Pines City Colleges Biochemistry MLG 6 PDF

Pines City Colleges GENERAL EDUCATION DEPARTMENT First Semester, A.Y. 2024-2025 Course Number: BIOCHEM 101 Course Title: BIOCHEMISTRY Modular Learning Guide #6 Topic: LIPIDS Expect...

Pines City Colleges GENERAL EDUCATION DEPARTMENT First Semester, A.Y. 2024-2025 Course Number: BIOCHEM 101 Course Title: BIOCHEMISTRY Modular Learning Guide #6 Topic: LIPIDS Expected Time of Completion: 6 Hours A. Learning Outcomes 1. Explain the nature, structure and functions of lipids 2. List down substances involved in the biotransformation of the three basic foodstuffs B. Learning Content Overview MLG 6 discusses lipids which is another source of energy. It includes the chemical composition, nature, structure, and functions of this class of compounds. Since the building blocks of lipids are fatty acids, a part of the lesson will deal with these molecules. Recap/Review of the Past Lesson In MLG 1, lipids were introduced as the secondary source of energy, provides elasticity to the cell, and serves as insulator. Furthermore, you also know that lipids are also called fats. Concepts LIPIDS are a heterogeneous group of compounds related more by their physical properties rather than by their chemical properties. Lipids contain a long hydrocarbon chain (nonpolar portion) and a terminal carboxyl group (polar portion). BIOMEDICAL IMPORTANCE: 1. An efficient source of energy, both directly and potentially when stored in the adipose tissue. 2. A thermal insulator in the subcutaneous tissues and around certain organs, while non-polar lipids act as electrical insulators allowing rapid propagation of depolarization waves along myelinated nerves. 3. Lipoproteins (combination of lipids and proteins) are important cellular constituents and serving also as the means of transporting lipids in the blood. 4. Knowledge of lipid biochemistry is important in understanding many current biomedical areas of interest, e.g., obesity, atherosclerosis and the role of various polyunsaturated fatty acids in nutrition and health. FUNCTIONS: 1. Fuel – Fatty acids, on breakdown, form acetyl-CoA, NADH, and FADH2, which are important sources of energy. When attached to glycerol, fatty acids may be stored as triglycerides (fats). 2. Cell membrane components - Lipids, particularly the phospholipids, glycolipids, and cholesterol are important cell membrane components throughout the body. Sphingomyelin, cerebrosides, and gangliosides are particularly important cell membrane constituents in the nervous system. 3. Steroid hormones are lipids a. Sex hormones b. Glucocorticoids c. Mineralocorticoids 4. Bile acids are lipids – Bile acids are substances that emulsify fats and increase their surface area for further breakdown in the gut for easy digestion. 5. Prostaglandins are lipids – These are lipids with diverse hormone-like functions. 6. The fat-soluble vitamins (A, D, E, and K) are lipids. 7. Lipids can combine with carbohydrates or proteins to form glycolipids and lipoproteins. 1|Page  PROPERTIES: 1. Relatively insoluble in water 2. Soluble in non-polar solvents such as ether, chloroform and benzene 3. Have a characteristic greasy feel and when brought in contact with a substance like paper, penetrates through it producing a translucent spot 4. When pure, neutral fats are odorless, tasteless and colorless (colors of certain fats are due to the pigments that are dissolved in them) 5. Non-volatile (do not easily evaporate) and produce characteristic crystals with definite melting point 6. Fat floats on water because it has a lower density than the latter 7. Hydrolysis – Fats are readily hydrolyzed by acids, enzymes or superheated steam with the liberation of fatty acids and glycerol. 8. Saponification – Saponification is the process of forming soap from fats and alkali. 9. Emulsification – Fats are emulsified to form smaller globules in order to increase the surface area. Greater surface area means greater solubility and digestibility. 