CE555-Chapter 20- Lecture Notes [Compatibility Mode]

CE555-Chapter 20- Lecture Notes [Compatibility Mode] -...

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1 Chapter 20 Metabolic Diversity: Phototrophy, Autotrophy, Chemolithotrophy, and Nitrogen Fixation Photosynthesis Photosynthesis is the most important biological process on Earth Ph t t h are organisms that carry out photosynthesi Phototrophs are organisms that carry out photosynthesis – Most phototrophs are also autotrophs (use CO2) • Photosynthesis requires light-sensitive pigments called chlorophyll • Photoautotrophy requires ATP production (energy) and CO 2 reduction (use energy and reducing power for carbon fixation) • Oxidation of H 2 O produces O 2 (oxygenic photosynthesis) • Oxygen not produced (anoxygenic photosynsthesis)
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2 Phototrophs obtain energy from light and capture it into ATP. Photosynthesis involves reactions in which ATP is generated and reactions in which ATP is consumed in the reduction of CO 2 by NADH. Phtotoheterotrophs need a reduced form of carbon and cannot “fix CO 2” from the air.
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3 Capturing light energy and turning it into chemical (ATP) by electron flow. Arrangement of Light-Harvesting Chlorophylls Figure 20.6
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4 Chlorophylls and Bacteriochlorophylls • Organisms must produce some form of chlorophyll (or bacteriochlorophyll) to be photosynthetic • Chlorophyll is a porphyrin • Number of different types of chlorophyll exist – Different chlorophylls have different absorption spectra • Chlorophyll pigments are located within special membranes Ikt l l d th l k id – In eukaryotes, called thylakoids – In prokaryotes, pigments are integrated into cytoplasmic membrane
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5 Structure and Spectra of Chloro- and Bacteriochlorophyll Figure 20.3b Absorption Spectrum The Chlorosome of Green Sulfur and Nonsulfur Bacteria Figure 20.7 Model of Chromosome Structure
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6 Anoxygenic Photosynthesis Anoxygenic photosynthesis is found in at least four phyla of Bacteria • Electron transport reactions occur in the reaction center of anoxygenic phototrophs • Reducing power for CO 2 fixation comes from reductants present in the environment (i.e., H 2 S, Fe 2+ , or NO 2- ) – Requires reverse electron transport for NADH production in purple phototrophs Example of Electron Flow in Anoxygenic Photosynthesis Electrons flowing through the quinone pool pump H+ out of cell setting up proton motive force, which results in ATP production via H+ entry into cell through ATPase Figure 20.14
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7 e- to NADPH Anoxygenic Photosynthesis (con’t) ATP is made from cycling of electrons which • ATP is made from cycling of electrons which produces Proton Motive Force – However, reducing CO2 to cellular components requires reducing power (NADPH or NADH). Where does this come from? • Reverse electron flow to reduce NADP+ from quinone pool – Electrons have to be pumped into this cycle from outside sources (electron donors), so electrons can be siphoned off to reduce NADP+ to NADPH.
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8 Oxygenic Photosynthesis • Requires electron flow in two photosystems that are connected.
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CE555-Chapter 20- Lecture Notes [Compatibility Mode] -...

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