Question

During Citric Acid cycle, the various organic acid undergo decarboxylation. Which of the following organic acids of the above cycle have $4C$, $5C$ and $6C$ respectively?

• A. Pyruvic acid, Malic acid and $\alpha$-Ketoglutaric acid
• B. Pyruvic acid, $\alpha$-Ketoglutaric acid and Citric acid
• C. Oxaloacetic acid, Citric acid and Succinic acid
• D. Succinic acid, $\alpha$-Ketoglutaric acid and citric acid

Answer 1

Answer: (D)

Succinic acid, $\alpha$-Ketoglutaric acid and citric acid

Answer 2

In the citric acid cycle, a $4 C$ oxaloacetic acid combines with $2 C$ acetyl $CoA$ to give rise to $6 C$ citric acid. Isocitrate is an isomer of citric acid. The decarboxylation of citric acid produces a $5 C\, \alpha$-Ketoglutaric acid. This further undergoes decarboxylation to give rise to $4 C$ succinic acid and further converts to $4 C$ malic acid and oxaloacetic acid. Pyruvic acid or pyruvate is a $3 C$ compound. A representation of the citric acid cycle (Krebs cycle) is given below: