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Unformatted text preview: citric acid cycle are connected! “Krebs bicycle ” Catabolism of purine nucleotides Primates excrete much more nitrogen as urea via the urea cycle (Chapter 18) than as uric acid from purine degradation. Fish excrete much more nitrogen as NH 4+ than as urea produced by the pathway shown here. 5 Part 3: biosynthesis of amino acids A. B. C. D. E. F. α-ketoglutarate amino acids family 3-Phosphoglycerate amino acids family Oxaloacetate and Pyruvate amino acids families Aromatic amino acids family Histidine family Molecules derived from amino acids Part 3: biosynthesis of amino acids
Most bacteria and plants are able to synthesize the 20 amino acids. Mammals can synthesized only half of them. Amino acids that are not needed in the diet are nonessential aas whereas those that are needed are called essential aas. 6 All aas are derived from intermediates in glycolysis, the citric acid cycle or the pentose phosphate pathway. Glu and Gln are the main source of nitrogen. Overview of aa synthesis (Chapter 22) aa Glucogenic and ketogenic Summary of aa catabolism (Chapter 18) 7 Amino acid biosynthetic families grouped by metabolic precursor + H Important amino acid precursors to remember Phosphoenolpyruvate α- ketoglutarate 3- phosphoglycerate Pyruvate Oxaloacetate
H Erythrose 4-phosphate Ribose-5 phosphate In addition to all these precursors, an important intermediate is PRPP: Ribose-5 phosphate + ATP PRPP + AMP ribose phosphate pyrophosphokinase
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