Textbook Question
Draw the pH–activity profile for an enzyme that has one catalytic group at the active site:
b. the catalytic group is a general-base catalyst with a pKa = 7.2.
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Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 22 - Catalysis in Organic Reactions and in Enzymatic ReactionsProblem 21a
Bruice 8th EditionCh. 22 - Catalysis in Organic Reactions and in Enzymatic ReactionsProblem 21aChapter 23, Problem 21a
Draw the pH–activity profile for an enzyme that has one catalytic group at the active site:
a. the catalytic group is a general-acid catalyst with a pKa = 5.6.
Verified step by step guidance1
Understand the concept of a pH–activity profile: This graph shows how the activity of an enzyme changes with pH. The activity is influenced by the ionization state of the catalytic group at the active site, which depends on its pKa value.
Identify the catalytic group as a general-acid catalyst: A general-acid catalyst donates a proton during the reaction. Its activity is highest when it is protonated, which occurs at pH values below its pKa.
Determine the ionization state of the catalytic group: At pH values below the pKa (5.6), the catalytic group will be mostly protonated and active. At pH values above the pKa, the group will be mostly deprotonated and less active.
Sketch the pH–activity profile: The enzyme activity will be high at low pH, decrease as the pH approaches the pKa (5.6), and drop significantly at higher pH values. The profile will resemble a bell-shaped curve centered around the pKa value.
Label the graph: On the x-axis, plot the pH values, and on the y-axis, plot the enzyme activity. Mark the pKa (5.6) on the graph as the point where the activity begins to decline significantly due to deprotonation of the catalytic group.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
pH-Activity Profile
The pH-activity profile of an enzyme illustrates how the enzyme's activity varies with changes in pH. It typically shows a bell-shaped curve, where enzyme activity is optimal at a specific pH and decreases at more acidic or basic conditions. Understanding this profile is crucial for determining the optimal conditions for enzyme function and can indicate the ionization state of active site residues.
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General-Acid Catalysis
General-acid catalysis involves the donation of a proton (H+) from a catalytic group to a substrate, facilitating a chemical reaction. This process is dependent on the pKa of the catalytic group, which determines its protonation state at a given pH. In this case, with a pKa of 5.6, the catalytic group will be protonated at lower pH values, enhancing its ability to donate protons and thus influence the enzyme's activity.
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pKa and Ionization
The pKa value of a functional group indicates the pH at which half of the molecules of that group are protonated and half are deprotonated. For the catalytic group with a pKa of 5.6, at pH values below this, the group is predominantly protonated, while above this pH, it becomes deprotonated. This transition is critical for understanding how changes in pH affect the enzyme's catalytic efficiency and overall activity.
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