which all carbon– carbon bonds are single bonds.  Examples include:  Propionic acid  Palmitic acid  Stearic acid
  • 23.
    CLASSIFICATION OF FATTYACIDS 2. Unsaturated Fatty Acids  They are classified further according to degree of unsaturation. a) Monounsaturated Fatty Acids (MUFA’s) b) Polyunsaturated Fatty Acids (PUFA’s)
  • 24.
    CLASSIFICATION OF FATTYACIDS a) Monounsaturated Fatty Acids  A monounsaturated fatty acid is a fatty acid with a carbon chain in which one carbon–carbon double bond is present.  For example, Oleic acid is a monounsaturated fatty acid, that is found in nearly all fats.
  • 25.
    CLASSIFICATION OF FATTYACIDS b) Polyunsaturated Fatty Acids  A polyunsaturated fatty acid is a fatty acid with a carbon chain in which two or more carbon–carbon double bonds are present.  Up to six double bonds are found in biochemically important PUFAs; they include: • Dienoic acids series have two double bonds, e.g. linoleic acid • Trienoic acids series have three double bonds, e.g. linolenic acid • Tetraenoic acid series with four double bonds, e.g. arachidonic acid
  • 26.
    NOMENCLATURE OF FATTYACIDS  The systematic nomenclature of the fatty acids is based on the Genevan system.  According to this system, the fatty acid is named after the hydrocarbon with the same number of carbon atoms.  The suffix -oic is written in place of the final letter e in the name of the hydrocarbon. The names of saturated fatty acids end with the suffix –anoic e.g., Octadecanoic acid. The names of unsaturated fatty acids end with the suffix –enoic e.g., Octadecenoic acid (Oleic acid).
  • 27.
    NOMENCLATURE OF FATTYACIDS  The position of carbon atoms in the fatty acid chain is indicated either:  By numbering - in which case the carboxyl carbon is numbered as C1, the carbon adjacent to C1 as C2 and so on; or  By the use of Greek letters - in which case C2 is denoted as a-carbon, C3 as b-carbon and so on, while the terminal methyl (-CH3) carbon is known as w-carbon.
  • 28.
    NOMENCLATURE OF FATTYACIDS  The notation most commonly used for fatty acids indicates the: • Number of carbon atoms, and • Number of double bonds.  The notation 18:0 denotes an C18 fatty acid with no double bonds, while 18:1 signifies an C18 fatty acid with one double bond.
  • 29.
    NOMENCLATURE OF FATTYACIDS  To specify double-bond positioning within the carbon chain of an unsaturated fatty acid, the preceding notation is expanded by adding the Greek capital letter delta (D) followed by one or more superscript numbers.  The notation 18:3(D9,12,15) denotes a C18 PUFA with three double bonds at locations between carbons 9 and 10, 12 and 13, and 15 and 16.
  • 30.
    SELECTED FATTY ACIDSOF BIOLOGICAL IMPORTANCE Saturated Fatty Acids Common Name Structural Notation Formula Common Sources Lauric Acid 12:0 CH3(CH2)10COOH Laurel oil, Spermaceti Myristic Acid 14:0 CH3(CH2)12COOH Butter and wool fat Palmitic Acid 16:0 CH3(CH2)14COOH Palm Oil Stearic Acid 18:0 CH3(CH2)16COOH Animal and plant fats Arachidic Acid 20:0 CH3(CH2)18COOH Peanut Oil
  • 31.
    SELECTED FATTY ACIDSOF BIOLOGICAL IMPORTANCE Unsaturated Fatty Acids Common Name Structural Notation Formula Common Sources Oleic Acid 18:1 – D9 CH3(CH2)7CH=CH(CH2)7COOH Animal and plant fats Linoleic Acid 18:2 – D9,12 CH3(CH2)4CH=CH(CH2)CH=CH(CH2)7COOH Peanut & cottonseed Oil Linolenic Acid 18:3 – D9,12,15 CH3(CH2CH=CH)3(CH2)7COOH Linseed Oil Arachidonic Acid 20:4 – D5,8,11,14 CH3 (CH2)4(CH=CHCH2) 4(CH2)2COOH Animal fats
  • 32.
