Cytosolic side SP T3 G6Pase ER lumen HO+ Glucose P:+ Glucose 6-phosphate Glucose 6-phosphatase converts glucose 6-Pto lucose in the ER lumen of liver and kidney cells
Glucose 6-phosphatase converts glucose 6-P to glucose in the ER lumen of liver and kidney cells
6. More energy is consumed in gluconeogenesis than produced in glycolysis Six high-energy phosphate groups are required when two. molecules of pyruvates are converted to one. glucose via gluconeogenesis pathway. e Two molecules of aTP are produced when one glucose molecule is converted to two pyruvate molecules via glycolysis pathway. The NADH needed for gluconeogenesis is either provided by lactate dehydrogenation in the cytosol or exported from mitochondria matrix via malate during one path for convert ing pyruvate to PEP
6. More energy is consumed in gluconeogenesis than produced in glycolysis • Six high-energy phosphate groups are required when two molecules of pyruvates are converted to one glucose via gluconeogenesis pathway. • Two molecules of ATP are produced when one glucose molecule is converted to two pyruvate molecules via glycolysis pathway. • The NADH needed for gluconeogenesis is either provided by lactate dehydrogenation in the cytosol or exported from mitochondria matrix via malate during one path for converting pyruvate to PEP
Table 19-2 Sequential reactions in gluconeogenesis starting from pyruvate Pyruvate+ HCO3+ ATP oxaloacetate ADP Pi+H+ Oxaloacetate GTP phosphoenolpyruvate+ CO2+ GDP Phosphoenolpyruvate HgO 2-phosphoglycerate A Phosphoglycerate 3-phosphoglycerate 3-Phosphoglycerate ATP 1,3-bisphosphoglycerate ADP H L3-Bisphosphoglycerate + NADH +H+ glyceraldehyde-3-phosphate+ NAD*+ Pi Glyceraldehyde-3-phosphate dihydroxyacetone phosphate Glyceraldehyde-3-phosphate+ dihydroxyacetone phosphate fructose-1, 6-bisphosphate Fructose-1, 6-bisphosphate + H2O fructose-6-phosphate + Pi Fructose-6-phosphate glucose-6-phosphate Glucose-6-phosphate H2o glucose Pi Sum: 2 Pyruvate 4ATP +2GTP+ 2NADH +4H2O glucose 4ADP +2GDP+ 6P,+2NAD*++2H The overall AG for gluconeogenesis in cell is about -16 kJ/mol ose+2ADP+2P;+2NAD+一 2 pyruvate+ 2ATP+ 2NADH +2H++2H,O The overall AG for glycolysis in cell is about-63 kJ/mol 3
The overall G for gluconeogenesis in cell is about -16 kJ/mol The overall G for glycolysis in cell is about –63 kJ/mol
1. Many amino acids but not fatty acids are glucogenic in mammals The amino acids that can be converted to pyruvate or citric acid cycle intermediates are glucogenic Net conversion of acetyl-CoA to pyruvate( the oxidative decarboxylation of pyruvate is irreversible or oxaloacetate does not occur in mammals, thus neither Lys and Leu nor eyen-numbered fatty acids are glucogenic in mammals; but net conversion of acetyl-Coa to oxaloacetate occurs in organisms like plants and bacteria that have the glyoxylate cycle Fatty acid oxidation provide an important energy source for gluconeogenesis
7. Many amino acids but not fatty acids are glucogenic in mammals • The amino acids that can be converted to pyruvate or citric acid cycle intermediates are glucogenic. • Net conversion of acetyl-CoA to pyruvate (the oxidative decarboxylation of pyruvate is irreversible) or oxaloacetate does not occur in mammals, thus neither Lys and Leu nor even-numbered fatty acids are glucogenic in mammals; but net conversion of acetyl-CoA to oxaloacetate occurs in organisms like plants and bacteria that have the glyoxylate cycle. • Fatty acid oxidation provide an important energy source for gluconeogenesis
8. Gluconeogenesis and glycolysis are reciprocally regulated to avoid futile cycles that waste ATP consumption If the three pairs of bypassing reactions of glucose degradation and synthesis occur simultaneously, ATP will be consumed for heat generation, being often (not always) an energy wasting process To avoid such futile cycling processes the two pathways are regulated coordinately and reciprocall (相反地) a common; regulator molecule having opposite effect towards the pair of enzymes catalyzing the bypa assing reactions
8. Gluconeogenesis and glycolysis are reciprocally regulated to avoid futile cycles that waste ATP consumption • If the three pairs of bypassing reactions of glucose degradation and synthesis occur simultaneously, ATP will be consumed for heat generation, being often (not always) an energy wasting process. • To avoid such futile cycling processes, the two pathways are regulated coordinately and reciprocally (相反地): a common regulator molecule having opposite effect towards the pair of enzymes catalyzing the bypassing reactions