Lipids - BIOMOL LEC PPT 3 PDF

Lipids COMPILED AND ARRANGED BY JUSTIN RACHELLE P. DIMAGUIBA  Learning objectives To describe the molecular structure of a lipid To classify different types of lipids To name types of lipids To describe the physical and chemical properties of lipids ...

Lipids COMPILED AND ARRANGED BY JUSTIN RACHELLE P. DIMAGUIBA  Learning objectives To describe the molecular structure of a lipid To classify different types of lipids To name types of lipids To describe the physical and chemical properties of lipids  Lipids Organic molecules characterized by their solubility in non polar solvents such as ether, chloroform, and acetone hydrophobic Function as energy storage, protection of organs, insulation, and absorption of vitamins Others are energy sources, hormones or vitamins  Structure of Lipids made of the elements Carbon, Hydrogen and Oxygen, but have a much lower proportion of water than other molecules such as carbohydrates Unlike polysaccharides and proteins, lipids are not polymers—they lack a repeating monomeric unit. They are made from two molecules: Glycerol and Fatty Acids Structure of Lipids  Structure of Lipids A glycerol molecule is made up of three carbon atoms with a hydroxyl group attached to it and hydrogen atoms occupying the remaining positions. Fatty acids consist of an acid group at one end of the molecule and a hydrocarbon chain, which is usually denoted by the letter ‘R’. They may be saturated or unsaturated. A fatty acid is saturated if every possible bond is made with a Hydrogen atom, such that there exist no C=C bonds.  Saturated FAs A fatty acid is saturated if every possible bond is made with a Hydrogen atom, such that there exist no C=C bonds.  Unsaturated FAs Unsaturated fatty acids, on the other hand, do contain C=C bonds. Monounsaturated fatty acids have one C=C bond, and polyunsaturated have more than one C=C bond. Structure of Triglycerides Triglycerides are lipids consisting of one glycerol molecule bonded with three fatty acid molecules. bonds between the molecules are covalent and are called ester bonds They are formed during a condensation reaction. The charges are evenly distributed around the molecule so hydrogen bonds to not form with water molecules making them insoluble in water. Structure of Triglycerides Classification of Lipids  Simple Lipids Esters of fatty acids with various alcohols: a) Neutral fats (Triacylglycerol, TG): These are tri-esters of fatty acids with glycerol. b) Waxes are esters of fatty acids with higher monohydroxy aliphatic alcohols. True waxes are esters of higher fatty acids with cetyl alcohol (C16H33OH) or other higher straight chain alcohols. Cholesterol esters are esters of fatty acid with cholesterol. Vit A and Vit D esters are palmitic or stearic acids esters of Vit A (Retinol) or Vit D respectively.  Example of Simple Lipids Waxes Waxes are “esters” (an organic compound made by replacing the hydrogen with acid by an alkyl or another organic group) formed from long-chain carboxylic acids and long-alcohols. Waxes are seen all over in nature. The leaves and fruits of many plants have waxy coatings, which may protect them from dehydration and small predators. The feathers of birds and the fur of some animals have similar coatings which serve as a water repellent. Carnauba wax is valued for its toughness and water resistance(great for car wax).  Compound Lipids Esters of fatty acids containing groups, other than, and in addition, to an alcohol and fatty acids. a) Phospholipids: They are found chiefly in animal tissues. They are substituted fats containing in addition to fatty acid and glycerol, a phosphoric acid residue, a nitrogenous base and other substituents.  Examples of Compound Lipids Phospholipids Membranes are chiefly made of phospholipids which are Phosphoacylglycerols. Triacylglycerols and phosphoacylglycerols are similar however the terminal OH group of the phosphoacylglycerol is esterified with phosphoric acid instead of fatty acid which leads to the formation of phosphatidic acid. The name phospholipid comes from the fact that phosphoacylglycerols are lipids that contain a phosphate group. Phospholipids  Phospholipids (Phosphatides): They are found chiefly in animal tissues. Substituted fats, consisting of phosphatidic acid; composed of glycerol, fatty acids and phosphoric acid found in ester linkage to a