Biological Macromolecules Lab Report

BIOL 130 Lab Report
Identifying Two Macromolecules - Carbohydrates and Proteins

9/26/2013
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INTRODUCTION As the name suggests, macromolecules are large molecules that make up more than 90% of the total cell mass. These biological macromolecules vary greatly in size - from several hundred to several hundred million molecular weight units - and are made up of monomer units. There are four major classes of biological macromolecules: proteins, carbohydrates, lipids, and nucleic acids (Sheeler & Bianchi, 1980). Proteins are made up of polymers of amino acids. The shape and structure of a cell is defined by proteins (Alberts et al., 1989). Carbohydrates are made up of polymers of simple sugars called monosaccharides.
These biological macromolecules are to be identified by the changes in colour through three different tests - Iodine Test for starch and glycogen, Benedict 's Test for reducing sugars, and Biuret Test for Proteins. However, only two macromolecules are being identified in this experiment - carbohydrates and proteins. There are 12 solutions to be tested in this experiment. The Iodine test is used to indentify starch and glycogen in the given solutions. Of the 12 solutions, solution 8 is a starch solution and solution 7 is a glycogen solution. Starch solutions turn blue-black when Iodine solution is added to it. This is due to the formation of polyiodide chains when the Iodine solution mixes with starch. Starch contains both amylose and amylopectin. The amylose molecules in starch form helices at the locations where the Iodine molecules assemble. This cause a dark blue-black colour change ("Starch-iodine test", 2008). Therefore, solution 8 should turn blue-black when Iodine solution is added to it since it is a starch solution. However, glycogen solutions turn red-brown when Iodine solution is added. The chemical structure of glycogen is similar to the structure of amylopectin. Glycogen is highly branched. These branches are formed through acetal linkages. It is because of the highly branched structure of glycogen that solutions of glycogen turn red-brown in Iodine solutions (Ophardt, 2003). Thus,
Benedict 's solution contains Cu+2 ions that are blue in colour. This means that when Benedict 's solution is added to clear transparent or translucent solutions, the solutions turn light blue due to the presence of the Cu+2 ions. Out of the 12 solutions, solution 10 (beer) was a light brown-yellow colour, while the remaining 11 were either transparent or translucent. Thus, when Benedict 's solution was added to solution 10 (beer), it turned blue-green. It then turned into a thick pale yellow colour indicating that a reaction had taken place and it was positive. This is because although solution 10 (beer) did not turn red-brown, there was a colour change and a coloured precipitate was formed. After adding the Benedict 's solution to the remaining 11 solutions, the test tubes were put into a beaker on a hot plate and were left to boil for about 5 minutes. Five of the solutions changed from a light blue colour to different shades of red-brown. When Benedict 's solution is added to reducing sugars, the Cu+2 ions for a red-brown precipitate of Copper (I) Oxide causing all sugar solutions to turn red-brown (Hunt, n.d.). Solution 1 (1% glucose solution) turned light red-brown, solution 3 (1% maltose solution) turned red-brown, solution 4 (honey solution) turned brown almost instantly, solution 6 (1% lactose solution) turned red, and solution 12 (unknown 318) turned red orange. This indicated that