Question

Identify $A,B\&C$ in the given figure (Krebs cycle)

• A. A- oxaloacetic acid, B- succinic acid, C- $\alpha$-ketoglutaric acid
• B. A- succinic acid, B- $\alpha$-ketoglutaric acid, C- oxaloacetic acid
• C. A- $\alpha$-ketoglutaric acid, B- oxaloacetic acid, C- Succinic acid
• D. A- oxaloacetic acid, B- $\alpha$-ketoglutaric acid, C- Succinic acid

Answer 1

The correct option is D A- oxaloacetic acid, B- $\alpha$-ketoglutaric acid, C- Succinic acid

Every pyruvate molecule produced by glycolysis enters the Krebs cycle as Acetyl CoA. Acetyl CoA combines with the 4C-oxaloacetate to form a 6C- compound that is citric acid. Citric acid is then oxidized breaking one of the C-C bonds to form carbon dioxide and reduce NAD to NADH. Therefore citric acid loses a carbon to form the only 5C - compound in Kreb's cycle, $\alpha$-ketoglutaric acid. The $\alpha$-ketoglutaric acid is similarly oxidized to form a 4C-compound, Succinic acid. Succinic acid is oxidized to fumaric acid and $FA{D}^{+}isreducedtoFAD{H}_2$. In this reaction oxaloacetic acid is the only intermediate that is regenerated in Krebs cycle.