Nt1310 Unit 2 Research Paper

Words: 617
Pages: 3

FIG 1

FIG 2

The electrons used to create a molecule of NADPH from NADP+ come from 2 molecules of water. The electrons are transferred via an electron transport chain(ETC), and, as the electron moves from higher energy states to lower energy states, energy is used to translocate protons into the thylakoid lumen. The two photosystems use a central reaction centre which is surrounded by light harvesting antenna pigments to absorb energy from light to aid this process.

Energy from light with a wavelength <680nm is absorbed in Photosystem II (PSII) and is used to excite the electron (photoexcitation). This electron is therefore transferred to the electron acceptor plastoquinone and taken away. This results in PSII splitting a water molecule using a manganese cluster at the water-oxidising complex (WOC), removing electrons into PSII and releasing 4H+ and O2 per water molecule. The H+ released contributes to the generation of a hydrogen ion concentration gradient.
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The core of the complex is formed by 2 32kDa subunits, D1 and D2. They have 5 a-helices that span the membrane, and pair of chlorophyll α. This special pair, known as P680, transfers electrons to a pheophytin half way across the membrane, before finally passing an electron onto the plastoquinone which is tightly bound to the complex (QA). QA passes the electron onto QB, which can freely move to interchange with the intra-membrane plastoquinone pool, and when 2 e- are delivered, using 2H+ from the stroma, it is reduced to PQH2. Plastoquinone can be compared to ubiquinone in mitochondrial ETC. PSII catalyses the reduction of plastoquinone to plastoquinol (PQH2) using the energy of 4 photons and 4 e- from water. There is the translocation of 1 H+ per