KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Gluconeogenesis Dr. Bibi Kulsoom

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM 2 Glucose used g/h Time Sources of Glucose & its Consumption Exogenous (diet) Body glycogen Gluconeogenesis

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Gluco= Glucose, neo= new, genesis= creation Pathways responsible for converting noncarbohydrate precursors to glucose. Organs (or tissues): occurs mainly in liver and also in kidneys. Liver Kidney

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Gluconeogenesis The cellular location of the enzymes involved in this process are mitochondrial matrix and cytoplasm. Mitochondrial matrix Cytoplasm Liver cell

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Glucose Pyruvate Gluconeogenesis Glycolysis Gluconeogenesis

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Components Required for Gluconeogenesis  Precursors(substances that will contribute to the structure) for glucose.  Enzymes  Specific transporters from mitochondria to cytosol.  Regulators  Energy: ATP, GTP & NADH 6

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Precursors of Gluconeogenesis 1.Glucogenic amino acids 2.Lactate 3.Glycerol 4.Propionate 5.Intermediates of glycolysis and TCA

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Glucogenic 1.Alanine 2.Arginine 3.Asparagine 4.Aspartic acid 5.Cysteine 6.Glutamic acid 7.Glutamine 8.Glycine 9.Histidine 10.Methionine 11.Proline 12.Serine 13.Threonine 14.Valine Glucogenic & Ketogenic 15.Isoleucine 16.Phenylalanine 17.Tryptophan 18.Tyrosine Precursors of Gluconeogenesis : Glucogenic Amino Acids

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Propionate Lactate Precursors of Gluconeogenesis : Lactate & Propionate

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Precursors of Gluconeogenesis : Glycerol Liver Blood Adipose tissue Triacylglycerol Glycerol + Free Fatty acids Glycerol Glycerol phosphate Dihydroxy acetone phosphate Glycerol Kinase Gluconeogenesis Glycerol is released during the hydrolysis of triacylgycerols in adipose tissue and is delivered to the liver, where it is converted to dihydroxyacetone.

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Muscle Glucose Pyruvate Lactate Glucose Pyruvate Glucose Liver Blood Glycogen Precursors of Gluconeogenesis : Cori Cycle Lactate generated in muscle tissue is delivered to the liver, where it is converted back to glucose. Gluconeogenesis

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Muscle Glucose Pyruvate Alanine Glutamate  -Ketoglutarate Alanine Glucose Pyruvate Glutamate  -Ketoglutarate Glucose Liver Blood Precursors of Gluconeogenesis : Glucose Alanine Cycle Alanine from muscle breakdown is released in blood which can be taken up by liver, where it is converted to glucose. Gluconeogenesis

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Steps in Gluconeogenesis Gluconeogenesis is mostly the reversal of reactions in glycolysis. Seven glycolytic reactions are reversible. Three glycolytic reactions are irreversible and are replaced by four.

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Glucose Glucose-6-P Fructose-6-P Glyceraldehyde 3-P Dihydroxy-acetone phosphate PyruvateLactate Oxaloacetatate 2-Phosphoglycerate Phosphoenolpyruvate 1,3-Bisphosphoglycerate 3-Phosphoglycerate Cytoplasm Cell membrane Fructose-1,6-BP Bypass 1 Bypass 2 Bypass 3

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Pyruvate Bypass 1: Carboxylation of Pyruvate and PEP Generation Malate Matrix of mitochondria Cytosol PEP=Phosphoenolpyruvate

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Pyruvate enters into mitochondrial matrix and is converted to oxaloacetate. The enzyme is pyruvate carboxylase, which is activated by increased acetyl-CoA. Bypass 1: Carboxylation of Pyruvate and PEP Generation  Acetyl CoA Pyruvate carboxylase (Inactive) Pyruvate carboxylase (Inactive) Pyruvate carboxylase (Active) Pyruvate carboxylase (Active) Oxaloacetate is either converted into PEP or malate. PEP and malate both are transported to cytosol through specific transporters. Malate is converted back to oxaloacetate and subsequently to PEP. Levels of acetyl CoA can be increased in prolonged fasting and diabetes mellitus. PyruvateOxaloacetate +

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Bypass 2: Dephosphorylation of Fructose 1,6-bisphosphate Fructose-6-P Fructose-1,6- Bisphosphate Fructose 1,6 bisphosphatase Phosphofructo kinase -1 P P Fructose 1, 6-bisphosphatase is the enzyme and it is highly regulated.

