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Ch.21 The Generation of Biochemical Energy
McMurry - Fundamentals of GOB 8th Edition
McMurry8th EditionFundamentals of GOBISBN: 9780134015187Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.21 The Generation of Biochemical EnergyProblem 24b
Chapter 21, Problem 24b

The reaction that follows is catalyzed by isocitrate dehydrogenase and occurs in two steps, the first of which (step A) is formation of an unstable intermediates (shown in brackets).

b. In which step is CO2 evolved and a hydrogen ion added?

Verified step by step guidance
1
Step 1: Understand the reaction context. The reaction involves isocitrate dehydrogenase, an enzyme that catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate in the citric acid cycle. This reaction occurs in two steps: (A) formation of an unstable intermediate and (B) subsequent decarboxylation.
Step 2: Analyze the reaction mechanism. In step A, isocitrate undergoes oxidation, facilitated by the enzyme, to form an unstable intermediate. This step does not involve the release of CO₂ or the addition of a hydrogen ion.
Step 3: Focus on step B. In this step, the unstable intermediate undergoes decarboxylation, which means a carbon dioxide (CO₂) molecule is released. Additionally, a hydrogen ion (H⁺) is added to the reaction system as part of the process.
Step 4: Identify the role of cofactors. During this reaction, NAD⁺ (or NADP⁺ in some cases) acts as an electron acceptor, becoming reduced to NADH (or NADPH) as it gains electrons and a proton (H⁺). This is a key part of the reaction mechanism.
Step 5: Conclude that CO₂ evolution and H⁺ addition occur in step B, which is the decarboxylation step. This step is critical for the progression of the citric acid cycle and energy production in cellular metabolism.

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Key Concepts

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

Isocitrate Dehydrogenase

Isocitrate dehydrogenase is an enzyme that plays a crucial role in the citric acid cycle (Krebs cycle) by catalyzing the oxidative decarboxylation of isocitrate to alpha-ketoglutarate. This reaction is significant for energy production in cellular respiration, as it facilitates the conversion of isocitrate into a more energy-rich compound while releasing carbon dioxide (CO₂) as a byproduct.
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Decarboxylation

Decarboxylation is a chemical reaction that involves the removal of a carboxyl group (-COOH) from a molecule, resulting in the release of carbon dioxide (CO₂). In the context of the citric acid cycle, this process is essential for transforming substrates into more reactive forms, contributing to the overall energy yield of cellular metabolism.
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Hydrogen Ion Addition

The addition of a hydrogen ion (H⁺) during biochemical reactions often indicates a reduction process, where a substrate gains electrons. In the context of the reaction catalyzed by isocitrate dehydrogenase, the addition of H⁺ can be associated with the conversion of isocitrate to alpha-ketoglutarate, highlighting the importance of electron transfer in metabolic pathways.
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Related Practice
Textbook Question

For the first step in fatty acid catabolism, we say that ATP is used to “drive” the reaction that links the fatty acid with coenzyme-A. Without ATP hydrolysis, would you predict that the linking of fatty acid to coenzyme-A would be ­exergonic or endergonic? In fatty acid CoA synthesis, the hydrolysis of the ATP portion is based on what major strategy of metabolism?

Textbook Question

Since no molecular oxygen participates in the citric acid cycle, the steps in which acetyl groups are oxidized to CO2 involve removal of hydride ions and hydrogen ions. What is the acceptor of hydride ions? What is the acceptor of hydrogen ions?

Textbook Question

The reaction that follows is catalyzed by isocitrate dehydrogenase and occurs in two steps, the first of which (step A) is formation of an unstable intermediates (shown in brackets).

a. In which step is a coenzyme needed? Identify the coenzyme.

Textbook Question

The reaction that follows is catalyzed by isocitrate dehydrogenase and occurs in two steps, the first of which (step A) is formation of an unstable intermediates (shown in brackets).

c. Which of the structures shown can be described as a β-keto acid?

Textbook Question

The reaction that follows is catalyzed by isocitrate dehydrogenase and occurs in two steps, the first of which (step A) is formation of an unstable intermediates (shown in brackets).

d. To what class of enzymes does isocitrate dehydrogenase, the enzyme that catalyzes this reaction, belong?

Textbook Question

The electron-transport chain uses several different metal ions, especially iron, copper, zinc, and manganese. Why are metals used frequently in these two pathways? What can metals do better than organic biomolecules?