IV. Understanding Electron Transport – Looking at Table 14.1 (“Electron Tower”),

Question

IV. Understanding Electron Transport – Looking at Table 14.1 (“Electron Tower”), you can see the different Eo values of a variety of redox reactions. Use the information in that table to answer the questions below in 1-2 complete sentences for each. (2 pts)

1. With Glucose as the electron donor – which electron acceptor would yield more energy – iron (Fe+3), Nitrate (NO3-) or Oxygen? Why?

2. Could succinate donate electrons to H2? Could it donate electrons to nitrate (NO3)? Why or why not?

3. Pure fermenters, such as Streptococcus pyogenes lack several enzymes of the TCA cycle and many components of a typical electron transport chain. They do, however, all have ATP synthetase embedded in their cytoplasmic membranes and will use it to produce a PMF. How could they use this enzyme to produce a PMF and why would it be advantageous for them to do so?

Table 14.1 Electron tower" of standard reduction potentials.2 Electron acceptor E" (mv) electron donor [CH20] glucose + H20-430 NADH + H+ CH4 + 2H2O CO2+4H* +4e 2H + 2e NAD++ 2H+ +2e S° + H+ +e co2 + 2H+ + 3H2 + 2e- SO42-+ 1 0H48e- FAD +2H + 2e FMN +2H* +2e Menaquinone + Fumarate +2H +2e Ubiquinone + 2H+ + 2e-_| NO3 2H +2e -420 320 280 240 -220 HS H2S + 4H2O -220 -190 2H++ 2e- Menaquino! ubiquinol NH4+ + 2H2O -74 Succinate +110 +420 +440 +460 +740 +770 +820 Mn2+ +, 2H20 MnO2 + 4H + 2e NO3 6H +5e Fe + e %02 +2H +2e Fe2+ (at pH 2) Values taken from Rudolf K. Thauer, Kurt Jungermann, and Karl Decker. 1977 Energy conservation in chemotrophic anaerobic bacteria. Bacteriological Reviews 41:100-180. Voltage potentials for redox couples when all concentrations are 1 M at pH 2 This value is for free FAD; FAD bound to a specific flavoprotein has a different E depends on its protein environment. that

Explanation / Answer

1) The reduction potentials of iron (Fe3+) is +770mV, nitrate (NO3-) is +740mV and oxygen is +820mV. When glucose acts as electron donor it produces 430mV of energy. Of the iron, nitrate and oxygen, oxygen has the highest redox potential. So, when glucose acts as electron donor, oxygen acting as electron acceptor will yield maximum energy.

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