Phototrophy Conversion of radiant energy from the sun into ATP and NADPH
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Transcript of Phototrophy Conversion of radiant energy from the sun into ATP and NADPH
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• Phototrophy – Conversion of radiant energy from the sun into
ATP and NADPH
• Autotrophy involves carbon fixation– Conversion of inorganic carbon into organic
molecules
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• Photoautotrophy– Involves light rx (energy step)
and dark rx (carbon fixing step)
– Photophosphorylation (light rx) provides ATP and reducing power (NADPH) to power the Calvin-Benson Cycle (dark rx)
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• 3 types of phototrophy– Oxygenic phototrophy– Anoxygenic phototrophy– Rhodopsin based phototrophy
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• Pathways of oxygenic light reaction– Pair of chlorophyll based photosystems embedded in
membrane• Chloroplast or plasma membrane
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Cyclic photophosphorylation produces only ATP
Non-cyclic photophosphorylation produces ATP, NADPH and O2
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• Pathways of anoxygenic light reaction– Single bacteriochlorophyll based photosystem – Limited to cyclic photophosphorylation– Use different methods to generate reducing power – Molecules other than water are used as electron donor– O2 is not produced
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• Archaea have no chlorophyll based photosystems• They utilize a membrane protein called
bacteriorhodopsin to capture radiant energy• In oxygen poor environments the pigment functions
as a light-driven proton pump
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Dark rx uses ATP and NADPH to fix carbon
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Chemolithotrophy
• Inorganic compounds serve as electron donors and energy source
• Common electron donors include – H, reduced N, S or Fe
• Photolithrotrophs require additional energy from sun– Purple bacteria
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• Low energy yield so they consume high quantities of inorganic molecules– Significant ecological impact
• Iron bacteria – oxidize ferrous iron (Fe2+) into ferric iron (Fe3+)– Ferrobacillus ferrooxidans
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• Nitrifying bacteria – oxidize ammonia (NH3) to nitrate (NO3)– Nitrosomonas and Nitrobacter
• Hydrogen bacteria – oxidize hydrogen gas (H2) to water (H2O)– Alcoligenes eutrophus
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• Sulfur Oxidizing Bacteria – oxidize sulfides, sulfur and thiosulfate to
sulfuric acid (H2SO4) – Thiobacillus thiooxidans
• Many chemolithotrophs are autotrophic using CO2 as carbon source– Use reverse electron flow to reduce NAD
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Reverse electron flow is necessary for chemolithoautotrophs to generate reducing power
NADH reduction by sulfide and nitrite
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• Chemolithoautotrophy is very inefficient– much of the energy is expended on generating
reducing power rather than ATP– Many will grow as heterotrophs if supplied with
organic carbon sources
• Many can grow either aerobically or anaerobically by varying the final electron acceptor