lecture 38___16 - MCB 354 Lecture 16 Amino Acid...

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MCB 354 Lecture 16 Amino Acid Biosynthesis Reading in Lehninger : Chapter 22
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Nitrogen cycle: - N2 “fixed” from the atmosphere - biologically available N recycled - soil bacteria have key roles e- from reduced ferredoxin, NAD(P)H = anaerobic process in bacteria use NO3- as terminal e- acceptor to generate transmembrane pH gradient to make ATP +5 +3 -3 0 Nitrification = NH4+ NO2- NO3- = energy-yielding oxidation 16-1
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N2 + 3 H2 2 NH3: at 500°C, 300 ATM, Fe catalyst Carried out by certain bacteria: - free-living soil bacteria - symbiotic bacteria in root nodules of legumes - cyanobacteria (=blue-green algae) Industrial: Issue: N N bond is very stable: bond energy = 225 kcal/mol Nitrogen fixation Biological: N2 + 8 e- + 8 H+ + 16 ATP 2 NH3 + 16 ADP + 16 Pi + H2 at biological temps, 0.8 ATM 16-2
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Symbiotic N2-fixing bacteria in nodules of legume roots Symbiotic bacteria inside root nodule cell nucleus Root nodules 16-3
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Nitrogen fixation N2 + 8 e- + 8 H+ + 16 ATP 2 NH3 + 16 ADP + 16 Pi + H2 N2 fixation carried out by the nitrogenase complex: = 2 metalloproteins, “ reductase ” and “ nitrogenase ”: Reductase: - contains Fe-S redox center, oxidized/reduced by 1 e- transfers - receives e- from Ferredoxin and transfers the e- to nitrogenase - 2 ATP hydrolyzed/ e- transferred - ATP-binding enhances reducing power of the reductase ( E ’° -0.25 V - -0.4 V), which is required for e- transfer - ATP-binding causes conformational change that promotes binding of reductase to nitrogenase - ATP hydrolysis triggers e- transfer to nitrogenase and promotes dissociation 16-4
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lecture 38___16 - MCB 354 Lecture 16 Amino Acid...

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