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Lecture

Identification of some macromolecules.docx

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Department
Biology
Course
BIOL 130L
Professor
Dragana Miskovic
Semester
Fall

Description
The recognition of macromolecules through the use of iodine, benedict’s, and biuret testing Joshua Fernandez ID# 2051 5215 Mohanad Znbaqa Vishaul Latchman and Aman Karblari Section 010 BIOL 130L Thursday 2:30pm-5:20pm B2-Biology 2 149 September 19, 2013 Introduction: The Purpose of this lab is to test 12 different samples containing macromolecules, and identify which solutions change colour, showing with test tubes contain starch, sugars, and protein. The first test used is the iodine test. The iodine test tests for the presence of starch, and/or glycogen present in the solution. For the identification of starch, the colour of iodine before the test is a clear solution. The colour of the starch before the test is a clear solution. “After the iodine solution has been mixed with the starch, the solution turns blue-black in color” (Marineman). The colour of glycogen before the iodine is a clear solution. The iodine is still colourless. “After the glycogen and the iodine are mixed together, the result is a brown-blue color” (Chemistry Laboratory). The structure of starch is “simple polysaccharides only composed of glucose units, primarily starch in plants, functioning as long term storage of glucose, contained for energy production” (Essential cell Biology). The structure of glycogen is “chains of glucose subunits connected by 1g 4 glycosidic bonds. Contrast to starch, which are linear strands of glucose, glycogen is a branched structure. Present at these branch points, we have 1g6 glycosidic linkages” (Glycogen). The test works “by the molecule of iodine slipping inside the amylose coil” (Starch). The test works for glycogen in a similar fashion. The next test is Benedict’s test. Benedict’s test tests for the presence of reducing sugars present in the solution. For the identification of Benedict’s, the colour of Benedict’s beforehand is light blue. The sugars are colorless. “After the Benedict’s solution and a reducing sugar have been mixed, then the substance is to be heated, and the resulting solution has red precipitate” (Benedict’s Solution). “Sugars are arranged in the shape of a ring. The corners of this ring like structure contain carbon atoms. In order for these structures to be produced, the carbonyl atom bonds with the carbon next to it, forming a ring structure among the carbons” (Carbohydrates). “Sugars can be extremely long, to the extent where large polymers of sugar are called Carbohydrates. These long strands of sugar containing Carbon are known as straight chain sugars” (Carbohydrates). For the Benedict’s solution, “If a sugar contains an aldehyde group, which is a carbon double bonded to oxygen, and has hydrogen attached as well, with one open R group, that sugar is known as a reducing sugar. The aldehyde present in the sugar is readily oxidized to a carboxylic acid. However in order for that oxidation to occur, that cyclic form must first open up to give that readily reactive aldehyde up” (Ch25). “The test works by the reducing sugars being reduced, from a two plus copper ion, to a one plus copper ion. Through this reduction, we are able to obtain a red precipitate, called Copper (I) Oxide” (Ch25). The final test in this lab is the Biuret test. The Biuret test tests for the presence of proteins within the solutions. The colour of the protein before the test is colourless. The colour of the protein when mixed with the sodium hydroxide is a light blue colour. “After the protein has been mixed with the light blue solution, the colour changes to a violet shade” (Biuret Test). “The structure of a protein molecule is very complex. Every protein is composed of chains of amino acids, which are held together by peptide bonds. Each protein is different by the folding it has received” (Essential Cell Biology). “The test works by the copper two ions being connected with the nitrogen atoms, causing a colour change of blue to violet. The colour change is dependent on how many peptide bonds are present within the molecule. If more bonds are present, then the colour change is much more intense” (Re: How does biuret reagent). Methods and Materials: “Refer to Biology 130L Introduction to Cell Biology Lab Manual, BIOL 130L, Dr. Dragana Miskovic, Department of Biology, Fall 2013. pp. 14-18 (Department of Biology, University of Waterloo, Fall 2013). The experiment was performed without any deviation.” Results: Table #1: Results of Iodide test for starch and glycogen Solutions Positive/Negative Qualitative Observations 1% Glucose solution - Yellow in Colour 0.3% Glucose-1-phosphate - Dark yellowish brown 1% Maltose solution - Dark yellow in colour Honey solution - Dark yellow in colour 1% sucrose solution - Dark brown/yellowish 1% lactose solution - Dark yellow/brown 1% glycogen solution + Dark brown with a slight yellow tint, slightly reddish 1% starch solution + Black in colour, very dark Protein - Light yellowish colour Beer - Slightly dark yellow/brown Distilled Water - Light yellow/brown Unknown Solution #279 + Dark brown/yellow in colour, slightly reddish as well *The Table above represents the results of the iodine test for detecting starch and glycogen. The positive sign indicates the presence of starch or glycogen * Table #2: Benedict’s test for reducing sugars Solutions Positive/Negative Qualitative Observations 1% Glucose solution + Dark red, slightly brown 0.3% Glucose-1-phosphate - Still light blue colour, no change 1% Maltose solution + Dark red, darker than glucose Honey solution + Dark orange, slightly brown 1% sucrose solution - Still light blue, no color change 1% lactose solution + Darkish red, slightly lighter than glucose 1% glycogen solution - Light blue colour, no colour change 1% starch solution - Light blue colour, with a small green tint Protein - Dark blue on top, with a lighter blue on the bottom Beer + Darker, milk like yellow infused brown Distilled Water - Still light blue in colour, no change Unknown Solution #279 - Green/blue color *The above table represents the results for the Benedict’s test. The positive sign indicates the presence of reducing sugars* Table #3: Biuret test for protein Solutions Positive/Negative Qualitative Observations 1% Glucose solution - Very light blue colour, almost no blue at all 0.3% Glucose-1-phosphate - Very light blue colour, almost the same as 1% glucose 1% Maltose solution - Very light blue, almost colourless Honey solution -
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