Lab 2: Carbohydrates and Protein/Lipids

Lab 2: Carbohydrates and Protein/Lipid

Laboratory 2, AP Biology 2011

Spurthi Tarugu, Kavinmozhi Caldwell, Chelsea Mbakwe, Radha Dave, Navya Kondeti
Abstract:
Almost all living organisms contain four organic compounds, two of which are lipids and proteins. Lipids are made up of one molecule of glycerol and three molecules of fatty acids, resulting in a triglyceride. Fatty acids are what make lipids non-polar and unable to dissolve in water. Proteins are inherently important to any living organism. They control cell process, provide support, and transport substances within a cell. They can even take the form of enzymes and hormones, regulating cells. These important cells are made up of polymers of amino acids whose functional groups are a carboxyl group and a free amino group. Both organic compound contribute to our lives, and our health is heavily dependent on them. Knowing how they operate is to partially understand the mechanics of the human body.

Introduction:

In the medical field today,  tests are run to determine the presence or absence of a particular substance, whether it be protein, carbohydrates, or lipids. These tests are run in order to see if said person has the required count of said substance. In the same way that tests are done in the lab in order to determine the presence or absence of something, that is the same way we approached both the Carbohydrate and Protein/Lipid Lab. Through the use of indicators we determined the presence or absence of organic compounds.

Methods:
     Carbohydrates Lab:
            Part 1 (Lugol’s Test for Starch):
                        First, we obtained a test tube rack and 5 test tubes. We filled each test tube with each of the following solutions: glucose, starch, galactose, sucrose, and distilled water. Each test tube was filled with at least 2-3 mL of one solution. We labeled each test tube with the name of the solution that the test tube contains. After that, we added 2-3 mL of Lugol’s solution to each test tube and then gently rocked it back and forth to mix the solutions. Lastly, we recorded any color changes in our chart.
Part 2 (Benedict’s Test for Reducing Sugar)
                        First we got a test tube rack and 7 test tubes. Them, we labeled each of the test tubes with the appropriate label: glucose, sucrose, maltose, starch, ribose, galactose, and distilled water. Then, we filled each test tube with one designated solution. We turned on the hot plate. Then, we got a beaker, filled it halfway with water, and placed it on the hot plate. After placing the beaker on the hot plate, we filled the test tubes with about 2-3 mL of the Benedict’s solution. The, we placed all of the test tubes in the beaker, using a clamp or an insulated glove, for several minutes. We observed any color changes, and recorded our observations in the table.

     Protein/Lipids Lab
            Part 1 (Visual Test for Lipid):
                        First, we filled a petri dish half way with tap water. Then, we put one drop of vegetable oil into the petri dish with an eyedropper. Lastly, we observed the vegetable oil in the water, and recorded our observations.
Part 2 (Biuret Test for Protein):
                        First, we obtained a test tube rack with 4 test tubes. Each test tube was labeled with the labels of the solutions which are glucose, starch, egg albumin, and distilled water.Then, we placed 2-3 mL of each solution into the assigned test tube. After that, we turned the solutions into alkaline solutions (pH greater than 7) by adding 2-3 mL of 10% sodium hydroxide. Then, we added several drops of 1% copper sulfate solution to each test tube. We gently rocked the test tubes back and forth, mixing the copper sulfate with the alkaline solution. Lastly, we recorded any color changes in our chart.
Part 3 (Unknown solution)
                        First, we obtained a test tube rack and 9 test tubes. Our teacher provided us with three unknown solutions, A,B, and C. We filled 3 test tubes with the solution A, the next 3 with solution B, and the last 3 with solution C. The first set of three test tubes (A,B, and C) were infused with drops of Lugol’s iodine. We gently shook these test tubes, and observed any color changes. We recorded our observations in our chart. Then, we turned on the hot plate. We willed a 500 mL beaker half way and waited for the water to turn hot. In the next set of 3 test tubes (A,B, and C), we put a few drops of Benedict’s solution into it, gently shook the test tubes back and forth and immersed all 3 of the test tubes into the boiling water. After a few minutes, we observed the color of the test tubes and recorded our observations in the table. We took the last set of 3 test tubes (A, B, and C) and put a few drops of biuret reagent into it. We gently shook the test tubes, and observed the test tubes for color change. We recorded these observations into a table.

