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Name: ___________________________
Lab 2: Chemistry
Cell Chemistry
Learning Outcomes
· Learn to perform simple tests to indicate the presence of specific chemicals
· Use this knowledge to determine the composition of an unknown solution
· Explain the mechanism by which the tests used determine the presence of sugars, starch, and protein. (i.e., color change)
· Apply knowledge of human cell structure, biological macromolecules, and basic metabolic processes through laboratory investigation
Introduction
All living things are composed of four basic classes of molecules: ca
ohydrates, proteins, lipids, and nucleic acids. In this lab we will be studying ca
ohydrates (starch and sugar), proteins and lipids (fats and oils). We will be using reagents (indicator chemicals) to detect the presence of these different classes of molecules in water solutions.
In most cases we will be looking for some obvious visual change, such as a change in color, as an indication that a particular type of molecule is present. When such a change is observed, the test is said to be positive for the presence of that particular molecule. In order to be assured that the physical changes we see are only due to the presence of the molecule, a control reaction is always performed for comparison. In the following experiments, distilled water will be used as the control substance and provides a negative result.
Activity 1: Testing for the Presence of Starch in Solution
Ca
ohydrates
Ca
ohydrates are the starches and sugars. Sugars (monosaccharides) are rather simple molecules made up of ca
on, hydrogen and oxygen. Starches are polysaccharides, or long chains (polymers) of simple sugars (monosaccharides). In this exercise, we will be using an indicator chemical (IKI solution or Lugol’s Reagent) in order to detect the presence of starch in various solutions.
Materials
3 clean test tubes Test tube rack
Dropper bottle of 1% glucose (sugar) Dropper bottle of distilled (DI) wate
Dropper bottle of 1% amylose (starch) Sharpie marker or grease pencil
Dropper bottle of IKI solution (Lugol’s Reagent)
Procedure
1. Using a Sharpie marker or grease pencil, label the top of one test tube as “DI”, one as “sugar”, and one as “starch”.
2. To each tube, add 5 drops of IKI solution. Record the color of the IKI reagent in the table below (“Reagent Color”). *Caution: IKI can stain and burn the skin!
3. Add 5 drops of distilled water to the tube marked “DI”.
4. Add 5 drops of 1% glucose (sugar) to the tube marked “sugar”.
5. Add 5 drops of 1% amylose (starch) to the tube marked “starch”.
6. Gently shake each tube. Record the color of the sample in the table below (“Color after addition of sample”). Make note of any color changes that occu
ed.
7. In the “Conclusion” column, place a “+” if the tube is positive for starch or a “–” if the tube is negative for starch.
8. Use soap, water, and a test tube
ush to clean the test tubes and place them in the rack to dry. Be certain they are not touching one another when you place them in the rack.
Reagent Colo
Sample
Colo
(after addition of sample)
Color Change
(yes or no?)
Conclusion
Water (DI)
1% Glucose (sugar)
1% Amylose (starch)
What does the IKI reagent test for? _________________________________________________
What color indicates a positive reaction? ____________________________________________
Activity 2: Testing for the Presence of Sugar in Solution
Simple sugars (monosaccharides) are ca
ohydrate monomers, meaning they can be bonded together to form polysaccharides such as starch. In this exercise, we will be using another indicator chemical (Benedict’s reagent) in order to detect the presence of sugar in various solutions.
Materials
3 clean test tubes Test tube rack
Dropper bottle of 1% glucose (sugar) Dropper bottle of distilled (DI) wate
Dropper bottle of 1% amylose (starch) Dropper bottle of Benedict’s reagent
Sharpie marker or grease pencil
Procedure
1. Obtain three clean test tubes and label them as you did in Activity 1 for the starch test.
2. Add 10 drops of Benedict’s solution to each test tube. Record the color of the Benedict’s reagent in the table below (“Reagent Color”).
3. Add 10 drops of distilled water to the tube marked “DI”.
4. Add 10 drops of 1% glucose (sugar) to the tube marked “sugar.
5. Add 10 drops of 1% amylose (starch) to the tube marked “starch”.
6. Gently shake each tube.
7. Place all three test tubes in a beaker of boiling water on the hot plate at the rear of the classroom. Make a note of the beaker where you placed your test tubes, as the whole class will have tubes in beakers.
8. Allow the tubes to heat for 10 minutes (or less; watch for a color change).
9. Use a test tube holder to carefully remove the tubes. Ca
y your test tube rack with you to retrieve your test tubes from the hot water bath. Do NOT walk around the room ca
ying test tubes with the test tube holder.
10. Record the color of the sample in the table below (“Color after addition of sample”). Make note of any color changes that occu
ed.
11. In the “Conclusion” column, place a “+” if the tube is positive for sugar or a “–” if the tube is negative for sugar.
12. Use soap, water, and a test tube
ush to clean the test tubes and place them in the rack to dry. Be certain they are not touching one another when you place them in the rack.
Reagent Colo
Sample
Colo
(after addition of sample)
Color Change
(yes or no?)
Conclusion
Wate
1% Glucose (sugar)
1% Amylose (starch)
What does the Benedict’s reagent test for? ___________________________________________
What color indicates a positive reaction? ____________________________________________
Activity 3: Testing for the Presence of Protein in Solution
Proteins
Proteins are complex a
angements of amino acids. The amino acids are linked to each other in long chains. In this exercise, a special compound, Biuret’s reagent, will be used to detect proteins dissolved in solution.
Materials
2 clean test tubes Test tube rack
Dropper bottle of distilled (DI) water Sharpie marker or grease pencil
Dropper bottle of 1% gelatin Dropper bottle of Biuret’s reagent
Procedure
1. Use the Sharpie or grease pencil to mark one test tube as “protein” and the other as “DI”.
2. Add 10 drops of Biuret’s reagent to each test tube. Record the color of the Biuret’s reagent in the table below (“Reagent Color”).
3. Add 5 drops of 1% gelatin to the “protein” test tube.
4. Add 5 drops of distilled water to the “DI” test tube.
5. Gently shake each tube.
6. Wait a few minutes and Record the color of the sample in the table below (“Color after addition of sample”). Make note of any color changes that occu
ed.
7. In the “Conclusion” column, place a “+” if the tube is positive for protein or a “–” if the tube is negative for protein.
8. Use soap, water, and a test tube
ush to clean the test tubes and place them in the rack to dry. Be certain they are not touching one another.
Reagent Colo
Sample
Colo
(after addition of sample)
Color Change
(yes or no?)
Conclusion
Wate
1% Gelatin
(protein)
What does the Biuret’s reagent test for? ____________________________________________
What color indicates a positive reaction? ___________________________________________
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