Answers
Basic Chemistry for Investigating Living Systems
Exercise 1: Testing for the Presence of Proteins in Cells
Results:
Table 1: Biuret Reagent Test for Protein in Cells
Test Tube
Contains
Hypothesis:
Contains Protein Yes or No?
Final Color
Is test substance present/absent?
1
Water
No
nearly colorless
absent
2
Albumen
Yes
amber-purple
present – lesser concentration
3
Amylase
Yes
lavender-purple
present – high concentration
4
Potato Starch
No
nearly colorless
absent
5
Onion Juice
No
amber-purple
present – lesser concentration
6
Potato Juice
No
amber -purple
present – lesser concentration
.
Any time you see a chemical with an ending, -ase, assume it is an enzyme. Enzymes are proteins.
Conclusions:
A. What is the test substance? The test substance is protein.
B. Which test tube represents the control? The tube that contained distilled water (tube 1) was the test tube that represents the control. Why? When protein molecules are present, Biuret Reagent reacts with the protein to form a violet color. Tube number one is the control tube because it is distilled water and has no protein; the tube is colorless. If one knows that colorless represents no protein and violet color represents the presence of protein, one can use tube one to determine whether or not protein is present. (More information. You can look up Biuret Reagent to actually see how the chemical reaction occurs.)
C. Which test tube contained the most test substance? The tube that contained the most test substance is amylase (tube 3).
D. Other than the control, which test tube contained the least test substance? None of the test tubes contained protein. If there would have been a reaction I would assume that there was some cross contamination.
E. Did the results agree with your initial hypothesis in every case? My results did agree with my initial hypothesis in every case. Why or why not? My hypothesis was correct when I expected...