19. Enzymes

Pepsin, a peptidase that hydrolyzes proteins, functions in the stomach at an optimum pH of 1.5 to 2.0.

Which of the following would cause an increase in its activity?

Sucrase has an optimum pH range of 4.5 – 7.0. Which of the following statements is true?

What do we mean when we say an enzyme is saturated with substrate? When an enzyme is saturated with substrate, how does adding more (a) substrate and (b) enzyme affect the rate of the reaction?

How do you explain the observation that pepsin, a digestive enzyme found in the stomach, has a high catalytic activity at pH 1.5, while trypsin, an enzyme of the small intestine, has no activity at pH 1.5?

What general effects would you expect the following changes to have on the rate of an enzyme-catalyzed reaction for an enzyme that has its maximum activity at body temperature (about 37°C)?

a. Raising the temperature from 37°C to 70°C

What general effects would you expect the following changes to have on the rate of an enzyme-catalyzed reaction for an enzyme that has its maximum activity at body temperature (about 37°C)?

c. Adding an organic solvent, such as methanol

What general effects would you expect the following changes to have on the rate of an enzyme-catalyzed reaction for an enzyme that has its maximum activity at body temperature (about 37°C)?

c. Adding an oxidizing agent, such as hydrogen peroxide

How will changing the conditions in an enzymatic reaction affect the rate of that reaction? Explain why in each case.

f. Decreasing the amount of substrate by half

Apple slices and peeled potatoes rapidly brown in open air due to the presence of phenolases. Phenolases cause the oxidation of phenolic molecules like tyrosine to quinones, colored molecules responsible for the brown colors seen. An experiment comparing the time it took for a change to occur in the color of apple slices versus potato slices was done to test for phenolase activity. Then, a second experiment was done with new apple and potato slices with H2O2 measuring time until bubbles appeared. <IMAGE>

b. Which sample contains more catalase? Why?

Trypsin, a peptidase that hydrolyzes polypeptides, functions in the small intestine at an optimum pH of 7.7 to 8.0. How is the rate of a trypsin-catalyzed reaction affected by each of the following conditions?

b. running the reaction at 75 °C

Pepsin, a peptidase that hydrolyzes proteins, functions in the stomach at an optimum pH of 1.5 to 2.0. How is the rate of a pepsin-catalyzed reaction affected by each of the following conditions?

a. changing the pH to 5.0

The following graph shows the activity versus pH curves for pepsin, sucrase, and trypsin. Estimate the optimum pH for each.

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Refer to the graph in problem 16.45 to determine if the reaction rate in each condition will be at the optimum rate or not.

a. trypsin, pH 5.0

Adults who are lactose intolerant cannot break down the disaccharide in milk products. To help digest dairy food, a product known as Lactaid can be added to milk and the milk then refrigerated for 24 hours. (16.4, 16.5)

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b. What might happen to the enzyme if the Lactaid were stored at 55 °C?

Fresh pineapple contains the enzyme bromelain that hydrolyzes peptide bonds in proteins. (16.3, 16.4, 16.5)

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a. The directions for a gelatin (protein) dessert say not to add fresh pineapple. However, canned pineapple where pineapple is heated to high temperatures can be added. Why?