MG-Biology

PSI and PSII

The questions:

1)are the lecturers implying that in PSl the ejected electrons dont enter the ETC? from my understanding... it's such tt the electrons actually enters the ETC and are transferred to protein ferredoxin before being used to reduce NADP.. is my concept wrong?

From PSI, the electrons can enter two pathways:

(i) It can leave the photophosphrylation cycle to reduce NADP, therefore the pathway of the electron is known as non-cyclic photophosphorylation. The PSI which is short of an electron will be stabilised by another electron from the ETC. That electron would have to come from PSII which have been excited by light energy. The PSII would be in turn stabilised by the electron derived from the photolysis of water.


(ii) It can re-enter the ETC, in turn drives the production of ATP and then returning back to the PSII, stabilising it. Thus this will be cyclic photophosphorylation.


2)replacement of electron loss from PSl the same in both cyclic and non-cyclic phhotophosphorylation?

Cycling photophosphorylation involves PSI (simply: electron from PSI stabalises PSI). Non-cyclic photophosphorylation involves both PSI and PSII.

In cyclic photophosphorylation, the electron comes from PSI, while in non-cyclic photophosphorylation, it comes from PSII and PSII is stabilised by electron from the photolysis of water.

MG

posted by MG-Biology @ 11:14 AM