Lecture 5: Lipid - Abdullahi Umar Ibrahim

LECTURE 5: LIPID Asst. Prof. Dr Abdullahi Umar Ibrahim Definition Classification Biological importance  Definition Lipids are a heterogeneous group of organic compounds that are insolub­le in water and soluble in non-polar organic solvents. Lipid, i...

LECTURE 5: LIPID Asst. Prof. Dr Abdullahi Umar Ibrahim Definition Classification Biological importance  Definition Lipids are a heterogeneous group of organic compounds that are insolub­le in water and soluble in non-polar organic solvents. Lipid, include diverse group of organic compounds including fats, oils, hormones, and certain components of membranes that are grouped together because they do not interact appreciably with water. They naturally occur: in most plants, animals, microorganisms  Main Function Energy Storage Making Biological Membranes Insulation (Thermal) help keeps plant and animals warm Protection – e.g. protecting plant leaves from drying up Buoyancy (ability to float in water e.g. fish) Acting as hormones Act as the structural component of the body and provide the hydrophobic barrier that permits partitioning of the aqueous contents of the cell and subcellular structures. FUNCTIONS OF LIPIDS Precursor Structural of many Storage componen Act as Protection steroid form of t of cell thermal of internal hormones energy membran insulator organs , vitamin e. D FUNCTIONS OF LIPIDS Fats serve Helps in as Acts as Lipoprotei Improve absorptio surfactant electric ns taste and n of fat s by insulators transporti palatabilit soluble reducing in ng lipids y. vitamins surface neurons. tension.  Properties Lipids may be either liquids or non- crystalline solids at room temperature. Pure fats and oils are colorless, odorless, and tasteless. They are energy-rich organic molecules Insoluble in water Soluble in organic solvents like alcohol, chloroform, acetone, benzene, etc. No ionic charges Solid triglycerols (Fats) have high proportions of saturated fatty acids. Liquid triglycerols (Oils) have high proportions of unsaturated fatty acids.  CLASSIFICATION Lipids can be classified according to their hydrolysis products and according to similarities in their molecular structures. Three major subclasses are recognized:  Structure of lipid Lipids are made of 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. Lipid = [Glycerol + Fatty acid + X] Glycerol 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 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’ and methyl group. Fatty acids contain an even number of carbon atoms, from 4 to 36, bonded in an unbranched chain. Most of the bonds between carbon atoms are single bonds. TYPES OF FATY ACIDS Saturated fatty acids: When a fatty acid is saturated it is an indication that there are no carbon-carbon double bonds (If all of these bonds are single bonds, the fatty acid is said to be saturated). The saturated fatty acids have higher melting points than unsaturated acids of the corresponding size due to their ability to pack their molecules together thus leading to a straight rod-like shape. TYPES OF FATY ACIDS Unsaturated fatty acids: If a fatty acid has more than one double bond then this is an indication that it is an unsaturated fatty acid. “Most naturally occurring fatty acids contain an even number of carbon atoms and are unbranched.” Unsaturated fatty acids, on the other hand, have a cis-double bond(s) that create a kink in their structure which doesn’t allow them to group their molecules in straight rod-like shape.  Cis- and Trans-Fatty Acids Compared Almost all natural unsaturated fatty acids have cis stereochemistry in C=C’s. Small amounts of trans are produced in stomachs of ruminating animals by partial enzymatic hydrogenation of polyunsaturated fats, and thus are present in small amounts in milk and butter Commercial Hydrogenation of Fatty Acids H H H H H R partial H2 catalyst C C R C C R + C C R R H H R H ‘cis’ ‘trans’ unsaturated saturated unsaturated natural natural unnatural good bad bad Length of carbon chain Stearic acid – 18-carbon, saturated Simplified structure Oleic acid – 18-carbon, monounsaturated Linoleic acid – 18-carbon, polyunsaturated  Bonds A fatty acid is saturated if every possible bond is made with a Hydrogen atom, such that there exist no C=C bonds. 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.  