Gluconeogenesis ppt gate notes pptx.pptx
- 1. Learning Biology With Sudarshan SudarshanMandal M.Sc in Zoology(Banaras Hindu University) Qualified in Net Ls,Gate,IIT jam ,Bhu Pet,Wbset
- 3. Definition • Gluconeogenesis isa major regulatory process in the liver and kidneys by which noncarbohydrate substrates; namely glycerol, lactate, propionate, and glucogenic amino acids; are converted to glucose 6-phosphate (Glc-6-P), and then to either free glucose or glycogen
- 4. Site • The liverand kidneys are the major organs containing the full complement of gluconeogenic enzymes (i.e., pyruvate carboxylase, PEP carboxykinase, fructose 1,6- bisphosphatase, and glucose 6-phosphatase) • It occurs in all animal ,plants ,fungi and micro- organism.
- 6. Reaction of Gluconeogenesis •Gluconeogenesis and glycolysis are not identical pathways running in opposite directions,although they do share several steps . • 7 out of 10 enzymatic reactions of gluconeogenesis are reverse of glycolytic reaction. • Three reactions of glycolysis are esentially irreversible .
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- 9. Reaction of Gluconeogenesis •Three irreversible steps are – 1.Conversion of glucose 6 phosphate catalyzed by hexokinase. 2.The conversion of fructose 6-phosphate to fructose 1,6 bis phosphate by PFK-1. 3.The conversion of phosphoenol pyruvate by pyruvate kinase.
- 10. Reaction of Gluconeogenesis •These three reactions are characterized by a large negative free energy change ,where as other glycolytic reaction have ΔG near 0. • In Gluconeogenesis these irreversible steps are bypassed by a separate set of enzymes.
- 11. Reaction of Gluconeogenesis conversionof Pyruvate to PEP • Pyruvate can not be converted directly to PEP. The conversion requires two reactions that serve to bypass irreversible step of glycolysis. • Pyruvate is first transported from the cytosol into mitochondria or is generated from alanine within mitpchondria by transamination.
- 12. Reaction of gluconeogenesis •Then pyruvate carboxylase ,mitochondrial enzyme that requires the coenzyme biotin,converts pruvate to oxaloacetate. • Pyruvate+Hco3-+ATP oxaloacetate+ADP+Pi
- 13. Reaction of gluconeogenesis •Oxaloacetate cannot directly cross the inner mitochondrial membrane. Therefore, it is converted to malate or to aspartate, which can cross the mitochondrial membrane and be reconverted to oxaloacetate in the cytosol. • Oxaloacetate is decarboxylated by phosphoenolpyruvate carboxykinase to form phosphoenolpyruvate. This reaction requires GTP.
- 14. Reactions of Gluconeogenesis •Phosphoenolpyruvate is converted to fructose 1,6-bisphosphate by reversal of the glycolytic reactions.
- 15. Reactions of Gluconeogenesis Conversionof 1,6 BP to F-6 P • Second bypass reaction. • Fructose-1, 6-bisphosphate is converted to fructose-6-phosphate in a reaction that releases inorganic phosphate and is catalyzed by fructose-1,6-bisphosphatase. • The highly exergonic irreversible reaction is catalyzed by Fructose 1,6bisphosphatase.
- 16. Reactions of Gluconeogenesis (Conversionof G-6 P to Glucose) • Third bypass. • Glucose-6-phosphate releases inorganic phosphate, which produces free glucose that enters the blood. The enzyme involved is glucose 6-phosphatase.
- 17. Net requirements tomake one glucose molecule • Thus, the net requirements to make one glucose molecule are: • Two pyruvate. • Four ATP and two GTP. • Two NADH. • Six H2O •
- 18. Significance • Gluconeogenesis isneeded to meet the demands for plasma glucose between meals, which then becomes particularly important as an energy substrate for nerves, erythrocytes, and other largely anaerobic cell types. Failure of this process can lead to brain dysfunction, coma, and death.