In Krebs cycle, the following reactions are involved in the production of 15 ATP molecules by oxidation of food stuffs
1. Oxidation of pyruvic acid to acetyl Co-A
2. Oxidation of alpha-ketoglutaric acid
3. Oxidation of isocitrate
4. Oxidation of malate
5. Oxidation of succinate
6. Conversion of succinyl Coenzyme-A to succinic acid.
The correct sequence of these reactions is:

Options

A. 1, 2, 4, 3, 5, 6
B. 1, 3, 2, 6, 5, 4
C. 1, 4, 3, 2, 5, 6
D. 1, 2, 4, 5, 3, 6

Answer

To determine the correct sequence of reactions in the Krebs cycle from the provided list, we need to follow the pathway of the cycle step by step. Here’s the breakdown:

### Step-by-Step Solution:

1. **Oxidation of Pyruvic Acid to Acetyl Co-A**:
- The first step in the Krebs cycle is the conversion of pyruvic acid (produced from glycolysis) into acetyl Coenzyme A (acetyl Co-A). This reaction is catalyzed by the pyruvate dehydrogenase complex.

2. **Formation of Citrate**:
- Acetyl Co-A then combines with oxaloacetate to form citrate. This step is not explicitly mentioned in the options but is essential for the cycle to proceed.

3. **Oxidation of Isocitrate**:
- Citrate is then converted into isocitrate through a rearrangement reaction. The isocitrate is subsequently oxidized to form alpha-ketoglutarate. This is the second reaction in the sequence.

4. **Oxidation of Alpha-Ketoglutaric Acid**:
- Alpha-ketoglutarate is further oxidized to succinyl Coenzyme A. This step is the third reaction in the sequence.

5. **Conversion of Succinyl Coenzyme A to Succinic Acid**:
- Succinyl Co-A is then converted into succinic acid. This is the fourth reaction in the sequence.

6. **Oxidation of Succinate**:
- Succinic acid is oxidized to fumarate. This is the fifth reaction in the sequence.

7. **Oxidation of Malate**:
- Fumarate is then hydrated to form malate, which is subsequently oxidized to regenerate oxaloacetate. This is the sixth reaction in the sequence.

### Correct Sequence:
Based on the above steps, the correct sequence of reactions in the Krebs cycle is:
1. Oxidation of pyruvic acid to acetyl Co-A (Step 1)
2. Oxidation of isocitrate (Step 3)
3. Oxidation of alpha-ketoglutaric acid (Step 2)
4. Conversion of succinyl Coenzyme A to succinic acid (Step 6)
5. Oxidation of succinate (Step 5)
6. Oxidation of malate (Step 4)

Thus, the correct order is **1, 3, 2, 6, 5, 4**.