Question

someone simplify the photosystems II and I for me please

Answer 1

Err...photosynthesis?

Answer 2

Is that what this is from?

Answer 3

No I think there is being talked about the photosyntems... you know, where chlorophyll is transporting electrons to and is being brought into a excited state.

Answer 4

But Enthuse you want to know how the protein-complex is working?

Answer 5

Yes, basically how the photosystems within the chloroplasts

Answer 6

Sure I'll be glad to look at it later today,

Answer 7

Photosystem II: The chemical reaction.
Photosystem II catalyze the light-driven transfer of electrons from water to plastoquinone. This electron acceptor closely resembles ubiqionone (cf. ETC). Plastquinone cycles between an oxidized form (shown as Q) and a reduced form (shown as QH2). The overall reaction catalyzed by the photosystem II is:
\[Q + 2 H _{2}O + Light \rightarrow Q _{2} + 2 QH _{2}\]
The electrons in QH2 are at a higher redox potential than those in H2O. Photosystem II drives the reaction in a thermodynamically uphill direction by using the free energy of light.

Photosystem II: The photochemistry.
The photochemistry begins with excitation of a special pair of chlorophyll molecules that are bound by the D1 and D2 subunits on the protein complex. The special pair is often called P680, becuase the chlorophyll a molecules of the special pair absorb light at 680 nm. In the momement the excitation of P680 happens, P680 transfers an electron to a nearby pheophytin. From there, the electron is transferred first to a tightly bound plastoquinone at site Qa and then to a mobile plastoquinone at site Qb. With the arrival of a second electron and the uptake of two protons, the mobile plastoquinone is reduced to QH2. At this point, the energy of 2 photons has been safely and efficiently stored in the reducing potential of QH2. in order to optain the electrons in the first place, there is the use of a manganese center. this center consist of a calcium ion and four manganese ions (we belive it was evolutionary selected becuase of all the oxidation states for manganese Mn(II), Mn (III), Mn(IV) and Mn(V), The manganse center in its reduced form oxidizes two molecules of water to form a single molecule of oxygen. Each time the absorbance of a photon kicks an electron out of P680, the positively charged P680 extracts an electron from the manganese center. However we know that the electrons don't come directly form the manganese ions. A tyrosine resideue (called Z) of subunit D1 in photosystem II is the immediate electron donor, forming a tyrosine radical. The tyrosine radical removes electrons from the manganese ions, that remove electrons from water insted forming O2 and protons. We use to say that 4 photons most be absorbed to extract four electrons from a water molecule.
The 2 protons that are taken up with the reduction of Q to QH2 come from the stroma, and the 4 protons that are liberated in the course of water oxidation are released into the lumen. The distribution of protons generates a proton gradient across the thylakoid lumen compared with the stroma.

So to sum up photosystem II, all the above can be said in one sentence: "Photosystem II transfers electrons from water to Plastoquinone (Q) and generates a proton gradient".