FATTY ACIDS Hydrogenated – addition of hydrogen to unsaturated fat 1. Makes it more “solid” or firm 2. Effects stability and protects against oxidation; more “shelf- stable” 3. Widely used by food industry in margarine, shortening, peanut butter, baked goods & snack food Hydrogenation Triglycerides Triglycerides are lipids consisting of one glycerol molecule bonded with three fatty acid molecules. Triglyceride molecules contain mostly carbon and hydrogen atoms, with only six oxygen atoms per molecule The 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. Simple lipids (a) Fats and oils which yield fatty acids and glycerol upon hydrolysis. (b) Waxes, which yield fatty acids and long-chain alcohols upon hydrolysis. (a) Fats and oils Both types of com­pounds are called triacylglycerols because they are esters composed of three fatty acids joined to glycerol, trihydroxy alcohol. The difference is on the basis of their physical states at room temperature. It is customary to call a lipid a fat if it is solid at 25°C, and oil if it is a liquid at the same temperature. These differences in melting points reflect diffe­rences in the degree of unsaturation of the constituent fatty acids. DIFFERENCE BETWEEN FAT AND OIL Fats differ from oils only in that they are solid at room temperature, while oils are liquid. Fats and oils share a common molecular structure. This structural formula shows that fats and oils contain three ester functional groups. Fats and oils are esters of the tri-alcohol, glycerol (or glycerin). Therefore, fats and oils are commonly called triglycerides, although a more accurate name is triacylglycerols. One of the reactions of triglycerides is hydrolysis of the ester groups HYDROLYSIS This hydrolysis reaction produces glycerol and fatty acids, which are carboxylic acids derived from fats and oils. In the fatty acids, Ra, Rb, and Rc, represent groups of carbon and hydrogen atoms in which the carbon atoms are attached to each other in an unbranched chain. Soaps, Detergents and Micelles Soaps Sodium or potassium salts of fatty acids are called soaps. They are obtained by basic hydrolysis of triglycerides which is called saponification. Micelles In aqueous solution, the long chain carboxylic acids arrange themselves in spherical clusters called micelles. Soap contains the cleaning property because nonpolar oil that carry dirt dissolve in the nonpolar interior of the micelle and are carried out away with the soap during rinsing. Detergents Since soap can undergo precipitation (soap scum) in hard water due to reaction with calcium and magnesium ions, synthetic soaps (salt of benzenesulphonic acid) called detergents have been developed that don’t form soap scum in hard water. b. WAXES L IPI D Waxes are water-repelling solids that are part of the protective coatings of a number of living things, including the leaves of plants, the fur of animals, and the feathers of birds. Waxes are usually mixtures of esters in which both the alkyl and acyl group are unbranched and contain a dozen or more carbon atoms. Beeswax, for example, contains the ester triacontyl hexadecanoate as one component of a complex mixture of hydrocarbons, alcohols, and esters. Fatty acids normally occur naturally as esters; fats, oils, phospholipids, and waxes all are unique types of fatty acid esters. There is, however, an important class of fatty acid derivatives that exists and carries out its biological role in the form of the free acid. This class of fatty acid derivatives (b) Waxes Wax is an ester of long-chain alcohol (usually mono-hydroxy) and a fatty acid (i.e. are esters of long chain carboxylic acids with long chain alcohols). The acids and alcohols normally found in waxes have chains of the order of 12-34 carbon atoms in length. Artificial waxes For example, beeswax contains a 26 carbon carboxylic acid and a 30 carbon alcohol component, while carnauba wax has a 32 carbon carboxylic acid component and a 34 carbon alcohol component. Natural waxes Waxes are also common in living organisms. For example, wax is found on the surfaces of some leaves, where it serves as protectant against parasites and minimizes the evaporation of water. Similarly, the feathers of birds are coated with wax to make them water repellent. Waxes are used commercially to make cosmetics, candles, ointments, and protective polishes. Compound lipids (a) Phospholipids, Lipids that contain a phosphate group are called phospholipids. These lipids form membranes by arranging themselves in a lipid bilayer. The polar hydrophilic groups of the phospholipids are on the outside of the bilayer, while non-polar fatty acid tail form interior of the bilayer Phospholipids in foods: Lecithin, egg yolks, soybeans, wheat germ, peanuts They may be glycerophospholipids or sphingophospholipid depending upon the alcohol group present (glycerol or sphingosine). Phospholipids belong to the lipid family of Phospholipids biological polymers. A phospholipid is composed of two fatty acids, a glycerol unit, a phosphate group, and a polar molecule. The polar head region in the phosphate group of the molecule is hydrophilic (attracted to water), while the fatty acid tail is hydrophobic (repelled by water). When placed in water, phospholipids will orient themselves into a bilayer in which the non-polar tail region faces the inner area of the bilayer. The polar head region faces outward and interacts with the liquid. Phospholipids form a lipid bilayer in which their hydrophilic head areas spontaneously arrange to face the aqueous cytosol and the extracellular fluid, while their hydrophobic tail areas face away from the cytosol and extracellular fluid. The lipid bilayer is semi-permeable, allowing only certain molecules to diffuse across the membrane to enter or exit the cell. 1. Glycerophospholipids Glycerophospholipids are made by combining glycerol, two fatty acids, a phosphate group, and an alcohol. 2. Sphingophospholipids Sphingophospholipids are made by combining sphingosine, a fatty acid, a phosphate group, and an alcohol. (b) Glycolipids, which yield fatty acids, sphingosine or glycerol, and a carbo­hydrate upon hydrolysis. They may also be glyceroglycolipids or sphingoglycolipid depending upon the alcohol group present (glycerol or sphingosine). Or they are sphingolipids that contain carbohydrates (usually monosaccharides). They are also referred to as cerebrosides because of their abundance in brain tissue. C) Sphingolipids are complex lipids that contain sphingosine instead of glycerol. One important type of sphingolipids are the sphingomyelins Derived lipids: Hydrolysis product of simple and compound lipids is called derived lipids. They include fatty acid, glycerol, sphingosine and steroid derivatives. Steroid derivatives are phenanthrene structures that are quite different from lipids made up of fatty acids. Steroids Steroids are lipids having a tetracyclic system composed of three six membered rings and one five membered ring (4 total rings). Their non-polar character allows them to cross the cell membranes, so they can leave the cells in that they are produced and enter their target cells. Steroids can be broadly classified into five groups: glucocorticoids, mineralocorticoids, androgens, estrogens, and progestins.  Glucocorticoids are involved in metabolism of glucose, proteins and fatty acids. Cortisone is an example for this type of steroid. Cortisone is used as anti-inflammatory agent to treat arthritis. Mineralocorticoids are responsible for the increased reabsorption of Na+ , Cl- and HCO3 - ions by the kidneys that can lead to an increase in the blood pressure. Aldosterone is an example of a mineralocorticoid. Antrogens are male sex hormones. They are responsible for the development of male secondary sex characteristics during puberty. Testosterone is an example of androgens. Estrone and estradiol are female sex hormones known as estrogens. They are responsible for the development of female secondary characteristics and secreted by the ovaries. Estrogens also regulate the menstrual cycle. Progesterone is the hormone that is essential for the maintenance of pregnancy. It also prevents ovulation during pregnancy Cholesterol In animals, the most abundant member of steroid is cholesterol, which is the precursor of all other steroids. is the most abundant steroid in the body. It is an essential component of cell membranes, and is a precursor for other steroids, such as the bile salts, sex hormones, vitamin D, and the adrenocorticoid hormones. Terpenes Terpenes are available in nature as a diverse class of lipids. Some of them are used as spices, perfumes and medicines for thousands of years. The terpenes having functional groups such as OH and carbonyl group are called terpenoids BIOLOGICAL FUNCTION OF TRIGLYCERIDES Animals: The main biological function of triglycerides is as a fuel. The normal human body stores sufficient energy in fat for several weeks survival. This storage ability helps the organism deal with unpredictable variations in the food supply. Plants: Plants, too, store energy in fats and oils. Oils are particularly common in seeds, where the stored energy helps seedlings during germination, until they can exploit solar energy through photosynthesis. Comprehensive functions of Lipids Triglycerides: is sequestered as fat in adipose cells, which serve as the energy-storage depot for organisms and also provide thermal insulation. Some lipids such as steroid hormones serve as chemical messengers between cells, tissues, and organs, and others communicate signals between biochemical systems within a single cell. The membranes of cells and organelles (structures within cells) are microscopically thin structures formed from two layers of phospholipid molecules. Membranes function to separate individual cells from their environments and to compartmentalize the cell interior into structures that carry out special functions. So important is this compartmentalizing function that membranes, and the lipids that form them, must have been essential to the origin of life itself. Fat Digestion Overview Health Effects of Fats Excess fat intake contributes to many diseases including: 1. Obesity 2. Diabetes 3. Cancer 4. Heart disease  How? 1. High fat diets = high kcal diets 2. High saturated fat intake raises blood cholesterol 3. High fat intakes may promote cancer  POSSIBLE QUESTIONS What is Lipid and state 5 functions of Lipid Know the structure of Lipid (i.e. what is made up not drawing the structure) Triglycerides is made up…….., Fatty acid is made up of 3 components………..,………….,………….. What is the difference between unsaturated and saturated fatty acid and state 1 example each What is saponification? Phospholipids are made up…………………,………………………, ……………………, What is steroids and list 5 steroids What is cholesterol