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UMass Amherst MICROBIO 310 - Types of Photosynthesis and Oxidation

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Microbio 310 1st Edition Lecture 16 Outline of Last Lecture I. 12.4 The Genomes of Eukaryotic OrganellesII. 12.6 MetagenomicsIII. 12.7 Microarrays and the TranscriptomeIV. 12.10 Gene Families, Duplications, and DeletionsV. 12.11 Horizontal Gene Transfer and Genome StabilityVI. 12.12 Transposons and Insertion SequencesVII. 12.13 Evolution of Virulence: Pathogenicity IslandsOutline of Current Lecture I. 13.1 PhotosynthesisII. 13.2 Chlorophylls and BacteriochlorophyllsIII. 13.3 Carotenoids and PhycobilinsIV. 13.4 Anoxygenic PhotosynthesisV. 13.5 Oxygenic PhotosynthesisVI. 13.6 The Energetics of ChemolithotrophyVII. 13.7 Hydrogen OxidationVIII. 13.9 Iron OxidationCurrent Lecture13.1 PhotosynthesisThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.• Photosynthesis is the conversion of light energy to chemical energy– Phototrophs carry out photosynthesis – Most phototrophs are also autotrophs• Photosynthesis requires light-sensitive pigments called chlorophylls• Photoautotrophy requires ATP production and CO2 reduction• Photoautotrophy– Oxidation of H2O produces O2 (oxygenic photosynthesis)– Oxygen not produced (anoxygenic photosynthesis)13.2 Chlorophylls and Bacteriochlorophylls• Organisms must produce some form of chlorophyll, a light-capturing molecule, (or bacteriochlorophyll) to be photosynthetic • Chlorophyll is related to porphyrins (heme) from Citric Acid Cycle• Number of different types of chlorophyll exist– Different chlorophylls have different absorption spectra • Cyanobacteria produce chlorophyll a • Prochlorophytes produce chlorophyll a and b• Anoxygenic phototrophs produce bacteriochlorophylls• Chlorophyll pigments are located within special membranes– In eukaryotes, called thylakoids – In prokaryotes, pigments are integrated into cytoplasmic membrane• Reaction centers participate directly in the conversion of light energy to ATP• Antenna pigments funnel light energy to reaction centers • Chlorosomes function as massive antenna complexes (associated with outer membrane, funnel light to reaction centers)– Found in green sulfur bacteria– And green nonsulfur bacteria13.3 Carotenoids and Phycobilins• Phototrophic organisms have accessory pigments in addition to chlorophyll, including carotenoids and phycobiliproteins • Carotenoids– Always found in phototrophic organisms– Typically yellow, red, brown, or green and absorb blue light– Energy absorbed by carotenoids can be transferred to a reaction center– Prevent photooxidative damage to cells– Antioxidant (lycopene tomatoes): neutralize free radicals13.4 Anoxygenic Photosynthesis• Anoxygenic photosynthesis is found in four phyla of Bacteria• Photosynthesis apparatus embedded in membranes • Electron transport reactions occur in the reaction center of anoxygenic phototrophs• Reducing power for CO2 fixation comes from reductants present in the environment (i.e., H2S, Fe2+, or NO2 but NOT H20)– Requires reverse electron transport for NADH production in purple phototrophs– Electrons are transported in the membrane through a series of proteins and cytochromes• For a purple bacterium to grow autotrophically, the formation of ATP is Not enough– Reducing power (NADH) is also necessary– Reduced substances such as H2S are oxidized and the electrons eventually end up in the “quinone pool” of the photosynthetic membrane13.5 Oxygenic Photosynthesis• Oxygenic phototrophs use light to generate ATP (portable energy) and NADPH (portable electrons)• The two light reactions are called photosystem I and photosystem II• “Z scheme” of photosynthesis – Flow of electrons looks like a Z turned on its side– Photosystem II transfers energy to photosystem I13.6 The Energetics of Chemolithotrophy• Chemolithotrophs are organisms that obtain energy from the oxidation of inorganic compounds• Mixotrophs are chemolithotrophs that require organic carbon as a carbon source• Many sources of reduced molecules exist in the environment• The oxidation of different reduced compounds yields varying amounts of energy13.7 Hydrogen Oxidation• Anaerobic H2-oxidizing Bacteria and Archaea are known• Catalyzed by hydrogenase- takes protons and electrons from H2• Calvin cycle and hydrogenase enzymes allow chemolithotrophic growth13.9 Iron Oxidation• Ferrous iron (Fe2+) oxidized to ferric iron (Fe3+)• Ferric hydroxide [Fe(OH)3] precipitates in water (sign of iron-oxidizing bacterial growth)• Many Fe oxidizers can grow at pH < 1 (very acidic pH)– Often associated with acidic pollution from coal mining activities• Some anoxygenic phototrophs can oxidize Fe2+ anaerobically using Fe2+ as an electron donor for CO2 reduction• Ferrous iron oxidation begins in the periplasm, where rusticyanin oxidizes Fe2+ to Fe3+ • Rusticyanin then reduces cytochrome c, and this subsequently reduces cytochrome a• Cytochrome a interacts with O2 to form H2O• ATP is synthesized from ATPases in the membrane• Autotrophy in Acidithiobacillus ferrooxidans is driven by the Calvin cycle• Ferrous iron can be oxidized under anoxic conditions (very low/no oxygen) by certain anoxygenic phototrophic


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UMass Amherst MICROBIO 310 - Types of Photosynthesis and Oxidation

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