Lipids (Introduction and Classification) PDF

LIPIDS (Introduction and Classification of Lipids) objectives 1. Define lipids 2. Differentiate the two major classes of lipids 3. Understand the biological significance of lipids 4. Describe the properties of lipids 5. Classify lipids and fixed oils WHAT ARE LIPIDS? Lipids are biomolecules...

LIPIDS (Introduction and Classification of Lipids) objectives 1. Define lipids 2. Differentiate the two major classes of lipids 3. Understand the biological significance of lipids 4. Describe the properties of lipids 5. Classify lipids and fixed oils WHAT ARE LIPIDS? Lipids are biomolecules that are soluble in organic solvents and insoluble in water. They are esters of fatty acids Mostly hydrocarbons REVIEW: Carboxylic acids Alcohol Esters WHAT ARE LIPIDS? They are utilizable by living organisms: Storage of energy –Lipids represent highly reduced forms of carbon and, upon oxidation in metabolism, yield large amounts of energy, making them molecules of choice for metabolic energy storage. Membrane Components- lipids provide insoluble compartments containing aqueous solutions Messengers- lipids serve as chemical messengers a. Primary messengers – steroid hormones, eicosanoids b. Secondary messengers – prostaglandins and thromboxanes BIOLOGICAL SIGNIFICANCE: 1. Secondary source of energy 2. Insulating material –prevents the escape of heat 3. Important cellular constituents - Occurs both in the cell membrane and mitochondria within the cytoplasm and acting as a means of transporting fatty acids to the different parts of the body 4. Storage form of energy 5. Metabolic regulators (steroid hormones and prostaglandins) BIOLOGICAL SIGNIFICANCE: 6. Acts as surfactants, detergents, and emulsifying agents (amphipathic lipids) 7. Give shape and contour to the body 8. Protect internal organs by providing cushioning effect. 9. Help in absorption of fat soluble vitamins (A,D,E, and K) 10. Improve taste and palatability of food. 11. Important dietary constituents (essential fatty acids, fat-soluble vitamins, and micronutrients are contained in the fat of natural foods). 12. Dietary supplementation with long-chain omega- 3 fatty acids is believed to have beneficial effects in a number of chronic diseases, including cardiovascular disease, rheumatoid arthritis, and dementia. PROPERTIES OF LIPIDS: 1. Greasy to touch, leaves a permanent oily stain on paper 2. Lighter than water 3. Soluble in organic solvent, insoluble in water 4. When pure, colorless with bland odor and taste 5. Yellow color in fat is due to carotene (provit. A) 6. When heated strongly, undergoes decomposition forming acrid flammable vapors and when ignited, they burn with a sooty flame. Acridity is due to acrolein aka “propenal” PHYSICAL CONSTANTS: 1. Refractive index - increases with increasing chain length and increasing unsaturation 1. Melting/solidification point - Lipids melt and solidify over a temperature range because of the mixture of fatty acids - The solidification point is the temperature at which all lipids in a mixture are in a solid state - The melting point refers to the temperature at which a lipid transitions from a solid state to a liquid state. - The more saturated the fatty acid and the longer the length of the carbon chain, the higher is the melting point PHYSICAL CONSTANTS: 3. Viscosity - resistance to flow 4. Specific gravity - The specific gravity of the fats is less than 1 (about 0.86) and, therefore, they float on water surface. 5. Optical rotation - is the ability of the compound to rotate plane polarized light to the right or to the left. two major classes of lipids NON-SAPONIFIABLE SAPONIFIABLE - cannot be broken up into smaller - contains one or more ester groups molecules by hydrolysis. Do not have allowing it to undergo hydrolysis in the ester bond, hence they cannot be presence of an acid, base, or enzyme saponified. forming SOAP. Contain esters, which can undergo saponification. a. Simple lipids — contain two types of components (a fatty acid and an alcohol) b. Complex lipids — contain more than two components (fatty acids, an alcohol, and other components) two major classes of lipids NON-SAPONIFIABLE SAPONIFIABLE 1. Triglycerides (fats and oils) – fatty acids + glycerol. 1. Steroids - cholesterol and 2. Phospholipids – critical for cell hormones (testosterone, estrogen) membranes. eg. lecithin 2. Fat-soluble Vitamins (A,D,E,K) 3. Waxes – fatty acids + long-chain 3. Terpenes - found in essential oils, alcohols. they give off that intoxicating aroma. 4. Glycolipids – lipids (fats) + sugar group, involved in cell signaling.  WHAT ARE FATTY ACIDS? RCOOH A fatty acid has a carboxyl group at the polar end (“Head”) and a hydrocarbon chain at the nonpolar “tail”. Fatty acids are amphipathic (they possess both polar and nonpolar groups) compounds because the carboxyl group is hydrophilic and the hydrocarbon tail is hydrophobic. Most of the fatty acids found in nature have an even number of carbon atoms (usually 14 to 24).  2 main types of fatty acids 1. Saturated Fatty acids - if there are only single bonds, the fatty acid 2. Unsaturated Fatty acids - If there are carbon–carbon double bonds or triple bonds in the chain - In unsaturated fatty acids, the stereochemistry at the double bond is usually cis rather than trans. - A cis double bond puts a kink in the long-chain hydrocarbon tail.  