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Lect_14_AAI - BIS 103 14 Amino acid biosynthesis I Ammonia...

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BIS 103 - 14 - Amino acid biosynthesis I Ammonia assimilation and transamination Glutamine synthetase Glutamate synthase Glutamic acid transaminase Pyridoxal phosphate Glutamic dehydrogenase Regulation of glutamine synthetase 2nd midterm High: 200 Low: 50 Median: 135
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In the last lecture we discussed how nitrogen fixation occurred to convert atmospheric nitrogen to NH 3 . We also showed that HNO 2 and HNO 3 could be brought down by rainfall to the soil and that plants and micro- organisms could also use HNO 2 and HNO 3 as nitrogen sources. In both cases nitrogen was finally reduced to NH 3 , which is the form that is assimilated into organic nitrogen. The assimilation is into amino acids.
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The roles of amino acids -components of proteins -precursors for purine and pyrimidine nucleotides -precursors for co-factors such as NAD, NADP, CoASH, folic acid -precursors for porphyrins found in heme and chlorophyll -precursors for small polypeptide hormones such as glucagon, insulin somatostatin, endorphins, etc. -precursors for neurotransmitters such as serotonin, epinephrine, acetylcholine, dopamine, enkaphlins, etc. -precursors for vasodilator, such histamine
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The carbon sources for amino acids are as follows: Glucose PPP His, Trp, Tyr, Phe 3-PGA Ser, Gly, Cys Pyruvate Ala, Val, Leu Oxaloacetate (TCA) Asp, Asn, Lys, Met, Thr, Ile α -Ketoglutarate (TCA) Glu, Gln, Pro, Arg, Lys Amino acids are composed of a carbon skeleton and nitrogen, and two of the amino acids contain sulfur.
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The sulfur source is as follows : inorganic sulfur H 2 S Cys + Met The nitrogen source is as follows : N 2 NH 3 Gln Glu α -keto acids amino acids NO 3 -
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Essential amino acids Plants and many microorganisms can synthesize all 20 amino acids and furnish amino acids directly or indirectly to other organisms. Not all organisms can synthesize every amino acid. The white rat and humans can make 10 amino acids, but require 10 essential amino acids in their diets: Essential amino acids : Pvt Tim Hall PVT : Phe, Val, Thr TIM : Trp, Ile, Met HALL : His, Arg*, Leu, Lys Arg* is conditionally essential (young or ill)
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The biosynthetic pathways for amino acids are varied and can be complex and long; e.g. for histidine synthesis, there are 10 enzymatic steps. Most of the essential amino acids for humans are made by long, complex pathways. The non-essential amino acids have relatively short biosynthetic pathways. The genes for complex biosynthetic pathways have been deleted from the human genome. We save energy by consuming already formed amino acids.
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N 2 + 8H + + 8 e - + 16 ATP + 16 H 2 O 2 NH 3 + H 2 + 16 ADP + 16 Pi DNR, DN Inorganic N is taken into organic compounds as NH 3 Recall that during biological nitrogen fixation, N 2 was reduced to NH 3
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BIS 103 -#14 - Path of NH 3 into amino acids - assimilation of NH 3 Incorporation of nitrogen (NH 3 ) into amino acids involves 3 enzymes 1. Glutamine synthetase : Glu + NH 3 + ATP Gln + ADP + Pi 2. Glutamate synthase : Gln + α -KG + NADPH + H + 2 Glu 3. Transaminase : Glu + α -keto acid amino acid + α -KG How is nitrogen incorporated into organic compounds?
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