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Similarities between photophosphorylation and oxidative phosphorylation e H+ gradient formation e Energy from electrons is used for H+ translocation H+ ATP synthesis is driven by H+ gradient H+ H+ H+ H+ Proton e pump H+ ATP synthase ATP ADP+Pi Energy source: electrons NADH FADH2 Differences between photophosphorylation and oxidative phosphorylation Energy source: light e H+ H+ H+ H+ H+ Proton pump O2 H+ NADP+ ATP ATP synthase + H H O 2 ADP+Pi By-product: NADPH water By-product: electrons Photosynthesis: The light reactions (photophosphorylation) Chlorophyll (or other pigments) absorbs light energy and conserve it as ATP and NADPH. Not all photosynthetic organisms use H2O as electron donor in photosynthesis; thus not all of them produce O2 while they produce ATP and NADPH. There are two types of photosynthesis: oxygenic (producing oxygen) photosynthesis and anoxygenic (not producing oxygen) photosynthesis. Only organisms with two photosystems can do oxygenic photosynthesis. At lease half of the photosynthsis in this world is done by microorganisms (algae, photosynthetic eukaryotes and photosynthetic bacteria). p724 Thylakoid membrane (lamellae) Outer membrane Inner membrane lumen stroma grana Chloroplast has photosystems with closely arranged chlorophyll p729 Cyanobacteria & red algae also contain similar structures called phycobilisome to facilitate light absorption p727 The major light absorbing pigment in higher plants Alternating single and double bonds give strong absorption in the visible light p726 The accessory pigment in bacteria and algae p726 What wavelength of light chlorophyll absorbs? p725 Chlorophylls can cover part of the spectrum – blue and red p727 The part of spectrum covered by chlorophylls coincides with the action spectrum of photosynthesis Accessory pigment: the red-orange -carotene p726 Accessory pigment: lutein (the red-orange isoprenoid) -carotene and lutein can help plant absorb more light Phycoerythrin and phycocyanin can absorb light that other pigments cannot absorb Anoxygenic photosynthesis (ferredoxin) (pheophytin) (restore RC to original state) (restore RC to original state) (PSII) (PSI) p731 The Z scheme of oxygenic photosynthesis (special form of chlorophyll) (phylloquinone) (pheophytin) (plastoquinone) Green bacteria type Purple bacteria type p733 (A1) PSI and PSII on thylakoid membrane are separated to prevent Excition Larceny LHCII holds grana together p736 Granal stacking by LHCII is regulated by light intensity ATP LHCII Pi -Thr-OH -ThrP ADP nonappressed appressed Protein kinase PPase Low High light light [PQH2] [PQ] Cytochrome b6f complex p737 Oxidative phosphorylation and photophosphorylation has something in common in cyanobacteria p738 D1 D2 QA QB Fe Pheo Pheo e e P680 Tyr e e Mn e4H +e O e2 Mn e Mn e Mn 2H2O Oxygen-evolving complex (water-splitting complex) p739 N P p741 N N N p742 bacteriorhodopsin p744 All-trans-retinal Proton transport 13-cis-retinol Chloroplast from higher plants is probably evolved from endosymbiotic bacteria (prochlorophytes) Chloroplast from red algae is probably evolved from cyanobacteria p1062 p723