Saturated: The bonds between all the carbons are single bonds. Solid at room temperature Mainly animal fats (bacon grease, Saturated Fats lard) Unsaturated: There is at least one double or triple bond between carbons present. Liquid at room temperature Mainly plant based fats (olive oil, peanut oil) as well as oily fish (Tuna, Sardines) Unsaturated Fats Fatty acids are either saturated (all carbon–carbon bonds are single bonds) or unsaturated (with one or more double bonds in the hydrocarbon chain). If a fatty acid has a single double bond, it is said to be monounsaturated and if it has more than one, polyunsaturated. EXAMPLES OF SATURATED AND UNSATURATED FATTY ACIDS Free rotation around each of the carbon–carbon bonds makes saturated fatty acids extremely flexible molecules. Saturated fatty acids adopt the straight conformation  Unsaturated fatty acids are slightly more abundant in nature than saturated fatty acids, especially in higher plants. The most common unsaturated fatty acid is oleic acid, or 18:1(9), with the number in parentheses indicating that the double bond is between carbons 9 and 10. The number of double bonds in an unsaturated fatty acid varies typically from one to four, but, in bacteria, this number rarely exceeds one. Double bonds also tend fatty acids to bend or kink  Saturated Fatty Acids Formula Common Name Melting Point CH3(CH2)10CO2H lauric acid 45 ºC CH3(CH2)12CO2H myristic acid 55 ºC CH3(CH2)14CO2H palmitic acid 63 ºC CH3(CH2)16CO2H stearic acid 69 ºC CH3(CH2)18CO2H arachidic acid 76 ºC Unsaturated Fatty Acids Formula Common Name Melting Point CH3(CH2)5CH=CH(CH2)7CO2H palmitoleic acid 0 ºC CH3(CH2)7CH=CH(CH2)7CO2H oleic acid 13 ºC CH3(CH2)4CH=CHCH2CH=CH(C linoleic acid -5 ºC H2)7CO2H CH3CH2CH=CHCH2CH=CHCH2 linolenic acid -11 ºC CH=CH(CH2)7CO2H CH3(CH2)4(CH=CHCH2)4(CH2)2C arachidonic acid -49 ºC O 2H Unsaturated fatty acids have lower melting points than saturated ones. Plant oils are liquid at room temperature because they have higher proportions of unsaturated fatty acids than do animal fats, which tend to be solids. Some fatty acids are not synthesized by mammals and yet are necessary for normal growth and life. These essential fatty acids include linoleic (Omega 6) and a–linolenic acids (Omega 3). These must be obtained by mammals in their diet (specifically from plant sources).  HOW TO NAME FATTY ACIDS 1. Common name 2. Systematic name 3. Symbol denoting number of carbon: no. of double bonds Triacylglycerols (triglycerides) Glycerol is a simple compound that contains three hydroxyl groups When all three of the alcohol groups form ester linkages with fatty acids, the resulting compound is a triacylglycerol; an older name for this type of compound is triglyceride.  If all three fatty acid groups are the same, the molecule is called a simple triacylglycerol. Examples include tristearoylglycerol (common name tristearin) and trioleoylglycerol (triolein). Mixed triacylglycerols contain two or three different fatty acids. Triacylglycerols in animals are found primarily in the adipose tissue (body fat), which serves as a depot or storage site for lipids.  Properties of Triglycerides A. Physical state Fat- A mixture of triglycerides containing a high proportion of long-chain, saturated fatty acids Oil- A mixture of triglycerides containing a high proportion of long-chain, unsaturated fatty acids or short-chain, saturated fatty acids Triglycerides The physical properties of triglycerides depend on the fatty acid components. Melting points of fatty acids increases as the number of carbons in the hydrocarbon chains increases and as the number of double bonds decreases. Triglycerides rich in unsaturated fatty acids are generally liquid at room temperature and are called oils Triglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature and are called fats.  Hydrogenation Hydrogen can be added across the carbon to carbon double bond in an unsaturated fatty acid This reaction is called hydrogenation and decreases the level of unsaturation in the fatty acid  Hydrogenation Conversion of unsaturated liquid oils to solid fats; Reduction of carbon–carbon double bonds to single bonds by treating them with hydrogen and a catalyst In practice, the degree of hardening is carefully controlled to produce fats of a desired consistency. The resulting fats are sold for kitchen use Margarine and other butter substitutes are produced by partial hydrogenation of polyunsaturated oils derived from corn, cottonseed, peanut, and soybean oils. The hardening process is the source of trans fatty acids  Saponification Saponification: the base-promoted hydrolysis of fats and oils in aqueous NaOH produces glycerol and a mixture of fatty acid sodium salts called soaps. 1. Energy-stored lipids – triacylgycerols 2. Membrane lipids – phospholipids, sphingoglycolipids and cholesterol 3. Emulsification lipids – bile acids, synthesize in liver, stored in gall bladder 4. Chemical messenger lipids – steroid hormones and eicosanoids 5. Protective-coating lipids – biological waxes (ex. Canobal wax, paraffin wax) CLASSIFICATION OF LIPIDS Figure 21-1 Schematic diagram of simple and complex lipids. CLASSIFICATION OF LIPIDS I. Simple Lipid III. Derived Lipids 1. Fats 1. Fatty acids 2. Oils aka “Fixed oils” 2. Alcohols - Non-drying oil - Semi-drying oils - Drying oils 1. Waxes I. Complex/Compound Lipids 1. Phospholipids - Lecithin or Phosphatidylcholine - Cephalin or Phosphatidylethanolamine 1. Glycolipids  Simple Lipids Fats Fixed oils - with saturated fatty acids - with unsaturated fatty acids - from animals - from vegetable - solid in room temperature - liquid in room temperature - except Cod liver oil - except Cocoa butter (Theobroma cacao)  Simple Lipids Fixed oils C. Drying oil A. Non-drying oil - Iodine value: >/= 120 - Iodine value: