Question

The reduction of NADP$^+$ to NADPH occurs in

• A. HMP shunt
• B. Calvin Cycle
• C. Glycolysis
• D. EMP (1988)

Hint:

The pentose phosphate pathway is an important source of NADPH, especially for anabolic reactions and the defense against oxidative stress.

Answer 1

The Correct Option is A

The reduction of NADP\(^+\) to NADPH primarily occurs in the HMP shunt (Hexose Monophosphate shunt), also known as the pentose phosphate pathway. This pathway is involved in the oxidation of glucose-6-phosphate and generates NADPH as well as ribose-5-phosphate, which is essential for nucleic acid and nucleotide biosynthesis.

(1) HMP Shunt (Pentose Phosphate Pathway):
- This pathway includes two main phases: the oxidative phase, where NADP\(^+\) is reduced to NADPH, and the non-oxidative phase, which generates sugars for biosynthesis.
- NADPH produced in this pathway is used for various biosynthetic processes and in cellular protection against oxidative stress.

(2) Why Other Options Are Incorrect:
- Calvin Cycle (Option 2) is involved in carbon fixation and also produces NADPH, but it is not the primary pathway for NADPH generation. The Calvin cycle relies on NADPH produced by the HMP shunt.
- Glycolysis (Option 3) is the breakdown of glucose to pyruvate and does not directly produce NADPH.
- EMP (1988) (Option 4) is a mistaken reference, as there is no well-known pathway by that name.

Conclusion: The reduction of NADP\(^+\) to NADPH primarily occurs in the HMP shunt, also known as the pentose phosphate pathway, and is essential for many biosynthetic and detoxification processes.