Question

An important feature of the HMP shunt pathway is:
A. It yields more ATP (Please use (a) in options)
B. It yields NADPH
C. It yields NAD
D. It yields $FAD{H}_2$

Answer 1

Hint: HMP (Hexose Monophosphate) shunt pathway is an alternative to the glycolysis pathway.

Complete answer:
It yields NADPH. Depending upon the demand of NADPH in tissues, the HMP shunt pathway is chosen over the glycolysis pathway. HMP shunt pathway produces NADPH (nicotinamide adenine dinucleotide phosphate) and ribose-5-phosphate. HMP shunt pathway occurs in both oxidative (irreversible) and non-oxidative (reversible) phases. It takes place in the cytoplasm. In the oxidative pathway the starting product glucose (6-carbon sugar) is converted in a series of steps to yield the final product as ribulose-5-phosphate and NADPH as a by-product (at intermediate and final steps of the pathway). During the non-oxidative phase, the ribulose-5-phosphate is converted to ribose-5-phosphate through a series of independent reactions, and no NADPH is produced during the non-oxidative phase of HMP shunt pathway. Ribose-5-phosphate produced then undergoes a series of reactions to form different ribose sugar that compromises genetic materials like DNA and RNA molecules.

Additional Information:
Series of step in HMP shunt pathway:

Oxidative phase:
- Glucose-6-phosphate is converted to 6-phosphogluconolactone using glucose-6-phosphate dehydrogenase (G6PD) enzyme and also involves the conversion of NADP+ to NADPH molecule.
- 6-phosphogluconolactone is then converted to 6-phosphogluconate with the breakdown of a water molecule to release H+ ions. This step uses the Gluconolactonase enzyme.
- 6-phosphogluconate is then converted to Ribulose-5-phosphate in presence of 6-phosphogluconate dehydrogenase enzyme. This step also involves the production of NADPH + $C{O}_2$ from NADP+ molecules.

Non-oxidative phase:
- Ribulose-6-phosphate is either converted to Ribose-5-phosphate in presence of Ribulose-5-phosphate isomerase as an enzyme or is converted to Xylulose-5-phosphate in presence of Ribulose-5-phosphate-3-epimerase enzyme.
- In the presence of the Transketolase enzyme, the product from step 4 is then converted to Glyceraldehyde-3-phosphate and Sedoheptulose-7-phosphate.
- In the presence of the Transaldolase enzyme, the products from step 5 are converted to Fructose-6-phosphate (enters glycolysis pathway) and Erythrose-4-phosphate.
- Erythrose-4-phosphate and Xylulose-5-phosphate then in presence of Transketolase enzyme forms Glyceraldehyde-3-phosphate and Fructose-6-phosphate (both molecules can then enter glycolysis pathway)

Note: NADPH is an important molecule involved in a plethora of functions throughout the body. Eg- It is involved in the synthesis of steroids and fatty acids, important in the respiratory burst process and is an important component of the immune response in phagolysosomes.