Veterinary Biochemistry Lecture 3 on Lipids PDF

Veterinary Biochemistry Hazim Omar Khalifa, BVSC, MVSC, PhD Department of Veterinary Medicine College of Agriculture and Veterinary Medicine UAE University Lipid Chemistry  Lipid The lipids are a heterogeneous group of...

Veterinary Biochemistry Hazim Omar Khalifa, BVSC, MVSC, PhD Department of Veterinary Medicine College of Agriculture and Veterinary Medicine UAE University Lipid Chemistry  Lipid The lipids are a heterogeneous group of compounds related to the fatty acids. They are characterized by the following: ❖ Relatively insoluble in water. ❖ Soluble in non-polar solvents (fat solvents) e.g. ether, chloroform and benzene. ❖ Chemically' lipids are composed of C, H, and O, some lipids contain in addition nitrogen and phosphorus.  Lipid Importance of lipids: 1. High energy value. Dietary lipids supply 20-25% of the daily caloric requirements. 2. Lipids are of higher caloric value than carbohydrates and proteins in diet. 3. Their caloric values are calculated as 9.4, 4.1, and 4.0 Kcal/gm respectively. 4. Lipids form 10% of body weight. 5. They contain essential fatty acids that are essential for normal growth. 6. They provide fat-soluble vitamins (A, D, E and K). 7. Render food is more palatable. 8. Preservation of body temperature (insulator for heat).  Lipid 9. They serve as a protective coating and support of internal organs such as kidneys. 10. Combination of fats and proteins (lipoproteins) are important cellular constituents, occurring both in the cell membrane and in the mitochondria within the cytoplasm, also lipoproteins serve as the means of transporting lipids in the blood. 11. Lipids as cell surface compounds are concerned with cell recognition, species specificity, and tissue immunity. 12. Lipids are important structural constituents of the nervous tissues, through its action as an electrical insulator allowing rapid propagation of depolarization waves along myelinated nerve. 13. Obesity and atherosclerosis are the metabolic disorders of lipids constituents. Lipid  Lipid CLASSIFICATION OF LIPIDS: 1- Simple lipids: 2- Compound Lipids: 3- Derived lipids: 1- Simple lipids: These are esters of fatty acids with various alcohols and include: 1- Triglycerides or neutral fat or ordinary fats and oils. They are esters of glycerol (trihydroxy or trihydric alcohol) and fatty acids (3 moles per mole neutral fat). Alpha-linolenic acid Oleic acid Palmitic acid Glycerol Fatty acids  Lipid 2- Waxes: they are esters of fatty acids with higher monohydric high molecular weight alcohols. Fatty Acids  Lipid The fundamental building blocks of many lipids. Fatty acids are long-chain carboxylic acids, it is the long nonpolar tails of fatty acids that are responsible for most of the fatty or oily characteristics of fats. The carboxyl group, or polar head of fatty acids, is very hydrophilic under conditions of physiological pH, where it exists as the carboxylate anion COO.  Classification of fatty acids Fatty acids Acc. To No. of Acc. To degree Acc. To chain carbon atoms of saturation length Odd numbered Even numbered Saturated fatty Unsaturated Short chain Long chain fatty acids fatty acids acid fatty acid Polyunsaturated Monounsaturated FAs  Classification of fatty acids 1-Depending on the total number of carbon atoms: A. Even chain: They have carbon atoms 2,4,6 and similar series. Most of the naturally occurring lipids contain even chain fatty acids. B. Odd chain: They have carbon atoms 3, 5, 7, etc. Odd-numbered fatty acids are seen in microbial cell walls. They are also present in milk.  Classification of fatty acids 2- According to chain length of fatty acids: A. Short-chain fatty acids (lower fatty acids): * Contain 2-10 carbons. * Liquid at room temperature * Soluble in water. * Volatile * Acetic acid (2 carbons) CH3-COOH * Butyric acid (4 carbons) In butter CH3 -(CH2)2-COOH. * Caproic acid (6 carbons) in butter, palm oil, and coconut CH3-(CH2)4-COOH * Caprylic acid (8 carbon) in butter and palm oil CH3-(CH2)6-COOH. * Capric acid (10 carbon) in butter, palm oil, and coconut CH3-(CH2)8-COOH.  Classification of fatty acids B. Long-chain fatty acids: * More than 10 carbons. * Solid. * Soluble in fat solvents. * Non-volatile. * Lauric acid (12 carbon) in vegetable oils: CH3-(CH2)10 -COOH. * Myristic acid (14 carbon) in lard, cod liver oil : CH3-(CH2)12 -COOH. * Palmitic acid (16 carbon) in butter and palm oil: CH3-(CH2)14 -COOH. * Stearic acid (18 carbon) in butter and vegetable oils: CH3-(CH2)16 -COOH. * Arachidic acid (20 carbon) in peanut: CH3-(CH2)18 -COOH. * Beharic acid (22 carbon) in seeds: CH3-(CH2)20 -COOH. * Lignoceric acid (24 carbon) in peanut and phospholipids: CH3-(CH2)22 -COOH.  