Ch22.2 - Plants can carry out A. nitrogen assimilation. B....

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Unformatted text preview: Plants can carry out A. nitrogen assimilation. B. denitrification. C. nitrification. D. nitrogen fixation. The nitrogen cycle: Nitrogen Assimilation (plants & Bacteria) Nitrogen fxation -- the nitrogenase complex Dinitrogenase reductase : dimer oF 2 identical subunits (blue and green), each dimer contains a single 4e-4S redox center and two binding sites For ATP Dinitrogenase : tetramer (2 copies oF 2 subunits = pink and gray) contains 2 pair oF 4e-4S centers and 2 e-Mo coFactors dinitrogenase dinitrogenase reductase igure 22-3 N 2 + 3H 2 2NH 3 The overall reaction of nitrogen Fxation: N 2 + 10H + + 8e- + 16ATP 2NH 4 + + 16ADP + 16P i + H 2 ATP binding causes conformational change in dinitrogenase reductase, which lowers its redox potential ( E o ) from -0.3 to -0.42 V. ATP hydrolysis thought to facilitate dissociation of the reductase. Allowing reduction of N 2 : N 2 + 6H + + 6e- 2NH 3 E o = -0.34V Nitrogen Fxation -- the nitrogenase complex Figure 22-7 Covalent modifcations o glutamine synthetase: What would be the effect of high cellular [ATP] on GS activity? Glutamine amidotransferases: Reactions requiring transfer of ammonia from glutamine are found in amino acid, purine and Pyrimidine biosynthesis. Both glutamine and glutamate are important sources of nitrogen for biosynthesis as you will see Synthesis of cysteine in bacteria and plants : Figure 22-13 Chapter 22 -- Biosynthesis of amino acids and related molecules Chorismate is an intermediate in the synthesis of which amino acid? A. serine B. proline C. phenylalanine D. cysteine Figure 22-9 Overview of amino acid biosynthesis Weve already learned ways to make glutamate and glutamine. Lets talk about making proline and arginine from glutamate in bacteria Figure 22-10 Arginine Figure 22-10 Proline synthesis Figure 22-10 Arginine (next slide) Arginine synthesis in bacteria Arginine synthesis in bacteria (continued) Bacteria dont have arginase (to reform ornithine), but they can make arginine. Figure 22-10 Arginine Why is Glu acetylated in Arg pathway? Arginine Arginine synthesis in mammals : Proline Urea cycle enzymes Arginine arginase Figure 22-12 Pathway for serine synthesis in all organisms Figure 22-12 Synthesis of glycine from serine (all organisms): Figure 22-13 Synthesis of cysteine in bacteria and plants : Cysteine...
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This note was uploaded on 09/21/2010 for the course CH 53380 taught by Professor Raymond during the Spring '10 term at University of Texas at Austin.

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Ch22.2 - Plants can carry out A. nitrogen assimilation. B....

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