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c13 amino acid metabolism.pdf

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Biological Sciences
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Daman Bawa

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Lecture 12 Prtotien Metabolism NNoteboook: bioc13 CCeaated: 2013-08-12 11:30 AM Updaated: 2013-09-28 9:53 PM UURL: file:/// Humans can only synthesize about 10 of the 20 amino acids (the simpler non-essential amino acids). In animals, proteases present in stomach and intestines cleave the peptide bond to yield amino acids and small oligopeptides. Carbon skeletons of all twenty amino acids are derived from just 7 metabolic intermediates: 3 glycolytic pathway intermediates: 1. 3-phosphoglycerate 2. phosphophenolpyruvate 3. pyruvate 2 pentose phosphate pathway intermediates: 1. ribose-5-phosphate 2. erythrose-4-phosphate 2-citrate cycle intermadiates: 1. α-ketoglutarate 2. oxaloacetate Can make any amino acid out of these 7 intermediates. The duodenum secretes a protease called enteropeptidase, which activates several proteolytic enzyme precursors (zymogen) released from the pancreas. One of the pancreatic zymogen is trypsinogen which is cleaved to form the endopeptidase trypsin Trypsin cleaves numerous pancreatic zymogens, including chymotrypsinogen, proelastase and procarboxypepetidases A and B, as well as, trypsinogen itself to amplify the proteolytic cascade. amino acids can be generated by degradation of cellular protein which has 2 pathways: 1. An ATP-independent process that occurs inside vesicles called lysosomes 2. ATP-dependent process that targets specific proteins for degradation in Proteasomes if they have a Ubiquitin molecule/ tag covalently attached to lysine residue Ubiquitin is a 76 amino acid protein found in all eukaryotic cells that is specifically attached to proteins by ubiquitin ligating enzymes. The proteins are cleaved by endo and exo-proteases/peptidases to individual amino acids Most amino acids are de-aminated first by a process called transamination. Transferring the amino group to an α-ketoacid. To yield an α-keto acid of the original amino acid and a new amino acid. a-ketoglutarate is the main amino acid acceptor and yields glutamate and a keto acid Glutamate’s amino group can be transfer
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