    ISOMERISM IN FATTYACIDS  The unsaturated fatty acids exhibit geometric (or cis-trans) isomerism at the double bonds.  In biochemically important MUFAs, the configuration about the double bond is nearly always cis rather than trans.  ‘Cis’ form is comparatively unstable and is more reactive.  For example, Oleic acid can exist in two forms: cis-oleic acid and trans-oleic acid which is also called elaidic acid.
  • 33.
  • 34.
    ISOMERISM IN FATTYACIDS  ‘Cis’ configuration creates a rigid 30o bend, or kink, in the fatty acid chain that is not found in saturated fatty acids.  Such a bend affects the physical properties of a fatty acid.
  • 35.
    ESSENTIAL FATTY ACIDS Essential fatty acids are those polyunsaturated fatty acids that cannot be synthesized by our cells and we should obtain them from plants through diet.  Linoleic acid and linolenic acid are the only essential fatty acids for animals.  Other polyunsaturated fatty acids can be synthesized from these essential fatty acids.  For example, arachidonic acid can be synthesized only from linoleic acid.  Therefore, in deficiency of linoleic acid, arachidonic acid also becomes an essential fatty acids.
  • 36.
    IMPORTANCE OF ESSENTIALFATTY ACIDS  Linoleic acid is the starting material for the biosynthesis of arachidonic acid.  Arachidonic acid is the major starting material for eicosanoids, substances that help regulate blood pressure, clotting, and several other important body functions.  Linolenic acid is the starting material for the biosynthesis of two additional omega-3 fatty acids. Linolenic acid (18:3) → EPA (20:5) → DHA (22:6)
  • 37.
    IMPORTANCE OF ESSENTIALFATTY ACIDS  EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are important constituents of the communication membranes of the brain and are necessary for normal brain development.  EPA and DHA are also active in the retina of the eye.
  • 39.
    NEUTRAL FATS (TRIACYLGLYCEROLS (TAG)OR TRIGLYCERIDES)  Triacylglycerol, also called triglycerides, are composed of three fatty acids bonded by an ester linkage to glycerol.
  • 40.
    TYPES OF NEUTRALFATS  Triacylglycerol are of two types: 1. Simple Triacylglycerol 2. Mixed Triacylglycerol  Naturally occurring simple triacylglycerols are rare.  Most biochemically important triacylglycerols are mixed triacylglycerols.
  • 41.
    TYPES OF NEUTRALFATS 1. Simple Triacylglycerol  These types of triacylglycerol contain the same types of fatty acids at the three carbon atoms.  The triacylglycerol produced from glycerol and three molecules of stearic acid is an example of a simple triacylglycerol.
  • 42.
    ACTIVITY Draw the structuralformula of the triacylglycerol produced from the reaction between glycerol and three molecules of Lauric acid.
  • 43.
    TYPES OF NEUTRALFATS 2. Mixed Triacylglycerol  These types of triacylglycerol contain more than one kind of fatty acid molecule.  Figure shows the structure of a mixed triacylglycerol in which one fatty acid is saturated, another monounsaturated, and the third polyunsaturated.
  • 44.
    FATS AND OILS FATS A fat is a triacylglycerol mixture that is a solid or a semi-solid at room temperature (25◦C).  Generally, fats are obtained from animal sources.  All fats, even highly saturated fats, contain some unsaturated fatty acids. OILS  An oil is a triacylglycerol mixture that is a liquid at room temperature (25 ◦C).  Generally, oils are obtained from plant sources.  All oils, even polyunsaturated oils, contain some saturated fatty acids.
  • 45.
    5. Write keyreactions for fats and oils. Learning Objective
  • 46.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS 1. Hydrolysis  Fats can be hydrolyzed in the presence of an acid or a base.  Under acidic conditions, the hydrolysis products are glycerol and fatty acids.  Under basic conditions, the hydrolysis products are glycerol and fatty acid salts.  Within the human body, triacylglycerol hydrolysis occurs during the process of digestion by the specific fat-splitting enzymes called lipases, for example pancreatic lipase.
  • 47.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS  Triacylglycerol is sequentially hydrolyzed to diacylglycerol and monoacylglycerol and finally glycerol plus 3 fatty acids.
  • 48.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS 2. Saponification  Hydrolysis of a fat by an alkali such as sodium hydroxide or potassium hydroxide is called saponification.  For fats and oils, the products of saponification are glycerol and fatty acid salts.
  • 49.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS
  • 50.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS 3. Hydrogenation  Hydrogenation involves hydrogen addition across carbon–carbon double bonds, which increases the degree of saturation as some double bonds are converted to single bonds.
  • 51.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS  Many food products are produced via partial hydrogenation.  In partial hydrogenation some, but not all, of the double bonds present are converted into single bonds.  In this manner, liquids (usually plant oils) are converted into semi-solid materials.  This is the basis of Banaspati (Dalda) manufacture, where inedible and cheap oils like cotton seed oil are hydrogenated and converted to edible solid fat.
  • 52.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS
  • 53.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS 4. Oxidation  Fats very rich in unsaturated fatty acids such as linseed oil undergo spontaneous oxidation at the double bond forming aldehyde and carboxylic acid products.  The short-chain aldehydes and carboxylic acids so produced often have objectionable odors, and fats and oils containing them are said to have become rancid.  To avoid this unwanted oxidation process, commercially prepared foods containing fats and oils always contain antioxidants.  Two naturally occurring antioxidants are vitamin C and vitamin E.
  • 54.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS 5. Rancidity  The unpleasant taste and odor developed by most natural fats on aging is refereed to as rancidity.  Hydrolytic rancidity is due to partial hydrolysis of the fats due to traces of hydrolytic enzymes present in naturally occurring fats and oils.  Oxidative rancidity is the result of partial oxidation of unsaturated fatty acids with resultant formation of epoxides and peroxides of small molecular weight fatty acids by peroxides and free radicals.  The same process, if it occurs in vivo will affect the integrity of biomembranes, leading to cell death.
  • 55.
    CHEMICAL REACTIONS OFTRIACYLGLYCEROLS  Many natural vegetable fats and oils may contain antioxidants like vitamin E which prevent onset of rancidity. Therefore, vegetable fats can be preserved for a longer time than animal fats.
  • 56.
    CHARACTERIZATION OF FATOR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS)  Fat constants or numbers are test necessary to:  Identify a pure fat  Assess the degree of adulteration  Determine the proportions of different types of fat in a mixture
  • 57.
    CHARACTERIZATION OF FATOR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 1. Saponification Number  Saponification number is defined as the number of milligrams of potassium hydroxide required to saponify one gram of fat.  It is inversely proportional to the molecular weight of fat.  This value is high in fats containing a short chain fatty acids.  For example, the saponification number of:  Butter = 220  Coconut oil = 260
  • 58.
    CHARACTERIZATION OF FATOR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 2. Acid Number  Acid number is the number of milligrams of KOH required to neutralize the free fatty acids present in one gram of fat.  It is used for the detection of hydrolytic rancidity because it measures the amount of free fatty acids present.  Acid number is directly proportional to the rancidity.
  • 59.
    CHARACTERIZATION OF FATOR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 3. Iodine Number  Iodine number is the number of grams of iodine absorbed by 100 grams of fat.  It is an index of the degree of unsaturation and is directly proportional to the content of unsaturated fatty acids.  Higher the iodine number, higher is the degree of unsaturation, e.g.  Butter = 28,  Sunflower oil = 130
  • 60.
    CHARACTERIZATION OF FATOR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 4. Acetyl Number  Acetyl number is the number of milligrams of KOH needed to neutralize the acetic acid liberated from hydrolysis of 1gm of acetylated fat.  The natural fat that contains fatty acids with free hydroxyl groups are converted into acetylated fat by reaction with acetic anhydride.  Thus, acetyl number is a measure of the amount of hydroxy fatty acids in fat content.
  • 61.