10. Rancidity – Fats when exposed to oxidizing agents like air, moisture, dirt, heat, bacteria and lipid oxidase will form odorous ketones and aldehydes which then alters the pH, color, taste, consistency, and nutritional value of the fat. Rancidity damages the accessory food factors like carotene, vitamin A, and vitamin E. Rancid fat aside from being unpalatable may even be toxic. 11. Detergency – Detergency refers to the ability of fats to form bubbles which absorb dirt particles and are washed away by water. Specific Properties Used to Identify Fats: 1. Physical Properties a. Melting point – temperature when fats soften b. Softening point – temperature at which the column of fat rises in the capillary tube c. Slipping point – temperature at which the fat rises in the cylinder d. Shot melting point – temperature at which a small lead shot falls through a sample e. Refractive index – degree of deflection of light that occurs when it passes from one transparent medium to another f. Smoke point – temperature at which a fat or oil gives off a thin bluish smoke g. Flash point – temperature at which the mixtures of vapor and air will ignite h. Fire point – temperature at which the substance will sustain continued combustion i. Turbidity point – temperature at which turbidity is first detectable 2. Chemical Properties a. Reichert Meissl Number – number of milliliters of 0.1N alkali required to neutralize the volatile water- soluble fatty acids in a 5-gram sample of fat b. Hehner Value – a measure of the amount of fatty acids which are insoluble in water c. Polenske Number – number of milliliters of 0.1N alkali necessary to neutralize the volatile water- insoluble fatty acids which are present in 5-gram sample of fat d. Kirschner Value – a measure of the potential amount of soluble silver salts in the Reichert Meissl distillate e. Saponification Number – number of milligrams of potassium hydroxide required to saponify 1 gram of fat or oil f. Iodine Number – number grams of iodine or iodine compound absorbed by 100 grams of fat g. Acetyl Value – a measure of the amount of hydroxyl fatty acids present in a fat Fat Iodine Number Saponification Reichert Meissl Acetyl Number Number Number Butter 26-28 210-230 17-34.5 1.9-8.6 Castor oil 84 175-183 1.4 146-150 Coconut oil 6-10 253-262 6.6-7.5 2 Cod liver oil 137-166 171-189 0.2 1.1 Cottonseed oil 103-111 194-196 0.95 21-25 Human fat 65-69 194-198 0.4 Lard 47-66.5 195-203 0.5-0.8 2.6 Linseed oil 175-202 188-195 0.95 4 Olive oil 79-88 185-196 0.6-1.5 10.5 2|Page  CLASSIFICATIONS (by Bloors): I. SIMPLE LIPIDS – esters of fatty acids with various alcohols Esterification – a chemical reaction whereby an ester if formed by the elimination of water and the bonding of an alcohol and an organic acid. Note: Triglyceride is an ester derived from glycerol and three fatty acids. Triglyceride is a general term referring to esters (fats) of glycerol. A. NEUTRAL FATS – esters of fatty acids with glycerol (hence called acylglycerols); fat in the liquid state is known as oil Some fats are visible, like butter, lard, and margarine. There are also fats considered as invisible, like dairy products, eggs, and meat. Glycerol (also called glycerine) is the simplest trihydric alcohol. It is an oily, colorless, heavy liquid having a sweet taste. It is used in pharmaceutical and cosmetic preparations. B. WAXES – esters of fatty acids with higher molecular weight monohydric alcohols 1. True waxes 2. Cholesterol waxes 3. Vitamin A esters 4. Vitamin D esters Examples: 1. Lanolin is widely used as a base for ointments and as an emollient for the skin. 2. Spermaceti is secreted by the sperm whale and is used in the manufacture of candles, cosmetics, ointments and in the pharmaceutical preparations known as cerates to give them a firmer consistency than the usual ointments. 3. Beeswax is taken from the honeycomb and is used in shoe polishes, candles, wax paper and the manufacture of artificial flowers. 4. Carnauba wax is a very hard wax capable of producing a high polish; is obtained from the leaves of the Brazilian palm tree and is used in automobile and floor waxes and in deodorant sticks. 