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Chloroplast

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Chloroplast

Postby Precognition » Fri Sep 17, 2010 8:25 pm

Right so Chloroplast a. release a high energy electron when they recieve light energy from pigments. So chloroplast samples are extracted and placed into a reagent which turns blue when oxidised and colourless when reduced, and when sunlight is shone on them the reagent turns colourless as it is reduced by the electrons given off. When ADP + Pi is added to this mix, why is the reagent reduced faster/turns blue quicker?
Is it because the ADP + Pi uses the extra energy from the electron to phosphorylate into ATP, therefore the electron reduces the reagent quicker as it has less energy?

Please enlighten me, Thanks.
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Re: Chloroplast

Postby jonmoulton » Fri Sep 17, 2010 9:31 pm

It sounds like your chromogenic redox reagent is standing in for NADPH/NADP+. Normally thylakoid electron transport sets up an H+ gradient that spills back through an ATPase to make ATP from ADP and Pi. If you supply ADP and Pi, you are making it easier for the H+ to move through the ATPase. You are also decreasing the H+ gradient across the thylakoid, so the light reactions are moving H+ against a shallower gradient. This can increase the rate of hydrogen ion transport if there is enough electron acceptor available to soak up the electrons from the thylakoid electron transport chain. In this case, there are several available electron acceptors: NADP+ and the chromogenic dye.

"why is the reagent reduced faster/turns blue quicker?" Would it do both? Reduction turns it colorless, right? If it's turning blue, doesn't that mean it is being oxidized?

"Is it because the ADP + Pi uses the extra energy from the electron to phosphorylate into ATP, therefore the electron reduces the reagent quicker as it has less energy?"
At any particular instant, the electron that reduces the dye is not the same electron that is dropping though the ATPase. These processes are separated in space in and involve different electrons.
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Postby Precognition » Fri Sep 17, 2010 9:39 pm

Ah extreme typos by me, meant turns colourless quicker. sorry for the misunderstanding.
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