Carbohydrates

INTRODUCTION A theme that we have seen and studied in this class is that a particular form or structure of a molecule plays a significant role in the function of that molecule. Since we are interested in the function of molecules. it helps to study their structure. One of the major classes of organic compounds found in cells are carbohydrates. These carbohydrate are made of carbon, hydrogen, and oxygen in a ratio of 1:2:1 respectively with a general formula of X(CH2O)n. When the carbohydrates consists of one unit of sugar, X=1, it is called monosaccharide. If it consists of 2 units, X=2, the carbohydrate is called disaccharide. Carbohydrates made up of more than two units, X>2, are called polysaccharides. Carbohydrates can also be branched or unbranched depending on the type of linkage. Those with alpha 1:4 linkages are linear or unbranched, while those with alpha 1:6 linkages are branched. Carbohydrates are necessary biomolecules because they play a role in energy metabolism as a source of potential chemical energy, also they are important building blocks for other biomolecules.The word carbohydrate is very general, so in order to understand these molecules more precisely, we need to be able to identify more specific classifications. Our experiments try to accomplish this using three common bioassay tests. The first, the Benedict test, will test various compound for reducing sugars. All six-carbon hexose sugars are reducing carbohydrates, as are most disaccharide. Sucrose is the exception. Most polsaccharides are not reducing. Secondly, we have the Barfoed test which is designed to test for monosaccharides. The third and final Iodine test is used to test for polysaccharides that are either branched or unbranched. By combining these tests we were able to make accurate predictions about the carbohydrate contents of a given sample.Now, let's take a closer look at how these bioassays do work. The Benedict and the Barfoed tests are based on the reaction of cupric ions with aldehyde or ketone groups. In the presence of a reactive group, the blue cupric ions are reduced to red cuprous ions. The Benedict test is a basic solution and upon heating turns green, yellow, orange or brick red which indicates a positive reaction. The final color is dependent on the number of reactive sites available; green indicates few sites, yellow more, and red denotes many sites. The Barfoed solution is acidic and only free aldehyde or ketone groups of monosaccharides can reduce the blue ions to red ions. The color change to red will occur immediately. The lack of a change indicates only that the solution is not a monosaccharide. The iodine test is used for polysaccharides. Iodine combines with any existing alpha helices. The more coiled the sample the darker the iodine will turn. The color change can range from deep black-blue with a sample of many coils to a rust red violet with fewer coils and more branchings. When there are no coils, there is no color change. Mono and disaccharides give negative results.In summary, this lab attempts to investigate several different samples by means of series of tests, and based on the combined results of all three tests we can attempt to understand the carbohydrate composition of unknown samples. We hope to be able to predict the results of three bioassays for an unknown solution if given its saccharide type and reducing property. We should also be able to predict the saccharide type and reducing capability of an unknown solution if given the results of the three bioassays.MATERIALS AND METHODS* Like any other experiment, this experiment needs some specific materials including, beaker, graduated cylinder, hot plate, 11 test tubes, test tube holder, wax pencil, liquid soap, and test tube brush. Also, we used the Barfoed reagent, Benedict reagent, and iodine reagent. Our eleven samples were distilled water (control), glucose, fructose, maltose, lactose, sucrose, glycogen, starch, potato soup, and dilute honey.First, we marked our test tubes with the wax pencil to keep track on the subtances, then we place the eleven samples in the corresponding tubes. The first test that we performed was Benedict, followed by Barfoed, ending with iodine test. When needed the samples were heated and our results were immediately recorded in the following tables. In all three cases distilled water was used as a control.*The details of the materials and the methods can be obtained from the lab manual: Experiments in Biology, From chemistry to sex by Linda