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).


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

Verified step by step guidance

1. Step 1: Understand the reaction context. This reaction is part of the citric acid cycle, where isocitrate is converted to α-ketoglutarate.
2. Step 2: Identify the role of isocitrate dehydrogenase. This enzyme catalyzes the oxidative decarboxylation of isocitrate, leading to the release of CO₂.
3. Step 3: Recognize the two steps involved. Step A involves the formation of an unstable intermediate, while the subsequent step involves further transformation.
4. Step 4: Determine where CO₂ is evolved. In the oxidative decarboxylation process, CO₂ is released when the unstable intermediate is converted to α-ketoglutarate.
5. Step 5: Identify the addition of a hydrogen ion. During the conversion of the intermediate to α-ketoglutarate, a hydrogen ion (H⁺) is typically involved in the reduction of NAD⁺ to NADH.

Key Concepts

Isocitrate Dehydrogenase

Isocitrate dehydrogenase is an enzyme that plays a crucial role in the citric acid cycle (Krebs cycle). It catalyzes the oxidative decarboxylation of isocitrate to alpha-ketoglutarate, facilitating the release of carbon dioxide (CO₂) and the reduction of NAD+ to NADH. Understanding its function is essential for analyzing metabolic pathways and the steps involved in cellular respiration.

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 vital for energy production, as it helps convert substrates into more energy-rich compounds while releasing CO₂ as a byproduct. Identifying which step involves decarboxylation is key to answering the question.

Hydrogen Ion Addition

The addition of a hydrogen ion (H+) in biochemical reactions often indicates a reduction process or the formation of a more complex molecule. In the context of the citric acid cycle, understanding when and how hydrogen ions are added can clarify the electron transfer processes and the overall energy yield of the cycle. This concept is important for determining the specific step in which H+ is introduced alongside CO₂ evolution.