Question

A reduction of NADP to $NADPH_2$ takes place in

(A) EMP-pathway

(B) HMP-shunt

(C) Calvin cycle

(D) Glycolysis

Answer 1

Hint: NADPH is formed from $NADP^{+}$. The source of NADPH in animals and other non-photosynthetic organisms is the pentose phosphate pathway.

Complete answer:

Breakdown of sugars (glucose) happens in the body by glycolysis followed by Kreb's cycle (tricarboxylic acid cycle) bringing about the energy as ATP. Glucose can then again additionally go through an alternate pathway to create different items needed by the cells. One of these substitute pathways is the pentose phosphate pathway or additionally called as hexose monophosphate pathway in which oxidation of glucose 6-phosphate happens to create pentoses. The destiny of glucose whether to go through glycolysis or the hexose monophosphate pathway is chosen by the general groupings of $NADP^{+}$ and NADPH. The stage begins with the oxidation of glucose 6-phosphate by the protein glucose 6-phosphate dehydrogenase to yield 6-phosphogluconolactone. This enzyme is an NADP subordinate enzyme, where ${NADP^+}$ accepts an electron to shape NADPH + $H^{+}$.

Additional Information: NADPH + $H^{+}$ production takes place in four specific steps; in which $NADP^{+}$ can react with 2$H^{+}$ and 2e in alternative ways. The steps are given as: 

- At first $NADP^{+}$ accepts an active electron to form active NADP.  

- Next active NADP attracts hydrogen ion ($H^{+}$) to form $NADP^{+}$. 

- After that $NADP^{+}$ accepts another active electron to form active NADPH.

- Lastly active NADPH attracts another hydrogen ion ($H^{+}$) to form NADPH + $H^{+}$

Hence the correct answer is Option (B).

Note: The hexose monophosphate pathway is additionally called the pentose phosphate pathway. It happens in the cytoplasm and is a significant source of NADPH and 5-carbon sugars. This pathway comprises two irreversible oxidative reactions and a progression of reversible sugar-phosphate changes. No ATP is burned-through or created legitimately. Carbon 1 is eliminated from glucose-6-phosphate ($G_6P$) as $CO_2$, and 2 NADPH are created for each $G_6P$ entering the pathway. This pathway likewise creates ribose-phosphate for nucleotide formation.