Identification of Biological Molecules

Identification of Biological Molecules - Identification of...

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Identification of Biological Molecules All living things are essentially composed of the same basic groups of molecules. The four types of carbon-based molecules you will perform chemical tests for in this laboratory exercise are carbohydrates (sugars and starch) , lipids , amino acids , and proteins . These molecules come from what you eat, so many of the samples you test will be food products. Objectives When you have finished this lab, you will be able to 1. list the four groups of biological molecules. 2. explain the necessity of using controls in experiments. 3. define all boldface terms. 4. distinguish positive from negative test results. Note: Goggles must be worn for all parts of this exercise. Procedures: Molecules that are built the same way can be expected to behave nearly the same in a chemical reaction. In this lab you will perform tests to detect the presence of several classes of molecules and macromolecules (large molecules). When performing chemical tests, first a set of standards or controls , is done against which you may compare your results. A negative control uses a substance that will not react with the chemicals. This will show you what a negative result looks like. A positive control is a substance that will react with the chemicals. It will show you a positive result. Be sure you follow directions and carefully measure out the proper amount of each material. Carbohydrates: Carbohydrates like sugars and starches are important sources of energy in your diet. Foods like pasta, bread and potatoes are examples of the complex carbohydrates dieticians suggest we eat more of while lessening our intake of refined “quick-energy” sugars like sucrose (table sugar) and high fructose corn syrup, a component of many sweetened foods and drinks. Spring 2006 1
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Sugar Test Simple sugars can be detected using Benedict’s test. Benedict’s reagent changes color (after heating) in the presence of these molecules. However, some other sugars and starches are structurally different enough that they do not give a positive test (a color change). Perform the following tests: 1. Number 7 test tubes and add your initials. 2. Add equal amounts of Benedict’s reagent and the proper sample (see Table 1). 3. Heat in the boiling water bath for 5 to 10 minutes. Remove the hot tubes with test tube holders and place them in your test tube rack. 4. Record your results and interpretations (what those results mean; e.g., does the sample contain sugar?) in Table 1. The color you get also indicates how much simple sugar is present. For instance, blue-green = small amount, yellow = medium, and red-orange = a large amount. Table 1. Results of Benedict’s test for sugars Tube # Sample Material Final Color Interpretation of Results 1 Water Clear blue No simple sugars present 2 Glucose 3 Onion juice* 4 Potato juice* 5 Sucrose 6 Mashed green banana* 7 Mashed ripe banana* *To make a sample of these items, cut a small cube of the material, add a small amount of water
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Identification of Biological Molecules - Identification of...

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