nitrogenous base. Examples of Phospholipids Lecithin: Lecithin is found in brain, egg yolk and organ meats. Phosphatidyl choline or serine—phosphatide linked to choline; a lipotropic agent; important in fat metabolism and transport— are used as emulsifying agent in the food industry. Examples of Phospholipids Cephalin: Occurs predominantly in nervous tissue. Phosphatidyl ethanolamine; phosphatide linkage to serine or ethanolamine. Examples of Phospholipids Plasmalogen: They are found in brain, heart and muscle. Examples of Phospholipids Lipositol: They are found in brain, heart, kidneys and plant tissues together with phytic acid. Phosphatidyl inositol means phosphatide linked to inositol. Their rapid synthesis and degradation takes place in brain. Examples of Phospholipids Sphingomyelin: They are found in nervous tissue, brain and red blood cells. Sphingosine containing phosphatide; yields fatty acids, choline, sphingosine, phosphoric acid and no glycerol. Examples of Compound Lipids Glycolipids Lipids containing carbohydrate moiety are called glycolipids. They contain a special alcohol called sphingosine or sphingol and nitrogenous base in addition to fatty acids but does not contain phosphoric acid or glycerol. Examples of Glycolipids Cerebroside or Glycolipid or Glycosphingosides: They are found in myeline sheaths of nerves, brain and other tissues. They upon hydrolysis yields sphingosine, galactose (or glucose) and fatty acids. Examples of Glycolipids Ganglioside: Found in the brain, nerve tissue and other selected tissues, notably spleen. They contain a ceramide linked to hexose (glucose or galactose), neuraminic acid, sphingosine and fatty acids. Examples of Glycolipids Sulfolipid: They are found in white matter of brain, liver and testicle, also found in plant chloroplast. They are sulphur-containing glycolipid. In sulfolipid, sulphate is present in ester linkage to galactose. Examples of Glycolipids Aminolipids (Proteolipids): They are found in brain and nerve tissue. They are the complexes of protein and lipids.  Derived Lipids Hydrolysis product of simple and compound lipids is called derived lipids. They include fatty acid, glycerol, sphingosine and steroid derivatives. Derivatives obtained by hydrolysis of those given in group I and II, which still possess the general characteristics of lipids. a) Fatty acids may be saturated, unsaturated or cyclic. b) Monoglycerides (monoacylglycerol) and Diglycerides (diacylglycerol) c) Alcohols Examples of Derived Lipids Fatty Acids a carboxylic acid either saturated, or unsaturated a vital constituent of lipids and is released during fasting from triacylglycerols to accommodate the energy requirements of the body Fatty Acid Structure  Systematic naming of the fatty acids Saturated fatty acids PREFIX: # of hydrocarbons SUFFIX: -anoic Ex: 1. Capric acid (C-10)= decanoic acid 2. Palmitic acid (C-16)= hexadecanoic acid  Systematic naming of the fatty acids Polyunsaturated fatty acids PREFIX: # of hydrocarbons SUFFIX: -enoic (1 double bond), dienoic( 2 double bonds), etc Ex: 1. Linoleic acid (C-18:2)= cis, cis-9,12,-octadecadienoic acid 2. Gamma-Linolenic acid (18:3) 6,9,12-octadecadatrieonic acid  Trivial names contain no clues to the structures one must learn the name and associate it with a separately learned structure names typically derive from a common source of the compound or the source from which it was first isolated EX: palmitic acid is found in palm oil oleic acid is a major constituent of olive oil (oleum) stearic (from the Greek word meaning solid) acid is solid at room temperature Spiders (arachnids) contain arachidonic acid  Greek letters denote positions relative to the carboxyl carbon Classification of Fatty Acids  Types of fatty acids Based on carbon chain length a. Long-chain fatty acid (C-12 to C-26) b. Medium chain fatty acid (C-8 and C-10) c. Short-chain fatty acid (C-4 and C-6) Types of fatty acids Based on carbon to carbon bonds a. Saturated fatty acids (SFAs) b. Monounsaturated fatty acids (MUFAs) c. Polyunsaturated fatty acids (PUFAs)  Examples of Unsaturated Fatty Acid In its symbols form First no. represent C numbers and Second no. represent the double bond. Greek letter delta( ) signifies double bond. Types of fatty acids Fatty acids with carbon-carbon double bond are unsaturated. Saturated fatty acids lack this double carbon bonding.  