5. Paraffin wax is a mixture of high-molecular-weight hydrocarbons separated during the fractionation of petroleum; used in the manufacture of candles. Note: The human skin secretes a wax which keeps the skin soft and pliable (can be bent or repeatedly stretched without breaking). II. COMPOUND/COMPLEX LIPIDS – esters of fatty acids containing groups in addition to an alcohol and a fatty acid A. PHOSPHOLIPIDS/PHOSPHATIDS – lipids containing, in addition to fatty acids and an alcohol, a phosphoric acid residue; they frequently have nitrogen-containing bases and other substituents 1. Lecithin – When freshly prepared it is waxlike in appearance but turns brown on exposure to air due to oxidation. On hydrolysis it yields 2 molecules of fatty acids and 1 molecule each of phosphoric acid, glycerol and choline. It mobilizes cholesterol or simply, it prevents the deposition of cholesterol. 3|Page  Note: Lecithinase is an enzyme present in cobra venom and poisonous spiders which hydrolyzes lecithin. It removes the unsaturated fatty acids from lecithin producing lysolecithin. The latter has a hemolyzing action on the red blood cell and this result into the poisonous effect of the venom. 2. Cephalin – Its chemical structure is similar to lecithin but its nitrogenous base is cholamine (ethanolamine). It is a thromboplastic substance which means it initiates the process of blood coagulation. 3. Sphingomyelin (phosphatidyl sphingosine choline) – It is a phosphatid that do not contain the glycerol component. On hydrolysis it yields fatty acids, phosphoric acid and 2 nitrogenous bases (sphingosine and choline). 4. Plasmalogen – It is similar to lecithin-cephalin group except that the 2 OH of glycerol which ordinarily would be esterified to fatty acids are instead bound in acetal linkage to fatty acid aldehyde. 5. Lipositol (phosphatidyl inositol) – It was first discovered in acid-fast bacteria and later found also in soybeans and brain tissue. 4|Page  6. Phosphatidyl serine – It is found in the brain and in small amounts in the blood. 7. Cardiolipin – It is a double phosphoglyceride found abundantly in the inner membrane of mitochondria and bacterial membranes. Note: Phospholipids are amphipathic molecules (molecules having both hydrophobic and hydrophilic groups) with a polar portion (phosphate) and a nonpolar portion. B. GLYCOLIPIDS/GLYCOSPHINGOLIPIDS – lipids containing a fatty acid, sphingosine and carbohydrate 1. Phosphoinositides – These are phosphatides containing inositol and play an important role in the transport mechanism of the cells. 5|Page  2. Cerebrosides – These molecules occur mostly in the medullary sheath of the nerves and the white matter of the brain. example: kerasin, phrenosin, nervone, oxynervone. C. SULFOLIPIDS – It is a sulfuric acid ester of cerebron. D. AMINOLIPIDS – Lipids that contain amino groups. 6|Page  E. LIPOPROTEINS – These are substances of fat and protein which provides the main transport form of fat substances in the bloodstream. III. PRECURSOR or DERIVED LIPIDS – products of the hydrolysis of simple and compound lipids, but still exhibiting the general physical characteristics of lipids A. FATTY ACIDS 1. Saturated fatty acids are fatty acids with no double bonds. These substances are liquid at ordinary room temperature and are volatile. Example: Formic acid (1) = ants and stinging nettles Acetic acid (2) end product of carbohydrate fermentation Propionic acid (3) by rumen organisms Butyric acid (4) certain fats in small amount (especially butter) Valeric acid (5) Caproic acid (6) small amounts in many fats (including butter) Caprylic acid (8) especially those of plant origin (coconut, Capric acid (10) nut, and palm oil) Lauric acid (12) = spermaceti, cinnamon, palm kernel, coconut oils, laurels, butter Myristic acid (14) = nutmeg, palm kernel, coconut oils, myrtles, butter Palmitic acid (16) common in all animal and plant fats Stearic acid (18) Arachidic acid (20) = peanut oil Behenic acid (22) = seeds Lignoceric acid (24) = cerebrosides, peanut oil Note: The number enclosed in parentheses refers to the