- Protein Metabolism 1 Reading Gropper 4th ed Ch 7 pp 184188 194206 Gropper 5th ed Ch 6 pp 194198 208222 Objectives for today Review digestion and

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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 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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4 “Essentiality/Dispensability” of amino acids Totally indispensable Lysine, threonine, histidine Present in animal protein; 1 or more lacking in some plant foods Also “essential” (but can be synthesized) Leucine, isoleucine, valine, tryptophan, methionine, phenylalanine Conditionally dispensable (but needed in some disease states) Tyrosine, cysteine, proline, arginine, glutamine
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5 “Essentiality/Dispensability” of amino acids Dispensable/nonessential Alanine, arginine*, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine *Sufficient arginine needed for growth in children
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6 “Essentiality/Dispensability” of amino acids Except for the totally indispensable amino acids (lysine, threonine, histidine), essentiality is conditional upon Quality and composition of diet Stage of life Disease
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7 The Essential and Non-essential Amino Acids Essential Nonessential Methionine b Alanine Glutamine
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8 Table 6-2e, p. 189
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9 Protein Digestion Proteins must be broken down into individual amino acids and small peptides for absorption
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10 Protein Absorption Small intestine is 95-99% efficient in extracting amino acids from the lumen Most absorption occurs in proximal (upper) small intestine 67% of amino acids are absorbed as peptides, 33% as free amino acids Most peptides are hydrolyzed by cytoplasmic proteases
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11 Fig. 2-19, p. 46
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Protein Transport 12 Uppercase=Na + -dependent Lowercase=Na + -independent Most amino acids use Na+- dependent transporters Size of side chain and neutrality of AA increases its affinity Essential absorbed fastest (Met,Leu,Isoleu, and valine) Glutamate and Aspartate slowest Di- and Tripeptides absorbed more efficiently (PEPT1-H + cotransporter)
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13 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 Chylomicrons and HDL Digestive enzymes Hormones Nitrogen-containing compounds
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14 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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This note was uploaded on 05/10/2011 for the course NTR 342 taught by Professor Tillman during the Spring '09 term at University of Texas at Austin.

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- Protein Metabolism 1 Reading Gropper 4th ed Ch 7 pp 184188 194206 Gropper 5th ed Ch 6 pp 194198 208222 Objectives for today Review digestion and

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