12 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 12...

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PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 12 The Phototrophs Part 1
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Chlorophyll-based photosynthesis is confined to the domain Bacteria Five phyla of bacteria contain photosynthetic represent- atives. All the oxygenic prokaryotic photosynthetic organisms are included in the cyanobacteria. Anoxygenic photosynthetic bacteria contain much simpler photosyn- thetic complexes that are the evolutionary ancestors of the two linked photosystems found in cyanobacteria, algae and plants. The bacteriorhodopsin-based form of photosynthesis is clearly a separate evolutionary invention and is mechanistically unrelated to chlorophyll- based photosynthesis. The of chloroplasts from eukaryotic algae and plants have unquestionably been derived from bacterial forms via endosymbiosis. genomes.tgen.org/intro.html
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Phototrophic organisms switch their mode of metabolism depending on the resources available in their habitat. Most phototrophs are also autotrophs; however, some can also use organic carbon as a carbon source. Photohetero- trophy typically represses photoautotrophy. The growth of a photoautotroph involves 2 distinct reactions: ATP production and CO 2 reduction to organic compounds. For autotrophic growth, energy is supplied by ATP and electrons for the reduction of CO 2 come from NAD(P)H. Electron donors include H 2 S, S 0 , S 2 O 3 2- , Fe 2+ , or H 2 in anoxygenic photosynthesis and H 2 O in oxygenic photosynthesis. H 2 O is a poor electron donor, so oxygenic phototrophs require light for both reducing power and energy conservation.
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Chlorophyll is found in oxygenic phototrophs and bacteriochlorophyll in anoxygenic phototrophs. The molecule is a porphyrin, like cytochromes, but instead of containing an iron atom, it contains magnesium. Yellow and green indicate differences in the two molecules. Hydro- phobic alcohol side chains allow the molecule to associate with membranes. Absorption specta of chlorophyll (green) and bacterio- chlorophyll (red). In the green curve, peaks at 680 and 430 nm are due to chlorophyll a ; the peak at 480 nm is due to carotenoids. Chlorophyll a is green because it absorbs red and blue light and transmits green light. In the red curve, peaks at 870, 805, 590, and 360 nm are due to bacteriochlorpyll a , while peaks at 525 and 475 nm are due to carotenoids.
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Structure of all known bacteriochlorophylls - Bchl
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http://www.bact.wisc.edu/themicrobialworld/metabolism.html
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12 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 12...

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