Biologically Important Molecules
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By completing lab exercise 6 : Biologically Important Molecules, we are able to perform tests such as the Benedicts Test for Reducing Sugars, Iodine Test, Biuret Test, Sudan IV Test, and lastly the Grease-Spot Test that detect the presence of biologically important carbohydrates, protein lipids and nucleic acids. Most known compounds in living organism are if fact carbohydrates, lipids, proteins, and nucleic acids. Each of these macromolecules are tested differently. The Benedicts test identifies reducing sugars based on their ability to reduce cupric ions to cuprous oxide at basic pH resulting in a green to reddish orange color. The basis for the iodine test for starch is since starch is a coiled polymer of glucose, the iodine interacts with the coiled molecules turning bluish black. The Biuret test, tests for proteins by checking if there are the presence of long chain polypeptides, in doing so cause a color change of violet. The Sudan IV test for lipids is based the it lipids ability to absorb pigment such as the Sudan IV
Materials and Methods:
Obtain seven labeled test tubes, and add each material being tested to its own test tube. Then add 2mL of benedict solution to each tube and place the test tubes in a gently boiling water bath for 3 minutes, observe any color change if any at all. After the 3 minutes remove the test tubes leaving them to cool to room temperature, then record observations in table 6.1. Iodine Test
Obtain seven labeled test tubes adding materials that are being tested to their own specific test tube. Add six drops of iodine to each tube record any color changes in table 6.1. Biuret Test
Obtain five labeled test tubes adding the materials being tested to the test tubes, then add 2mLof 2.5% sodium Hydroxide to each test tube. Record any color change in table 6.2. Solubility of Lipids in Polar and Nonpolar Solvents
Obtain two test tubes. In one tube add 5 mL of water and to the other add 5 mL of acetone. Then add a few drops of vegetable oil to each tube and record observation. Sudan IV Test
Obtain five labeled test tube adding materials to each test tube. Add five drops of water to test tube one and five drops of Sudan IV to the remaining test tubes. Record color changes in table 6.3.
Obtain a piece of brown wrapping paper and using an eye dropper add a drop or salad oil, water, honey, potato juice and onion juice to different corner near a different corner of the paper. Allow the fluids to evaporate then hold the paper up to light and write down any observations about each spot in table 6.4.
In the benedicts test we tested different solutions for reducing sugars. While one solutions changed color to green or a reddish brown color, others did not. Since the Onion juice, glucose solution and the reducing sugar solution changed color to either green or dark red color. this is proof that the solutions where able to change cupric ions into cuprous oxide. The other solutions such as the water potato juice and so on did not react to the Benedict’s reagent meaning they did not have free aldehydes or ketones with their solutions.
In the Iodine test for starch, lonely two of the substance reacted with the iodine. The potato juice and the starch solution turn to a dark blackish color when the iodine was added shows that there are coiled carbohydrates that are with the juice and starch solution. As for the solutions and substance that did not react with the iodine that does not meant that there are not carbohydrates with in the solutions only that the carbohydrates are not in a coiled structure, since iodine will not react with carbohydrates unless they are coiled polymers.
In the Biuret test, we tested several solutions for protein and only two solution came up as a positive reaction. The egg albumen and the amino acid solutions had a violet color change meaning there was the presence of at least one long chain polypeptide causing thelor change and a positive reaction for both test substances. Other solution such the protein solution did not result in a positive reaction because it is possible that there only individual amino acids cause in not to give a positive reaction.
In the solubility of lipids in polar and non-polar solvents the results where to be expected which the water and the vegetable oil. After adding the vegetable oil into the test tube containing water the oil did not mix, it stayed on top of the water and together. In the acetone after the vegetable oil was added the acetone became cloud. This shows that lipids are soluble in acetone (a non-polar substance) and not in water (a polar substance).
In the Sudan IV test for Lipids, four solutions where tested, one which gave a positive reaction. The vegetable oil and the Sudan IV solution gave a positive reacting since the reddish pigment of the Sudan IV was absorbed in the vegetable oil. As for the other solutions it is possible that they contain lipid but did not give a clear reaction to whether or not they do as in the reaction with the vegetable oil. The water and Sudan IV solution changed color because they simply mixed in or the water could have not been 100% clean. In the Grease-spot the test, we applied several different food product solutions to a piece of brown paper allowing it to dry. The purpose of this was to see which solution contained lipids by seeing if they left a translucent grease mark. All the substances produced a grease mark except the water. The grease mark of the other four solutions all looked the similar while the mark that was left by the water was dry but just wrinkled and no grease mark.
Vodopich, Darrell S., and Randy Moore. “Biologically Important Molecules.” Biology Laboratory Manual. New York: McGraw-Hill, 2014. 57-70. Print. Mason, Kenneth A., Jonathan B. Losos, Susan R. Singer, Peter H. Raven, and George B. Johnson. Biology. N.p.: n.p., n.d. Print.