Lipid Chemistry Past Paper PDF

‫ْ‬ ‫ُ‬ ‫َوقل َّرب زدني‬ ‫ْ‬ ‫عل ًما‬ ‫سورة طه ‪ -‬اآلية ‪114‬‬  Lipid Chemistry Directed by Pro.Dr/ Maathir kamel   Intended learning outcomes (ILOs): A) Knowledge and Understanding By the end of the course, students should be able to: 1. Define...

‫ْ‬ ‫ُ‬ ‫َوقل َّرب زدني‬ ‫ْ‬ ‫عل ًما‬ ‫سورة طه ‪ -‬اآلية ‪114‬‬  Lipid Chemistry Directed by Pro.Dr/ Maathir kamel   Intended learning outcomes (ILOs): A) Knowledge and Understanding By the end of the course, students should be able to: 1. Define simple and complex lipids 2. Indicate the structure saturated and unsaturated fatty acids 3. Explain the importance of essential fatty acids and eicosanoids 4. Outlines the structure of triacylgycerol, phospholipids, and glycophopholipids and indicate their importance B) Professional and Practical Skills B1. Identify the physical and chemical properties of lipids.  Lipids are heterogenous organic compounds formed of alcohol and fatty acid. They have the common property of being insoluble in water and soluble in non-polar solvents such as ether, chloroform and benzene.   Importance of lipids: 1. In the body, fat serves as an efficient source of energy, each 1 gm of fat gives 9.3 Kcal. 2. It serves as thermal insulators in the subcutaneous tissues and around certain organs e.g kidney. 3. Lipids act as electrical insulators, allowing rapid propagation of the depolarization waves along the myelinated nerves. The fat content of nerve tissue is high. 4. Lipoproteins (combination of fat and protein) serve as means of transporting lipids in the blood. They occur both in the cell membrane and in the mitochondria within the cytoplasm. 5. The fat of natural foods contains fat-soluble vitamins and essential fatty acids.   Classification of lipids: (A) Simple lipids: These are esters of fatty acids with alcohol. According to the alcohol, they are sub classified into: 1. Neutral fats: These are esters of fatty acids with glycerol. A fat in the liquid state is called oil. 2. Waxes: These are esters of fatty acids with higher molecular weight monohydric alcohols. (B) Complex lipids: These are esters of fatty acids with alcohol containing in addition other groups. According to these groups, they are sub classified into: (1) Phospholipids: These contain in addition to fatty acids and an alcohol, a phosphoric acid residue. (2) Glycolipids (Glycosphingolipids): These contain in addition to fatty acids and sphingosin and carbohydrate. (3) Proteolipids: These contain in addition to fatty acids and alcohols, a protein radical. (4) Other complex lipids: Such as sulfolipids and amino lipids. (C) Precursor lipids and derived lipids: These include substances obtained by the hydrolysis of the above groups. They include: fatty acids, glycerol, steroids, alcohols in addition to glycerol and sterols, fatty aldehydes and ketone bodies, hydrocarbons,  GLYCEROL Glycerol is colorless, odorless and sweet liquid which is miscible with water, insoluble in fat solvent. Glycerol is a trihydric alcohol which can be esterified with one, two or three fatty acids giving mono-, di-, or triacylglyceol respectively.  Glycerol is always phosphorylated at C-3 by the enzyme glycerokinase giving glycerol-3 phosphate.  FATTY ACIDS Fatty acids are monocarboxylic acids, which occur mainly as esters in natural fats & oils. Fatty acids occurring in natural fats are usually straight chain & contain an even-number of carbon atoms. Carbon atoms are numbered from the carboxyl carbon (carbon No.1). The carbon atom adjacent to the carboxyl group is known as C-2. Fatty acids may be saturated (containing no double bonds) or unsaturated (containing one or more double bonds). (A) Saturated fatty acids: Saturated fatty acids contain no double bonds with general formula CnH2nO2 and occur in nature. Saturated fatty acids include: Acetic acid:CH3COOH. It is an end product of carbohydrate fermentation by rumen organisms. Propionic acid: CH3CH2COOH. Butyric acid:CH3CH2CH2COOH. It occurs in small amounts in certain fats (especially butter). Valeric acid: CH3(CH2)3COOH.  