Identifying Macromolecules in Solutions

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In order to determine whether starch or glycogen are present within the solutions, iodine drops are added to each of the twelve solutions. If the solution appears to be a blue-black colour, then starch is present within the solution. A positive glycogen result however, will yield a colour change of a reddish-brown colour. With that being said, after all the solutions were mixed with iodine drops, three solutions yielded a positive result. Solution 8 (1% starch solution) was a positive reaction and contained starch due to the fact that the solution had turned a blue-black colour. The following reaction did not contain any errors due to the fact that the original solution to which the iodine solution was placed was originally 1% starch solution. When iodine is mixed with starch, a blue-black colour is present. The reason for this is because the iodine and starch complex contain energy level spacings, which is solely for absorbing visible light, hence the reason the solution has an intense blue colour (Albert, B 2013). Afterward, it was discovered that solution 7 (1% glycogen) contained glycogen and was a positive reaction because the colour of the solution turned into a red-brown. The reason why the solution changed colour is because glycogen is a highly branched structure, and with the addition of iodine to the solution, it causes the solution to turn red-brown colour (“Starch”, 2013). Ultimately, all other solution failed to show any colour change, resulting in a negative reaction.

Afterwards, reducing sugars were tested for by using Benedict’s solution, which contains blue cupric ions (Cu++) (Alberts, B 2013). This indicates that when Benedict’s solution is added with a solution that contains a reducing sugar, the solution itself will change to faint blue colour due to the presence of Cu(++) ions (Alberts, B 2013). With that being said, when Benedict’s solution was added to solution 10 (beer), the beer underwent a colour change from yellow-brown to blue-green. Once heated, the beer turned into a thick pale brown-yellow colour, indicating a positive reaction. Although the solution did not experience a red-brown, a colour change still occurred as well as the formation of a precipitate within the test tube. Solution 1 (1% glucose) experienced a red-brown colour change along with solution 3 (%1 maltose solution), solution 4 (honey solution) and lastly solution 6 (1% lactose solution). Since the following solution underwent a colour change, this indicates that reducing sugars are present within these solutions and are all positive results.

Finally, protein was tested for with the use of Biuret testing. Each of the twelve solutions received 2mL of 10% sodium hydroxide, along with 5 drops of 1% copper sulfate in each test tube. In order to indicate a positive reaction, the solutions will turn violet after adding sodium hydroxide and copper sulfate. The reason why this occurs is because the Cu(++) ions bond to the nitrogen molecule of the amino acid, causing a colour change (Ophardt, 2003). With that being said, solution 9 (protein solution) became a violet purple, which concludes that there is presence of protein molecules. Also, solution 12 (Unknown 174) yielded a positive reaction because the solution colour turned violet, indicating the presence of protein molecules within the solution. Ultimately, all other solutions did not experience a colour change, resulting in a negative test result.

After conducting the iodine test, Benedict’s solution test and biuret test, it is known that unknown solution 174 is a protein. The reason why this holds true is because the solution tested negative for both iodine (starch/glycogen) and Benedict’s test (reducing sugars) and tested positive for the biuret test (protein). Nonetheless, in conclusion, unknown 174 is a protein.

References:

Alberts, B., Bray, D., Lewis, J., Raff, M., Roberts, K., & Watson, J. (1989).Molecular Biology of The Cell (Second ed.). New York: Garland Publishing Inc.

Department of Biology. (2013, Fall). BIOLOGY 130L Cell Biology Laboratory Manual Waterloo: University of Waterloo

Karp Gerald. (2013). Cell and Molecular Biology (7th ed.) New York: Garland Publishing Inc.

Ophardt, C. (2003). Carbohydrates. (2003).Elmhurst College: Elmhurst, Illinois. Retrieved September 24, 2013, from http://www.elmhurst.edu/~chm/vchembook/5 47glycogen.html

Pollard, T. D., & Earnshaw, W. C. (2004).Cell biology (Rev. reprint. ed.). Philadelphia, Pa.: Saunders.

Starch (chemical compound) -- Encyclopedia Britannica. (n.d.).Encyclopedia Britannica.

Retrieved September 24, 2013, from http://www.britannica.com/EBchecked/topic /563582/starch

Starch-iodine test - definition from Biology-Online.org. (2008, June 6). Life Science Reference -

Biology Online. Retrieved September 25, 2013, from http://www.biologyonline.org/dictionary/Starch-iodine_test