Question

Why is it important that nadp+ reductase is on the stromal side of the thylakoid membrane?

Answer 1

It is important that the FNR or Nadp+reductase enzyme is on the stromal side or covering of the plant's Thylakoid membrane because they participate in photosynthesis. NADPH cycling can only be achieved with light and cannot operate in the dark and stromal side provides the needed light.

Answer 2

The NADP+ reductase is present on the outer side of the thylakoid membrane so as to release NADPH on the stromal side where it can be used during dark reaction along with ATP to form glucose.

Further Explanation:

The light reaction or energy-producing phase of photosynthesis takes place in the thylakoid membrane forming ATP and NADPH. These molecules are then utilized during the dark reaction to produce sugars that occur in the stroma. The ATP is the energy-storing molecule while NADPH is the reduced electron carrier.

NADP+ reductase or ferredoxin NADP+ reductase (FNR) is an enzyme that catalyzes the last step of the light reaction during photosynthesis that is the transfer of electrons from ferredoxin (reduced) to NADP+ and results in the formation of NADPH and ferredoxin (oxidized). This enzyme is located on the outer periphery of the thylakoid membrane. When FNR accepts electrons from ferredoxin it releases NADPH on the outside of the thylakoid membrane or the stroma as FNR faces outwards. NADPH cycling is a vital step and can occur only in the presence of light. The stromal side provides optimal light for the reaction to take place.

The ATP is also formed in the light reaction as the movement of electrons from one carrier to another releasing some sort of energy which is used to pump proton (H+) to the lumen from the stroma. The transfer of protons back to the stroma takes place through ATP synthase resulting in the formation of ATP.The ATP and NADPH are formed on the stromal side and are used in the dark reaction to proceed photosynthesis further and form a glucose molecule from carbon dioxide.

Therefore, the presence of NADP+ reductase on the stromal side is important so as to form NADPH on the outer side and perform the NADPH cycling efficiently.

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Answer Details:

Grade: College Biology

Subject: Biology

Chapter: Photosynthesis

Keywords:

Photosynthesis, light reaction, dark  reaction, thylakoid membrane, stroma, lumen, NADP+ reductase, FNR, ATP, NADPH, ferredoxin.