Chemical Composition of Cells Essay

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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 …show more content…

d. Add one drop of I2KI solution to each of the wells and record your result in the table below. Table 2. Iodine Test Results Spot water glucose sucrose starch onion slice potato slice Color positive or negative? e. Please answer the following questions about your results: 1. Did you expect water to turn blue-black in the presence of IKI? Why did we test it? 2. What general statement can you make about the differences between carbohydrate storage in onions compared to potatoes? 3. Why didn’t glucose give a positive result? B) Proteins Proteins are made up of chains of amino acids. Each protein folds into a characteristic three dimensional shape that is essential to its function. They perform a variety of functions in cells and are probably the most diverse macromolecule in living systems. The Biuret test detects the presence of proteins and short peptides (short chains of amino acids). Biuret reagent contains a strong solution of sodium hydroxide (NaOH) and a very small amount of dilute copper sulfate solution. The reagent changes color in the presence of a protein because the amino groups in the amino acids react with the copper ions producing a violet color. A negative result is blue. 1. Number four clean test tubes 1-4. 2. Place 1 ml (or 20 drops) of the following solutions into each tube: water, egg albumin, starch, and chicken broth. 3. Add 3 drops of Buiret reagent to each tube and gently shake

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