Video Transcript
What happens to the coenzyme NADP+
in the light-dependent stage of photosynthesis? (A) It loses electrons and a
phosphate ion to become NAD. (B) It gains an oxygen ion to
become oxidized NADP, NADPO+. (C) It gains electrons and H+ ions
to become reduced NADP, NADPH. Or (D) it loses electrons and a H+
ion to form NADP+.
The reactions in the
light-dependent stage of photosynthesis largely occur within the electron transport
chain, which is located in the thylakoid membranes of the chloroplast. Let’s have a look at the electron
transport chain in more detail and see if we can spot what happens to the coenzyme
NADP.
The electron transport chain in the
thylakoid membrane consists of photosystems, electron carriers, and proton
pumps. Light that hits the chloroplasts of
the plant is initially absorbed by photosystem two. The absorption of light excites the
electrons in photosystem two. These electrons then move down the
electron chain, losing energy as they go. Light is then absorbed by
photosystem one, which again excites the electrons. The electrons are then passed to an
enzyme called NADP reductase. But what does NADP reductase
do? Let’s have a closer look. NADP reductase catalyzes the
conversion of the coenzyme NADP+ into NADPH. For this to happen, NADP+ gains two
electrons and a hydrogen ion. Because NADP has gained electrons,
we say it has been reduced. So we also call NADPH reduced
NADP.
Let’s go back to our answer options
to see which one is correct. Using what we now know about the
light-dependent stage of photosynthesis, we can see that our correct answer is
(C). NADP+ gains electrons and H+ ions
to become reduced NADP, or NADPH.
