11SprNTR342--CarbMet02102011

11SprNTR342--CarbMet02102011 - Carbohydrate Metabolism 2...

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Carbohydrate Metabolism 2 Reading: Gropper 4 th ed, Ch 4, pp. 79–80, 87–94 Gropper 5 th ed, Ch 3, pp. 71–72, 82–89
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2 Objectives for today: Review absorption and transport of monosaccharides other than glucose Learn energetics of: glycolysis the Krebs cycle (citric acid cycle, tricarboxylic acid cycle, TCA cycle)
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3 Overview: Glucose Metabolism
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4 Absorption of galactose Dietary sources: lactose (milk); peas Released from lactose by lactase in the brush border (proximal small intestine) Lactase is stereospecific for the β 1-4 linkage A stereoisomer of glucose Absorbed into mucosal cells by active transport by the SGLT1 symporter (like glucose) Transported to blood by GLUT2, then to liver Converted to galactose 1-P; enters glycolysis Also synthesized by the body for glycoproteins
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5 Fig. 4-4b, p. 76 4 4 1 1 galactose galactose glucose glucose 1 1 1-4) 1-4) 4 4
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6 Metabolism of galactose in liver Galactose Galactose 1-P ATP ADP Galactokinase UDP-Galactose Glucose 1-P UDP-Glucose Uridyl transferase Epimerase UDP-Glucose Glucose 6-P Phosphoglucomutase GLYCOLYSIS
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7 Galactosemia Defects of galactokinase, uridyltransferase, or epimerase Recessive inheritance; rare (1/30,000 births) 75% fatal if not detected by newborn screening Raised on soy milk rather than breast fed Galactose + NADPH Galactitol Galactitol causes water diffusion into lens, increasing osmotic pressure; cataracts Glycolation and NADPH depletion also cause damage Mental retardation, liver damage, death
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8 Absorption of fructose Dietary sources: sucrose; high-fructose corn syrup; honey, fruits, and vegetables Released from sucrose by sucrase in the brush border Absorbed from the lumen of the gut by GLUT5 (facilitative transport) Facilitative transport slower than active transport May also be taken up by active transport in conjunction with a glucose co-carrier(?) (but not by SGLT1) Better absorption in the presence of glucose Fructose Malabsorption common Due to GLUT5 deficiency
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9 Transport of fructose
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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.

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11SprNTR342--CarbMet02102011 - Carbohydrate Metabolism 2...

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