Identifying Biological Molecules with Colorimetric Chemical Tests

1305 Words Apr 13th, 2013 6 Pages
Identifying Biological Molecules with Colorimetric Chemical Tests

Objectives
Perform a series of accurate tests on biological molecules to detect the presence of carbohydrates and proteins, as well as the action of an enzyme on specific molecules.

Introduction
Unknown biological molecules can be correctly identified using various tests, including colorimetric chemical tests. Colorimetric tests are when a chemical reagent, such as Benedict’s, is used on a substance or solution and a certain color change occurs as a response. Carbohydrates and proteins, two of the larger types of biological molecules, also called macromolecules, are actually chains of molecules called polymers. The smaller molecules that build up these chains are
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The results for Benedict’s test for reducing sugars before hydrolysis, the control dH2O had no color change, as well as sucrose and raffinose. Gelatin became a dark blue and egg albumin a light greyish blue. Glucose yielded a dark orange, milk albumin turned orange, and starch had a yellow precipitate. In the Benedict’s test for reducing sugars by hot acid hydrolysis, the control dH2O was blue or no reaction. Glucose turned a brownish-orange; sucrose, a reddish-brown, raffinose, light pink; starch, a dark yellowish-orange; gelatin, violet; milk powder, a light yellow; and egg albumin, a greyish-violet. In the Lugol’s test for polysaccharides, the control dH2O turned yellow or no reaction, as well as glucose, sucrose, raffinose, milk powder and albumin. Starch was clear with blue-violet on the bottom (precipitate) and gelatin turned a slightly opaque white. In the test for polysaccharides remaining after hydrolysis with Lugol’s solution the control dH2O was yellow or no reaction. Glucose, sucrose, raffinose, starch and gelatin also had no reaction. Milk powder had a white precipitate and particle suspension. Egg albumin had an even greater white precipitate and particle suspension. In Biuret’s test for proteins there was no reaction for dH2O, glucose, sucrose, raffinose, and starch. Gelatin, milk powder and egg albumin all turned slightly violet with bubbles. In part 2 of the lab, we tested the effect of the enzyme invertase on dH2O (the control), sucrose, and
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