From the reduction potentials provided for archaea bacteria electron transport w
ID: 39436 • Letter: F
Question
From the reduction potentials provided for archaea bacteria electron transport what is the order of electron carriers that would be involved in the transfer of electrons from H2 to CO2 to make HCOOH (see below)? It is not necessary to use all of the reactions. Remember electron transport is reversed from the way we normally think of it since the proton gradient is the driving force. Assume each step must be driven by the flow of protons and explain your rationale briefly
Half Reactions for Archaeabacteria
E
Half Reactions for Archaeabacteria
E
Explanation / Answer
The Wood-Ljungdahl pathway is found in a broad range of phylogenetic classes, and is used in both the oxidative and reductive reactions. The pathway is used in the reductive direction for energy conservation and autotrophic carbon assimilation in archea bacteria. When methanogens grow on H2 + CO2, they use the Wood-Ljungdahl pathway in the reductive direction (like acetogens) for CO2 fixation, however, they conserve energy by the conversion of H2 + CO2 to methane. Given that hydrogenotrophic methanogens assimilate CO2 into acetyl-CoA, it is intriguing that they do not make a mixture of methane and acetate. Presumably this is governed by thermodynamics, since the formation of methane is ?36 kJ/mol more favorable than acetate synthesis. Aceticlastic methanogens exploit this advantageous equilibrium to generate metabolic energy by interfacing the Wood-Ljungdahl pathway to the pathway of methanogenesis. In this reverse direction, the combined actions of acetate kinase and phosphotransacetylase catalyze the conversion of acetate into acetyl-CoA. Sulfate reducing bacteria also run the Wood-Ljungdahl pathway in reverse and generate metabolic energy by coupling the endergonic oxidation of acetate to H2 and CO2. to the exergonic reduction of sulfate to sulfide (?G0
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