    CHARACTERIZATION OF FATOR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS)  Castor oil because of its high content of ricinoleic acid has a high acetyl number.  Acetyl number of some oils are:  Castor oil = 146-150  Cod Liver oil = 1.1  Cotton Seed oil = 21-25  Olive oil = 10.5
  • 62.
    CHARACTERIZATION OF FATOR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS) 4. Reichert Meissl Number  Reichert-Meissl number is the numbers of milliliters of 0.1N alkali required to neutralize the volatile acid obtained from 5g of a fat, which has been saponified then acidified to liberate the fatty acids and then steam distilled.  It is also known as volatile fatty acid number.  Reichert Meissl value for:  Butter = 26  Coconut oil = 7.
  • 63.
    CHARACTERIZATION OF FATOR IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS)  It is less than one for other edible oils.  The admixture of certain fats may be used to prepare synthetic butter which may simulate butter in most of the constants except RM value and hence, can be detected.
  • 64.
    WAXES  Waxes areesters of long-chain saturated and unsaturated fatty acids with long-chain monohydroxy alcohols.  The fatty acids range in between C14 and C36 and the alcohols range from C16 to C36.
  • 65.
    WAXES  Beeswax, forexample, contains a wax (1-triacontyl palmitate) with the following structure:
  • 66.
    WAXES  Waxes generallyhave higher melting points than fats (60 to 100°C) and are harder.  Animals and plants often use them for protective coatings.  In plants, waxes are secreted as surface coating to prevent excessive evaporation and to protect against parasites.  In animals, waxes are secreted by cutaneous glands as a protective coating to keep the skin pliable, lubricated and water-proof.
  • 67.
    WAXES  Important waxesinclude carnauba wax (from a Brazilian palm tree), lanolin (from lamb’s wool), beeswax, and spermaceti (from whales).  These substances are used to make cosmetics, polishes, candles, and ointments.  Sperm whale wax (spermaceti) and beeswax are composed mainly of palmitic acid esterified with either hexacosanol, CH3(CH2)24.CH2OH or triacontanol, CH3(CH2)28.CH2OH.
  • 68.
    6. What areComplex or Compound Lipids? Learning Objective
  • 70.
    7. Describe chemistryand classification of Phospholipids. Learning Objective
  • 71.
    PHOSPHOLIPIDS  Phospholipids arethe most abundant membrane lipids.  They serve primarily as structural components of membranes and are never stored in large quantities.  They differ from triglycerides in possessing usually one hydrophilic polar “head” group and usually two hydrophobic nonpolar “tails”.  For this reason, they are often called polar lipids.
  • 72.
     There aretwo classes of phospholipids: A. Glycerophospholipids or Phosphoglycerides B. Sphingophospholipids or Phosphosphingosides
  • 73.
    PHOSPHOLIPIDS A. Glycerophospholipids  Inthese compounds, glycerol is linked by ester bonds to two fatty acids and one phosphate, which in turn is linked by ester bond to another alcohol (usually amino alcohol).  Phosphoglycerides serve as a major component of cell membranes.
  • 74.
  • 75.
    PHOSPHOLIPIDS  The alcoholattached to the phosphate group in a phosphoglyceride is usually one of three amino alcohols: choline, ethanolamine, or serine.
  • 76.
    PHOSPHOLIPIDS  Phosphoglycerides containingthese three amino alcohols are respectively known as phosphatidylcholines, phosphatidylethanolamines, and phosphatidylserines.  Phosphatidylcholines are also known as lecithins.  Phosphatidylethanolamines and phosphatidylserines are also known as cephalins.  Another important group of glycerophospholipids is the phosphatidylinositols (PI), in which the alcohol is inositol.  In phosphatidylinositol, inositol is present as the stereoisomer myoinositol.
  • 78.
    PHOSPHOLIPIDS a) Lecithins  Variousoil seeds like soybean and the yeasts are important sources from plant world.  In animals, they are distributed in liver, brain, nerve tissues, sperm and egg yolk.  Dipalmitoyl lecithin is an important phosphatidylcholine found in lungs, secreted by pulmonary type II epithelial cell.  It acts as a lung surfactant and is necessary for normal lung function.  It reduces surface tension in the alveoli, thereby prevents alveolar collapse.
