Question

Choose the correct combination of labeling the number of carbon compounds in the substrate molecules, involved in the citric acid cycle.

• A. A - 4C, B - 6C, C - 5C, D - 4C, E - 4C
• B. A - 6C, B - 5C, C - 4C, D - 3C, E - 2C
• C. A - 2C, B - 3C, C - 4C, D - 5C, E - 6C
• D. A - 4C, B - 5C, C - 6C, D - 4C, E - 4C
• E. A - 4C, B - 6C, C - 4C, D - 4C, E - 4C

Answer 1

The correct option is A A - 4C, B - 6C, C - 5C, D - 4C, E - 4C

In the Krebs cycle, oxaloacetic acid, a 4 carbon compound reacts with acetyl coenzyme A to form citric acid, a 6 carbon compound. Citric acid undergoes decarboxylation and forms ketoglutaric acid which are a 5 carbon compound. Ketoglutaric acid undergoes the second decarboxylation to form succinic acid, a 4 carbon compound. Finally succinic acid changes to fumaric acid and then malic acid by hydration reaction.

So, the correct answer is option A.