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Bypass 3: Dephosphorylation of Glucose-6-Phosphate Glucose Glucose-6-P Glucose-6 Phosphatase Glucokinase or Hexokinase P P Glucose 6-phosphatase is the enzyme which removes phosphate from the glucose. This free glucose can move out of the liver cells to maintain blood level. This enzyme is present only in liver and kidney. Muscle tissue lack this enzyme, so muscle glycogen cannot be used to maintain blood glucose level.

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Liver cell Cytoplasm KULSOOM Nucleus TCA Cycle Glucose Pyruvate Glycerol GLUT Pyruvate Phosphenolpyruvate Glucogenic amino acids Mitochondrial Matrix Triacylglycerol Lactate Glucose 6-P Glycogen, glycoproteins, other monosaccharaides, disaccharides

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Regulators Energy indicators – High energy indicators: Citrate, ATP. – Low energy indicators: AMP. Allosteric regulator: Fructose 2,6-bisphosphate,. Hormones: Insulin, Glucagon etc.

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Cytoplasm of liver cell F-6-P Fructose 1,6-bisphosphate Inactivation F 6-P  F 2,6-BP Glucagon  cAMP Active Protein Kinase A Phosphofructokinase 2 P P  Citrate Phosphofructokinase 1 + Citrate Citrate, ATP +  F- 2,6-BP, AMP Insulin Protein Phosphatases Fructose 1,6 bisphosphatase F 6-P= Fructose 6-Phosphate F 2,6-BP=Fructose 2,6-bisphosphate

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Glucagon  cAMP Active Protein Kinase A Pyruvate kinase P P Insulin Protein Phosphatases ActiveInactive Phospho- enolpyruvate Pyruvate Pyruvate kinase converts phosphoenolpyruvate into pyruvate. Pyruvate Kinase Regulation This enzyme is phosphorylated by glucagon which is the inactive form. Thus in the presence of glucagon phosphoenolpyruvate conversion to pyruvate is reduced and it is used for glucose production. Cytoplasm  F 1,6-BP + Acetyl CoA, Alanine, long chain fatty acids, ATP Liver cell All glycolytic tissue including liver

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Glycolysis & Gluconeogenesis Comparison of Regulation

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Glucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate Phosphoenolpyruvate Pyruvate + Glucagon - Insulin F 2,6-bisphosphate Insulin AMP + - ATP Citrate Glucagon Insulin F 1,6-bisphosphate - ATP Alanine + Hexokinase (or Glucokiase) Phosphofructokinase Pyruvate kinase - H+H+ + Glucose F 6-P - GLYCOLYSIS GLUCONEOGENESIS Fructose 2,6- bisphosphatase Oxaloacetate Pyruvate carboxylase - - F 2,6-bisphosphate AMP Citrate + - ADP - Acetyl CoA + + Glucagon - Insulin Phosphoenol-pyruvate carboxykinase Glucose 6- phosphatase G 6-P -

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Energy Consumption in Gluconeogenesis

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Glucose Glucose-6-P Fructose-6-P Glyceraldehyde 3-P Dihydroxy-acetone phosphate 2 Pyruvate 2 Lactate 2 Oxaloacetatate 2 2-Phosphoglycerate 2 Phosphoenolpyruvate 2 1,3-Bisphosphoglycerate 2 3-Phosphoglycerate Cytoplasm Cell membrane Fructose-1,6-P Bypass #1 Bypass #2 Bypass #3 2ATP 2ADP 2GTP 2GDP 2ATP 2ADP 2NADH 2NAD +

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM Enzyme Deficiencies Findings mostly observed during these Deficiencies: Pyruvate Carboxylase Deficiency: Frucose 1,6 bisphosphatase Deficiency: Glucose 6-Phosphatase Deficiency Pyruvate Carboxylase Deficiency: Frucose 1,6 bisphosphatase Deficiency: Glucose 6-Phosphatase Deficiency FindingExplanation Onset of symptoms: infancyMutant gene is inherited Hypoglycemia & poor tolerance to fastingAbsence of gluconeogenesis Lactic acidosisLactic acid accumulates as it cannot be used as precursor of glucose Hepatomegalyaccumulation of glycogen and fat in the liver (more fat mobilization in the body) General developmental delay & mental retardation (sometimes) No enough energy for efficient cell division

KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM KULSOOMKULSOOM 28 Sources of Glucose & its Consumption TIME AFTER CARBOHYDRATE CONSUMPTION 0-4 hrs 4-16 hrs hrs 2-24 days 24 days...

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