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Midterm

Effect of Using Several Tests to identify macromolecules

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Department
Biology
Course
BIOL 130L
Professor
Cecile Deveax
Semester
Fall

Description
THE EFFECT OF USING SEVERAL TESTS TO IDENTIFY SOME MACROMOLECULES 1 Introduction: 1 Biological macromolecules are large molecules made up of smaller organic molecules . There are four types of macromolecules: Carbohydrates, Proteins Lipids and Nucleic Acids. Each smaller molecule is known as monomers. They are covalently bonded together to create a larger polymer molecule . Carbohydrates are made up of three base elements: Carbon, Hydrogen and Oxygen. The simplest carbohydrate is a monosaccharide (simple sugar). An example of a simple sugar is glucose, which is created during photosynthesis. When two of these monosaccharides are bonded together, a polysaccharide (complex sugar) is created . In this lab, starch and glycogen are used as polysaccharides. Starch is a storage polysaccharide found in plants while Glycogen is an energy storage polysaccharide found in animals. Proteins are the most complex and functionally diverse molecules of living organisms. They are created by RNA during DNA Transcription and Translation . The base elements of proteins are C, H, O and N. Proteins are made up of monomers called amino acids. There are twenty different amino acids that can be bonded together in unique combinations to create a polypeptide chain, the polymer unit for proteins . There are several chemical tests used for the identification of the types of macromolecules and compounds present in cells. The purpose of this investigation is to conduct several tests (Iodine, Benedict's and Biuret) to detect the presence of macromolecules in different solutions. Firstly, to test for the presence of starch and glycogen, the Iodine Test is used. Iodine is a yellow coloured solution used to distinguish starch from other monosaccharides, 7 disaccharides and polysaccharides . When iodine is added to a solution and it changes its colour to blue-black then it indicates a positive test control for the presence of starch. When iodine is 2 added to a liquid solution and it changes its colour to reddish brown then it indicates the presence of glycogen .7 To test for the presence of reducing sugars, Benedict's test is used. Benedict's solution is 2+ blue in colour due to the presence of copper (Cu )ions. But when it is combined and heated with a substance containing glucose in a chain form, the cupric ions (Cu ) are reduced to + 7 cuprous (Cu ) ions and then oxidized to form copper (II) oxide (Cu O) . 2opper oxide is an insoluble in water forming a precipitate. When benedict's solution is added to the liquid solution, a positive test control is the change of the clear light blue solution to a range from yellow or green to red or brown solution in boiling water bath (using hot plate) for the presence of a reducing sugar. When benedict's solution is added to a liquid solution and the blue colour stays 6 the same then it indicates a negative test control for the presence of a reducing sugar . Lastly, to test for the presence of proteins, the Biuret Test is used. Biuret test is a chemical test used to detect the presence of peptide bonds in a solution. The solution is made of sodium hydroxide and copper (II) sulphate. In a positive test, copper (II) ions are reduced to copper (I) ions that forms a complex with the nitrogen and carbon of the peptide bond . This blue solution turns into violet colour in the presence of protein indicating that the test is positive. It indicates a negative test for presence of proteins when the solution contains the original blue colour. Materials and Methods: Refer to experiment information section, BIOL 130L, 2012, 16-20. Note: No changes were made to procedure in this experiment from the referred section 3 Results: Table 1. Positive and Negative Controls for Iodine Test Determined by Initial and Final Colour of Different Types of Solutions Test Tube (#) Type of Solution Initial Colour Final Colour Results (+/-) 1 Glucose Transparent Yellow - 2 Glucose-1-phosphate Transparent Yellow - 3 Maltose Transparent Yellow - 4 Honey Transparent Yellow - 5 Sucrose Transparent Yellow - 6 Lactose Transparent Yellow - 7 Glycogen Transparent Reddish Brown + 8 Starch Transparent Blue-Black + 9 Protein Transparent Yellow - 10 Beer Transparent Yellow - Distilled Water Transparent Yellow 11 - 12 Unknown Transparent Blue-Black + *Table 1 shows the results of using the Iodine test for different solutions. When a drop of iodine is added to a drop of liquid solution from each test tube on a spot-plate, two observations are noted. If the iodine turns to blue-black in colour then it indicates a positive test control for the starch polysaccharide. If iodine turns to a reddish brown in colour then it indicates the presence of glycogen polysaccharide. A negative test control is indicated by yellow colour change. Table 2. Positive and Negative Controls for Benedict's Test Determined by Initial and Final Colour of Different Types of Solutions Test Tube (#) Type of Solution Initial Colour Final Colour Results (+/-) 1 Glucose Clear, blue Reddish Brown + 2 Glucose-1- Clear, blue Blue - phosphate 3 Maltose Clear, blue Reddish Brown + 4 Honey Clear, blue Reddish Brown + 5 Sucrose Clear, blue Blue - 6 Lactose Clear, blue Reddish Brown + 7 Glycogen Clear, blue Blue - 8 Starch
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