photosystem 1 and II

[arpitpatel86]

i think i get it but confused on some parts

photosystem 1....cyclic phosphorylation.....ONLY ATP produced....light strikes p700 pigment which gets excited and then returs to ground state and in the procdss producing atp

photosys II....noncyclic....produces ATP and NADPH....the thing im confused on is does the light strike p700 first or p680....bc it says photons of light excite electrons in p700 in photosytem 1. however, instead of returning to p700 along the carrier chain, the high energy electrons are transferred to the elctrons acceptor NADP+ and this prodces NADPH which results in p700 electrons holes and thus is a powerful oxidizing agent. when light strikes p680 in photo sys II electrons are excited and then thes electrons travel down the same elctron carrier chain used by cyclic electron flow until they reach p700 and fill the elctron holes now p680 has the hole and water is oxidized and spilt which and the elctrons produced fill the hole of this one.

so does p700 first get excited and produces nadph which results in a hole...then p680 gets excited to fill this hole then water is oxidized to fill p680 hole?

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[tsav23]

Photosystem II occurs before photosystem I. p680 get oxidized and the cytochromic carriers transfer the electrons to photosystem I. At Photo I is where they give off ATP across the lumen or make NADPH to be used for the calvin cycle.

 

[arpitpatel86]

how does photosystem II occur b4 I?

doesnt the p700 first get excited and then it's electrons are passed to NADPh....then P680 gets excited and it convers the hole of p700

so the p680 is photo sys II
and p700 is phot sys I...so wouldnt this have to happen first?

 

[tsav23]

The reason why Photosystem II occurs first is because it has a wavelength of 680 nm, which is shorter that Photosystem I which is 700 nm. Light penetrates Photo II first.

Now the reason why the second part of photosynthesis is called photosystem I is because scientists believed it evolved first, therefore they named it photosystem I. Very confusing, but that is what scientists do.

 

[yakuza]

I don't think photosyn II makes ATP and NADPH..

 

[osimsDDS]

photosystem I produces only ATP under non-cyclic photosynthesis while photosystem II oxidizes H20 to give its electrons to Photosystem I so that it can reduce NADP to NADPH and also make ATP this is known as non-cyclic photosynthesis.... check this out and you will understand it

http://fig.cox.miami.edu/~cmallery/150/phts/cyclic.jpg

 

[yakuza]

photosystem I produces only ATP under non-cyclic photosynthesis while photosystem II oxidizes H20 to give its electrons to Photosystem I so that it can reduce NADP to NADPH and also make ATP this is known as non-cyclic photosynthesis.... check this out and you will understand it

http://fig.cox.miami.edu/~cmallery/150/phts/cyclic.jpg

I was thinking photoSystem. So, does photosynthesis II include all the the steps photosystem II ---2electrons--> electron chain --2electrons--> photosystem II........?

 

[osimsDDS]

photosynthesis II?? wuts that?? I am not sure i understand your question sorry...

 

[yakuza]

photosynthesis II?? wuts that?? I am not sure i understand your question sorry...

He said photosys so I was thinking photosystem II for some reason..
But what I meant was I don't think photosystem II actually makes ATP or NADPH, it just aids the process of making it.

 

[osimsDDS]

yea true, helps in the process of *

 

[gkhan]

they are labeled I and II in the order they were discovered.

I was discovered first, although it comes 2nd in the cycle.
hope that helps.

 

[osimsDDS]

it only comes second in non-cyclic, during cyclic Photosystem I is the primary one...

Non-cyclic:
Photosystem II gives its electrons from oxidizing H2O to Photosystem I where it then "helps" in producing NADPH and ATP

Cyclic:
Photosystem I is excited and "helps" in producing ATP