Results
Chart 3-1 Results for Benedict’s test for Reducing Sugars

Sugars Precipitate or Color Change Interpretation
Fructose orange positive for reducing sugar
Sucrose blue negative for reducing sugar
Starch blue negative for reducing sugar
Distilled Water blue negative for reducing sugar

Chart 3-1 Results for Lugol’s Test for Starch

Sugars Precipitate or Color Change Interpretation
Fructose yellow negative for starch
Sucrose dark orange positive for starch
Starch yellow negative for starch
Distilled Water yellow negative for starch

Chart 3-5 Results of Biuret test for Protein

Sugars Precipitate or Color Change Interpretation
Egg albumin Sky blue Negative for Protein
Glucose Light blue Negative for Protein
Starch Turquoise Negative for Protein
Distilled Water Dark blue/Deep Purple Positive for Protein

Chart 3-6 Testing the composition of common substances

Substance or unknown Sugar (Benedict’s testing) Lipids Proteins (Biuret testing) Starch (Lugol’s testing)
A Positive Negative Negative Negative
B Negative Negative Positive Positive
C Negative Positive Negative Negative

Discussion

3-1 Carbohydrates
What was the purpose of including the tube of distilled water in each test?
            The distilled water served as a control for the experiment. It helped us compare and contrast the results of the other liquids in the other test tubes with those of water.
What would you have concluded if the tube of distilled water had shown a positive reaction in either test?
            If the tube of distilled water had shown a positive reaction, then I would have concluded that the sample was contaminated.
What would you have done in this case?
            If the sample was contaminated, I would have gotten rid of the contaminated sample and started the testing for the distilled water from the beginning.
What can you conclude about the difference in arrangement or bonding of the functional adehyde or ketone groups in glucose as compared to sucrose?
            Adehyde is composed of a ketone. When comparing the difference in arrangement or bonding of the functional group in glucose, we are able to see that adehyde and ketone are vital components of glucose. On the other hand, those functional groups are not present in sucrose.
Some plants store food as sugar, while others store it as starch. Suggest a test for determining which storage reserve is used in a vegetable you might find at the market?
The Benedict’s test for reducing sugar and the lugol’s test for starch will help determine which storage reserve is used in a vegetable at the market. If a certain vegetable was to display a positive reaction for the Benedict’s test, we will be able to conclude that it stored food as sugars. The same goes for starches except vice versa. With a Lugol’s test we would be able to determine if a vegetable stores food as starch.

3-2 Lipids
In a petri dish half-filled with tap water, add one drop of vegetable oil, either by using an eyedropper or by stirring the water with a glass rod that has been dipped in the oil. Observe what happens at the surface of the water, and record your observations.
The oil particles refuse to blend in with the water. Because of the density of oil and water, the oil continues to float on top of the water without mixing. The oil has a lower density than water. The vegetable oil can easily be differentiated from the tap water in the petri dish.
You may have observed this reaction of oil and water in everyday experience. Interpret your observations in terms of the structure of the vegetable oil molecule and its ability (or inability) to hydrogen-bond with water.
The vegetable oil is not mixing with the water, so it does not have the ability to hydrogen-bond with the water. Because of this fact, we have deduced that vegetable oil is non-polar.
What can you say about the relative densities of oil and water?
The relative density of oil is lower than that of water due to the fact that oil floats on top of water.
In light of your answer to the previous question, what function other than energy storage does fatty blubber serve in a whale?
Fatty blubber in whale, because its fat is less dense than water, may help the whale float. Also, blubber helps insulate the whale.

3-3 Amino Acids and Protein
If a substance gave a positive result with ninhydrin regeant and a negative result with the Biuret regeant, what would you conclue about its composition?
The ninhydrin reagent tests for amino acids while the biuret tests for protein. If the ninydrin test is positive and the biuret test is negative, then the composition is made up of amino acids.

3-4 Testing the composition of common substances
Which substances were present in Unknown #1?
In unknown #1, sugar was the only substance that was present.
Which substances were present in Unknown #2?
            In unknown #2, starch and protein were present.

Conclusion
The purpose of this lab was to test various substances including fructose, sucrose, starch distilled water, glucose, and egg albumin for presence or absence of reducing sugars, starch, sugar, proteins, and lipids. Throughout this lab we observed that the sugar fructose was positive for reducing sugar but negative for starch while sucrose was negative for both reducing sugar and starch.The starch was negative for reducing sugar, starch, and proteins. Starch should obviously be positive for starch, but our test came out negative, so we believe that the test tube labeled “starch” contained a different solution. We also learned that distilled water was negative for reducing sugars and starch but positive for proteins. Distilled water should not have had any proteins in it, so we hypothesized that our sample was contaminated. Another thing we observed was that the vegetable oil was non-polar because it does not have the ability to hydrogen-bond.

Literature Cited
“LabBench.” Prentice Hall Bridge Page. Web. 27 Sept. 2011.

<http://www.phschool.com/science/biology_place/labbench/lab1/intro.html&gt;.