NAME__________________________________________________DATE_____________________PERIOD______
The Effect of pH on Pepsin Activity (Albumin Hydrolysis)
Problem Statement: How does altering the pH level affect pepsin’s ability to digest the protein
albumin?
Background Information:
Pepsinogen is an inactive enzyme (protein) produced by cells lining the stomach (gastric cells). In
the presence of hydrochloric acid (HCl), pepsinogen is converted to the active enzyme, pepsin.
This particular enzyme’s functions best at a pH of 2-3. The primary function of pepsin is to catalyse
reactions involving proteins (hydrolysis reaction). Pepsin, in the presence of water, will catalyse or
digest protein molecules (polypeptides) found in the stomach into dipeptides and amino acids.
Further protein digestion occurs in the small intestine. The stomach is the first place in the body
where digestion of proteins occurs.
Hypothesis:
Variables:
Independent Variable
Dependent Variable
Controlled Variables
Materials per Group (for 2 Trials):
Egg White Suspension
(Store Brand – Clara)
6 Test Tubes
Safety Goggles
1% Pepsin Solution
.1M/.5M/1M/2M HCL
Hot Water Bath (37◦
Celsius)
Timer (+/- ____ s)
6 Strips pH Paper or pH
Probe
Thermometer (+/-_____◦
Celsius)
.125/.25M Sodium
Carbonate
6 Pipettes (+/-___mL)
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
Label six test tubes A1 – A6 or B1-B6 (depending on your group assignment).
Each group will be performing 1 trial.
Using a graduated pipette, place 5 cm3 of egg-white suspension in each tube.
Using a graduated pipette, place 1 cm3 of acid or alkali in each tube using the table
below as a guide.
Place both sets of test tubes in the water bath (37◦C) BEFORE adding the pepsin.
Use a graduated pipette to add 1 cm3 pepsin solution to each tube, and start timing. Time
how long it takes for the solution in each tube to become clear.
Compare the pH of each tube by taking a sample with a clean dropping pipette and
touching the tip of the pipette on to a piece of pH test paper so that a small drop of liquid
runs on to it. A calibrated pH probe may also be used.
Repeat for each tube, rinsing the pipette between samples.
Raw Data:
Table 1.0 (Period 2)
Tube
A1
A2
A3
A4
A5
A6
Egg-white suspension and 1% pepsin
+:
2M HCl
1M HCl
0.5M HCl
0.1M HCl
0.25M sodium carbonate
0.125M sodium carbonate
Table 2.0 (Period 2)
Tube
B1
B2
B3
B4
B5
B6
Egg-white suspension and
boiled/denatured pepsin +:
2M HCl
1M HCl
0.5M HCl
0.1M HCl
0.25M sodium carbonate
0.125M sodium carbonate
Table 3.0 (Period 4)
Tube
A1
A2
A3
A4
A5
A6
Egg-white suspension and pepsin +:
2M HCl
1M HCl
0.5M HCl
0.1M HCl
0.25M sodium carbonate
0.125M sodium carbonate
Table 4.0 (Period 4)
Tube
B1
B2
B3
B4
B5
B6
Egg-white suspension and
boiled/denatured pepsin +:
2M HCl
1M HCl
0.5M HCl
0.1M HCl
0.25M sodium carbonate
0.125M sodium carbonate
Qualitative Observations:
Sample Calculations:
Processed Data Table:
Graph(s):
Conclusion(s):