Question

In pentose phosphate shunt, the number of NADPH formed per glucose molecule is

• A. 12
• B. 6
• C. 2
• D. 10

Answer 1

Answer: (A)

12

Pentose phosphate pathway is an alternate pathway for the aerobic respiration of glucose in which a molecule of glucose is oxidised to carbon dioxide producing 12 molecules of reduced NADP. The steps of this pathway are as follows:

1. It starts with the oxidation of 6 molecules of glucose-6-phosphate in the presence of coenzyme NADP to 6-phosphogluconolactone in the presence of enzyme glucose 6-phosphate dehydrogenase. 6 molecules of NADP are reduced in the reaction producing 6 molecules of NADPH.

Glucose-6-phosphate+ NADP→ 6-Phosphogluconolactone + NADPH₂

_{2. 6-phosphogluconolactone is hydrolysed by enzyme lactonase to produce 6 molecules of 6-phosphogluconic acid.}

_{3. Phosphogluconic acid is oxidatively decarboxylated by the enzyme 6-phosphogluconic acid dehydrogenase. 6 molecules of NADP are reduced, 6 molecules of carbon dioxide are released and 6 molecules of ribulose-5-phosphate are produced.}

6-phosphogluconic acid + NADP→ ribulose-5-phosphate + NADPH₂ + CO₂

Thus, a total of 12 NADPH molecules are produced in this pathway.

Thus, the correct answer is option A.