What is photophosphorylation and how many ATP are produced per NADPH in non-cyclic flow?

What is photophosphorylation and how many ATP are produced per NADPH in non-cyclic flow?

• A. Photophosphorylation is ATP synthesis driven by a proton gradient; in non-cyclic flow the ratio is about 3 ATP per 2 NADPH (roughly 1.5 ATP per NADPH).
• B. Photophosphorylation refers to NADPH production without ATP.
• C. It is the direct transfer of electrons to molecular oxygen.
• D. It occurs only in prokaryotes.

Answer: (C)

Photophosphorylation is ATP synthesis driven by a proton gradient across the thylakoid membrane, created by the light-driven electron transport during photosynthesis. As electrons are passed from water through photosystem II, the cytochrome b6f complex, and photosystem I to NADP+, protons are pumped across the membrane. This builds a proton motive force that powers ATP synthase to make ATP. In non-cyclic flow, electrons ultimately reduce NADP+ to NADPH as well, so you get both ATP and NADPH from the same electron transport chain. The practical yield is about 3 ATP for every 2 NADPH produced, which is roughly 1.5 ATP per NADPH. This reflects the balance between ATP demand and NADPH production in the light reactions. NADPH production without ATP isn’t how this process works, and the final electron acceptor is NADP+, not molecular oxygen, in the main non-cyclic pathway. Photophosphorylation also isn’t limited to prokaryotes; it occurs in plants, algae, and cyanobacteria as well.

Photophosphorylation is ATP synthesis driven by a proton gradient across the thylakoid membrane, created by the light-driven electron transport during photosynthesis. As electrons are passed from water through photosystem II, the cytochrome b6f complex, and photosystem I to NADP+, protons are pumped across the membrane. This builds a proton motive force that powers ATP synthase to make ATP. In non-cyclic flow, electrons ultimately reduce NADP+ to NADPH as well, so you get both ATP and NADPH from the same electron transport chain. The practical yield is about 3 ATP for every 2 NADPH produced, which is roughly 1.5 ATP per NADPH. This reflects the balance between ATP demand and NADPH production in the light reactions.

NADPH production without ATP isn’t how this process works, and the final electron acceptor is NADP+, not molecular oxygen, in the main non-cyclic pathway. Photophosphorylation also isn’t limited to prokaryotes; it occurs in plants, algae, and cyanobacteria as well.