Caproic acid:CH3(CH2)4COOH. Palmitic acid: CH3(CH2)14COOH. Common in animal and plant fats. Stearic acid: CH3(CH2)16COOH. Common in animal and plant fats. Lignoceric acid: CH3(CH2)22COOH. Found in cerebrosides and peanut oil.  (B) Unsaturated fatty acids: These contain one or more double bonds. The number and position of double bonds can be indicated by the greek letter delta e.gΔ9 means a double bond between carbon atoms 9 and 10 of the fatty acids as in oleic acid.  The position of double bonds can be indicated according to its relation to the methyl carbon as, omega-6 in linoleic and arachidonic acids and omega-3 in linolenic acid.  Unsaturated fatty acids: According to the degree of unsaturation, they are subdivided into: (1) Monounsaturated (monoethenoid) fatty acids: These contain one double bond ; general formula CnH2n– 1-COOH. Examples include: palmitoteic and oleic acids. Palmitoleic acid: (C16: Δ9) CH3-(CH2)5-10CH=9CH-(CH2)7COOH (ω-7) Oleic acid: (C18:Δ9) CH3-(CH2)7-10CH=9CH-(CH2)7.COOH (ω-9) (2) Poly unsaturated ( potyethenoid) fatty acids: These contain 2 or more double bonds. Examples include: Linoleic acid: (C 18:2,∆ 9,12) (ω-6) CH3-(CH2)4- 13CH=12CH.CH2.10CH=9CH-(CH2)7.COOH Linolenic acid: (C18: 3,∆ 9,12,15) (ω-3) CH3-.(CH2.CH=CH)3-(CH2)7.COOH Arachidonic acid: (C20: 4, ∆5,8,11,14) (ω-6) CH3-(CH2)3.(CH2.CH=CH)4-(CH2)3.COOH CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH  Essential fatty acids These are polyunsaturated fatty acids cannot be synthesized in the body at a sufficient rate and must be taken in diet e.g. linoleic acid and linolenic acid. Sources 1- Plant oils e.g. corn oil, safflower, sunflower and linseed oil. 2- Fish oils e.g. shark liver oils which contain ω-3 polyunsaturated fatty acids. Importance of essential fatty acids: They are important for: 1- Formation of phospholipids and cholesterol ester. 2- Enter in structure of cell membrane and are required for the fluidity of cell membrane. 3- Normal growth. 4- They protect against atherosclerosis and coronary heart disease by decreasing cholesterol and LDL. 5- Arachidonic acid is a precursor of eicosanoids.   Properties of fatty acids: The chain length & degree of unsaturation affect the physical and physiological properties of fatty acids. These properties include: (1) Solubility: The short chain fatty acids (FA) up to 6 are soluble in water, while the long chain ones are insoluble in water soluble in fat solvent. (2) Melting point: The melting point of FA increases with the chain length and decreases according to the unsaturation. Thus acetic and oleic acids are liquids while palmitic & stearic acids are solids  Triacylglycerols (Neutral fats) The triacyiglycerol (triglycerides) are esters of fatty acids with glycerol. They are the main storage forms of Fat.  Oils are triacylglycerol with high content of unsaturated FA → low Tm = fluid at room temperature.  Fats are triacylglycerols with high content of saturated FA → high Tm = solid at room temperature.. Chemical properties of triacylglycerols:: (1) Hydrogenation (Hardening): Unsaturated FA adds 2 hydrogen atoms per double bond, forming the corresponding saturated FA e.g. oleic acid gives stearic acid. Adding H2 to saturate the double bonds of unsaturated FA of oils → Solid Fat. (3) Addition of oxygen (Oxygenation): The unsaturated FA in fats add 2 oxygen atoms per double bond, forming peroxides which are unstable, breaking into short chain aldehydes, ketons and acids. (4) Rancidity: Rancidity is the development of bad odor and taste in the fat. It is caused by its exposure to moisture, oxygen, warmth, light and certain metals as copper and lead.  Rancidity forms peroxides which break into short chain aldehydes, ketones, alcohols, and acids  Peroxidation of lipids is responsible for the deterioration of food and also for damage to the tissues in vivo causing cancer, inflammatory disease, atherosclerosis and aging. Rancidity can be prevented by phenols and anti- oxidants, avoidance of exposure to oxygen of the air, moisture or bacteria..  