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Protein Metabolism I - Protein Metabolism 1 Reading Gropper...

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Protein Metabolism 1 Reading: Gropper 4 th ed, Ch 7, pp. 184–188, 194–206 Gropper 5 th ed, Ch 6, pp. 194–198, 208–222
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2 Objectives for today: Review digestion and absorption of proteins Amino acid transport and absorption Amino acid catabolism Urea cycle Carbon skeletons
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3 OVERVIEW OF METABOLIC PATHWAYS   Amino  Acids Glucose-6-P Pyruvate ATP Acetyl-CoA Urea AND SYSTEMS OF ENERGY METABOLISM b a o e h p Nucleic  Acids GLYCOGEN PROTEIN TRIACYLGLYCEROLS d c Ribose-5-P f g i j k l a b Glucose Lactate n m Ketone  Bodies Free Fatty Acids
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4 Protein Sources Animal products: meat, poultry, fish, and dairy (except butter, sour cream, and cream cheese) Plant products: grains (and grain products), legumes, and vegetables Endogenous proteins: secreted digestive enzymes and glycoproteins (17 g/day) and shed mucosal cells (50 g/day)
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5 Protein Absorption Small intestine is 95-99% efficient in extracting amino acids from the lumen 67% of amino acids are absorbed as peptides, 33% as free amino acids Most peptides are hydrolyzed by cytoplasmic proteases
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6 Fig. 2-19, p. 46
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7 Intestinal Cell Amino Acid Use Energy via catabolism Synthesis of proteins/N-containing compounds Structural proteins for new intestinal cells Nucleotides Apoproteins for lipoprotein formation Digestive enzymes Hormones Nitrogen-containing compounds
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8 Intestinal Cell Amino Acid Use (cont.) Most dietary amino acids are transported into portal blood unchanged Exceptions: Glutamine Glutamate Aspartate Arginine Methionine Cysteine Most of their metabolism goes on in the intestinal cell
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Major energy source for intestinal cells Spares dietary glucose & fatty acids for other tissues Stimulates intestinal growth/proliferation, inhibits bacterial translocation, and facilitates mucus production Uses up to 10g/day Glutamine converted to glutamate and ammonia 9 Intestinal Glutamine Use
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Undergoes transamination to α- KG Amino group donated to pyruvate to form alanine (taken up by liver) OR synthesizes proline (taken up by liver) OR synthesizes ornithine (along with aspartate) and ultimately citrulline OR synthesizes glutathione (along with glycine and cysteine) Liver takes up roughly 90% of dietary glutamate 10 Intestinal Glutamate Use
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Transamination with α- KG or pyruvate α- KG Aspartate Pyruvate Glutamate Oxaloacetate Alanine Not much gets out alive to enter portal circulation 11 Intestinal Aspartate Use
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