Select the correct statement w.r.t. Krebs cycle

Options

A. Occurs in cytoplasm and mitochondria in the absence of `O_(2)`
B. Favoured by coenzyme `NADP^(+)`
C. Intermediate products contain four, five and six carbon atoms
D. Substrate molecule is a 3C compound

Answer

### Step-by-Step Solution:

1. **Understanding the Krebs Cycle**: The Krebs cycle, also known as the tricarboxylic acid (TCA) cycle or citric acid cycle, is a crucial metabolic pathway that occurs in the mitochondria of cells. It is responsible for the oxidation of acetyl-CoA to produce energy.

2. **Analyzing the Statements**:
- **Statement 1**: "It occurs in the cytoplasm and the mitochondria in the absence of oxygen."
- This statement is incorrect. The Krebs cycle occurs exclusively in the mitochondria and requires oxygen, although it does not directly use oxygen.

- **Statement 2**: "It is favored by the coenzyme NADP+."
- This statement is also incorrect. The Krebs cycle primarily uses NAD+ (not NADP+) as a coenzyme, which gets reduced to NADH during the cycle.

- **Statement 3**: "Intermediate products contain four, five, and six carbon atoms."
- This statement is correct. The Krebs cycle involves various intermediates, including:
- 4-carbon compound: Succinyl CoA
- 5-carbon compound: α-Ketoglutarate (5-ketoglutamic acid)
- 6-carbon compound: Citrate

- **Statement 4**: "The substrate molecule is a 3-carbon compound."
- This statement is incorrect. The substrate molecule for the Krebs cycle is oxaloacetate, which is a 4-carbon compound. It combines with acetyl-CoA (a 2-carbon compound) to form citrate (a 6-carbon compound).

3. **Conclusion**: After analyzing all the statements, the correct statement regarding the Krebs cycle is the third one, which mentions the presence of intermediate products containing four, five, and six carbon atoms.

### Final Answer:
The correct statement with respect to the Krebs cycle is: "Intermediate products contain the four, five, and six carbon atoms."

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