The Use of Controls and Indicators to Find What Macromolecules are in an Unknown Essay Example

for reducing alkaline solutions. Among these reducing sugars are monosaccharides and most disaccharides (Answers Corporation, 2008). This is possible because Benedict's solution is an excellent alkaline-based indicator of reducing sugars.

The presence of reducing sugars can be indicated through a solution that contains cupric sulphate. The aldehyde group in the reducing sugar reduces the cupric sulphate to cuprous ions. Heating the cuprous ions produces a precipitate of cuprous oxide that ranges in color from yellow to green or red to brown. A positive result indicates the presence of reducing sugars (Pearson Education, 2007). Similarly, Biuret solution detects proteins and peptides. The solution is made up of a mixture of copper II sulphate and potassium hydroxide. The copper atoms in the solution react with the peptide bonds in proteins, thereby causing a change in color, indicating the presence of proteins and peptides.

When a substance undergoes a violet colour change from light blue, it indicates the presence of proteins, which are made up of various arrangements of 20 distinct amino acids. These amino acids are connected by peptide bonds as explained by Holland (1999). Negative and positive controls were included in the experiments.

All the controls served the purpose of identifying the possible unknown. The controls were composed of transparent liquids, with the exception of honey (which was slightly yellow) and beer (brown). More information about the salivary amylase experiment can be found in


salivary amylase experiment


The Iodine solution test for glycogen and starch relied on 1% glycogen solution and 1% starch solution as positive controls.

In the experiment, glycogen and starch, both polysaccharides, turned

into the expected colors of brown and dark blue respectively due to the staining of their polysaccharide coils by the iodine solution. The negative controls remained unchanged in color and stayed pale yellow. Beer was darker in color compared to the negative controls, but this was because it had an initial coloration. The results were expected as the other controls were mostly simple sugars and proteins not containing polysaccharide coils. The unknown substance yielded a positive result as it turned brown indicating the presence of glycogen. In the reducing sugar test using Benedict's solution, five positive controls were observed. (Answers Corporation, 2008)

The glucose solution, maltose solution, honey, lactose solution, and beer served as positive controls. The expected positive results were obtained from the glucose, maltose, and lactose solutions due to their aldehyde or ketone functional groups which can reduce cupric sulphate to cuprous ions and combine with oxygen, forming a precipitate called cuprous oxide (Pearson Education, 2007). Honey contains glucose and fructose monosaccharides that also possess this functional group, explaining its positive result (Wikipedia, 2008). Beer's main component, malt, is rich in maltose, a disaccharide that also contains this functional group (Wikipedia, 2008). The unknown sample also produced a positive result as evidenced by the formation of a precipitate and a change in color to burnt orange upon exposure to the Benedict's solution.

The Biuret solution test for protein yielded only one positive control, which was expected as the test was designed to indicate the presence of protein. The copper in the solution reacted with the peptide bonds formed by amino acids in the protein, resulting in a violet color (Holland, 1999). While honey turned a

darker yellow shade, it is probable that preservatives present within the honey reacted with the Biuret solution. Beer retained its brown color due to its darker hue, indicating a negative result.

Unknown number 281 did not yield a positive result for protein and was found to contain glycogen and reducing sugar based on the results of the Iodine Test for Starch and Glycogen (Table 1) and the Benedict's Test for Reducing Sugars (Table 3). The results for the positive controls in both experiments were similar to those for the unknown when mixed with iodine solution and Benedict's solution. The Biuret test results for the unknown were similar to the negative control, indicating its lack of protein content.

The controls were effective in facilitating the determination of which macromolecules were present in the unknown sample as they allowed for comparison and contrast.