Question

Which of the following electron Carrier is located towards outer side
of thylakoid membrane or stromal side, in between PSII and PSI
(1)Plastocyanin (2) Plastoquinone
(3)Phaeophytin (4) Cytochrome b6F

If you know the answer, explain it.​

Answer 1

plastoquinone

Explanation:

Structure of the Thylakoid Membrane and PET Reactions

The thylakoid membrane is constituted by a lipid matrix that maintains its fluidity, allows an electrochemical potential difference across this membrane, and harbors all four main protein complexes of the OPh machinery (Fig. 1): photosystem I (PSI), photosystem II (PSII), cytochrome b6f complex (Cyt b6f), and ATP synthase. Moreover, this lipid matrix embeds low molecular-weight carriers, plastoquinone-9 (PQ) (Scheme 1A) and plastocyanin (PC), which are the electron and proton shuttles between PSII and PSI, respectively, via Cyt b6f.1,3,4 Finally, an ATP synthase complex utilizes the energy stored in the proton gradient established across the thylakoid membrane by PET to synthesize ATP.

Answer 2

Oxygenic photosynthesis is indispensable both for the development and maintenance of life on earth by converting light energy into chemical energy and by producing molecular oxygen and consuming carbon dioxide. This latter process has been responsible for reducing the CO2 from its very high levels in the primitive atmosphere to the present low levels and thus reducing global temperatures to levels conducive to the development of life. Photosystem I and photosystem II are the two multi-protein complexes that contain the pigments necessary to harvest photons and use light energy to catalyse the primary photosynthetic endergonic reactions producing high energy compounds. Both photosystems are highly organised membrane supercomplexes composed of a core complex, containing the reaction centre where electron transport is initiated, and of a peripheral antenna system, which is important for light harvesting and photosynthetic activity regulation. If on the one hand both the chemical reactions catalysed by the two photosystems and their detailed structure are different, on the other hand they share many similarities. In this review we discuss and compare various aspects of the organisation, functioning and regulation of plant photosystems by comparing them for similarities and differences as obtained by structural, biochemical and spectroscopic investigations.

Keywords: Plant photosystems, light harvesting complexes, energy transfer, electron transfer, photoprotection.