Krebs' cycle starts with the formation of a six carbon compound by reaction between

Options

A. fumaric acid and pyruvic acid
B. OA A and acetyl CoA
C. malic acid and acetyl CoA
D. succinic acid and pyruvic acid.

Explanation

To solve the question regarding the starting point of the Krebs cycle, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding the Krebs Cycle**:
- The Krebs cycle, also known as the citric acid cycle or TCA cycle, is a crucial part of cellular respiration that takes place in the mitochondria of cells.

2. **Identifying Key Reactants**:
- The cycle begins with the combination of specific molecules. The key reactants involved in the initiation of the Krebs cycle are oxaloacetic acid and acetyl-CoA.

3. **Formation of the Six-Carbon Compound**:
- When acetyl-CoA (which is a 2-carbon molecule) combines with oxaloacetic acid (which is a 4-carbon molecule), they form citric acid (also known as citrate), which is a 6-carbon compound.

4. **Conclusion**:
- Therefore, the Krebs cycle starts with the formation of a six-carbon compound (citric acid) by the reaction between oxaloacetic acid and acetyl-CoA.

### Final Answer:
The Krebs cycle starts with the formation of a six-carbon compound by the reaction between **oxaloacetic acid and acetyl-CoA**.

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