11SPRNTR342bb-CarbMet3 - Carbohydrate Metabolism 3 Reading:...

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Carbohydrate Metabolism 3 Reading: Gropper 4 th ed, Ch 1, pp. 6–7; Ch 3, pp. 62–69; Ch 4, pp. 93–99 Gropper 5 th ed, Ch 1, pp. 6–8; Ch 3, pp. 88–100
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2 Objectives for today: Take-home messages on glycolysis and the Krebs cycle Review the electron transport chain and oxidative phosphorylation Overview of the “shuttle systems” Malate-aspartate shuttle Glycerol-3-P shuttle Hexosemonophosphate shunt (HMP shunt, pentose phosphate pathway, phosphogluconate pathway) Gluconeogenesis
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3 Overview: Glucose Metabolism
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4 Glycolysis 1 st pathway in breakdown of monosaccharides to produce energy and 3-carbon intermediates 1 glucose converted to 2 pyruvate molecules 2 ATP used to prime pathway 4 ATP produced Net yield per glucose molecule: 2 ATP + 2 NADH NADH transfers electrons in mitochondria (aerobic conditions) produces 2 ATP (brain, skeletal muscle) or 3 ATP (liver, kidney, heart) Net ATP production/glucose = 6–8 ATP
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5 ATP ADP Glucose Hexokinase or Glucokinase Glucose-6-P Fructose-6-P Phosphoglucose isomerase Aldolase A Dihydroxyacetone P + Glyceraldehyde-3-P 2 molecules of Glyceraldehyde-3-P Glyceraldehyde-3-P Phase 3 of glycolysis Triose phosphate isomerase ATP ADP Phosphofructokinase-1 Fructose-1,6-BP Phase one Phase two The phases of the glycolytic pathway (DHAP)
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6 ATP ATP Pglycerate kinase Glyceraldehyde-3-P (from first half of glycolysis) Phosphoenolpyruvate Enolase Glyceraldehyde-3-P dehydrogenase 1,3-BisPglycerate 3-Pglycerate Phospho- glycerol mutase 2-Pglycerate Pyruvate Pyruvate kinase NAD + + P i NADH + H + ADP ADP The reduction-oxidation and ATP formation phase (phase three)
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7 Summary of glycolysis Glucose, galactose are activated by phosphorylation and converted to fructose-6-P Fructose-6-P is phosphorylated by phosphofructokinase-1 (PFK-1) to fructose-1,6-bisP Rate-limiting step Very negative G o ; irreversible reaction Highly regulated reaction Prevents simultaneous glycolysis and gluconeogenesis Hint: Key reactions are often irreversible. Fructose-6-P ATP ADP Fructose-1,6-P PFK-1
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8 Activation energy A B Exothermic - G Endothermic + Fig. 3-3, p. 56
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9 Phosphofructose kinase 1 (PFK-1) Irreversible reaction Commits substrate to glycolysis Allosteric regulation Inhibited by ATP, citrate Activated by AMP Activated by fructose 2,6-bisphosphate (F-2,6-bisP) F-2,6,-bisP levels controlled by bifunctional enzyme with phosphorylation and dephosphorylation activities Glucagon inhibits glycolysis and stimulates gluconeogenesis by increasing dephosphorylation and decreasing phosphorylation activities
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10 Summary of glycolysis (cont.) Fructose-1,6-bis-P is split, yielding DHAP and glyceraldehyde-3-P DHAP isomerizes to glyceraldehyde-3-P
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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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11SPRNTR342bb-CarbMet3 - Carbohydrate Metabolism 3 Reading:...

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