BIOCHEMISTRY LAB # 7 LIPIDS

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1 Name: Per: Performance: BIOCHEMISTRY LAB # 7 LIPIDS BACKGROUND Lipids are a class of biological molecules that are grouped based on their similarities in solubility. Lipids are not soluble in water. Lipids are soluble in nonpolar solvents such as ether, chloroform, and benzene. Fatty acids, waxes, triglycerides, glycerophospholipids and steroids are classes of compounds that are classified as lipids due to their similar solubility properties. Lipids are a very diverse group of molecules that can be divided into five major subgroups based on their structure and function in the body. Identify the lipid classes described below: 1. : long chain hydrocarbons with a carboxyl groups, parts of triglycerides and phospholipids 2. : important mediators of immune response 3. : food and body fats/oil 4. : contain lipid hormones and cholesterols 5. : main component of cell membranes Cosmetics: Lotions are mixtures of fats and water that have been hydrolyzed. The fat lubricates the top layer of the skin, the water moves across the skin to hydrated deeper layers. In order to form a homogeneous mixture of fats and water, an has to be added, which are molecules having hydrophillic parts that love water and lipophillic parts that love fats. Vitamins: Several vitamins are fat soluble, i.e Vitamins A, D, E, K. Therefore, they can be better absorbed if eaten with some fat that keeps them dissolved and facilitates the uptake. The picture below shows Vitamin E. Circle and label the hydrophilic and hydrophobic parts of the Vitamin

2 Name: Per: Performance: PROCEDURE A. MODEL BUILDING: Triglycerides Materials: Organic model kit A.1. Build a model of glycerol and three molecules of ethanoic acid. What are the functional groups on each? Draw their structure as you see it, use appropriate colors. A.2. Form ester bonds between the hydroxyl groups on the glycerol and the carboxylic acid groups of the ethanoic acid molecules. In the process, three molecules of water are removed. What is the specific name of the product. Draw the reaction below in Kekule.. The reverse Rx splitting Fats and Oils into their components is called, which means you break each bond by inserting a molecule of water. Add an arrow to the equation to show the reverse Rx. B. PHYSICAL PROPERTIES OF SOME LIPIDS AND FATTY ACIDS Materials: Micro-centrifuge tubes, dropper bottles or solids: stearic acid, oleic acid, olive oil, safflower oil, lecithin, cholesterol, vitamin A, spatulas, methylene chloride To seven separate micro-centrifuge tubes, add 5 drops or a small amount of solid lipid (3-4 granules) of the following substances: a. stearic acid e. lecithin b. oleic acid f. cholesterol c. olive oil g. vitamin A d. safflower oil B1: Describe their appearance in the table below B2: Describe their smell in the table below B3: Solubility in Polar Solvent: Add about 1.0 ml of water to each centrifuge tube. Cap the tubes and shake to mix. Record your observations in the table below B4. Solubility in a Nonpolar Solvent: Prepare 7 more fresh test tubes with a.-g. Add 0.5 ml methylene chloride CH 2 Cl 2 to each sample. Record the solubility of the lipids. Save the tubes and samples of stearic acid, oleic acid, olive oil and safflower oil for part C.

3 Name: Per: Performance: B. PHYSICAL PROPERTIES OF SOME LIPIDS AND FATTY ACIDS Lipid B.1. Appearance B.2. Odor Observations B.3. Soluble in water? B.4. Soluble in CH 2 Cl 2? Stearic acid Oleic acid Olive oil Safflower oil Lecithin Cholesterol Vitamin A

4 [Type text] C. BROMINE TEST FOR UNSATURATION The bromine test for unsaturation The presence of unsaturation (the presence of double bonds) in fatty acids and triglycerides can be detected using the bromine test. In this test you will add a bromine solution drop wise to the sample and observe any color changes. The orange color of the bromine will fade rapidly with lipids that contain unsaturations, until all the double bonds have reacted with the bromine. Lipids that have no double bonds will immediately develop a orange color that does not fade. Materials: Samples from B.4, 1% Br 2 in methylene chloride. To the the samples saved from B4: stearic acid, oleic oil, olive oil and safflower oil in methylene chloride, add 1% bromine solution drop by drop until a pale orange color is obtained or a max of 25 drops have been added. Avoid contact with bromine solution; it can cause painful burns. Do not breathe the fumes! Record your observations below. Determine if the red-orange color fades rapidly or persists. C. BROMINE TEST FOR UNSATURATION Lipid Fatty acids Drops of Bromine added Observations Stearic acid Oleic acid Triglycerides Safflower oil Olive oil 4

