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Biological Molecules: Abstract

Throughout biology, structure determines function. As we begin to discover this theme, the lab completed serves as a prime example by testing for starch, reducing sugar, protein, and fat. On an atomic level, each of these molecules is composed of functional groups which distinguish to a certain extent a group’s chemical properties. As a result, these properties can be detected by specific tests such as an iodine test for starch, a Benedict’s test for reducing sugar, a Biuret test for protein, and a Sudan III test for fat. If amylose in starch is present, the effect is a deep, dark blue color when iodine is added because of starch’s unique coiled geometric arrangement. If none are present, then the color will remain orange or yellow. To test for the existence of a free aldehyde group, a Benedict’s test is conducted by heating a solution to form a precipitate that is blue, green, yellow, orange, or red in color; blue means there is no sugar present whereas the closer to brick-red the product is, the higher concentration of a reducing sugar is present. Consequently, a redox reaction occurs with the sugar oxidizing and the Benedict’s reagent reducing. The copper atoms in Biuret solution react with peptide bonds to produce a lavender or violet color, indicating the presence of proteins; otherwise, a light blue color appears if no protein is present. The Sudan III test reveals the nonpolar hydrocarbon groups remaining in the molecule by staining them red orange.

In the iodine test for starch, we decided that although both paper and potato contain starch since they turn black, the potato would have more glucose monomers. In the actual test, three tubes were obtained with varying amounts of starch along with one tube of glucose and another of water. While all the test tubes containing starch turned a black-blue color indicating that starch was present, I believe there should have been more starch in the more concentrated test tubes and thus a darker color from iodine. Glucose did not display a positive test since glucose is only the subunit of starch and not as branched so iodine didn’t recognize it. Also, obviously water did not include any trace of starch so it acted as a control in this experiment. In the Benedict’s test, water, egg white, honey, and glucose were placed in test tubes combined with Benedict’s solution and heated for three minutes. Water turned a blue color afterwards since it didn’t consist of reducing sugars and the glucose turned a dark red-brick color since it was a monosaccharide. Both water and glucose were controls to compare other observations with. Honey turned a yellow-brown color demonstrating that reducing sugar was present, but the egg white turned a grey-blue color signifying that there was no reducing sugar. In the Biuret test for protein, water and honey did not have protein present, even though egg white did. Egg white contains albumin, which turned a lavender color. Finally, in the Sudan III test, water, flour, and oil were dissolved in ethanol, transferred to filter paper, submerged in Sudan III solution, and then soaked in distilled water. It pointed out that oil, made of unsaturated fats, turned a faint pink color rather than a red orange color most likely because the paper was immersed longer than needed. Flour and water had no color change.

The Iodine test could be employed by farmers or paper manufacturers to determine the quantity of plant food available and the quality of paper. The Biuret test can especially be applied in the doctor’s office when examining urine samples. Protein leaks into the urine if the kidneys are damaged and by inspecting urine, early warnings may be spotted. Furthermore, urine could be analyzed for drug abuse, despite the fact that drugs may or may not include protein, as well as for diabetes. In order to test for diabetes, the Benedict’s test is utilized. In the same way as in the lab, urine may fluctuate in color depending on sugar content. If diabetes is diagnosed, treatment may then be appropriately administered. Though different from Sudan III, the closely related Sudan I is an oil-based industrial dye that is not permitted in food. Yet, it was discovered to have been illegally added to chili powder to enhance the red color. This substance chemically contaminates food and causes cancer. Testing if fats are present in foods can solve this problem.


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