Chemical Composition of Cells Essay

2012 Words Mar 23rd, 2011 9 Pages
BIOL 140 Lab—The Chemical Composition of Cells
Name ____________________________ I) Introduction All cells contain four major types of macromolecules: carbohydrates, lipids, nucleic acids, and proteins. In today’s lab, we will be studying three of the four-proteins, carbohydrates and lipids. Various chemical tests can be used to detect the presence of each of these molecules. Most of the tests involve a color change visible to the eye. If a color change is observed, the test is considered positive. If the color change is not observed, the test is negative, indicating that a particular molecule is not present. In all the chemical tests we will be performing, we will also be using a control. In most cases, the control will be a sample of
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C) Lipids Lipids are compounds that are insoluble in water, or hydrophobic. This class of macromolecules includes fats, oils, phospholipids, waxes, and steroids. Because all of these molecules share the property of being hydrophobic, we can exploit this property in tests for the presence of lipids. Like lipids, the colored dye Sudan III is hydrophobic, so they will tend to associate with each other. Polar or hydrophilic molecules will not associate with Sudan III, and, therefore, will not take up the dye. A positive result will be indicated by the presence of an orange-colored spot on the filter paper. Mostly colorless or spots with red particles should be considered negative. 1. Obtain a piece of filter paper and mark it with four equally spaced letters (so you know which spot came from which solution). Now draw a small circle near each letter. W = water C = cream M = milk O = oil 2. Using a pipet, add a small drop from each tube to the appropriate circle, returning the pipet to the appropriate solution.

3. Let the filter paper dry completely. 4. Soak the paper for three minutes in the dish containing the Sudan III solution. Only one group at a time should place their filter paper into the solution. 5. Use forceps to remove the paper from the dye. Rinse the paper for one minute using a squeeze bottle containing distilled water. 6. Record the spots on the table below Table 4. Sudan Test Results
Substance Tested water cream

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