light dependent reaction on photosynthesis

[biochemical]

I'm confused about cyclic and non-cyclic photophosporilation. Do they happen at the same time? And what connects them? Thanks a lot for the help...

[keef]

Cyclic Photophosphorylation

1. Light hits the chlorophyll, it takes on energy and moves to a higher energy state.

2. An electron acceptor, Ferredoxin, carries them to a carrier system which contains 3 enzymes.

3. As they move through this system, the energy the electrons are carrying is slowly released to turn 2ADP's and 2 into 2 x ATP's which are fed into the Dark Phase.

4. When the electron reaches the 3rd carrier enzyme it has lost all its extra energy and is brought back to the ground state. It is now ready to take on light energy again and repeat the process.


Non Cyclic Photophosphorylation

This process is a little more complicated that the cyclic process. There are many important processes occurring at the same time. It will be necessary to run the animation several times and focus in on one step at a time. Only then will it be possible to see them as a single process.

1) The non-cyclic process begins much in the same way as the cyclic process. An electron is hit by a photon of light energy and moves to a higher energy state. It is then accepted by Ferredoxin.

2) The ferredoxin carries the excited electron to another acceptor called NADP. When the NADP picks up the electron it becomes NADP-.

3) A molecule of water, H-O-H, splits into H+ and OH-. The H+ is attracted to the NADP- and bonds to it forming NADPH2. The H2 is then released into the dark phase and the NADP can return to pick up more excited electrons.

4) The OH- is carrying an extra electron which it releases to the enzyme carrier system. When this happens to 4OH's, water and O2 are formed which exit through the leaf.

5) The new electron travles through the enzyme carrier system in much the same way as in the cyclic process, making 2 molecules of ATP along the way.

6) It is clear to see that the electron the arrives back is not the same as the electron that started the process. This is why the process is referred to as being non-cyclic.

LAstly, they happen at the same time. cheers

[biochemical]

Thank U so much, Keith. It's really helpful...

[keef]

no prob dude. take care and good luck with your work

[kabuto]

Non Cyclic Photophosphorylation

This process is a little more complicated that the cyclic process. There are many important processes occurring at the same time. It will be necessary to run the animation several times and focus in on one step at a time. Only then will it be possible to see them as a single process.

where is the animation??

[kiekyon]

noncyclic phosphorylation produce ATP and NADPH
cyclic phosphorylation produce ATP but no NADPH

so, if NADPH level is high, we revert to cyclic phosphorylation

[MrMistery]

actually if you really want to be more catholic than the pope, there are 3 kinds of cyclic phosphorilation:
1. around photosystem I: produces ATP but no NADPH
2. around photosystem II: does not produce ATP nor NADPH, striclty as a protection mechanism when the electron flow id to great.
3.(what is reffered to as the water-water cycle): around both photosystems, and also strictly as a protection mechanism.

Botany is complicated i'm afraid..

[kiekyon]

actually if you really want to be more catholic than the pope, there are 3 kinds of cyclic phosphorilation:
1. around photosystem I: produces ATP but no NADPH
2. around photosystem II: does not produce ATP nor NADPH, striclty as a protection mechanism when the electron flow id to great.
3.(what is reffered to as the water-water cycle): around both photosystems, and also strictly as a protection mechanism.

Botany is complicated i'm afraid..

i dont know u can still call something as 'phosphorylation' without producing ATP???

[MrMistery]

good point. my mistake. three kinds of cyclic electron flow. in generalit's not good to say cyclic and non-cyclic phosphorilation, because the phosphorilation takes place in the same way, only the ways the electrons are transported are different. That's why we should always say "cyclic and noncyclic electron transport"

[éireann ní chiarráin]

Question: How to you actually go about making the ATP from ADP during cyclic and noncyclic photophosphorylation? Please respond!

Many thanks,
Éireann