Essay Questions

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Chapter 6

Essay Questions

This activity contains 7 questions.

Some enzymes catalyze reactions at rates close to, or even faster than, that expected of free diffusion (10⁸ to 10⁹ M^-1s^-1) of the substrate to the enzyme. Explain how this is possible.

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A fellow labmate suggests that, in order to increase the rate of reaction catalyzed by an enzyme you have cloned, you should design point mutations which decrease greatly the K_m for its substrate. Do you agree with this strategy? Explain your answer.

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A cascade of zymogen activations occurs both with digestive proteases and blood clotting proteases. List the benefits of this strategy.

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The cleavage of p-nitrophenylacetate by chymotrypsin yields the following data:

Explain why biphasic kinetics are observed (rapid initial cleavage followed by a slow rate of cleavage).

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Clinical Question

Blood clotting is assisted by the activation of a cascade of zymogen proteases. The activation of early factors in response to vascular injury results in the cleavage and activation of subsequent zymogens in the cascade. Ultimately, this cascade results in the proteolytic conversion of fibrinogen to fibrin, which forms a crosslinked mesh of fibers that help to form a plug. Blood clotting needs to respond to minute signals and to amplify them quickly. Describe why a zymogen cascade is ideally suited to this type of signal amplification.

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Clinical Question

The dependence of terestrial life on oxygen comes at cost. Partially reduced species of oxygen are highly reactive and can damage macromolecules. As a result, a number of antioxidant proteins have evolved that scavange these reactive oxygen species. One of these enzymes, superoxide dismustase, is discussed in the text. Another antioxidant enzyme, catalase, converts hydrogen peroxide to molecular oxygen and water. Catalase is remarkable in that it has a low affinity for its substrate (high Km), but a high maximal velocity (Vmax). Discuss why this might be an effective strategy for scavenging hydrogen peroxide.

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Clinical Question

Emphysema is caused by excessive cleavage of elastin by elastase, leading to inelastic lungs and poor oxygen exchange. From what you know about the regulation of trypsin activity, propose a likely mechanism for this phenomenon.

To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

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Essay Questions

Some enzymes catalyze reactions at rates close to, or even faster than, that expected of free diffusion (108 to 109 M-1s-1) of the substrate to the enzyme. Explain how this is possible.

A fellow labmate suggests that, in order to increase the rate of reaction catalyzed by an enzyme you have cloned, you should design point mutations which decrease greatly the Km for its substrate. Do you agree with this strategy? Explain your answer.

A cascade of zymogen activations occurs both with digestive proteases and blood clotting proteases. List the benefits of this strategy.

The cleavage of p-nitrophenylacetate by chymotrypsin yields the following data: Explain why biphasic kinetics are observed (rapid initial cleavage followed by a slow rate of cleavage).

Clinical QuestionEmphysema is caused by excessive cleavage of elastin by elastase, leading to inelastic lungs and poor oxygen exchange. From what you know about the regulation of trypsin activity, propose a likely mechanism for this phenomenon.

Some enzymes catalyze reactions at rates close to, or even faster than, that expected of free diffusion (10⁸ to 10⁹ M^-1s^-1) of the substrate to the enzyme. Explain how this is possible.

A fellow labmate suggests that, in order to increase the rate of reaction catalyzed by an enzyme you have cloned, you should design point mutations which decrease greatly the K_m for its substrate. Do you agree with this strategy? Explain your answer.

The cleavage of p-nitrophenylacetate by chymotrypsin yields the following data:

Explain why biphasic kinetics are observed (rapid initial cleavage followed by a slow rate of cleavage).

Clinical Question

Emphysema is caused by excessive cleavage of elastin by elastase, leading to inelastic lungs and poor oxygen exchange. From what you know about the regulation of trypsin activity, propose a likely mechanism for this phenomenon.