Exercise 8: Chemical and Physical Processes of Digestion: Activity 3: Assessing Pepsin Digestion of Protein Lab Report

Pre-lab Quiz ResultsYou scored 60% by answering 3 out of 5 questions correctly.

1. Where in the body does protein digestion begin?You correctly answered: b. the stomach

2. The substrate for pepsin isYou 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 with the negative controlsYour answer : a. are expected.Correct answer: d. are expected and validate the experiment.

5. A spectrophometer measuresYour answer : b. starch concentration.Correct answer: c. optical density.

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Experiment ResultsPredict Question:Predict Question: At which pH do you think pepsin will have the highest activity?Your answer : c. pH 9.0

Stop & Think Questions:Which of the following tubes are negative control tubes?Your answer : c. tube 4Correct answer: e. tubes 3 and 4

An optical density greater than zero indicates thatYou correctly answered: e. BAPNA digestion has occurred and pepsin is active.

Experiment Data:

Tube No. Reagent 1 Reagent 2 Reagent 3 Boiled Time Temp. OpticalDensity

1 Pepsin BAPNA pH 2.0 + 60 37 0.002 Pepsin BAPNA pH 2.0 - 60 37 0.403 Pepsin Water pH 2.0 - 60 37 0.004 Water BAPNA pH 2.0 - 60 37 0.005 Pepsin BAPNA pH 7.0 - 60 37 0.036 Pepsin BAPNA pH 9.0 - 60 37 0.00

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Post-lab Quiz ResultsYou scored 75% by answering 3 out of 4 questions correctly.

1. Pepsin would be most activeYou correctly answered: b. in the stomach.

2. Which two tubes validated the results of the experiment?Your answer: b. tubes 2 and 3Correct answer: c. tubes 3 and 4

3. With more enzyme activity the optical densityYou correctly answered: a. increased.

4. If pepsin were digesting an actual protein substrate, the product would beYou correctly answered: c. peptides and amino acids.

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Review Sheet Results1. Describe the effect that boiling had on pepsin and how you could tell that it had that effect.Your answer:pepsin activity break up ingested proteins and polypeptides into smaller peptide chains and free amino acids

2. Was your prediction correct about the optimal pH for pepsin activity? Discuss the physiological correlation behind yourresults.Your answer:pH has an influence on the activity of the enzyme pepsin

3. What do you think would happen if you reduce the incubation time to 30 minutes for tube 5?Your answer:do not absorb the light and will have an optical density near zero