Classification of fatty acids 2- Depending on the nature of hydrocarbon chain: A. Saturated fatty acids B. Unsaturated fatty acids contain one or more double bonds and be subclassified into Monounsaturated having single double bonds. Polyunsaturated with 2 or more double bonds.  Classification of fatty acids 1- Saturated fatty acids:- not contain any double bond: 1) Example: * Butyric acid * Caproic acid. * Caprylic acid. * Capric acid. * Lauric acid. * Myristic acid. * Palmitic acid. * Stearic acid. *Arachidic acid. * Behanic acid. * Lignocenic acid. 1) Unsaturated fatty acids:- Contain one or more double bonds. They can be classified into: a. Monounsaturated (monoenoic) fatty acids: contain one double bond e.g. ❖ Palmitoleic (16 carbon):CH3 - (CH2)5 -CH=CH-(CH2)7 -COOH. 16: 1;9 or D9 or w7 ❖ Oleic acid (18 carbon): CH3 - (CH2)7 -CH=CH-(CH2)7 -COOH. 18: 1;9 or D9 or w9 ❖ Nervonic acid (24 carbon): CH3 -(CH2)7 -CH=CH-(CH2)13 -COOH 24: 1;15 or D15 or w9  Classification of fatty acids b. Polyunsaturated (polyenoic) fatty acids: contain more than one double bond e.g. Linoleic (18 carbon): CH3 -(CH2)4 CH=CH-CH2 -CH=CH -(CH2)7 -COOH. 18: 3;9, 12 or D9, D12 or w6 Linolenic (18 carbon): CH3-CH2 -CH-CH-CH2CH=CH -CH2 -CH=CH-(CH2)7 –COOH 18: 3;9, 12, 15 or D9, D12, D15 or w3 Arachidonic acid (20 carbon) CH₃-(CH₂)₄-CH=CH-CH₂-CH=CH-CH₂-CH=CH-CH₂- CH=CH-(CH₂)₃-COOH : 20: 4; 5, 8, 11, 14 or D5, D8, D11, D14 or w6 Nomenclature  Nomenclature Numbering of carbons in saturated fatty acids The numbering of carbons in saturated fatty acids can be done by one of the following methods: 1- From carboxylic group (-COOH): first carbon will be -COOH then the second will be the adjacent carbon and so on. 2- From carbon next to -COOH: The carbon adjacent to -COOH will be a followed by α, β,σ and so on. 3- From last methyl (-CH3) carbon: That is called omega (w) carbon, followed by w2, w3, and so on.  Nomenclature Numbering of carbons in unsaturated fatty acids: 1- Delta (Δ ) numbering: It indicates the position of the double bond counted from the –COOH carbon. For example: Palmitoleic acid is: C16 :1Δ9. That means it has 16 carbons, 1 double bond between carbon 9 and carbon 10 counted from the -COOH end.  Nomenclature 2- Omega (ω) numbering: It indicates the position of double bond counted from the last methyl-CH3 carbon (ω). For example: Palmitoleic acid is: C16: 1 ω7. That means it has 16 carbons, 1 double bond between carbon 7 and carbon 8 counted from -CH3 (w1 carbon) Polyunsaturated fatty acids PUFA  Polyunsaturated fatty acids PUFA The human body can synthesize all except two of the fatty acids it needs. These two, alpha-linolenic acid (ALA) (an omega-3 fatty acid) and linoleic acid (LA) (an omega-6 fatty acid), are polyunsaturated fatty acids that contain 18 carbon atoms. Because they are not synthesized within the body and must be obtained from the diet, they are called essential fatty acids. Both are widely distributed in plant and fish oils.  Polyunsaturated fatty acids PUFA PUFA importance: Growth and fertility. Cell membrane formation. Protection against atherosclerosis and fatty liver (particularly omega-3 and omega-6 fatty acids), atherosclerosis refers to the buildup of fats, cholesterol, and other substances in and on your artery walls (plaque), which can restrict blood flow. The plaque can burst, triggering a blood clot. Eicosanoids synthesis. Eicosanoids  Eicosanoids They are cyclic compounds formed from cell membrane arachidonic acid by the formation of ring structure following the cyclization of the carbon chain. They include: prostaglandins (PGs), thromboxanes (TX), and leukotrienes (LT) Prostaglandins have hormonal-like action, vasodilatation during inflammation, and uterine and intestinal contraction. Leukotrienes for chemotaxis, bronchoconstriction, pro-inflammatory agent, and asthma participants.  Eicosanoids Formation of eicosanoids:` Eicosanoids are synthesized from arachidonic acid. The major dietary precursor for arachidonic acid synthesis is linoleate, which is present in plants. Arachidonic acid is then esterified in phospholipids located in the lipid bilayer of the cellular plasma membrane. The arachidonic acid is then released from membrane phospholipids. following the activation of membrane-bound phospholipase A2 or c. Arachidonic acid is mainly metabolized by two pathways, the cyclooxygenase (COX) pathway that produces prostaglandins and thromboxanes , and the lipoxygenase pathway that produces leukotrienes. Eicosanoids and the role of corticosteroids and NSAIDs Alcohols  Alcohols Alcohols are a part of lipids molecules, including glycerol, sphingosine, cholesterol and some higher alcohols. The most important alcohol in lipid molecule is glycerol. Glycerol is a colorless, odorless, viscous liquid miscible with water in all proportions. Heating glycerol with dehydrating agents such as H2SO4 or potassium hydrogen sulphate yields a compound known as acrolein which has an irritating pungent odor.  