number of carbon atoms in the fatty acid. 2. Unsaturated fatty acids are unstable and reactive due to the presence of the double bonds. These substances are liquid at ordinary room temperature and are non-volatile. a. Monoenoic acids i. Palmitoleic acid (16:1;9) = nearly all fats ii. Oleic acid [cis] (18:1;9) =possibly the most common fatty acid in natural foods iii. Elaidic acid [trans] (18:1;9) = hydrogenated and ruminant fats iv. Erucic acid (22:1;13) = rape and mustard seed oils v. Nervonic acid (24:1;15) = cerebrosides 7|Page  b. Dienoic acids i. Linoleic acid (18:2;9,12) = corn, peanut, cottonseed, soybean and many plant oils c. Trienoic acids i. γ-Linolenic acid (18:3;6,9,12) = some plants (oil of primrose) ii. α-Linolenic acid (18:3;9,12,15) = linseed oil d. Tetraenoic acids i. Stearidonic acid (18:4;6,9,12,15) = cod liver oil ii. Arachidonic acid (20:4;5,8,11,14) = peanut oil e. Pentaenoic acids i. Timnodonic acid (20:5;5,8,11,14,17) = fish oils (cod liver oil) ii. Clupanodonic acid (22:5;7,10,13,16,19) = fish oils f. Hexaenoic acids i. Cervonic acids (22:6;4,7,10,13,16,19) = fish oils Note: The unsaturated fatty acids constitute the essential fatty acids. The numbers enclosed in parentheses, indicates the number of carbon atoms, the number of double bonds and the location of the double bonds. Example: γ-Linolenic acid (18:3;6,9,12) – The fatty acid with this numbers has 18 carbon atoms, 3 double bonds located at carbons 6,9,12. Omega-3 and omega-6 are fats that the body cannot manufacture from other fats, so these fatty acids must be obtained from food. Omega-e fats are healthful because they help prevent clotting and swelling that increase the risk of heart attacks and cancer. 3. Cyclic fatty acids a. Hydnocarpic acid (plant origin) b. Chaulmoogric acid (plant origin) c. Phthioic acid (C26H52O2) – It is a liquid at ordinary room temperature that was shown to produce proliferation of epitheloid and giant cells. It is probably the agent responsible for the manifestation of tuberculosis. 4. Hydroxy fatty acids a. Saturated Examples: Dihydroxystearic acid – C17H33(OH)2COOH = castor oil Cerebronic acid – C23H46(OH)COOH = brain glycolipids Lanoceric acid – C31H61(OH)2COOH = wool fat b. Unsaturated Examples: Ricinoleic acid – C17H32(OH)COOH = castor oil Oxynervonic acid / Hydroxynervonic acid – C23H44(OH)COOH = glycolipids B. MONO- and DIGLYCERIDES – play an important role in the digestion of fat; act as detergents and emulsifying agents. C. ALCOHOLS – either straight chain, those containing the b-ionone ring or sterols. 1. Straight chain – products of hydrolysis of waxes 2. Alcohols containing b-ionone ring – vitamin A and some carotenols 8|Page  3. Sterols - aromatic alcohols which are derivatives of a simple steroid nucleus known as cyclopentanoperhydrophenanthrene. CHOLESTEROL is the representative member of sterols. It is the precursor of a large number of equally important steroids. It is a major constituent of the plasma membrane and of plasma lipoproteins. It is an unsaturated alcohol that forms colorless rhombic crystals with notches at the corner. CHOLESTEROL is an important amphipathic lipid, which allows it to play a structural role in membranes and in the outer layer of lipoproteins; a major constituent of gallstones; can be derived from diet or from biosynthesis. It is the precursor of all other steroids in the body: 1. corticosteroids 2. sex hormones 3. bile acids 4. vitamin D STAGES INVOLVED IN THE BIOSYNTHESIS OF CHOLESTEROL: 1. MEVALONATE, a six-carbon compound, is synthesized from acetyl CoA. 2. ISOPRENOID units are formed from mevalonate by loss of CO2. 3. Six isoprenoid units condense to form the intermediate, SQUALENE. 4. Squalene cyclises to give rise to the parent steroid, LANOSTEROL. 