Lect17-KR

Lect17-KR - Anaerobic respiration PMB/MCB 112 October 11,...

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Anaerobic respiration PMB/MCB 112 October 11, 2010
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Respiration , in the molecular sense, means passing electrons down an ETC and reducing an exogenous electron acceptor For almost all eukaryotes, that electron acceptor is oxygen But many bacteria can use alternative electron acceptors at the end of their electron transport chains This allows them to grow using respiration in the absence of oxygen
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Assimilative vs. dissimilative reduction In assimilative reduction , compounds are reduced for the purpose of building cellular macromolecules, and the cell only reduces the amount needed for growth Ex: NO 3 - reduced to –NH 2 groups SO 4 2- reduced to –SH groups In dissimilative reduction , compounds are reduced for the purpose of energy conservation, large amounts are reduced, and the cell excretes the reduced product into the environment Ex: NO 3 - reduced to NO 2 - , N 2 O or N 2 SO 4 2- reduced to HS-
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Anaerobic respiration systems 3) Methanogenesis CO 2 /CH 4 (-.23) 2) Ferric iron reduction 1) Nitrate reduction and denitrification 4) Perchlorate reduction ClO 4 - /Cl - E 0 ’ = 1.29 V
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Populations of microbes with different metabolic capacity occupy different regions of lakes and wetlands
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Denitrification is the conversion of nitrite into gaseous compounds that are lost from the soil and water Nitrate reduction denitrification
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E. coli can use O 2 or NO 3 - as an electron acceptor Some ETC components are shared by both pathways. Nitrate is only reduced to nitrite by E. coli . This process is called nitrate reduction . Fewer protons are transferred out of the cell during nitrate reduction than during oxygen reduction. Fewer protons are also transferred out of the cell during nitrate reduction than during full denitrification (next slide).
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Paracoccus denitrificans and Pseudomonas stutzeri reduce nitrate to nitrogen gas (nitrate reduction plus denitrification) This pathway pumps more protons than nitrate reduction to nitrite, since protons are also extruded by the nitric oxide reductase
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Lect17-KR - Anaerobic respiration PMB/MCB 112 October 11,...

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