Lectures 1 2010 - Biochemistry II(Bio 362 Lectures 1 2...

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Biochemistry II (Bio 362) Lectures 1 & 2 Amino Acid Metabolism Dr. Karzai Office: 244 CMM Learning is Not a Spectator Sport Your Full Participation is Required
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Key points: Amino Acid biosynthesis: -Intermediary metabolite precursors to non-essential AAs -Incorporation of N into AAs -Methyl Cycle, -THF, SAM Amino acids as precursors Amino Acid Degradation: -Flow of waste N from tissues to liver to Urea cycle -Urea cycle -Fate of carbon skeleton; Ketogenic vs. Glucogenic AAs Learning Objectives How is nitrogen “fixed” Ammonium is assimilated into amino acids Amino acids are made from precursors of major metabolic pathway THF as carrier of several activated forms of one carbon species SAM and the activated methyl cycle Amino acids as precursors many essential Biomolecules You are expected to know the structures of all 20 amino acids
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Essential & non-essential a.a. (for humans) Made by complex routes (in bacteria and plants) Made by simple reactions Organisms vary greatly in their ability to synthesize the standard aa: most bacteria and plants synthesize all 20, mammals about half of them (remainder = “essential aa”, must come from food) Mammalian cells lack enzymes to synthesize their carbon skeletons ( α -keto acids). These include: Isoleucine, leucine, & valine Lysine Threonine Tryptophan Phenylalanine (Tyr can be made from Phe.) Methionine (Cys can be made from Met.) Histidine (Essential for infants.) Essential amino acids must be consumed in the diet.
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H 3 N + CH C O O - Amino Acid R Side chain Carboxylic acid 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 is a Key Component of Amino Acids Nitrogen fixation N 2 + 3 H 2 2 NH 3 : at 500°C, 300 ATM, Fe catalyst Biological: N 2 + 8 e - + 8 H + + 16 ATP 2 NH 3 + 16 ADP + 16 P i + H 2 at biological temps, 0.8 ATM
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Symbiotic N 2 -fixing bacteria in nodules of legume roots Symbiotic bacteria inside root nodule cell nucleus Root nodules NH 4 + assimilation: glutamine & glutamate = entry points into metabolism Glutamate Dehydrogenase This Reaction Proceeds in Two Steps
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Step One; Shiff base formation Step two; Shiff base is reduced by transfer of a hydride ion from NADP (H)
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Glutamamine synthetase adds a second ammonium ion to form Glutamine * ATP dependent reaction Pay attention to how ATP is used. 6 Biosynthetic Families for aa citric acid cycle Citric acid cycle Glycolysis + pentose-P pathway Glycolysis Pentose-P pathway Glycolysis Note : - some aa are precursors of others (red boxes) - essential aa in bold Carbon skeletons come from intermediates in: citric acid cycle : oxaloacetate, α -ketoglutarate.
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