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Introduction of Glucose Metabolism Lecture-4

Introduction of Glucose Metabolism Lecture-4. GLUCONEOGENESIS. GLUCONEOGENESIS. Gluconeogenesis is the synthesis of glucose from glucogenic precursors which are not of carbohydrate origin ( gluconeogenic precursors) It occurs during prolonged fasting to synthesize glucose for tissues

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Introduction of Glucose Metabolism Lecture-4

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  1. Introduction of Glucose Metabolism Lecture-4 GLUCONEOGENESIS

  2. GLUCONEOGENESIS Gluconeogenesis is the synthesis of glucose from glucogenic precursors which are not of carbohydrate origin (gluconeogenic precursors) It occurs during prolonged fasting to synthesize glucose for tissues requiring continuous supply of glucose as a source of energy: Brain, RBCs, Kidney medulla, Lens, Cornea, Testes, sk.ms Gluconeogenesis occurs ONLY in the liver & kidneys

  3. Gluconeogenic precursors 1- Intermediates of glycolysis by reverse of steps of glycolysis (except 4 steps that need 4 different enzymes) 2- Intermediates of citric acid cycle are converted to oxalacetate then to glucose 3- Lactate Lactic acid formed of anaerobic glycolysis in cells as RBCs & skeletal muscles are transported in blood to liver to be converted to pyruvate then to glucose (Cori cycle) 4- Glycerol Glycerol is derived from the lipid triacylglycerol in adipose tissue. Glycerol is converted into dihydroxyactone phosphate (intermediate of glycolysis) then to glucose. 5- Glucogenicamino acids of proteins Glucogenic amino acids are deaminated to form a-ketoacids a-keto acids are converted to pyruvate or intermediates of citric acid cycle then to glucose

  4. GLUCOSE Triacylglycerol in adipose tissue Precursors of Gluconeogenesis Fatty acids Gluconeogenesis Glycerol Lactate Oxalacetate Pyruvate Intermediate of CITRIC ACID CYCLE Glucogenic amino acids in proteins as sk. ms.

  5. Glycerol as agluconeogenic Substrate Glycerol Kinase Glycerol Glycerol 3-phosphate ATP ADP NAD+ Glycerol 3-phosphate dehydrogenase NADH Glucose Dihydroxyacetone phosphate GK: Glycerol kinase only in liver & kidneys

  6. GlucogenicAmino Acids Glycine, Alanine Amino acids Pyruvate Aspartate Aspargine Glutamate Glutamine Amino acids Phenylalanin Tyrosine Methionine Valine

  7. Cori Cycle Lactate is a gluconeogenic precursor

  8. Unique enzymes of gluconeogenesis Reactions 1, 2, 3 & 4 are catalyzed by enzymes NOT used in glycolysis GLUCOSE 1- Pyruvate to oxalacatate by pyruvatecarboxylase 2- oxalacetate to phosphoenolpyruvate by PEP carboxykinase 3- Fructose 1,6 bisphosphate to fructose 6 phosphate by fructose 1,6 bisphosphatase 4- Glucose 6-phosphate to glucose by glucose 6-phosphatase GLUCONEOGENESIS Other reactions of gluconeogenesis are catalyzed by same enzymes of glycolysis in the reverse direction

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