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Ch.14 - Chemical Kinetics
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.14 - Chemical KineticsProblem 114
Chapter 14, Problem 114

One of the many remarkable enzymes in the human body is carbonic anhydrase, which catalyzes the interconversion of carbon dioxide and water with bicarbonate ion and protons. If it were not for this enzyme, the body could not rid itself rapidly enough of the CO2 accumulated by cell metabolism. The enzyme catalyzes the dehydration (release to air) of up to 107 CO2 molecules per second. Which components of this description correspond to the terms enzyme, substrate, and turnover number?

Verified step by step guidance
1
Identify the enzyme: In the given description, 'carbonic anhydrase' is mentioned as catalyzing a reaction. Therefore, carbonic anhydrase is the enzyme.
Identify the substrates: The substrates are the molecules that the enzyme acts upon to catalyze a reaction. In this case, the substrates are 'carbon dioxide and water' on one side of the reaction and 'bicarbonate ion and protons' on the other side.
Understand the term 'turnover number': Turnover number is a measure of the number of substrate molecules an enzyme can convert into product per second when the enzyme is fully saturated with substrate. It reflects the catalytic activity of the enzyme.
Relate turnover number to the enzyme's activity: According to the description, carbonic anhydrase can catalyze the dehydration of up to 10^7 CO2 molecules per second. Thus, the turnover number for carbonic anhydrase is 10^7.
Summarize the correspondence: The enzyme is carbonic anhydrase, the substrates are carbon dioxide and water (reactants) and bicarbonate ion and protons (products), and the turnover number is 10^7.

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Key Concepts

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

Enzyme

An enzyme is a biological catalyst that accelerates chemical reactions in living organisms. It achieves this by lowering the activation energy required for the reaction to occur, thus increasing the reaction rate. Enzymes are typically proteins and are highly specific, meaning they only catalyze particular reactions involving specific substrates.

Substrate

A substrate is the reactant molecule upon which an enzyme acts. In the context of the reaction catalyzed by carbonic anhydrase, the substrates are carbon dioxide (CO2) and water (H2O), which are converted into bicarbonate ions (HCO3-) and protons (H+). The interaction between the enzyme and its substrate is crucial for the enzyme's catalytic function.
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Turnover Number

The turnover number, often denoted as kcat, is a measure of the catalytic activity of an enzyme. It represents the maximum number of substrate molecules converted to product by a single enzyme molecule per unit time, under optimal conditions. In the case of carbonic anhydrase, the turnover number indicates its remarkable efficiency, as it can catalyze the conversion of up to 10^7 CO2 molecules per second.
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Related Practice
Textbook Question

Platinum nanoparticles of diameter 2 nm are important catalysts in carbon monoxide oxidation to carbon dioxide. Platinum crystallizes in a face-centered cubic arrangement with an edge length of 3.924 Å. (c) Using your results from (a) and (b), calculate the percentage of Pt atoms that are on the surface of a 2.0-nm nanoparticle. (d) Repeat these calculations for a 5.0-nm platinum nanoparticle.

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Textbook Question

Platinum nanoparticles of diameter 2 nm are important catalysts in carbon monoxide oxidation to carbon dioxide. Platinum crystallizes in a face-centered cubic arrangement with an edge length of 3.924 Å. (b) Estimate how many platinum atoms are on the surface of a 2.0-nm Pt sphere, using the surface area of a sphere (4πr2) and assuming that the 'footprint' of one Pt atom can be estimated from its atomic diameter of 2.8 A .

Textbook Question

In a hydrocarbon solution, the gold compound (CH3)3AuPH3 decomposes into ethane (C2H6) and a different gold compound, (CH3)AuPH3. The following mechanism has been proposed for the decomposition of (CH3)3AuPH3:

Step 1: (CH3)3AuPH3 k1⇌k-1 (CH3)3Au + PH3 (fast)

Step 2: (CH3)3Au k2→ C2H6 + (CH3)Au (slow)

Step 3: (CH3)Au + PH3 k3→ (CH3)AuPH3 (fast)

(f) What would be the effect on the reaction rate of adding PH3 to the solution of (CH3)3AuPH3?

Textbook Question

Enzymes are often described as following the two-step mechanism:

E + S ⇌ ES (fast)

ES → E + P (slow)

where E = enzyme, S = substrate, ES = enzyme9substrate complex, and P = product.

(a) If an enzyme follows this mechanism, what rate law is expected for the reaction?

Textbook Question

Enzymes are often described as following the two-step mechanism:

E + S  ⇌ ES (fast)

ES → E + P (slow)

where E = enzyme, S = substrate, ES = enzyme9substrate complex, and P = product.

(b) Molecules that can bind to the active site of an enzyme but are not converted into product are called enzyme inhibitors. Write an additional elementary step to add into the preceding mechanism to account for the reaction of E with I, an inhibitor.