Alcohols Glycerol is a saturated trihydric alcohol containing three (-OH) groups which can be esterified with fatty acids to form different types of acylglycerol depends upon the number and types of fatty acids to: 1. Monoacylglycerol: They are ester of one fatty acid with glycerol. 2. Diacylglycerol: They are ester of two fatty acids with glycerol. 3. Triacylglycerol: They are ester of three fatty acids with glycerol May be: a- Simple triacylglycerols: Contain one kind of fatty acids to form three esters.. b- Mixed triacylglycerol: Contains two or three different fatty acids.  Alcohols Function of triacylglycerols: 1. Triacylglycerols (triglycerides) are molecules in both animals and plants that represent a storage and yet labile source of energy. 2. Triacylglycerols are to provide protection against cold temperature. Fat is a poor conductor of heat. Because adipose tissue, with its high triacylglycerol content, is found throughout the body (especially under the skin), it acts to prevent heat loss in cold weather. Properties of fats  Properties of fats They are insoluble in water but soluble in fat solvents. Hydrolysis of glycerides with mineral acids or with water at high temperature and pressure yield glycerol and fatty acids. Alkaline hydrolysis of fats by boiling with alkali yields salts of fatty acids which are soaps. This process is termed saponification.  Properties of fats: Hardening of oils: When the vegetable fats are hydrogenated solid product is formed known as margarine. * A typical hydrogenation is the conversion of oleic acid to stearic acid. CH3 (CH2)7-CH = CH-(CH2)7-COOH + H2 → CH3-(CH2)16-COOH Oleic acid Stearic acid * The margarine is used in cocking process and is not subjected to rancidity changes. Fats and oils, if allowed to stand in contact for a long time with air and moisture in the presence of light and heat, the fat becomes rancid.  RANCIDITY ❖ The spoilage of fats occurs through the oxidation of unsaturated as well as saturated fatty acids of the glycerides. ❖ This spoilage (Rancidity) acquires the fat with a disagreeable taste and odor. Types of rancidity: A- Hydrolytic: ❖ Hydrolysis of fat glycerides by lipase enzyme of bacteria or molds at moisture and elevated temperature result in liberation of free fatty acids. ❖ This spoilage may be prevented by heat inactivation of the enzyme and keeping the fat away from moisture. ❖ The liberation of free butyric acid of butter fat causes a very objectionable odor and destroys the usefulness of the product.  RANCIDITY B- Oxidative or auto-oxidation: ❖ Oxidative rancidity is accelerated by exposure to heat, light, moisture and by the presence of certain metals (such as copper, nickel and iron). ❖ This occurs in the presence of atmospheric oxygen by a chain mechanism in which it is believed that under such forces of energy as heat and light (U.V. rays). ❖ A hydrogen atom escapes from the methylene group (CH2) adjacent to double bonded carbon. ❖ The loss of this hydrogen atom leaves the fatty acid molecule as a free radical. ❖ The free radical formed reacts with a molecule of atmospheric oxygen to form a peroxide-free radical. ❖ This peroxide free radical reacts with another unsaturated fatty acid removing a methylene hydrogen atom to produce a hydroperoxide and a new free fatty acid radical. ❖ So on a chain reaction start resulting in further oxidation of fat molecules.  RANCIDITY B- Oxidative or auto-oxidation: 1- Heat, light, moisture 2- hydrogen atom escapes 3- Free radical 4- Interact with O2 5- peroxide-free radical 5- Interact with UFA ❖ This type of auto oxidation can be prevented by removing oxygen by packing the fat under vacuum and by storage at low temperatures and by packing in light-proof containers and finally by the use of artificial antioxidants.  RANCIDITY C- Ketonic rancidity: Oxidation of certain saturated fatty acids by enzymes found in dry molds (Aspergillus and penicillin). O || R-CH2-CH2COOH → R-C-CH2-COOH * Rancidity is decreased by sterilization which destroys the mold spores. Effects of rancidity: Release of toxic and irritant substances as aldehydes, ketones and peroxides. Unpleasant odor and taste of fat. Loss of activity of fat-soluble vitamins present with lipids e.g. vit. A. Irritation of gastric and intestinal mucosa by the rancid fat leading to vomiting or diarrhea.