Where is NADPH formed during the light-dependent reactions?

Where is NADPH formed during the light-dependent reactions?

• A. NADPH is formed when NADP+ accepts electrons at the end of the electron transport chain at PSI
• B. NADPH is formed in the thylakoid lumen by water splitting
• C. NADPH is formed in the stroma near the chloroplast by the reduction at PSI
• D. NADPH is formed in the mitochondria

Answer: (C)

In the light-dependent reactions, NADPH is formed in the stroma of the chloroplast. After Photosystem I absorbs light, electrons are transferred to ferredoxin and then to the enzyme ferredoxin–NADP+ reductase (FNR) on the stromal side of the thylakoid membrane. FNR uses those electrons to reduce NADP+ to NADPH, so the molecule is produced in the stroma. Water splitting at the oxygen-evolving complex happens on the lumen side and supplies electrons, but NADPH formation itself occurs in the stroma, not in the lumen or mitochondria. This NADPH (along with ATP) powers carbon fixation in the Calvin cycle within the stroma.

In the light-dependent reactions, NADPH is formed in the stroma of the chloroplast. After Photosystem I absorbs light, electrons are transferred to ferredoxin and then to the enzyme ferredoxin–NADP+ reductase (FNR) on the stromal side of the thylakoid membrane. FNR uses those electrons to reduce NADP+ to NADPH, so the molecule is produced in the stroma. Water splitting at the oxygen-evolving complex happens on the lumen side and supplies electrons, but NADPH formation itself occurs in the stroma, not in the lumen or mitochondria. This NADPH (along with ATP) powers carbon fixation in the Calvin cycle within the stroma.