Education

Id of biological molecules lab

Description
1. Identification of Biological Molecules Introduction: Molecules of a certain class have similar chemical properties because they have the same functional groups. A…
Categories
Published
of 8
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
Share
Transcript
  • 1. Identification of Biological Molecules Introduction: Molecules of a certain class have similar chemical properties because they have the same functional groups. A chemical test that is sensitive to these groups can be used to identify molecules that are in that class. Practice the following tests by using them to see what various foods contain. In each test, you will be including a substance that does not react in the test to serve as the negative control. A substance known to give a reaction in the test would be a positive control. Carbohydrates: These molecules contain the aldehyde and alcohol functional groups. Certain mono- and disaccharides can be detected because of their aldehyde groups. Some polysaccharides can be detected because of their specific threedimensional structure. Carbohydrates, which are water soluble or hydrophilic substances, are not detected by their hydroxyl groups. Benedict’s Test: A reducing sugar test that depends on a free aldehyde group. Monosaccharides and some disaccharides have a free aldehyde group and consequently will react to give a positive Benedict’s test. Such a sugar acts as a reducing agent and is called a reducing sugar. The reaction proceeds as follows: O Benedict’s Reagent + R C Heat O Benedict’s Reagent + R C H Oxidized Form Reducing Sugar O H Reduced Form Acid Sugar This is a typical oxidation-reduction reaction in which the oxidation of the sugar occurs simultaneously with the reduction of the Benedict’s reagent. Remember that REDUCTION means removal of oxygen or addition of hydrogen. OXIDATION means addition of oxygen or removal of hydrogen. In this case, the sugar obviously gained an oxygen during the reaction and therefore the sugar underwent oxidation. Some disaccharides (e.g. sucrose) and all polysaccharides (e.g. starch) are not reducing sugars because they do not have free aldehyde groups. You will use the Benedict’s test to compare the reducing sugar (e.g. glucose and fructose) content of the foods listed on the data sheet. 1
  • 2. Identification of Biological Molecules A. Prepare the water bath: 1. You should have a test tube rack with ten (10) test tubes. Number the tubes 1-10 to correspond with the list of foods on your data sheet. 2. Prepare a boiling water bath for your test tubes by heating a half-full beaker of water on the hot plate. Leave the heat setting on the middle setting and do not let the beaker boil dry. B. Benedict’s Test: 1. Fill each test tube about 1cm full with the appropriate substance as listed on the data sheet (i.e. sample #1 in tube #1). The actual amount in each tube is not critical as long as the same amount of each substance is used in each tube. Be sure that you use only the specified dropper for the solution, and return that dropper to the appropriate solution so that you avoid contamination! 2. Add ten (10) drops of Benedict’s reagent to each tube and mix. 3. Heat the tubes for 4 minutes in the boiling water bath, then carefully remove the tubes using your test tube holder. 4. A change in color from clear blue to red or orange indicates an abundance of reducing sugars. A change to green indicates the presence of a smaller amount of reducing sugar. 5. Record your data then rinse the tubes out with water. Iodine Test: Another test, the Iodine Test, can be used to distinguish starch from mono-, di-, and other polysaccharides. Starch is a polymer of glucose in which the chains are coiled up in a particular way so that they can interact with the iodine molecules to give a distinctive blue-black color. Other polymers, even those of glucose, lack the precise coiled structure of starch and do not give the dark color. Thus the iodine test is a specific test for starch that depends on the precise three-dimensional coiling of the glucose polymer so that it can interact with iodine. 1. Fill each test tube about 1cm full with the appropriate substance as listed on the data sheet (i.e. sample #1 in tube #1). The actual amount in each tube is not critical as long as the same amount of each substance is used in each tube. Be sure that you use only the specified dropper for the solution, and return that dropper to the appropriate solution so that you avoid contamination! 2. Add five (5) drops of iodine solution to each test tube. 3. A positive test will give a blue-black color. A yellow or brown result is negative. 4. Record your data then rinse the tubes out with water. 2
  • 3. Identification of Biological Molecules Fats: A fat is a hydrophobic molecule consisting of a glycerol molecule joined to three fatty acids. The hydroxyl groups of the glycerol react with the carboxyl groups of the fatty acids in a condensation reaction, forming an ester linkage. These functional groups are therefore no longer available for a test reaction. Instead the Sudan III test depends on the detection of the remaining hydrocarbon groups. The colored dye, Sudan III, and the hydrocarbon groups are non-polar and stick tightly together in their polar surroundings. Simple hydrophobic interaction is the basis for this rather inelegant test. Sudan III Test: 1. Using a lead pencil and two (2) filter paper disks, mark the disks with a small circle evenly spaced, and number the circles to correspond appropriately with the substance as listed on the data table. 2. Add your initials somewhere on the filter paper disk. 3. Add a SMALL drop from the appropriate substance to the appropriate circled spot on the filter paper disk. Be sure that you use only the specified dropper for the solution, and return that dropper to the appropriate solution so that you avoid contamination! 