Saturated Fatty Acids fatty acids have a single C-C bond solid at room temperature usually contain 12-22 carbon atoms Ex: Ghee, Butter, Palmito-oleic acid etc.  Saturated Fatty Acids These belong to the acetic series and have the general formula of CnH2nO2 Palmitic acid make up about 15 to 50% of the total fatty acids in fats. Myristic and stearic acids are also present Tuberculo- stearic (10-methyl stearic acid) acid occurs in the lipids of human tubercle bacilli They are abundant in butter, animal fat, lard, coconut and peanut oil  Monounsaturated fatty acid fatty acids that have one double bond in the fatty acid chain with all of the remainder carbon atoms being single-bonded typically liquid at room temperature but start to turn solid when chilled EX: Olive oil, canola oil, peanut oil, safflower oil and sesame oil.  Monounsaturated fatty acid can help reduce bad cholesterol levels in the blood Lowers the risk of heart disease and stroke provides nutrients to help develop and maintain body’s cells. contribute vitamin E to the diet, an antioxidant vitamin  Polyunsaturated fatty acids contain more than one double bond in their backbone includes many important compounds, such as essential fatty acids give drying oils their characteristic property.  Polyunsaturated fatty acids can help reduce bad cholesterol levels in the blood which can lower your risk of heart disease and stroke Oils rich in polyunsaturated fats also provide essential fats that your body needs but can't produce itself – such as omega-6 and omega-3 fatty acids.  Polyunsaturated fatty acids Linoleic acid series (18 : 2; 9, 12) It contains two double bonds between C9 and C10; and between C12 and C13. Their general formula is CnH2n–3 COOH. Dietary sources: Linoleic acid is present in sufficient amounts in peanut oil, corn oil, cottonseed oil, soyabean oil and egg yolk  Polyunsaturated fatty acids Linolenic acid series (18 : 3; 9, 12, 15): It contains three double bonds between 9 and 10; 12 and 13; and 15 and 16. Their general formula is CnH2n–5 COOH. Dietary Source: Found frequently with linoleic acid, but particularly present in linseed oil, rapeseed oil, soybean oil, fish visceras and liver oil (cod liver oil).  Polyunsaturated fatty acids Arachidonic acid series (20 : 4; 5, 8, 11, 14): It contains four double bonds. Their general formula: CnH2n–7 COOH Dietary source: Found in small quantities with linoleic acid and linolenic acid but particularly found in peanut oil. Also found in animal fats including Liver fats.  Unsaturated Fatty acids have the Double C-C bond are LIQUID at room temperature If one double bond present in fatty acid it is called Monosaturated or Monoenoic fatty acids. If more than one double bond present in fatty acid it is called Polysaturated or Polyenoic fatty acid. For e.g. vegetable oil. Omega-3 polyunsaturated fatty acids found in oil from certain types of fish, vegetables, and other plant sources not made by the body and must be consumed in the diet are used together with diet and exercise to help lower triglyceride levels in the blood.  Omega-6 polyunsaturated fatty acids are used for reducing the risk of heart disease lower total cholesterol levels, lowering "bad" (LDL) cholesterol levels raising "good" (HDL) cholesterol levels Reduce the risk of cancer Omega-6 polyunsaturated fatty acids family of polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the n-6 position the sixth bond, counting from the methyl end. Examples of Derived Lipids Steroids The chemical messengers in our bodies are known as hormones which are organic compounds synthesized in glands and delivered by the bloodstream to certain tissues in order to stimulate or inhibit the desired process.  Steroids -Steroids are a type of hormone which is usually recognized by their tetracyclic skeleton, consisting of three fused six-membered and one five-membered ring -The four rings are designated as A, B, C & D as noted in blue, and the numbers in red represent the carbons.  Steroids Cholesterol is waxy like substance, found only in animal source foods. Triglycerides, LDL, HDL, VLDL are different types of cholesterol found in the blood cells. Cholesterol is an important lipid found in the cell membrane. It is a sterol, which means that cholesterol is a combination of steroid and alcohol. In the human body, cholesterol is synthesized in the liver.  