Clarification with P680...

[sfoksn]

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P680 is known to be participating in non-cyclic portion of photosynthesis.

It's supposed to cause hydrolysis, separating H2O into H+ and O2.

Now, my question is, how is this oxidizing process?

Sources say that P680 oxidizes water, but the water molecule is losing the O bonds?

Can anyone clarify, and help me think of a logical way to accept this?

Thank you.

 

[dentalWorks]

Here is the z-scheme of photosynthesis:

I am going to refer to the 3 arrows I have drawn in red (#1, #2, & #3)

Your asking about photosynthesis, before we get into the chemistry of why its called "oxidation", first we need to underastand that photosynthesis has 2 objectives:
1) make ATP ~ your not asking about this
2) obtain electrons from "spilling" of a water molecule so that these electrons eventually make their way to NADP+ to convert it to NADPH ~ this is what your asking.... This is arrow #3 in the figure above

So, look at arrow #1, thats the "low energy state" of P680, think of P680 as a protein that its main job is to SUCK UP ELECTRONS (aka oxidation) from water molecules.... This can only be done by providing P680 with energy (aka Light).

After light strikes the P680, it "sucks" 2 electrons from a water molecule (it splits the covalent bonds of water and the electrons of those bonds get vacuumed by P680).... When this happens, P680 becomes the "excited form of P680" (Arrow #2)

Ultimatly, the electron from Arrow #2, makes the complete pathway alllllll the way to that NADP+ to become NADPH (arrow #3)

This is why the process is called "oxidation"... cause your sucking up electrons from water.

Remember when you studied glycolysis? Glucose molecule is said to be "oxidized" by our cells because the cells are "sucking" the electrons from the glucose molecule....

 

[sfoksn]

Thank you for a detailed explanation.

I guess I was really sleepy or something!

I thought the oxidation and reduction happens all within the water molecule, so I see how H's are oxidized (H 0 charge to H + charge) and I thought the electrons would be sent to the oxygen. But it doesn't get sent to oxygen...

PII accepts them and xfer it to PI then PI uses those electrons to make energy rich nucleotide coenzyme like NADH. Reduce the NAD into NADH, right?

 

[dentalWorks]

I thought the oxidation and reduction happens all within the water molecule, so I see how H's are oxidized (H 0 charge to H + charge) and I thought the electrons would be sent to the oxygen. But it doesn't get sent to oxygen...

When your thinking about oxidation/reduction reactions, they happen in pairs and (generally) 2 molecules are involved (in our photo system model, the 2 molecules are P680 and water). In photosynthesis, Water gets oxidized (looses electrons) and P680 gets reduced (gains electrons)....but in litterateur, no one really says "the reduction of P680", its always referred to as an oxidation process (meaning oxidation of water)

PII accepts them and xfer it to PI then PI uses those electrons to make energy rich nucleotide coenzyme like NADH. Reduce the NAD into NADH, right?

NAD(H) is mostly involved in glycolysis
NADP(H) is mostly invovled in photosynthesis

But what your saying up there is correct
PII --> PI --> NADP+ ----(becomes)--->NADPH

 

[luv8724]

How I remember the Redox is

Oxidation: Gain of O2, loss of H2

Reduction: Loss of O2, Gain of H2

this is how it says in my ochem book which is easy to remember