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Ch.16 Amino Acids, Proteins, and Enzymes
Timberlake - Chemistry: An Introduction to General, Organic, and Biological Chemistry 14th Edition
Timberlake14th EditionChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9781292472249Not the one you use?Change textbook
All textbooksTimberlake 14th EditionCh.16 Amino Acids, Proteins, and EnzymesProblem 44a
Chapter 16, Problem 44a

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

Verified step by step guidance
1
Understand the role of pH in enzyme activity: Enzymes like pepsin have an optimum pH range where they function most effectively. For pepsin, this range is 1.5 to 2.0, which corresponds to the acidic environment of the stomach.
Recognize the effect of pH changes: When the pH deviates significantly from the enzyme's optimum range, the enzyme's structure (specifically its active site) can be altered. This is due to changes in the ionization of amino acid side chains, which are critical for substrate binding and catalysis.
Analyze the given condition: Changing the pH to 5.0 moves the environment to a less acidic (more neutral) condition, far outside pepsin's optimum pH range. This can lead to denaturation or a significant reduction in the enzyme's catalytic activity.
Relate the pH change to reaction rate: At pH 5.0, the rate of the pepsin-catalyzed reaction would decrease dramatically because the enzyme is no longer in its optimal functional state.
Conclude the impact: The pepsin-catalyzed reaction would slow down or potentially stop altogether at pH 5.0 due to the enzyme's reduced ability to bind substrates and catalyze the reaction effectively.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Enzyme Activity and pH

Enzymes, like pepsin, have an optimal pH range where they function most effectively. Outside this range, particularly at higher pH levels, the enzyme's structure can be altered, leading to decreased activity. For pepsin, which operates best at a pH of 1.5 to 2.0, a shift to pH 5.0 would likely result in reduced catalytic efficiency due to denaturation or altered active site conformation.
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Pepsin as a Peptidase

Pepsin is a type of peptidase, an enzyme that breaks down proteins into smaller peptides by hydrolyzing peptide bonds. It is secreted in an inactive form (pepsinogen) and activated in the acidic environment of the stomach. Understanding pepsin's role in protein digestion is crucial for analyzing how changes in conditions, like pH, impact its function.
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Enzyme Kinetics

Enzyme kinetics studies the rates of enzyme-catalyzed reactions and how they change in response to various factors, including substrate concentration, temperature, and pH. The Michaelis-Menten model is often used to describe these relationships, illustrating how reaction rates can be affected by changes in environmental conditions, such as the pH shift mentioned in the question.
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Related Practice
Textbook Question

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?

a. changing the pH to 3.0

Textbook Question

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

Textbook Question

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.

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a. trypsin, pH 5.0

Textbook Question

A patient arrives in an emergency department complaining of chest pains. What enzymes would you test for in the blood serum?

Textbook Question

Indicate whether each of the following describes a competitive or a noncompetitive enzyme inhibitor:

a. The inhibitor has a structure similar to the substrate.

Textbook Question

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

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