Steroids These compounds are biosynthesized by all living cells and are essential for the structural component of the cell membrane. In the cell membrane, the steroid ring structure of cholesterol provides a rigid hydrophobic structure that helps boost the rigidity of the cell membrane. Without cholesterol, the cell membrane would be too fluid. It is an important component of cell membranes and is also the basis for the synthesis of other steroids, including the sex hormones estradiol and testosterone, as well as other steroids such as cortisone and vitamin D.  Anabolic steroids pose health risks Anabolic steroids are abused by some athletes with serious consequences, including – violent mood swings, – depression, – liver damage, – cancer, – high cholesterol, and – high blood pressure. © 2012 Pearson Education, Inc. Examples of Derived Lipids Eicosanoids are signalling molecules made by the enzymatic or non-enzymatic oxidation of arachidonic acid or other polyunsaturated fatty acids (PUFAs) that are, similar to arachidonic acid, 20 carbon units in length. Examples of Derived Lipids Eicosanoids Most eicosanoids are produced from arachidonic acid, which is a polyunsaturated fatty acid that you get from eating foods like animal fats. They have many effects on your body, including inflammation, fever promotion, blood pressure regulation, and blood clotting. Three classes of eicosanoids There are three classes of eicosanoids: prostaglandins, thromboxane, and leukotrienes. various eicosanoids are produced in different cell types by different synthetic pathways, and have different target cells and biological actions.  Examples of Derived Lipids Ketone bodies Ketone bodies are produced by the liver and used peripherally as an energy source when glucose is not readily available. The two main ketone bodies are acetoacetate (AcAc) and 3-beta-hydroxybutyrate (3HB), while acetone is the third, and least abundant, ketone body.  Examples of Derived Lipids Ketone bodies Ketone bodies are readily transported into tissues outside the liver, where they are converted into acetyl-CoA —which then enters the citric acid cycle and is oxidized for energy. Examples of Derived Lipids  Examples of Derived Lipids Ketone bodies serves as energy fuels for extrahepatic tissues like brain, heart, or skeletal muscle play pivotal roles as signaling mediators, drivers of protein post-translational modification (PTM), and modulators of inflammation and oxidative stress.  Miscellaneous Lipids Squalene -a polyunsaturated hydrocarbon with a formula of C₃₀H₅₀ -found in certain fish oils, especially shark liver oil, in high amounts and some vegetable oils in relatively smaller amounts - Human sebum also contains 13% squalene as one of its major constituents.  Miscellaneous Lipids Carotenoids -are among the most widely distributed pigments and naturally exhibit red, orange and yellow colors -lipid-soluble pigments, which can be found in many kinds of fruit, vegetables, fungi, flowers and some kinds of animals (Ötles and Çagindi, 2008) Carotenoids are ubiquitous and essential pigments in photosynthesis. They absorb in the blue-green region of the solar spectrum and transfer the absorbed energy to (bacterio-)chlorophylls, and so expand the wavelength range of light that is able to drive photosynthesis. Physical Properties of Lipids Saturated fatty acids are solid at room temperature. Unsaturated fatty acids are liquid at room temperature. The long chain length of fatty acid has a high melting point than short-chain fatty acids. The solubility of fatty acids decrease due to increase in no. of the methylene group Presence of double bond increases the solubility of fatty acids. Acetic acid is completely miscible with water because it contains only 1 methyl group. Palmito-oleic acid is more soluble than palmitic acid. Fatty acids form salts with alkali and alkaline earth metal. Physical Properties of Lipids Salts of sodium, potassium, calcium, and magnesium are formed when fatty acids react with these salts. Fats have the specific gravity less than 1 and, also lower than water, therefore, they float on water. The melting point of fats depends upon their constituent fatty acids. Greater the amount of unsaturated fatty acids in the fat molecule, lower will be the melting point. Physical Properties of Lipids Freshly prepared fats are colorless, odorless and tasteless. Any color or taste is due to association with other foreign substances. Example: The yellow color of butter or is due to the presence of plant pigments carotene and xanthophyll.  