Exercise 8: Chemical and Physical Processes of Digestion: Activity 3: Assessing Pepsin Digestion of Protein Lab Report Pre-lab Quiz Results You scored 100% by answering 5 out of 5 questions correctly. 1. Where in the b body ody does protein digestion digestion begin? You correctly answered: b. the stomach 2. The substrate for pepsin is You correctly answered: d. protein and peptides. 3. In this activity the substrate you will be using to detect protein digestion is You correctly answered: d. BAPNA. 4. Negative results results with tthe he negative controls controls You correctly answered: d. are expected and validate the experiment. 5. A spectrophometer measures You correctly answered: c. optical density.
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Experiment Results Predict Question: Predict Question: At which pH do you think pepsin will have the highest activity? Your answer : a. pH 2.0 Stop & Think Questions: Which of the following tubes are negative control tubes? You correctly answered: e. tubes 3 and 4 An optical density greater than zero indicates that You correctly answered: e. BAPNA digestion has occurred and pepsin is active. Experiment Data: T u be N o .
Reagent 1
Reagent 2
Reagent 3
Boiled
Time
Temp.
1 2 3 4 5 6
Pepsin Pepsin Pepsin Water Pepsin Pepsin
BAP N A BAP N A Water BAP N A BAP N A BAP N A
pH 2.0 pH 2.0 pH 2.0 pH 2.0 pH 7.0 pH 9.0
+ -
60 60 60 60 60 60
37 37 37 37 37 37
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Optical Density 0.00 0.40 0.00 0.00 0.03 0.00
Post-lab Quiz Results You scored 75% by answering 3 out of 4 questions correctly. 1. Pepsin would be most active active You correctly answered: b. in the stomach. 2. Which two tubes validated the results of the experiment? You correctly answered: c. tubes 3 and 4 3. With more more enzyme activity the the optical density You correctly answered: a. increased. 4. If pepsin were digesting an actual protein substrate, the product would be Your answer: a. peptides. Correct answer: c. peptides and amino acids.
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Review Sheet Results 1. Describe the effect that boiling had on pepsin and how you could tell that it had that effect. effect. Your answer: Boiling greatly reduced the effect of pepsin. This could be seen in the first and second tube wherein the first was boiled and the second was not. The contents of the first tube did not turn yellow which shows that there was no pepsin activity. In the second tube, however, the yellow coloration col oration implies pepsin activity. Therefore, it is clear that heat denatured pepsin. 2. Was your prediction correct about the optimal pH for pepsin activity? Discuss the physiological correlation behind your results. Your answer: Yes, my prediction was correct. It can be seen that in the second tube, where a pH 2.0 buffer was mixed, optical density is 0.40, highest among all the others. Hence, pH 2.0 is the optimal pH for pepsin activity. 3. What do you think would happen if you reduce the incubation time to 30 minutes for tube 5? Your answer: Optical density will decrease.
