5C intermediate molecule in TCA cycle is

Options

A. Citric acid
B. Succinyl CoA
C. `alpha`-ketoglutamic acid
D. Fumaric acid

Answer

To find the 5C intermediate molecule in the TCA cycle, we will analyze the steps of the cycle and identify the relevant compounds.

### Step-by-Step Solution:

1. **Understanding the TCA Cycle**: The TCA cycle, also known as the Krebs cycle or citric acid cycle, is a series of chemical reactions used by all aerobic organisms to generate energy. It occurs in the mitochondria.

2. **Starting Point**: The cycle begins with the combination of acetyl CoA (derived from pyruvate) and oxaloacetic acid (4C) to form citric acid (6C).

3. **Formation of Citric Acid**: The first step involves the condensation of acetyl CoA (2C) with oxaloacetic acid (4C) to produce citric acid (6C).

4. **Conversion to 5C Intermediate**: As the cycle progresses, citric acid is converted into isocitrate (still 6C), and then isocitrate is oxidized and decarboxylated to form alpha-ketoglutarate (5C). This reaction releases one molecule of carbon dioxide (CO2) and reduces NAD+ to NADH.

5. **Identifying the 5C Intermediate**: The specific 5C intermediate formed in this step is alpha-ketoglutarate.

6. **Conclusion**: Therefore, the 5C intermediate molecule in the TCA cycle is alpha-ketoglutarate.

### Final Answer:
The 5C intermediate molecule in the TCA cycle is **alpha-ketoglutarate**.

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