Exercise 7: The Molecules of Life You are working in a laboratory that tests different foods to obtain information that will be used on the nutritional packaging labels for the product. In this exercise, you will be examining a number of foods for their content of carbohydrates, lipids and proteins. At the end of the exercise you should be able to describe which food types have the different types of biological molecules based on your test results. Introduction: In this exercise you will be performing assays for 4 different types of biological molecules that are commonly found in foods. You will assay a total of eight different foods for each of the types of molecules. Each of the assays must also have a positive control and a negative control run at the same time as the samples. This is so that you know what the test result will look like if the molecule is present or if it is absent. The controls you will use are listed in the directions for each test. For each of the assays, you will test the following foods along with the appropriate controls for that assay: • • • • • Whole Milk Apple juice Potato flakes Gelatin Egg White Activity 1: Biuret Test for Protein The Biuret (by-your-ett) assay for proteins measures the amount of protein present in a sample. The Biuret solution starts out a light blue color, and reacts with peptide bonds in proteins to form a copperprotein complex that is a violet-purple color. The greater the concentration of protein in the sample, the more intense the purple color will be. 1. Label a total of 7 test tubes with the names of the samples. Tube 1 is the positive control where you will add the protein BSA (Bovine serum albumin), and tube 2 is the negative control that will have deionized water added as the sample. You should expect to see a violet-purple color in the positive control tube, and a light blue color in the negative control tube. 2. On the Skill Check worksheet, look at each food on the list and predict (in the second column) whether you think the sample will contain protein or not. 3. Place a small amount of each sample into the appropriate test tube. If the sample is liquid, add approximately 1 ml of the sample using a plastic dropper pipette. If the sample is a solid, add a small amount (about the size of a fingernail) into the appropriate tube and then add approximately 1 ml of deionized water to the tube. If necessary, mash or grind the sample before adding it to the tube so that it will be able to mix with the assay reagents. For tube 1, add 1 ml of the BSA solution. To tube 2, add deionized water as the sample. 4. Add 1 ml of Biuret reagent to each tube. Gently mix the contents of the tube using the vortex mixer. Wait for 2 minutes. 5. Examine the contents of each tube and note the color. Compare your tubes to the negative and positive control tubes. Page 1 Exercise 7:The Molecules of Life 6. Record your observations on the Skill Check worksheet under Activity 1. Determine whether the sample contains protein or not, and record this conclusion in the fourth column on the worksheet. You will fill in the fifth column on nutrition label information later. Activity 2: Testing for Starch with Lugol’s Iodine (I2KI) Lugol’s iodine will react with starch (a polysaccharide, and complex carbohydrate) but will not react with monosaccharides or disaccharides. The reagent contains iodine and potassium iodide (I2KI). It changes from a yellowish-brown to blue-black in the presence of starch. 1. Label a total of 7 test tubes with the names of the samples. Tube 1 is the positive control that will have 1% corn starch added, and tube 2 is the negative control that will have deionized water added. The positive control should turn a blue-black color after the Lugol’s Iodine is added, while the negative control should remain a yellow-brown color. 2. On the Skill Check worksheet, look at each food listed in Table 2 and predict in column 2 whether the sample will have starch in it or not. 3. Place a small amount of each sample into the appropriate test tube. If the sample is liquid, add approximately 1 ml of the sample using a plastic dropper pipette. If the sample is a solid, add a small amount (about the size of a fingernail) into the appropriate tube and then add approximately 1 ml of deionized water to the tube. If necessary, mash or grind the sample before adding it to the tube so that it will be able to mix with the assay reagents. For tube 1, add 1 ml of the corn starch solution. To tube 2, add deionized water as the sample. 4. Add 5 drops of Lugol’s Iodine reagent to each tube. Gently mix the contents of the tube using the vortex mixer. Wait for 1 minute. 5. Examine the contents of each tube and note the color. Compare your tubes to the negative and positive control tubes. 6. Record your observations on the Skill Check worksheet in Table 2 column 3 (Assay Results). Decide if the sample contains starch or not based on your assay, and record this conclusion on the worksheet in column 4. You will record the nutrition label information later. Activity 3: Benedict’s Test for Reducing Sugars Benedict’s reagent (a blue colored solution containing copper ions) is used to test for the presence of reducing sugars. When a solution containing Benedict’s reagent and a reducing sugar is heated, the copper (II) ions in the Benedict’s reagent are reduced to copper (I) ions and the solution changes from blue to green to orange to red-orange to brick-red. A brick-red precipitate (solid), copper (I) oxide (Cu2O), may appear in the bottom of the tube. The more reducing sugar present in the mixture, the more precipitate will form. The reaction for Benedict’s test for reducing sugars can be shown as: 2 Cu+2 + 2 e- 2 Cu+1 Each copper (II) ion, Cu+2, is reduced to a copper (I) ion, Cu +1, by an electron from the reducing sugar. The reducing sugar is oxidized as a result of giving up its electron. 1. Label a total of 7 test tubes with the names of the samples. Tube 1 is the positive control and will have a solution of 10% glucose added, and tube 2 is the negative control and will have deionized water added. The positive control tube should turn an orange-red color when the assay has been completed, while the negative control tube should remain a blue-green color. Page 2 Exercise 7:The Molecules of Life 2. On the Skill Check worksheet, look at each food on the list and speculate whether the sample will have reducing sugar in it or not. 3. Place a small amount of each sample into the appropriate test tube. If the sample is liquid, add approximately 2 ml of the sample using a plastic dropper pipette. If the sample is a solid, add a small amount (about the size of a fingernail) into the appropriate tube and then add approximately 1 ml of deionized water to the tube. If necessary, mash or grind the sample before adding it to the tube so that it will be able to mix with the assay reagents. For tube 1, add 2 ml of the 10% glucose solution. To tube 2, add deionized water as the sample. 