Question that confuses me

[YoonS]

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1. During non-cyclic electron flow, the primary electron-holding product is

A. Camp
B. AMP
C. ATP
D. NADH
E. NADPH

The answer is C, but isn't it E???

 

[RCLEE]

Yes, I would think so. What I remember from reading KBB was that the non-cyclic e- flow goes to the NADPH, then the splitting of H2O (by photosystem II). The primary electron was from the photosysten I p700, so the e- should end up on the NADP+.

From Cliffs, the splitting of H2O created a H+ gradient that used 1.5 H+ to make anATP(?).

What test question was that from?

 

[Juggernauts]

The way I see the question, it is asking for primary holding product of the non-cyclic electron flow.

The noncyclic flow, electrons move down a concentration gradient from an excited state in P680, which creates ATP. And the primary molecule created is the only molecule created, ATP.

Once you get to p700 (where the cyclic flow is possible), the primary e' holding product is NADPH.

ADP and NADP+ are your electron acceptors for the light dependent reactions. Another way to ask about the electron acceptors is, Which products are reduced? Or Which products are NOT oxidizing agents of the light dependent reaction of photosynthesis?

ATP is the Primary electron holding agent for the noncyclic flow.
NADPH is the Primary electron holding agent for the cyclic flow.
and NADPH is your final electron acceptor for the light dependent reaction of photosynthesis.

I think that it kind of a crappy question because the only reason to enter the cyclic flow is to create more ATP. The question is a little misleading in my opinion.

I put in bold a couple of key words that I think are important for differentiating the actions of the molecules in the light dependent reactions. I hope that makes sense and or helps.

 

[Juggernauts]

Here is a pretty good application question relating to light dependent and light independent rxns. The question is not mine, I reworded it enough that I don't believe I am in danger of copy right law.

Since protons are removed from the stroma during the light reactions of photosynthesis. What relative pH would the enzyme rubisco function most optimally at?

A. The same pH.
B. Slightly higher than normal pH
C. Much lower than normal pH.
D. A & B
E. Slightly lower than normal pH.

 

[RCLEE]

ATP is the Primary electron holding agent for the noncyclic flow.
NADPH is the Primary electron holding agent for the cyclic flow.
and NADPH is your final electron acceptor for the light dependent reaction of photosynthesis.
.

You didn't get things mix up right?

Cyclic flow only makes ATP.

Noncyclic flow makes ATP and NADPH from what I remember.

 

[Juggernauts]

You didn't get things mix up right?

Cyclic flow only makes ATP.

Noncyclic flow makes ATP and NADPH from what I remember.

Your correct, ATP and NADPH are produced in the noncyclic flow.

I did mistype something though, thanks for questioning it.
Let me try again to be clearer.

ATP is the Primary electron holding product (first product produced) for the noncyclic flow. P680 photosystem II

NADPH is the Secondary electron holding product (second product produced) in the noncyclic flow. P700 photosystem I

ATP is also the Primary and Only electron holding product for the cyclic flow.

Clear as mud?

 

[recyrb]

Here is a pretty good application question relating to light dependent and light independent rxns. The question is not mine, I reworded it enough that I don't believe I am in danger of copy right law.

Since protons are removed from the stroma during the light reactions of photosynthesis. What relative pH would the enzyme rubisco function most optimally at?

A. The same pH.
B. Slightly higher than normal pH
C. Much lower than normal pH.
D. A & B
E. Slightly lower than normal pH.

answer C?? since protons flow into the stroma during chemosmosis which is the step just before initiation of the calvin cycle?

 

[Juggernauts]

answer C?? since protons flow into the stroma during chemosmosis which is the step just before initiation of the calvin cycle?

Answer B. Slightly Higher than Normal pH. Stroma is more basic environment.

Rubisco is in the stroma. Yes protons flow from the thylakoid lumen into the stroma via chemiosmosis, but chemiosmosis is the act of going down a concentration gradient. The thylakoid lumen always has a lower pH (more acidic) because it maintains a higher concentration of H+. This is accomplished by leaving the Hydrogens from the photolysis of the water molecule in the very beginning of photosynthesis, into the thylakoid lumen. The part where the sun light breaks up a water in order to replace the electrons that were used up by p680. Hope I explained that the way it sounds in my head.