4. Allow the paper to dry completely. 5. Soak the paper for three (3) minutes in the Sudan III stain. 6. Use forceps to remove the paper from the Sudan III stain. 7. Rinse the paper in the water bath for one (1) minute. 8. Examine the intensity of the staining of the spots and rate the staining on your data sheet as follows: 0 = no staining, + = faint orange, ++ = definite orange color Brown Paper Test: 1. Using a pencil, mark the strip of brown paper bag with small circles evenly spaced along the length of the paper, and number the circles to correspond appropriately with the substance as listed on the data table. 2. Add your initials somewhere on the paper. 3. Add a SMALL drop from the appropriate substance to the appropriate circled spot on the brown paper. Be sure that you use only the specified dropper for the solution, and return that dropper to the appropriate solution so that you avoid contamination! 4. Proceed with the rest of the lab and check your paper at the end. A positive test for lipids is a wet spot on the paper when viewed from the back. It may be helpful to hold the paper up in front of a bright light to look for a “wet” semi-translucent area. 5. Record your data. 3
  • 4. Identification of Biological Molecules Proteins: Proteins are polymers of amino acids in which the carboxyl group of one subunit joins head-to-tail with the amino group of its neighbor. In this case, the bound amino group is nevertheless sufficiently reactive to change the Biuret test reagent from blue to violet. Thus the basis of the test is a subtle interaction between the copper ions in the Biuret reagent and the amide bonds in the protein backbone. This test is specific for the amino group found in the peptide bonds of proteins. 1. 2. 3. 4. Fill each test tube about 1cm full with the appropriate substance as listed on the data sheet (i.e. sample #1 in tube #1). The actual amount in each tube is not critical as long as the same amount of each substance is used in each tube. Be sure that you use only the specified dropper for the solution, and return that dropper to the appropriate solution so that you avoid contamination! Add ten (10) drops of Biuret reagent to each tube and mix. This test may take a few minutes to complete the reaction. After a few minutes observe the tubes and note the color change. A color change from blue to violet indicates the presence of protein. Because the color change is more subtle for this test (blue and violet are very similar) you must observe the tubes very carefully. Record your data then rinse the tubes out with water. 4
  • 5. Identification of Biological Molecules 5
  • 6. Identification of Biological Molecules Name Partner Section Date Data Sheet Carbohydrates Benedict’s Iodine Test Test Tube # Substance 1 2 3 4 5 6 7 8 9 10 Sudan III Test Lipids Brown Paper Test Protein Biuret Test Distilled Water Syrup Potato Tofu Vegetable Oil Oatmeal Avocado White Grape Juice Lettuce Chicken Broth Questions: 1. Carbohydrates, which are water soluble are not detected by their hydroxyl groups. Why not? 2. Will ordinary table sugar give a positive test for Benedict’s solution? Why or why not? 3. Distilled water is obviously not a food, so what is its purpose in each of the tests? 4. If you get a positive test using the water; what does this mean? 5. According to tradition, chicken soup is a good food for persons who are ill. Based upon the following nutritional facts from a soup can, evaluate whether or not chicken soup is a good food. Amount/serving Total Fat 2g Sat. Fat 1g Cholest. 15mg Sodium 980mg %DV 3% 5% 5% 41% Amount/serving Total carb. 9g Fiber 1g Sugars 1g Protein 3g 6 %DV 3% 4%
  • 7. Identification of Biological Molecules 6. A. Using your data, identify the substance described by each of the following nutrition labels. HINT: Total Carbohydrate = sugars (simple sugars) + dietary fiber (cellulose) + starch Amount/serving Total Fat 0g Sat. Fat 0g Cholest. 0mg Sodium 20mg %DV 0% 0% 0% 1% Amount/serving Total carb. 38g Fiber 0g Sugars 36g Protein 0g %DV 13% 0% C. Amount/serving Total Fat 14g Sat. Fat 1.5g Cholest. 0mg Sodium 0mg %DV 5% 3% 0% 0% Amount/serving Total carb. 1g Fiber 0g Sugars 0g Protein 7g %DV 0% 4% %DV 4% 2% 0% 0% Amount/serving Total carb. 27g Fiber 4g Sugars 0g Protein 5g %DV 9% 16% 13% Identity: Reason: Identity: Reason: B. Amount/serving Total Fat 3.5g Sat. Fat 0.5g Cholest. 0mg Sodium 0mg %DV 21% 7% 0% 0% Amount/serving Total carb. 0g Fiber 0g Sugars 0g Protein 0g %DV 0% 0% D. Amount/serving Total Fat 2.5g Sat. Fat 0.5g Cholest. 0mg Sodium 0mg Identity: Reason: Identity: Reason: 7
  • 8. Identification of Biological Molecules Setup Stock solutions of 1. dH2O 2. Syrup 3. Potato 4. Tofu 5. Vegetable Oil 6. Oatmeal 7. Avocado 8. White Grape Juice 9. Lettuce 10. Chicken Broth Student Stations – 5x Benedict’s Solution – Wheaton Bottle Iodine Solution – Wheaton Bottle Biuret Solution – Wheaton Bottle Paper Bag Strips (2) Filter Paper Disks (4) Sudan III Stain Sudan III Rinse Test Tube Rack ` 10 Test Tubes Sharpie Marker Pencil 10 Small Erlenmeyer Flasks for stock solutions (labeled) 10 pipettes (1 per stock solution) 8
  • BD_Distribuite

    Dec 13, 2017

    GPAT 2

    Dec 13, 2017
    Search
    Related Search
    We Need Your Support
    Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

    Thanks to everyone for your continued support.

    No, Thanks
    SAVE OUR EARTH

    We need your sign to support Project to invent "SMART AND CONTROLLABLE REFLECTIVE BALLOONS" to cover the Sun and Save Our Earth.

    More details...

    Sign Now!

    We are very appreciated for your Prompt Action!

    x