Waxes Waxes are esters of fatty acids with higher molecular weight monohydric alcohols. They are solids and resistant to hydrolysis.  COMPOUND LIPIDS Compound lipids contain groups in addition to an alcohol and a fatty acid. They include the following: (A) Phospholipids (B) Glycolipids (C) Proteolipids  (A) Phospholipids I. Glycerophospholipids II.Shingolipids Phospholipids (phosphatides) are compound lipids containing a phosphate radical. They include:  Glycerophospholipids  They are the main lipid constituents of cell membranes.  They may be regarded as derivatives of phosphatidic acid. (1) Phosphatidic acid: It consists of glycerol esterified with 2 FA and phosphoric acid at the third position. -Phosphatidic acid is important as an intermediate in the synthesis of triacylglycerols and phosphoglycerols. It is not found in tissues. Glycerophospholipids include: (2) Phosphatidylcholines (Lecithins): Lecithins consist of phosphatidic acid esterified with choline.  The most important phospholipids of the cell membrane. They represent the body’s store of choline which is important in nervous transmission and acts as doner of methyl groups. Dipalmitoyl-lecithin (lung surfactant) is a very effective surface active agent, preventing adherence of the inner surfaces of the lungs.. It is absent from the lungs of premature infants causing respiratory distress syndrome. (3) Phosphatidyl ethanolamine (Cephalins): Cephalins consist of phosphatidic acid esterified with ethanolamine. It is present mainly in myelin sheath of nerves and liver cell membrane. Ethanolamine (6) Cardiolipin (Diphosphatidylglycerol): Cardiolipin consists of 2 molecules of phosphatidic acids connected through one molecule of glycerol. It is the major lipid of mitochondrial membranes.  II.Sphingophospholids  They contain sphingosine alcohol instead of glycerol e.g., Sphingomyelins which consists of:  Sphingosine + fatty acid (Ceramide) + phosphoric acid + choline  They are found in large quantities in brain and nerve tissue.  (B) Glycolipids These are lipids containing a carbohydrate radical. The major glycolipids found in animal tissues are glycosphingolipids. They contain ceramide and one or more sugars and include the following:- (1) Galactosylceramide (Galactocerebroside): It is the major glycosphingolipid of the brain and nervous tissues. Galactosylceramide consists of sphingosine, a fatty acid (usually C24) and galactose. (2) Glucosylceramide: This is the predominent simple glycosphingolipids of extraneural tissues. It consists of sphingosine, a fatty acid (C24) and glucose.  (C) Proteolipids These are complex lipids in which the lipid surrounds the protein, making the molecule insoluble in water and soluble in fats and fat solvents. Proteolipids are found in nervous tissues.  DERIVED LIPIDS Derived lipids include the following: (1) Fatty acids (2)Alcohols e.g. glycerol, myricylalcohol (C30), sterols, vitamins A &D and sphingosine. (3) Hydrocarbon e.g. squalene. (4) Steroids including: sterols, bile acids and steroid hormones. (5) Carotenoids. (6) Vitamins E.  INTERACTION OF LIPIDS WITH AQUEOUS PHASES Lipids are insoluble in water, since they contain a predominance of non- polar groups. However, phospholipids, sphingollpids, bile salts and to lesser extent cholesterol posses both polar groups (water-soluble or hydrophilic) and non-polar groups (water-insoluble or hydrophobic).These lipids are called amphipathic lipids. At oil-water interfaces, these lipids become oriented with the polar group in the water phase and the non-polar group in the oil phase. A bilayer of these amphipathic lipids has been suggested as a basic structure in biologic membranes e.g. plasma, nuclear, mitochondrial and lysosomal membranes. In such membranes, the lipid molecules arrange themselves so that the non-polar groups of the two bilayers are towards each other, while the polar groups are towards the surrounding aqueous phases.