Question

Consider the following statements about Pentose Phosphate pathway.
A. Generates NADH
B. Generates NADPH
C. Generates ATP
D. Occurs in the mitochondria
Choose the correct statement from the options given below:

• A. A only
• B. B only
• C. A, B and C only
• D. A and D only

Hint:

Remember: "PPP is in the cytosol, yields NADPH (for biosyntheses), and produces 0 ATP."
Do not confuse NADPH (used in anabolism) with NADH (used in catabolism/ATP generation).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The Pentose Phosphate Pathway (PPP), also known as the hexose monophosphate (HMP) shunt, is an alternative pathway of glucose metabolism that branches off from glycolysis.
It serves anabolic purposes rather than catabolic ones.

Step 2: Detailed Explanation:
The Pentose Phosphate Pathway consists of two main phases: an irreversible oxidative phase and a reversible non-oxidative phase.
Let us analyze the characteristics of this pathway relative to the proposed statements:
- Statement A is incorrect: The oxidative phase of the PPP involves the enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, both of which specifically use $\text{NADP}^+$ as an electron acceptor, producing NADPH, not NADH.
- Statement B is correct: The primary physiological role of the PPP is the generation of NADPH, which is essential for reductive biosynthetic reactions (such as fatty acid, cholesterol, and steroid synthesis) and for maintaining reduced glutathione to protect cells against oxidative damage.
- Statement C is incorrect: The PPP does not consume or produce any ATP molecules during its steps.
- Statement D is incorrect: All reactions of both the oxidative and non-oxidative phases of the PPP occur entirely in the cytosol of the cell, where anabolic lipogenesis takes place. It does not occur in the mitochondria.

Step 3: Final Answer:
Since only statement B is biochemically correct, the matching choice is (B).