5. CHOLESTEROL is formed from lanosterol after several further steps, including the loss of three methyl groups. ERGOSTEROL was discovered by Tanret from ergot. It is isolated from yeasts and certain mushrooms and is important as a precursor of vitamin D. When irradiated with ultraviolet light, it acquires antirachitic properties. D. MISCELLANEOUS 1. Aliphatic hydrocarbons 2. Vitamin D, E, and K 3. Squalene – a hydrocarbon found in shark liver and human sebum 4. Carotenoids KETOGENESIS – occurs in the mitochondria and involves the oxidation of fatty acids; ketone body production in the liver, in the form of: 1. acetoacetate 2. D-3-hydroxybutyrate 3. acetone EICOSANOIDS – formed by the bonding of arachidonate and some other C20 fatty acids with methylene; physiologically and pharmacologically active compounds known as: 1. prostaglandins (PG) 2. thromboxanes (TX) 3. leukotrienes (LT) 4. lipoxins (LX) BIOTRANSFORMATION OF THE THREE MAIN FOODSTUFFS: 9|Page CARBOHYDRATE  FATTY ACIDS AMINO ACIDS CO2 Acetyl-CoA Acetyl-CoA Malonyl-CoA Acetoacetyl-CoA Acetyl-CoA Fatty Acids Hydroxymethyl-glutaryl-CoA Acetogenins Prostaglandins Ketone Bodies Terpenes Triacylglycerols and other Cholesterol Complex Lipids Bile Acids Fecal Steroids Steroid Here are few notes about the substances in this biotransformation: Acetyl-Coenzyme A is the molecule that makes fats or burns them. It is the key precursor in the biosynthesis of many lipids. It is used in the synthesis of isoprenoid molecules, esters, and amides. A stands for acetyl, since one of the coA’s main job is to transfer two-carbon units in the form of acetyl between various biological molecules. Malonyl-Coenzyme A is a fatty precursor that is very important in the body’s regulation of fatty acid metabolism (it provides growing fatty acids chains with two units of carbon). 10 | P a g e Prostaglandins were first discovered and isolated from human semen in the 1930’s by Ulf von Euler of Sweden. The name came from the word prostate (thinking that they originated from the prostate gland, but in reality these substances exist and are synthesized in virtually all cells of the body). It is a lipid tissue hormone synthesized from long-chain fatty acids. It can cause smooth muscle contraction or relaxation, vasodilation, stimulation of blood clotting, activation of inflammatory response, production of pain and fever, induction of labor, and other reproductive processes. Acetoacetyl-Coenzyme A (C25H41O18N7P3S) is an intermediate product in the oxidation of fatty acids. Hydroxymethyl-glutaryl-Coenzyme A is an intermediate product in the biosynthesis of steroids. 11 | P a g e Acetogenins are natural substances from plant of the family Annonaceae. These compounds are very potent inhibitors of the NAD-ubiquinone reductase activity of the mammalian mitochondria. Terpenes are a class of molecules that contain either ten to fifteen carbon atoms built from the five-carbon building block isoprene. These substances are responsible for the odor and color of certain plants. Terpenes are found in a variety of spices and flavorings such as: 1. menthol in mint 2. citral in lemon 3. selinene in celery 4. zingiberene in ginger 5. β-carotene in carrots and other plants Structure of isoprene 12 | P a g e C. Learning Activities This activity will be rated (20 points). Write your answers on a whole piece of intermediate paper. What are cis and trans fatty acids? Draw the structure and give the names of 5 cis and 5 trans fatty acids. D. Resources For additional information and better understanding of lipids you make access the following websites: 1. What are lipids? https://www.news-medical.net/life-sciences/What-are-Lipids.aspx 2. Lipids https://www.britannica.com/science/lipid 3. Lipids https://www.khanacademy.org/science/biology/macromolecules/lipids/a/lipids 4. What are lipids? https://www.jove.com/science-education/10683/what-are-lipids 5. Lipids https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/lipids E. Assessment The assessment activity for this module will be a 25-point quiz next meeting. F. References Harvey, Richard and Denise Ferrier. (2017). Lippincott’s Illustrated Reviews: Biochemistry (7th edition). U.S.A.: Wolters Kluwer. Murray, Robert K. et al. (2015). Harper’s Illustrated Biochemistry (30th edition). U.S.A.: McGraw-Hill Book Company. Prepared by Cecilia L. Cabanilla Instructor 13 | P a g e