The first 5C dicarboxylic acid in Krebs' cycle which is used in nitrogen metabolism is

Options

A. (a) OAA
B. (b) Citric acid
C. (c) `alpha`-ketoglutaric acid
D. (d) Acetyl Co-A

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks for the first 5-carbon dicarboxylic acid in the Krebs cycle that is used in nitrogen metabolism.

2. **Identifying the Krebs Cycle:**
The Krebs cycle, also known as the citric acid cycle or TCA cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA.

3. **Recognizing the Key Compounds:**
In the Krebs cycle, the main compounds include citric acid, alpha-ketoglutarate, succinate, fumarate, and oxaloacetate. We need to focus on the 5-carbon dicarboxylic acids.

4. **Identifying the 5-Carbon Dicarboxylic Acid:**
The first 5-carbon dicarboxylic acid formed in the Krebs cycle is alpha-ketoglutarate. It is formed from the decarboxylation of isocitrate.

5. **Connection to Nitrogen Metabolism:**
Alpha-ketoglutarate plays a crucial role in nitrogen metabolism. It can undergo deamination to form glutamate, which is a precursor for amino acids. This process involves the incorporation of an amine group into the alpha-ketoglutarate structure.

6. **Conclusion:**
Based on the analysis, the correct answer to the question is alpha-ketoglutarate, which is option C.

**Final Answer:**
The first 5C dicarboxylic acid in the Krebs cycle which is used in nitrogen metabolism is **alpha-ketoglutarate** (option C).

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