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Similarities between photophosphorylation and oxidative phosphorylation H+ e H+ H+ H+ H+ Proton pump ATP synthase ATP H+ H+ ADP+Pi Differences between photophosphorylation and oxidative phosphorylation NADH FADH2 e H+ H+ H+ H+ H+ Proton pump O2 H+ H2O NADP+ ATP H+ NADPH ATP synthase ADP+Pi p723 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 The spectrum of electromagnetic radiation 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 (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 Cytochrome b6f complex p737 Oxidative phosphorylation and photophosphorylation has something in common in cyanobacteria p738 Oxygen-evolving complex (water-splitting complex) In protein subunit D1 of the PSII reaction center; the immediate electron donor to P680 can only accept one electron at a time Loses one electron and proton at a time to P680; electrically neutral Tyr free radical (Tyr•) is generated tyr• then regain its electron and proton by oxidizing four Mn in the water splitting complex; each transfer corresponds to one photon absorption Here the Mn complex takes four electrons from a pair of water molecules; releasing 4H+ and O2 Goes to lumen 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