  • 79.
    ACTIVITY  Draw thestructural formula for the glycerophospholipid that produces, upon hydrolysis, equimolar amounts of glycerol, phosphoric acid, and choline, and twice that molar amount of palmitic acid, the 16:0 fatty acid.
  • 80.
    PHOSPHOLIPIDS b) Cephalins  Phosphoglyceridesin which the alcohol is ethanolamine or serine, rather than choline, are called cephalins.  These compounds are found in heart and liver tissue and in high concentrations in the brain.  They are also found in blood platelets, where they play an important role in the blood-clotting process.
  • 81.
    PHOSPHOLIPIDS c) Phosphatidylinositol  Anotherimportant group of glycerophospholipids is the phosphatidylinositols (PI), in which the alcohol is inositol.  In phosphatidylinositol, inositol is present as the stereoisomer myoinositol.  Phosphatidylinositols in their higher phosphorylated form, such as phosphatidylinositol 4,5-bisphosphates (PIP2), serve as signaling molecules in chemical communication.
  • 83.
    PHOSPHOLIPIDS  Two lesscommon phosphoglycerides are: i. Plasmalogens ii. Cardiolipins
  • 84.
    PHOSPHOLIPIDS d) Plasmalogens  Plasmalogensconstitute about 10% of the phospholipids of the brain and muscle.  Structurally, these resemble lecithins and cephalins but have one of the fatty acids replaced by an unsaturated ether.  These are found in myelin and in cardiac muscle.  Plasmalogen is a platelet activating factor (PAF) and involved in platelet aggregation and degranulation.
  • 85.
    PHOSPHOLIPIDS e) Cardiolipin  Cardiolipinsare present in abundance in inner mitochondrial membranes, and their complete hydrolysis yields:  Four molecules of fatty acids  Three glycerol molecules  Two phosphate ions
  • 86.
    PHOSPHOLIPIDS B. Phosphosphingosides  Aphosphosphingosides is a lipid that contains one fatty acid and one phosphate group attached to a sphingosine molecule and an alcohol attached to the phosphate group.  All phospholipids derived from sphingosine have: 1. the fatty acid attached to the sphingosine —NH2 group via an amide linkage, 2. the phosphate group attached to the sphingosine terminal —OH group via an ester linkage, and 3. an additional alcohol esterified to the phosphate group.
  • 87.
    PHOSPHOLIPIDS B. Phosphosphingosides  Sphingophospholipidsin which the alcohol esterified to the phosphate group is choline are called sphingomyelins.  Sphingomyelins are found in all cell membranes and are important structural components of the myelin sheath.
  • 88.
    GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS A glycolipid is a complex lipid that contains both a fatty acid and a carbohydrate component attached to a sphingosine molecule.
  • 89.
    GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS a.Cerebrosides  Cerebrosides are the simplest sphingoglycolipid that contain a single monosaccharide unit—either glucose or galactose and named as glucocerebrosides and galactocerebrosides.  Cerebrosides are present in high concentrations in the white matter of the brain as well as in myelin sheathes.
  • 90.
    GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS a.Cerebrosides  Four types of cerebrosides have been characterized, depending upon the type of fatty acids they contain.  Kerasin−contains saturated C 24 lignoceric acid.  Phrenosin (cerebron)−contains a 2-hydroxy derivative of lignoceric acid called cerebronic acid.  Nervon−contains an unsaturated homologue of lignoceric acid called nervonic acid,  Oxynervon−contains a 2-hydroxy derivative of nervonic acid called oxynervonic acid.
  • 91.
    LAUGHTER TIME Because LAUGHTERis an instant Vacation!
  • 92.
    GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS b.Gangliosides  Gangliosides are more complex glycolipids that contain a branched chain of up to seven monosaccharide residues.  Gangliosides also generally contain sialic acid, which is usually N- acetylneuraminic acid (NANA) attached to ceramide (N-acylsphingosine).  These substances occur in the gray matter of the brain as well as in the myelin sheath.
  • 93.
    GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS b)Gangliosides  Several types of gangliosides such as GM1, GM2, GM3, etc. have been isolated from brain and other tissues.  The simplest ganglioside found in tissues is GM3.
  • 94.
  • 95.
    7. What areDerived Lipids? Learning Objective
  • 96.
    DERIVED LIPIDS  Unsponifiablecompounds obtained by hydrolysis of simple or compound lipids are called derived lipids.  Derived lipids include prostaglandins and related compounds, fat soluble vitamins and steroids.
  • 97.
    EICOSANOIDS  Eicosanoids arethe compounds derived from arachidonic acid that function as messenger lipids.  There are three principal types of eicosanoids: 1. Prostaglandins 2. Leukotrienes 3. Thromboxanes
  • 98.
    PROSTAGLANDINS  Prostaglandins werefirst detected in the seminal fluid, which is produced by the prostate gland and hence the name.  Chemically, they are considered to be derived from 20C cyclic saturated fatty acid, prostanoic acid.
  • 99.
    PROSTAGLANDINS  Some ofthe functions of prostaglandins are: • Control of blood pressure • Stimulation of smooth muscle contraction • Induction of inflammation • Inhibition of platelet aggregation
  • 100.
    LEUKOTRIENES  Leukotrienes arecompounds that, like prostaglandins, are derived from arachidonic acid.  They are found in leukocytes (white blood cells) and have three conjugated double bonds; these two facts account for the name.
  • 101.
    LEUKOTRIENES  Various inflammatoryand hypersensitivity (allergy) responses are associated with elevated levels of leukotrienes.  Leukotriene C produce long-lasting muscle contractions, especially in the lungs, and can cause asthma-like attacks.  One way to counteract the effects of leukotrienes is to inhibit their uptake by leukotriene receptors (LTRs) in the body.  A new antagonist of LTRs, zafirlukast, is used to treat and control chronic asthma.
  • 102.
    THROMBOXANES  Thromboxanes containcyclic ethers as part of their structures.  These compounds were called thromboxanes because they were first isolated from thrombocytes.  The most widely studied member of the group, thromboxane A2 (TxA2), is known to induce platelet aggregation and smooth-muscle contraction.
  • 103.
    STEROIDS  Steroids area group of compounds that contain cyclopentanoperhydrophenanthrene ring structure.  This ring is present in steroid hormones, bile acids, cholesterol etc.
  • 104.
    CHOLESTEROL  Cholesterol isa C27 steroid molecule that is a component of cell membranes and a precursor for other steroid-based lipids.  Cholesterol is amphipathic, with a:  Polar head, the hydroxyl group at C3 and a  Nonpolar the steroid nucleus and hydrocarbon side chain at C17.  Most of the cholesterol in the body exists as a cholesterol ester, with a fatty acid attached to the hydroxyl group at C3.
  • 105.
  • 106.
    CHOLESTEROL  Cholesterol iswidely distributed in all the cells of the body but particularly in nervous tissue.  It is synthesized in our body as well as supplied in the diet.  Cholesterol serves as the precursor for a variety of biologically important products, including: steroid hormones, bile acids and fat soluble vitamins.  It is a major structural constituent of the cell membranes and plasma lipoproteins.
  • 107.
    BILE ACIDS  Abile acid is a cholesterol derivative that functions as a lipid-emulsifying agent in the aqueous environment of the digestive tract.  Approximately one-third of the daily production of cholesterol by the liver is converted to bile acids.
  • 108.
    BILE ACIDS  Obtainedby oxidation of cholesterol, bile acids differ structurally from cholesterol in three respects: 1. They are tri- or dihydroxy cholesterol derivatives. 2. The carbon 17 side chain of cholesterol has been oxidized to a carboxylic acid. 3. The oxidized acid side chain is bonded to an amino acid (either glycine or taurine) through an amide linkage.  The presence of this amino acid attachment increases both the polarity of the bile acid and its water solubility.
  • 109.
    BILE ACIDS  Thethree major types of bile acids produced from cholesterol by biochemical oxidation are:  Cholic acid,  7-deoxycholic acid, and  12-deoxycholic acid.