How many six carbon organic acids occur in TCA cycle

Options

A. 1
B. 3
C. 2
D. 4

Answer

### Step-by-Step Solution:

1. **Understanding the TCA Cycle**: The TCA cycle, also known as the Krebs cycle or citric acid cycle, is a crucial metabolic pathway that plays a role in cellular respiration. It involves a series of chemical reactions used by all aerobic organisms to generate energy.

2. **Starting Compound**: The cycle begins with the condensation of an acetyl group (from acetyl-CoA) with oxaloacetic acid (a 4-carbon compound). This reaction produces citric acid (a 6-carbon compound) and releases water.

3. **Identifying 6-Carbon Compounds**: In the TCA cycle, there are several organic acids that contain six carbon atoms. The primary 6-carbon organic acids produced in the cycle include:
- Citric acid
- Cis-aconitic acid
- Isocitric acid
- Oxalosuccinic acid

4. **Counting the Compounds**: By listing the 6-carbon organic acids, we find that there are a total of four distinct 6-carbon organic acids that occur in the TCA cycle.

5. **Conclusion**: Therefore, the answer to the question of how many six-carbon organic acids occur in the TCA cycle is **four**.

### Final Answer:
There are **4 six-carbon organic acids** that occur in the TCA cycle.

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