Gluconeogenesis

1. Gluconeogenesis Dr. Bibi Kulsoom

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

3. 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 http://www.medgadget.com/archives/img/Kidney05-full.jpg

4. Gluconeogenesis The cellular location of the enzymes involved in this process are mitochondrial matrix and cytoplasm. Liver cell Mitochondrial matrix Cytoplasm Cytoplasm http://penrules.com/portfolio/illustration/mitochondria.html

5. Gluconeogenesis Glucose Glycolysis Gluconeogenesis Pyruvate

6. 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 http://www.stmarksjohnstownpa.org/cook1.gif

7. Precursors of Gluconeogenesis • Glucogenic amino acids • Lactate • Glycerol • Propionate • Intermediates of glycolysis and TCA

8. Precursors of Gluconeogenesis : Glucogenic Amino Acids Glucogenic Alanine Arginine Asparagine Aspartic acid Cysteine Glutamic acid Glutamine Glycine Histidine Methionine Proline Serine Threonine Valine Glucogenic& Ketogenic Isoleucine Phenylalanine Tryptophan Tyrosine

9. Precursors of Gluconeogenesis : Lactate & Propionate Lactate Propionate

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

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

12. 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. Liver Glucose Gluconeogenesis Pyruvate Glutamate Glucose Muscle -Ketoglutarate Alanine Glucose Pyruvate Alanine Blood Glutamate -Ketoglutarate Alanine

13. 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.

14. Glucose Cell membrane Bypass 3 Cytoplasm Glucose-6-P Fructose-6-P Bypass 2 Fructose-1,6-BP Dihydroxy-acetone phosphate Glyceraldehyde 3-P 1,3-Bisphosphoglycerate 3-Phosphoglycerate Oxaloacetatate 2-Phosphoglycerate Bypass 1 Lactate Pyruvate Phosphoenolpyruvate

15. Bypass 1: Carboxylation of Pyruvate and PEP Generation Malate Matrix of mitochondria Pyruvate Pyruvate Cytosol PEP=Phosphoenolpyruvate Pyruvate Pyruvate http://www.bioinfo.org.cn/book/biochemistry/chapt19/sim0.htm

16. Bypass 1: Carboxylation of Pyruvate and PEP Generation Pyruvate carboxylase (Inactive) • Pyruvate enters into mitochondrial matrix and is converted to oxaloacetate. The enzyme is pyruvate carboxylase, which is activated by increased acetyl-CoA. +  Acetyl CoA Pyruvate carboxylase (Active) • Levels of acetyl CoA can be increased in prolonged fasting and diabetes mellitus. Pyruvate Oxaloacetate • 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.

17. Bypass 2: Dephosphorylation of Fructose 1,6-bisphosphate Phosphofructokinase -1 Fructose-1,6-Bisphosphate Fructose-6-P • Fructose 1, 6-bisphosphatase is the enzyme and it is highly regulated. P Fructose 1,6 bisphosphatase

18. Bypass 3: Dephosphorylation of Glucose-6-Phosphate Glucokinase or Hexokinase Glucose Glucose-6-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. P Glucose-6 Phosphatase

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

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

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

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

23. Glycolysis & Gluconeogenesis Comparison of Regulation

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

25. Energy Consumption in Gluconeogenesis

26. Cell membrane Glucose Cytoplasm Bypass #3 Glucose-6-P Fructose-6-P Bypass #2 Fructose-1,6-P Dihydroxy-acetone phosphate Glyceraldehyde 3-P 2NAD+ 2NADH 2 1,3-Bisphosphoglycerate 2ADP 2ATP 23-Phosphoglycerate 2Oxaloacetatate 2GDP 2GTP 22-Phosphoglycerate 2ADP Bypass #1 2ATP 2Lactate 2Pyruvate 2Phosphoenolpyruvate

27. Enzyme Deficiencies • Pyruvate Carboxylase Deficiency: • Frucose 1,6 bisphosphatase Deficiency: • Glucose 6-Phosphatase Deficiency Findings mostly observed during these Deficiencies:

28. Sources of Glucose & its Consumption TIME AFTER CARBOHYDRATE CONSUMPTION 0-4 hrs 4-16 hrs 16-32 hrs 2-24 days 24 days ...

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