At how many place in kreb's cycle from pyruvic acid , the enzyme dehydrogenases are involved ?

Options

A. 3
B. 4
C. 5
D. 6

Answer

To determine how many times dehydrogenases are involved in the Krebs cycle from pyruvic acid, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Krebs Cycle**: The Krebs cycle, also known as the TCA (tricarboxylic acid) cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

2. **Entry of Pyruvic Acid**: Pyruvic acid, which is produced during glycolysis, enters the Krebs cycle. Before entering the cycle, pyruvic acid is converted into acetyl-CoA by the enzyme pyruvate dehydrogenase. This is the first instance of a dehydrogenase enzyme being involved.

3. **Identifying Dehydrogenase Enzymes**: Within the Krebs cycle, there are specific reactions where dehydrogenase enzymes play a crucial role:
- **First Reaction**: The conversion of pyruvate to acetyl-CoA involves **pyruvate dehydrogenase**.
- **Second Reaction**: The conversion of isocitrate to alpha-ketoglutarate involves **isocitrate dehydrogenase**.
- **Third Reaction**: The conversion of alpha-ketoglutarate to succinyl-CoA involves **alpha-ketoglutarate dehydrogenase**.

4. **Counting the Instances**: From the above analysis, we can see that dehydrogenases are involved in three distinct reactions in the Krebs cycle:
- Pyruvate to Acetyl-CoA (pyruvate dehydrogenase)
- Isocitrate to Alpha-Ketoglutarate (isocitrate dehydrogenase)
- Alpha-Ketoglutarate to Succinyl-CoA (alpha-ketoglutarate dehydrogenase)

5. **Conclusion**: Therefore, the total number of places where dehydrogenases are involved in the Krebs cycle from pyruvic acid is **three**.

### Final Answer:
**The enzyme dehydrogenases are involved at three places in the Krebs cycle from pyruvic acid.**

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