Which of the following of the following statement related to Kreb's cycle is not correct ?

Options

A. There is only reaction in Kreb's cycle where `FAD^+` is reduced to `FADH_2`
B. During conversion of succinyl CoA to succinic acid, a molecule of GTP is synthesized.
C. The cycle starts with reaction of acetyl CoA with pyruvic acid to form 6 C citric acid.
D. There are three reaction in the cycle where `NAD^+` is reduced to `NADH^+H^+`

Answer

To determine which statement related to the Krebs cycle is not correct, we will analyze each statement provided in the question.

### 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. It begins with the conversion of acetyl-CoA into citrate when it combines with oxaloacetate.

2. **Analyzing the Statements**:
- **Statement 1**: "There is only one reaction in the Krebs cycle where FAD+ is reduced to FADH2."
- This statement is **correct**. The reaction from succinate to fumarate is the only one where FAD+ is reduced to FADH2.

- **Statement 2**: "During conversion of succinyl-CoA to succinate, one molecule of GTP is synthesized."
- This statement is also **correct**. The conversion of succinyl-CoA to succinate indeed produces one molecule of GTP.

- **Statement 3**: "The cycle starts with acetyl-CoA."
- This statement is **partially correct**. While the cycle does start with acetyl-CoA, it combines with oxaloacetate to form citrate, not with pyruvic acid. Therefore, this statement is misleading and **incorrect**.

- **Statement 4**: "There are three reactions in which NAD+ is reduced to NADH."
- This statement is **correct**. The three reactions where NAD+ is reduced to NADH occur at isocitrate to alpha-ketoglutarate, alpha-ketoglutarate to succinyl-CoA, and malate to oxaloacetate.

3. **Conclusion**:
- The statement that is not correct is **Statement 3**: "The cycle starts with acetyl-CoA." This is misleading because it implies that acetyl-CoA combines with pyruvic acid, which is incorrect.

### Final Answer:
The statement related to the Krebs cycle that is not correct is: **"The cycle starts with acetyl-CoA"** (as it combines with oxaloacetate, not pyruvic acid).

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