BICH 411 1st Edition Lecture 19 Outline of Last Lecture I. Complex Lipid SynthesisII. Adding the head groupIII. Sphingolipid biosynthesisIV. EicosanoidsV. SteroidsVI. Lipid transport through the bodyVII. Membrane fusionOutline of Current Lecture I. Nitrogen MetabolismII. Nitrate AssimilationIII. Nitrogen FixationIV. Ammonium ion assimilationV. Making amino acidsCurrent LectureNitrogen Metabolism-nitrogen assimilation (a two-step pathway reducing NO3- to NH4+) is over 99% of nitrogen metabolism, while the remainder is nitrogen fixation (N2 to NH4+). Nitrogen in the environment is normally oxidized (N2 and NO3-). **Figure 25.1 would be good to know for a quiz**-Nitrogen assimilation is aerobic, while Nitrogen fixation is anaerobic. Nitrate Assimilation -Assimilation consists of reducing nitrate to nitrite (with 2 electrons and Nitrate reductase) and then reducing nitrite to ammonium (with 6 electrons and Nitrite reductase).-This process uses the thiol of an enzyme, FAD cofactor, cytochrome b, and MoCofactor (MoCo).*There are iron sulfur centers involved. **The electrons are from NADH.-Reduced ferrodoxins give electrons to Nitrite reductase via the iron-sulfur centers. (the ferrodoxins are used in both steps of nitrogen metabolism)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Nitrogen Fixation-starts with atmospheric nitrogen and is only in some prokaryotes-Reduced ferrodoxins, nitrogenase, ATP, and anaerobic conditions are required**Figure 25.4 - The challenge for nitrogen fixation is the high activation energy (from breaking the N2 triple bond).-Nitrogenase complex: 4 ATP are necessary for each pair of electrons, so with 4 pairs (8 electrons), 16 ATPs are required for each N2!! There’s an iron sulfur center and a MOCO involved. *Figure 25.6 shows this reaction-ADP inhibits nitrogenase. Ammonium can inhibit a step as wellAmmonium ion assimilation-Incorporating ammonia into organic molecules happens with 3 main reactions (not sequential):1. Carbamoyl-phosphate synthetase I (CPS I) : ammonium carbamoyl-P**This is the committed step in the Urea cycle-It requires 2 ATP (1 for bicarbonate, 1 to phosphorylate carbamate)2. Glutamate dehydrogenase (GDH) – the ammonium is used to form glutamate3. Glutamine synthetase (GS) – uses ammonium to form glutamine from glutamate-ATP required1. Carbamoyl-Phosphate Synthetase I – early in the Urea cycle**Figure 25.22 – Know this mechanism!! -assimilates ammonium directly-required to make Arginine2 & 3: used to make Glutamine-GDH/GS – occurs in organisms with tons of Nitrogensum reaction: 2NH4+ + α-ketoglutarate + NADPH +ATPglutamine + NADP+ + ADP + Pi + H2O-A 4th reaction, GS/GOGAT, is useful when there is a nitrogen limitation-GOGAT: glutamate synthase (Glutamate:oxo-glutarate amino transferase)-need to remake glutamate-sum of reactions 3 and 4 (GS/GOGAT) is:2 NH4+ + α-ketoglutarate + NADPH + 2 ATP  glutamine + NADP+ + 2 ADP + 2 Pi -a little more expensive since it takes 2 ATPMaking amino acids-mammals can only make 10 amino acids, the others must be consumedtable 25.1 shows the grouped amino acids**good test question: which amino acid plays the most central role: glutamate**figure 25.19 is good to know.-Ornithine is a precursor for some amino acids*it’s important to note that adults can make