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.

Verified step by step guidance

1. Step 1: Understand the reaction context. The reaction involves isocitrate dehydrogenase, an enzyme that catalyzes the conversion 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 conversion to the final product.
2. Step 2: Recall the role of coenzymes in enzymatic reactions. Coenzymes are non-protein molecules that assist enzymes by accepting or donating electrons, protons, or chemical groups during the reaction. Common coenzymes include NAD⁺, NADP⁺, FAD, and others.
3. Step 3: Analyze the reaction steps. In step A, the formation of the unstable intermediate does not typically involve a coenzyme. However, in step B, the conversion of the intermediate to α-ketoglutarate involves the oxidation of the intermediate, which requires a coenzyme to accept the electrons.
4. Step 4: Identify the specific coenzyme involved. In the isocitrate dehydrogenase reaction, the coenzyme NAD⁺ (or NADP⁺, depending on the isoform of the enzyme) is required to accept electrons during the oxidation step, forming NADH (or NADPH).
5. Step 5: Conclude that the coenzyme is needed in step B of the reaction, where it facilitates the oxidation of the intermediate to α-ketoglutarate by accepting electrons and becoming reduced to NADH (or NADPH).

Key Concepts

Isocitrate Dehydrogenase

Isocitrate dehydrogenase is an enzyme that catalyzes the oxidative decarboxylation of isocitrate to alpha-ketoglutarate in the citric acid cycle. This enzyme plays a crucial role in cellular respiration, facilitating the conversion of isocitrate while releasing carbon dioxide and reducing NAD+ to NADH. Understanding its function is essential for analyzing metabolic pathways.

Coenzymes

Coenzymes are organic molecules that assist enzymes in catalyzing reactions. They often act as carriers for chemical groups or electrons during enzymatic reactions. In the context of isocitrate dehydrogenase, coenzymes such as NAD+ are vital for the enzyme's activity, as they participate in the redox reactions that occur during the conversion of substrates.

Reaction Steps

In enzymatic reactions, steps refer to the sequential processes that substrates undergo to be converted into products. Each step may involve different intermediates and may require specific cofactors or coenzymes. Identifying which step requires a coenzyme is crucial for understanding the overall mechanism of the reaction and the role of each component involved.