5 [Type text] D. PREPARATION OF HAND LOTION Materials: Stearic acid, cetyl alcohol, lanolin (anhydrous), triethanolamine, glycerol, ethanol, commercial hand lotions, 100 ml beakers, hot water bath, ice, crystallizing dish, 50 ml graduated cylinder, spatula, beral pipette and stir rod. Obtain the following substances and combine in two 50 ml beakers as indicated on the following page. Use a laboratory balance/weigh paper to weigh out the solid substances, a dropper bottle to measure small volumes and a graduated cylinder to measure larger volumes. Beaker 1 Beaker 2 Stearic acid 1.5 g 4% Glycerin solution 25 ml Cetyl alcohol 0.5 g Lanolin (anhydrous) 1.0 g Triethanolamine 10 drops Place both beakers into a large water bath beaker (around 80 C) and heat for at least 2-3 minutes. Hold the edge of Beaker 1 and use a stir rod to mix the contents while melting. Be careful that the beaker does not tip over inside the bath. Remove the melted solids and heated glycerin solution, and while still warm, slowly pour the glycerin solution from Beaker 2 into the warm melted solids inside Beaker 1 as you stir. Add 2.5 ml of ethanol and a few drops of fragrance. Continue to stir for 1-2 minutes until a smooth, creamy lotion is obtained. D1. Describe the smoothness and appearance of the hand lotion. D.2. Compare your lotion with a commercially available one D.3. Compare the properties of your hand lotion with one where triethanolamine has been omitted - provided by teacher D.4. Compare the properties of your hand lotion with one where stearic acid has been omitted - provided by teacher D.5. Determine the ph of the hand lotions from D1, D2, D3, and D4. 5

6 PRE-LABORATORY QUESTIONS 1. Classify each of the compounds in part B of the procedure as a Fatty Acid, Triglyceride, Phospholipid or Steroid. 2. For making the lotion you need Glycerin (glycerol), Stearic acid, Cetyl alcohol, Lanolin, Triethanolamine. Draw the molecules in the space below, label them, circle/label the functional groups they have and determine whether they are polar or non-polar What is the function of each component in the lotion 3. Find a food label that contains lipids, cut it out and glue it in the space below. What food item is it? List which of the following lipids (and how much) your food items has. a. Saturated Fats b. Trans Fats c. Polyunsaturated Fats d. Monounsaturated Fats 4. A bromine (Br 2 ) will react with the double bonds and break them open. This reaction type is classified as reactions, as it adds a new element to a molecule with a double bond. Predict which of the substances below can react with Br 2 : a. 1-butene b. butane c. stearic acid d. oleic acid (find the structure in the book) 5. Below, draw the reaction of oleic acid with Bromine gas. How many Br 2 molecules do you need for complete saturation of this fatty acid? 6

7 D. PREPARATION OF HAND LOTION Description of the hand lotions D.1. D.2. (without triethanolamine) D.3. (without stearic acid) D.4. ph of hand lotions ph of commercial hand lotion Brand 7

8 QUESTIONS 1. In part B you made some observations of the physical properties of several lipids. What property (or properties) do all of the compounds have in common? Based on these common features why do you think these compounds were classified as lipids? 2. In part C you performed the bromine test for unsaturation. Based on your observations what compounds are unsaturated? 3. Based on your observations how can you use the bromine test to determine which compound is more unsaturated? 4. Based on the acid and base properties of triethanolamine (weak base) and stearic acid (weak acid), as well as your observations regarding the ph of lotions prepared with and without triethanolamine and stearic acid, provide a reason as to why these two compounds are used as ingredients in hand lotion. 5. Based your observations, in which lotion prepared is the water solubility of stearic acid improved? With or without triethanolamine? Explain. 8