4. Add 2 ml of Benedict’s reagent to each tube. Gently mix the contents of the tube using the vortex mixer. 5. Examine the contents of each tube and note the color. Compare your tubes to the negative and positive control tubes. 6. Carefully place all of the tubes in a beaker of boiling water and boil gently for 2 minutes. 7. After 2 minutes, use a test tube holder to remove the tubes from the boiling water; place them in a test tube rack and allow them to cool for at least 2 minutes. It may take several minutes for precipitate to be visible at the bottom of a tube. 8. Record your observations in the third column of Table 3 on the Skill Check worksheet under Activity 3. Determine whether the sample contains reducing sugar or not, and record this conclusion in column 5 of the worksheet. You will fill in the last column on nutrition label information later. Activity 4: Paper Test for Lipids If you have ever brought home doughnuts or muffins in a brown paper bag, you have already seen the results of this test. Often called, the “grease spot’ test, lipids that are present in foods will leave a translucent spot on brown paper. You will use a paper towel for this test. 1. On the Skill Check worksheet (Table 4), look at each food on the list and predict whether the sample will contain lipid. 2. Place a drop of each sample on a brown paper towel; leave at least 2 inches of space between each sample. Use a drop of corn oil as your positive control for the presence of lipid, and a drop of water as a negative control for this test. 3. Draw a circle around each of the spots with a pencil. Write the name of the sample under the circle. 4. With the back of a plastic teaspoon, gently rub each of the samples into the paper. Use the spoon to remove any excess solid material that is left on the paper towel. 5. Allow the spots on the paper to dry; if you perform this test early in the class, you can let the spots air dry; if not, use a hair dryer set on low to gently dry the spots. 6. Hold the paper towel up to the light and observe the spots. A substance containing lipids will leave a translucent, greasy looking spot on the paper. 7. Record your observations on the Skill Check worksheet under Activity 4. Determine whether the sample contains lipids or not, and record this information in the table. Activity 5: Analyzing your Data On the Skill Check worksheet, you will summarize what you have learned about the composition of the foods that have been tested and compare your results to known information about some of the foods. You can search for nutritional labels on the Internet. For each of the foods, compare your results with the information that you find on a nutritional data sheet. Each of the tables that you filled in with your data has one final column where you can add data from these sheets. Page 3 Exercise 7:The Molecules of Life Once you have done this, you can compile all of your data from the first tables into Table 5. Fill in each box in Table 5 with information about your results, and with the information you obtained from the nutritional data sheets. Do the two results agree? If they do not, think about why your results may be different from the information you just obtained. Activity 6: Communicating Your Results Now that you have looked at all of the data and compiled it in an orderly manner in Table 5, it is time to prepare your report describing what you have found. How did your predictions compare with your results? Were there any surprises in the foods tested, or did your results reflect your speculation on the contents of the foods? How did your data compare with the information you obtained from the nutrition data sheets? Did your results match the sheets? If not, why do you think your results were different? Why might certain molecules not show up on these tests even though they are there? Can you speculate why certain molecules are present in some of the foods and not in others (think about the origin of the food…plant, animal?)? Page 4 Exercise 7:The Molecules of Life Page 5 Exercise 7:The Molecules of Life Exercise 7: The Molecules of Life Skill Check Worksheet NAME:_________________________ Lab Section________________ Activity 1: Biuret Assay for Protein Table 1: Biuret Assay for Protein Your Prediction Positive Control (BSA) Negative Control (Water) Milk Actual Assay Results Description Purple Light blue purple Apple Juice Light blue Potato flakes Light blue Gelatin purple Egg White purple Notes: Protein Present? (Yes/No) Nutrition Label Information Activity 2: Lugol’s Iodine Test for Starch Table 2: Lugol’s Test for Starch Prediction Positive Control (1% corn starch) Negative Control (Water) Assay Results Description Dark Blue/black golden Milk golden Apple Juice golden Potato flakes Dark blue/black Gelatin golden Egg White golden Notes: Starch Present? (Yes/No) Nutrition Label Information Activity 3: Benedict’s Test for Reducing Sugars Table 3: Benedicts Test for Reducing Sugars Prediction Positive Control (10% Glucose) Negative Control (Water) Assay Results Description Brick red color Light blue Milk Orange-red color Apple Juice Orange-red color Potato flakes Yellow-green Gelatin Light blue Egg White Light blue Notes: Sugar Present? (Yes/No) Nutrition Label Information Activity 4: Paper Test for Lipids Table 4: Paper Test for Lipids Prediction Positive Control (Corn Oil) Negative Control (Water) Milk Assay Results Description Greasy spot No spot Slightly greasy spot Apple Juice No spot Potato flakes No spot Gelatin No spot Egg White No spot Notes: Lipids Present? (Yes/No) Nutrition Label Information Activity 5: Summary of Results Table 5: Summary of Biological Molecules in Foods Biuret test for Protein Milk Apple Juice Potato flakes Gelatin Egg White Lugol’s test for starch Benedicts test for reducing sugars Paper test for lipids Activity 6: Communicating Your Results In the space below, summarize the results of your tests. Did your results match your predictions? Were there any cases where you were surprised at the results you obtained? How did your results compare to the information from the nutritional data sheets? ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ____________________________________________________ ________________________________ 
Purchase answer to see full attachment