Chemical Properties of Lipids Hydrolysis Saponification Reactions due to unsaturation Saponification number and Iodine number Rancidity  Hydrolysis through heating of fats with water at high temperature and pressure The hydrolysis of ingested fats is efficiently accomplished by enzyme Lipase present in pancreatic juice. Hydrolysis of fats  Saponification By boiling with strong alkanes such as NaOH, the fats are readily decomposed into Glycerol and salts of constituent fatty acids (Soap).  Reactions due to Unsaturation The double bonds of unsaturated fatty acids in fats undergo the reaction such as: Hydrogenation Halogenation Oxidation  Hydrogenation -Hydrogen can be added across the C to C double bond -This reaction is called hydrogenation and decrease the level of unsaturation in the fatty acid  Trans Fatty Acid Overview one sub-type of fatty acid referred to trans fatty acids simply as trans fats helps preserve the shelf life of food To create a trans fat, an unsaturated fatty acid and force hydrogen ions in it, under high pressure  Health Effects of Trans Fats association between consumption of trans fats and heart disease no physiological need for the consumption of trans fats Trans fats occur in nature only to a small degree (and these may in fact be healthy) avoid manufactured trans fats partially hydrogenated oil on the label, there is trans fat in the product. hydrogenated soybean oil, not a healthy fat Manufacturers are now required to list the grams of trans fat on the label, but manufacturers can write 0 grams on the nutrition facts panel, even if there is 0.5 gram of trans fat. To figure out if a product has trans fat, look for partially hydrogenated and hydrogenated oil on the ingredient list.  Halogenation - Neutral fats containing unsaturated fatty acids have the ability if adding halogens (hydrogen / hydrogenation and iodine or iodination) at the double bonds - for the determination of the degree of unsaturation of the fat / oil that determines its biological value  Oxidation Polyunsaturated fatty acids are oxidized by non-enzymatic or enzymatic reactions. In non-enzymatic reaction, lipid peroxidation is an autoxidation process initiated by the attack of free radicals, such as reactive oxygen and nitrogen species (·OH and ONOO−).  Saponification Number the number of milligrams of KOH required to neutralized the fatty acids liberated from 1 gram of fat Short chain fatty acids have a higher saponification number. Long chain fatty acids have high MW and lower saponification number value= fewer number of carboxylic functional groups per unit mass of the fat. Example: Butterfats has a relatively higher saponification number, as it is rich in short-chain fatty acids. https://www.researchgate.net/publication/322818556_Coconut_Oil_Chemistry_and_Nutrition/figures?lo=1 Sample Computation on Saponification value in post-lab discussion  Iodine Number “The number of grams of iodine which will be absorbed by 100 grams of fat is termed its iodine number”. More unsaturated fatty acids have higher iodine number value than more saturated fatty acids. Sample Computation on Iodine number in post-lab discussion  Rancidity Many fats develop an unpleasant odor and taste when they are allowed to stand in contact with air at room temperature. Can be reduced by refrigeration  The Process of Rancidity Rancidity is due to two different processes: 1. Oxidative Rancidity 2. Hydrolytic Rancidity  Oxidative Rancidity Oxidation of fat molecules gives rise to some short chain aldehydes and ketones which have taste and odor. The oxygen of the air is necessary for the occurrence of this type of rancidity. Prevention from Oxidative Rancidity : This can be prevented by the addition of anti-oxidants such as Vitamin E to food containing fat.  Hydrolytic Rancidity due to the slow hydrolysis of fats In case of fats like butter results in the liberation of short chain fatty acids with odor and taste Hydrolysis of fats may be hastened by bacterial contaminants which produce enzyme lipase Rancidity also results in a loss of certain essential dietary constituents such as vitamins A and E, carotenes and linoleic acid. Hydrolytic rancidity of fats End of presentation